Journal of the Marine Biological Association of the United Kingdom, 2011, 91(1), 199 –208.
doi:10.1017/S0025315410001013
# Marine Biological Association of the United Kingdom, 2010
First insights into the biochemistry of
Sabella spallanzanii (Annelida: Polychaeta)
mucus: a potentially unexplored resource for
applicative purposes
loredana stabili1,2, roberto schirosi1, angela di benedetto3, alessandro merendino4,
luciano villanova4 and adriana giangrande2
1
Istituto per l’Ambiente Marino Costiero, Sezione di Taranto, 2Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali,
Università del Saliento, 73100 (Lecce), Italy, 3Dipartimento di Chimica e CIRCC, Università degli Studi di Bari, Campus
Universitario, 70126 Bari, Italy, 4Lachifarma s.r.l. Laboratorio Chimico Farmaceutico, Dipartimento Ricerca & Sviluppo S.S. 16 Zona
Industriale, 73010 Zollino (Lecce), Italy
Although mucus plays many different roles among marine invertebrates, relatively little is known about the link between biochemical structure and function. In the present study we focused on some physical and chemical properties of the polychaete
Sabella spallanzanii’s mucus such as viscosity, osmolarity, electrical conductivity, elemental composition, the protein and
carbohydrate content, the total lipids and fatty acid composition, and polychlorinated biphenyls (PCBs) contamination.
Moreover, an antimicrobial activity of the mucus was investigated. The water content of S. spallanzanii mucus was
96.2+0.3%. By dry weight 26+1.2% was protein, 8+0.21% was carbohydrate and only 0.1% lipid, much of the remainder
of the dry weight was inorganic (about 65.2%). The estimated PCBs content was ,0.005 mg g21. The mucus of S. spallanzanii
exerted a natural lysozyme-like activity and produced in vitro the growth inhibition of Vibrio anguillarum, Vibrio harveyi,
Pseudomonas aeruginosa and Candida albicans. The findings from this study contribute to improve the limited knowledge
available on the mucus composition in invertebrates and have implications for future investigations related to employment of
S. spallanzanii mucus as a source of compounds of pharmaceutical and marine technological interest.
Keywords: mucus, proteins, carbohydrates, lipids, PCBs, lysozyme, antimicrobial activity
Submitted 13 January 2010; accepted 22 March 2010; first published online 14 July 2010
INTRODUCTION
The term mucus is broadly used for any slimy secretion from
an epithelial surface produced by animals (Davis & Viney,
1998). It is a network of proteins and polysaccharides
entangled to form a weak gel containing more than 95%
water (Wainwright et al., 1976; Davies et al., 1990; Smith
et al., 1999). Invertebrates use mucus as an external surface
coating to reduce friction or hydrodynamic drag, and to
limit water loss. In addition mucus can serve as an aid in locomotion and feeding, a mating rope, or a ‘scaffolding’ that provides anchorage and protection for eggs and a barrier against
infection (Davies et al., 1990). In marine invertebrates, mucus
typically forms a slippery coating that prevents bacteria and
debris from accumulating on the body surface (Baier et al.,
1985) and possesses a number of defence mechanisms (Clare,
1995; Suzuki et al., 2003). These organisms require efficient
mucosal defence mechanisms as they are under constant
threat from a rich mixture of microorganisms in the surrounding water. Therefore, it is not surprising that these
Corresponding author:
L. Stabili
Email: loredana.stabili@iamc.cnr.it
organisms have developed an impressive array of secreted
compounds of the innate immune system including lytic compounds (Canicattı̀, 1989; Canicattı̀ & d’Ancona, 1990), bioactive peptides (Pomponi et al., 1998; Ebran et al., 2000),
toxins, carbohydrate anti-adhesives (Guzman-Murillo &
Ascenico, 2000; Bavington et al., 2004; Carsten & Schupp,
2008), lectins (Iwanaga & Lee, 2005) to reduce the bacterial
adhesion (McKenzie & Grigovala, 1996). In the Annellida
Polychaeta the epidermal gland cells produce a mucus that
has various functions thus mucus production constitutes a
key factor determining the ability of many polychaete
species to survive in their environment (Bonar, 1972). As
reported by Storch (1988) mucus intervenes in fertilization
and egg protection, consolidates the tunnel wall of burrowing
polychaetes and may also play a role in the absorption of
metabolites. Mouneyrac et al. (2003), in their studies on
Hediste diversicolor, suggested that the secretion of mucus
by gland cells in the epidermis is a specific response to toxicants. In sabellid polychaetes a heterogeneous mucus is
involved in different functions, such as the prevention of the
proliferation of pathogenic microorganisms, protection and
absorption of metabolites, as well as the building of the tube
(Mastrodonato et al., 2005). In particular, Sabellidae use
mucus to cement different substances in tube building,
mixing faeces, pseudofaeces and sediment (Dales, 1961;
199
200
loredana stabili et al.
Lewis, 1968). Three sets of glands add mucus to the particles
used in tube-building: the ciliated glandular epidermis
between the bases of the sacs, the mucous glands on the
inner sides of the parallel folds, and the mucous glands on
the under surface of the ventral collar folds. Because the particles were coated with mucus this churning causes them to
become entangled together in a common mass with the
mucus acting as a bio-adhesive in the tube building.
Inspired by biomimetic applications, there has been a
growing interest in the molecular mechanisms of adhesive
bonding in marine organisms because of the efficiency of
their adhesives in aqueous media compared with man-made
materials (Santos et al., 2009). Despite the technological
potential and roles in attachment, construction and obstruction, as well as in predation and defence (Graham, 2008) a
considerable dearth of information remains regarding the
biochemical composition of marine adhesives. Some studies
have focused on the characterization of permanent adhesives
characteristic of sessile organisms staying at the same place
throughout their adult life. Comparatively, non-permanent
adhesives, more hydrated than permanent ones and consisting
of a mixture of proteins and polysaccharides, have received
much less attention (Smith et al., 1999; Flammang et al.,
2002; Hamwood et al., 2002; DeMoor et al., 2003; Pawlicki
et al., 2004; Smith, 2006; Santos et al., 2009).
In the present study we focused on the polychaete Sabella
spallanzanii Gmelin, one of the best known and abundant
Mediterranean sabellid. In this species a large amount of
mucus is secreted when specimens are subjected to different
stress conditions. As suggested in previous investigations,
apart from the above described role in the tube building, the
mucus seems also to be involved in the fertilization process
and in defence (Canicattı̀ et al., 1992; Giangrande et al.,
2000). However, little is known about the biochemistry of S.
spallanzanii mucus. In the present work we describe, over
an annual cycle, some physical and chemical properties of S.
spallanzanii mucus such as viscosity, osmolarity, electrical
conductivity, elemental composition, the protein and carbohydrate content, the total lipids and fatty acid composition.
In addition polychlorinated biphenyls (PCBs) content was
evaluated in order to ascertain if it is below the maximum
accepted value of contamination in pharmaceutical preparations. Implications for future investigations related to
employment of S. spallanzanii mucus as a source of compounds of applied biotechnological interest are also discussed.
In particular, we explored the potential of this matrix either as
a good food source, on account of its nutritional value, or a
source of bioactive substances with antimicrobial activity of
pharmaceutical and marine technological interest.
for 30 minutes in a Petri dish. Within the secreted mucus,
we checked for trapped material by microscopic observations,
whilst we excluded any contamination of other excretion products by pH measurements. Secreted mucus was collected and
centrifuged at 12,000g for 30 minutes at 48C. A previous work
(Canicattı̀ et al., 1992) showed that the protein content of the
mucus varies between individuals. To avoid the introduction
of this variable, in the present work for each sampling
period the whole group of 200 individuals was pooled into
five samples of 40 worms which were stored at 2808C until
use.
Mucus viscosity, osmolarity and electrical
conductivity
The handling procedure and storage at 2808C for up to three
months did not affect the subsequent viscosity measurements
of mucus samples (data not shown), a similar finding to
Charman & Reid (1973) and Lopez-Vidriero et al. (1980).
Viscosity was measured at 200 rpm in 1-ml aliquots with a
cone-plate viscometer (cone angle of 1.5658, model LVT-C/
P 42, Brookfield Engineering Laboratories, USA) connected
to a circulating water bath (Thermoline, Australia) set at
17+0.18C. Due to differences in temperature and equipment
used between studies, comparison of viscosity data can be difficult without reference to a common, known viscosity. Thus
we documented the relative viscosity of mucus in respect to
the viscosity of water, similar to Rosen & Cornford (1971)
and Cone (1999). The viscosity of water is 1 centipoise (cP)
at 208C and only slightly dependent on temperature
(Withers, 1992).
Osmolarity was measured using a VAPRO vapour pressure
osmometer (model 5520, WESCOR, UT, USA). All measurements were carried out in triplicate. The electrical conductivity was measured by using a conductimeter GLP
31(Crison).
Water content
The wet weights of mucus of 15 samples for each sample period
(3 replicates for each of the five groups of 40 individuals) were
measured on an analytical balance. They were then dehydrated
in a SpeedVac and their dry weight was measured.
MATERIALS AND METHODS
Animals and samples preparation
Sampling was undertaken in the harbour of Brindisi (southern
Adriatic Sea, Italy) using SCUBA equipment (depth range ¼
5– 15 m) over four periods: April 2006 (T1), July 2006 (T2),
November 2006 (T3) and January 2007 (T4) (Figure 1). At
each sampling period 200 adult specimens of Sabella spallanzanii were collected and transferred to the laboratory. In order
to stimulate the secretion of the mucus, all the individuals
have been removed from the tube where they live and kept
Fig. 1. Map of the Apulian coast showing the location of the sampling site.
biochemistry of sabella spallanzanii mucus
Determination of the inorganic composition
The inorganic composition and the PCBs content were determined for each sample after lyophilization of sample solution
at 528C and 0.061 mbar using a LIO 5P CINQUEPASCAL
freeze-dryer.
Carbon, H and N analyses were performed using a 1106
Carlo Erba elemental analyser, while an AA-6200 Shimadzu
atomic absorption flame emission spectrophotometer was
used for the determination of Fe, Ca, Mg, Zn, Cu, K and
Na. A P/N 206-17143 Shimadzu hydride vapour generator
was coupled to the atomic absorption spectrophotometer in
order to analyse the Sn and Se content. In general, each
sample was mineralized to oxidize the organic fraction. To
this end a weighted sample of the mucus (≏10 mg) was
treated with HNO3 (1 ml) and H2SO4 96% w/w (2.5 ml) at
high temperature until no more fumes were released. The
residue was treated again with the acids two more times.
The final liquid residue was dissolved in water to give a
100 ml solution. For each element a calibration curve was
obtained by using standard solutions. The quantitative analysis of phosphorous was performed using a UV-1601 Shimadzu
spectrophotometer using the method reported in the literature
(Kitson & Mellon, 1944; Quinlan & Desesa, 1955). A 785
DMP Metrohm Titrino was used for the quantitative determination of the inorganic chloride using a pothenziometric
determination.
Determination of the PCBs content
The quantitative analysis of the PCBs was performed using a
gas chromatograph equipped with a capillary column (HT-5,
25 m × 0.22 mm × 0.10 mm) and connected with a mass
spectrometric detector (GC-MS). The oven temperature programme was as follows: 1258C for 1 minute; 258C min21 to
2008C; 48C min21 to 2608C, 608C for 1 minute (total run
time: 20 minutes) and the injector temperature was 3008C.
Helium was used as the carrier gas at a constant flow of
0.7 ml min21. The determination was done according to the
CEN 15308 method UNI EN 15308:2008 Characterization
of waste–Determination of selected PCBs in solid waste by
using capillary gas chromatography with electron capture or
mass spectrometric detection which take into account seven
congeners of PCBs (Table 1). Molecular weights and retention
times of these PCB congeners were also reported.
Protein and carbohydrate concentration
The protein concentration of each mucus sample was
measured using the Bradford assay (1976), with bovine
serum albumin (BIO-RAD) as standard.
The carbohydrate concentration of the mucus was assayed
using the method described by Dubois et al. (1956) and
Kennedy & Pagliuca (1994). The assay was calibrated with
known amounts of D-glucose.
Lysozyme-like activity
To detect lysozyme activity, inoculated Petri dishes were used
as standard assay; 700 ml of 5 mg/ml of dried Micrococcus
luteus cell walls (Sigma) were diluted in 7 ml of 0.05 M
PB-agarose (1.2%) (pH 5.0) then spread on a Petri dish.
Four wells of 6.3 mm diameters were sunk in the agarose gel
and each filled with 30 ml of mucus. The diameter of the
cleared zone of the four replicates was recorded after overnight incubation at 378C and compared with those of reference samples represented by hen egg-white lysozyme
(Merck, Darmstadt, Germany).
Microbial strains
Human and animal pathogenic bacteria were used, and these
were strains of Vibrio alginolyticus, Vibrio harveyi, Vibrio
anguillarum, Salmonella sp., Escherichia coli and
Pseudomonas aeruginosa. Three clinical isolates of human
pathogenic fungi were also used: Candida albicans, Candida
famata and Candida glabrata. Strains were routinely maintained at +48C on Marine Agar 2216 (Beckton Dickinson &
Co.), Luria –Bertani (LB), nutrient, or yeast peptone dextrose
(YPD) agar used for the marine bacteria, the human and
animal pathogenic bacteria, and the fungi, respectively.
Bacterial and yeast strains were always harvested during the
exponential growth phase, i.e. after 4 hours culture at 248C
or 378C for the pathogenic strains, under constant rotation
at 100 rpm.
Antimicrobial activity
To test antimicrobial activity, 50 ml of mucus sample were
added to 10 ml of bacterial or yeast suspension (108 cells
ml21). Normal growth controls consisted of bacteria or
yeast incubated with sterile liquid broth. After 30 minutes at
room temperature, with gentle stirring at 100 rpm, serial
dilutions of these suspensions were incubated in Petri dishes
between two layers of the above described specific nutritive
agar to obtain imprisoned bacterial or yeast forming punctiform colonies (technique of ‘colony forming units’ (CFU)).
Routinely, 1023, 1024 and 1025 dilutions were plated out in
triplicate. Percentages of inhibition were determined from
the differences in colony numbers in controls and tests, after
24-hours incubation at 248C for marine strains and at 378C
for the pathogenic strains. The percentage of bacteria or
yeast inhibited by mucus was inferred from the difference
between the number of emerging colonies in controls and in
tests.
Table 1. Molecular weights and retention times of the investigated polychlorinated biphenyl (PCB) congeners.
Investigated congener
Molecular
weight
Retention time
(min)
PCB-28: 2,4,4′ -trichlorobiphenyl
PCB-52:
2,2′ ,5,5′ -tetrachlorobiphenyl
PCB-101:
2,2′ ,4,5,5′ -pentachlorobiphenyl
PCB-118:
2,3′ 4,4′ ,5-pentachlorobiphenyl
PCB-138:
2,2′ ,3,4,4′ ,5′ -hexachlorobiphenyl
PCB-153:
2,2′ ,4,4′ 5,5′ -hexachlorobiphenyl
PCB-180:
2,2′ ,3,4,4′ ,5,5′ -heptachlorobiphenyl
258.55
291.99
14.84
16.18
326.44
19.81
326.44
23.26
360.88
24.83
360.88
27.08
395.33
32.17
201
202
loredana stabili et al.
Electrophoresis
Mucus samples were analysed by SDS-polyacrylamide gel
electrophoresis (SDS-PAGE). They were run on discontinuous gels, based on the method of Laemmli (1970) and the
detailed protocols of Hames (1990). The gels were 10% acrylamide, and were 8×9 cm by 1.0 mm thick. The migration
buffer consisted of 25 mM Tris, 192 mM glycine, pH 8.5.
After migration, gels were stained using Silver Stain kit
(Sigma). Kit of molecular standards (PageRulerTM Prestained
Protein Ladder range10-250 kDa) was purchased from
Fermentas. It is a mixture of eight recombinant, highly purified,
coloured proteins with apparent molecular weights of 10 to
250 kDa.
Total lipids and fatty acid analyses
Total lipids from each mucus sample were extracted according
to the method of Folch et al. (1957). The mucus was homogenized with chloroform/methanol (2/1) to a final volume
20 times the volume of the mucus sample. After centrifugation
and siphoning of the upper phase, the lower chloroform phase
contained the lipids. Total lipid content was determined by the
colorimetric enzymatic method (Zöllner & Kirsch, 1962)
using commercial kit (FAR—Verona, Italy).
Fatty acid composition was determined as described by
Budge & Parrish (2003). In this method, fatty acid methyl
esters (FAME) of lipid extracts of the mucus were prepared
using 14% BF3-MeOH mixture. Lipid extracts were dissolved
in 0.5 ml hexane and 1.5 ml 14% BF3-MeOH mixture. The
samples were flushed with nitrogen and heated for
90 minutes at 858C. After cooling to room temperature,
FAME were extracted three times with a mixture of 2 ml
hexane and 2 ml water, followed by centrifugation at 2000g
for 2 minutes. Hexane layers, which contained FAME were
separated, combined, and evaporated under a stream of nitrogen at room temperature. Analysis of fatty acid methyl esters
was performed by gas –liquid chromatography using a 6890
Hewlett Packard series gas chromatograph equipped with an
Omegawax 250 capillary column (Supelco, USA). The
column temperature programming was as follows: from 150
to 2508C at 48C min21 and maintained at 2508C. Helium
was used as the carrier gas at a flow of 1 ml min21. Methyl
esters of fatty acid were identified by a FAME mix (Supelco,
USA) as standard, by comparison of retention times, and
the results were reported as percentages of total identified
methyl esters fatty acids.
Triglycerides and total cholesterol
Triglycerides and total cholesterol were measured by the colorimetric enzymatic (Trinder, 1969; Bucolo & David, 1973)
using the commercial kit (SGM, Rome, Italy).
Statistical analysis
All the results were presented as the arithmetic mean of three
replications + standard deviation. Analysis of variance
(ANOVA) was used in order to evaluate differences among
the mean values of the measured parameters at the different
sampling periods. The analyses were performed by using the
Statsoft STATISTICA v. 6.0 (Statsoft, Inc., 2001).
RESULTS
Mucus viscosity, osmolarity and electrical
conductivity
When adult specimens of Sabella spallanzanii were removed
from their tubes and placed in a Petri dish, they immediately
secreted a copious colourless mucous material. Statistical
analysis revealed no significant differences among the viscosity values of mucus recorded in the four periods as well
as osmolarity. The mean viscosity value was 2.5+0.02 cPs
in respect to the 1 cPs viscosity of water measured at 208C
(Table 2). The mean osmolarity value was 1060+20
mosmol/l, showing as the worm mucus was iso-osmotic to
seawater (1152+25 mosmol/l). The mean electrical conductivity of mucus was 117+8 mS cm21 whilst the electrical conductivity of the seawater is 35 mS cm21.
Water and inorganic content
The water content of S. spallanzanii mucus was 96.2+0.3%
(Figure 2A). The residual part of the dried sample is mainly
represented by inorganic salts left over from evaporating seawater. Results of inorganic composition indeed showed that
the 65.2+2.3% of the dry weight was composed of inorganic
elements (Figure 2B). In particular Table 3 reports the mean
percentage of the elements detected in the mucus. Data
reveal that Cl and Na represent almost 60% of the lyophilized
samples. In all samples, magnesium, calcium, and potassium
each made up just 1.3 –4.5% of the inorganic content.
The PCBs content was estimated using the CEN method
15308 and was ,0.005 mg g21.
Protein and carbohydrate concentration
Statistical analysis revealed no significant differences either
among the protein concentrations of the mucus recorded in
the four periods, or among carbohydrate concentrations.
The mean protein content of S. spallanzanii mucus was
10.5+0.21 mg ml21 and the carbohydrate concentration, as
D-glucose equivalent, was (3.2+0.02 mg ml21). In addition
protein/glucose (PG) ratio for all replicates was 3.3 thus S.
spallanzanii mucus contains three times more protein than
carbohydrate (Table 2). By dry weight 26+1.2% was
protein, and 8+0.21% was carbohydrate (Figure 2B). As
already stated, much of the remainder of the dry weight was
inorganic (65.2+3.15%). Assuming that proteins and carbohydrates were the primary organic molecules present,
protein made up 76% of the organic material.
Table 2. Main physical–chemical characteristics of Sabella spallanzanii
mucus.
Water (%)
Total proteins (mg/ml)
Total lipids (mg/ml)
Triglycerides (mg/ml)
Cholesterol (mg/ml)
Carbohydrates (glucose equivalents mg/ml)
Inorganic
Viscosity 208C (cPs)
Osmolarity (mosmol/l)
Conductivity (mS cm21)
96+0.4
10.5+0.21
0.04+0.002
0.005+0.0003
0.002+0.0002
3.2+0.02
65.2+3.14
2.6+0.02
1060+20
117+8
biochemistry of sabella spallanzanii mucus
Fig. 2. Sabella spallanzanii mucus composition: (A) water content and dried
weight; (B) organic and inorganic residuals.
The electrophoretic analysis revealed at least ten major
protein bands, with molecular weights ranging from 16 to
90 kDa, and six minor components, with molecular weights
ranging from 14 to 116 kDa (Figure 3).
Lysozyme-like activity
Results from the standard assay on Petri dishes showed that
the mucus of S. spallanzanii exerted a natural lysozyme-like
activity. By the standard assay a mean diameter of lysis of
7.9 + 0.02 mm corresponding to 1.08 mg ml21 of hen eggwhite lysozyme was observed.
Antimicrobial activity
Our data enhance, in vitro, the presence in S. spallanzanii
mucus of an antimicrobial activity. This activity, as
shown in Table 4, was tested on Vibrio alginolyticus, Vibrio
harveyi, Vibrio anguillarum, Salmonella sp., Escherichia coli,
Pseudomonas aeruginosa, Candida albicans, Candida famata
and Candida glabrata. By way of plate assay, we were able
to quantify the degree of inhibition produced by the mucus
Table 3. Elements detected in mucus sample of Sabella spallanzanii.
Element
Content (%)
Cl
Na
Mg
H
K
Ca
C
N
Zn
Cu
Fe
P
Se
Sn
45.56+0.09
12.70+2.91
2.95+0.01
2.01+0.12
0.94+0.01
0.84+0.01
1.15+0.02
0.49+0.02
0.23+0.0003
Absent
Absent
Absent
Absent
Absent
66.8+3.19
Fig. 3. SDS-PAGE analysis of Sabella spallanzanii mucus. Panel A, mucus;
panel B, molecular weight standards furnished by Fermentas. Molecular
weights (kDa) of standard proteins are on the right.
on each strain. Vibrio anguillarum was the most inhibited
(55.6% growth inhibition). A lower percentage of inhibition
was instead measured on Pseudomonas aeruginosa and
Vibrio harveyi. Percentages of growth inhibition were respectively 21% and 17%. Among yeast only Candida albicans was
affected by the mucus treatment (13.6% growth inhibition).
The other examined strains were not affected in their
growth rate by the mucus.
Total lipids and fatty acid analyses
The results of the lipid analysis are presented in Figure 4. The
total mean lipid content of mucus was 0.004 + 0.0002 mg
ml21 corresponding to 0.1% of dry weight. The fatty acids
profile of S. spallanzanii mucus is shown in Table 5. Stearic
Table 4. Results of in vitro experiments showing the antimicrobial
activity of Sabella spallanzanii mucus.
Microbial strain
Growth inhibition (%)
Vibrio anguillarum
Vibrio harveyi
Vibrio alginolyticus
Salmonella sp.
Escherichia coli
Pseudomonas aeruginosa
Candida albicans
Candida famata
Candida glabrata
55.6
17
0
0
15
21
13.6
0
0
203
204
loredana stabili et al.
among polyunsaturated fatty acids, cis-13, 16-docosadienoic
acid methyl ester (22:2, n-6) and cis-11,14-eicosadienoic
acid methyl ester (20:2, n-6) were abundant. A considerable
contribution of undecanoic acid methyl ester (11:0), cis-11eicosenoic acid methyl ester (20:1) and a-linolenic acid
methyl ester (18:3) to the total fatty acids was also recorded.
Most of the fatty acids did not undergo statistically significant
changes during the period under study. The triglycerides and
the cholesterol concentrations were 0.005 + 0.0003 mg ml21
and 0.002 + 0.0002 mg ml21 respectively.
Fig. 4. Total lipid profile of Sabella spallanzanii mucus.
DISCUSSION
acid methyl (18:0) and palmitic acid methyl ester (16:0) were
the predominant saturated fatty acids, while, among monounsaturated fatty acids nervonic acid methyl ester (24:1) and
palmitoleic acid methyl ester (16:1) prevailed. Finally
Although mucus plays many different roles among marine
invertebrates, relatively little is known about the structure of
invertebrate mucous secretions and more in particular on
the link between biochemical structure and function. The
rheological properties of mucus, such as gelation, film formation, adhesiveness, and viscosity, are intimately related to
the chemical composition and structure of its components
and the forces which mould them into the elaborately organized three-dimensional structure of mucus. It is also reasonable to suggest that the physical –chemical properties are
intimately associated with the biological function of mucus.
The present work provides a preliminary step on this topic
describing some of the physical and chemical properties of
Sabella spallanzanii mucus. The viscosity of mucus is dictated
by its hydration state, which is dependent upon a Donnan
potential between mucins and the surrounding water
(Verdugo, 1984; Zuchelkowski et al., 1985; Gupta, 1989;
Cone, 1999). Osmolarity may also prove useful for mucus
characterization. Sabella spallanzanii mucus exhibits a low
viscosity (2.5 + 0.02 cPs) and its osmolarity is of the same
order of magnitude as the seawater such that mucus achieves
near ionic equilibrium with the surrounding medium. Thus
on account of these results we can infer that the mucus of
the studied polychaete is a fluid mucus.
As observed by different authors (Smith & Morin, 2002)
who found typical marine mucus having 96– 98% water, the
mucus of S. spallanzanii contains more than 90% water. The
high proportion of inorganic material (about 65.2%) presumably results from dried salts left over when the seawater in a
gel evaporates as already suggested by Smith et al. (1999)
and Smith & Morin (2002) who observed a similar proportion
of inorganic material in limpets’ and periwinkles’ mucus. By
contrast in other marine mucous secretions such as the
pedal mucus of Lottia gigantea and Collisella scabra and the
mucus of two species of littorinid, Littorina littorea and
Littorina obtusata, roughly less than 50% of the dry weight
was constituted of inorganic residue (Connor, 1986; Davies
et al., 1990).
The bulk of the organic material (about 35%) in the mucus
of the studied worm is composed of proteins ranging from 14
to 116 kDa and making up 76% of the organic material (26%
of the dry weight). Carbohydrates make up about 24% of the
organic material and 8% of the dry weight. Similar values
were recorded for limpets by Smith et al. (1999). Our results
are also in agreement with those reported by Flammang &
Walker (1997) and by Flammang et al. (1998) which provided
detailed information for the mucus secreted by sea star podia
composed of dry weight for 20% protein, and 8% carbohydrate, while much of the remainder was inorganic. The
Table 5. Fatty acids composition of Sabella spallanzanii mucus.
Saturated fatty acids
Percentage
6:0
8:0
10:0
11:0
12:0
13:0
14:0
15:0
16:0
17:0
18:0
20:0
22:0
23:0
24:0
0.46+0.02
0.77+0.02
0.18+0.02
17.68+0.5
0.34+0.02
1.30+0.02
2.35+0.04
0.83+0.02
17.86+0.3
0.37+0.02
26.68+0.6
1.28+0.05
0.17+0.02
0.00
0.00
Monounsaturated fatty acids
Percentage
14:1
15:1
16:1 n-7
17:1 n-8
18:1 n-9
18:1 n-7
20:1 n-9
22:1 n-9
24:1 n-9
0.39+0.02
0.49+0.02
1.50+0.02
0.77+0.02
0.84+0.02
0.84+0.02
0.88+0.02
0.00
7.93+0.02
13.65+0.16
Polyunsaturated fatty acids
Percentage
18:2 n-6
18:2 n-4
18:3 n-6
18:3 n-3
20:2 n-6
20:3 n-6
20:3 n-3
20:4 n-6
20:5 n-3
22:2 n-6
22:6 n-3
0.33+0.02
0.34+0.02
1.02+0.02
0.17+0.02
1.42+0.02
0.00
0.00
0.25+0.02
0.00
12.55+0.02
0.00
70.28+1.65
16.07+0.14
biochemistry of sabella spallanzanii mucus
co-occurrence of proteins and carbohydrates also seems to be
a common trait among non-permanent adhesives of marine
invertebrates, being observed, besides sea stars and sea
urchins, in sea cucumbers (DeMoor et al., 2003), snails
(Smith & Morin, 2002) and limpets (Smith, 2006). These
protein – carbohydrate complexes typically form highly
hydrated adhesives with viscoelastic properties (Flammang
et al., 1998; Smith, 2006) which contrast with the rigid
permanent proteinaceous adhesive cements. Finally, the
lipid content of S. spallanzanii mucus is very low and
accounted for 0.1% of dry weight.
Several studies attempted to estimate the nutritional values
of the mucus. Criteria such as ash content, biochemical constituents, caloric content, and the relative carbon and nitrogen
content are different aspects of the nutrient quality of mucus.
In corals, estimates of the nutritional value of mucus have
yielded variable results (Meikle, 1986; Meikle et al., 1987,
1988). Reported values for carbohydrate content range from
2.5 to 67% ash-free dry weight (AFDW), protein content
from 1.6 to 72.7% AFDW, and lipid from 0 to 93% AFDW
(Coffroth, 1990). Thus mucus from some species of corals is
considered a good food source serving as site of aggregation
for microorganisms and becoming heavily fouled. Thus sediment, faecal pellets, unidentifiable debris, bacteria, ciliates,
nauplii, ostracods, diatoms and filamentous algae were
observed on mucus, creating a heterogeneous community
(Paul et al., 1986; Coffroth, 1990). By contrast, S. spallanzanii
mucus was low in ash and contained low lipid content as well
as triglycerides, cholesterol and fatty acids suggesting that it
has a low nutritional value. These features together with the
high inorganic content and low organic one, suggest that it
is a poor food source.
An issue of interest is the proteic pattern of the S. spallanzanii mucus: as observed from the electrophoretic analysis, it
contains a complex of at least ten major and six minor proteins. This is in accordance with the general multiprotein
nature of other marine invertebrate adhesives. Researchers
on mussel byssus have so far identified nine proteins (for
review, see Sagert et al., 2006), whereas barnacle cement is
known to be made up of at least ten different proteins
(Kamino, 2006). For non-permanent adhesives, much less
information is available, but some multiprotein complexes
have been found in the adhesives of sea cucumbers and
limpets (for review, see Flammang, 2006; Smith, 2006).
Recently SDS-PAGE analysis of Paracentrotus lividus footprint material revealed that the soluble fraction contains
about 13 protein bands with molecular masses ranging from
10 to 200 kDa (Santos et al., 2009).
The presence in S. spallanzanii mucus of a haemolytic
activity (Canicattı̀ et al., 1992) and an antibacterial activity
suggest a role of this compartment in defending the worms
from microbial attack serving as medium into which the antimicrobial substances are released. In particular we observed a
lysozyme-like activity with a mean diameter of lysis of 7.9 +
0.02 mm on Petri dish assay corresponding to 1.08 mg ml21
of hen egg-white lysozyme. Morover, by the in vitro test, we
observed an antimicrobial activity towards several microorganisms including Vibrio anguillarum, Vibrio harveyi,
Pseudomonas aeruginosa and Candida albicans. The substrate
for lysozyme is contained not only in Gram-positive bacteria;
the lysozyme spectrum of the Gram-negative bacteria has
been established by Peterson & Hartsell (1955). Therefore,
in our case, it is possible to hypothesize that lysozyme from
S. spallanzanii mucus could be, at least in part, responsible
for the observed in vitro microbial growth inhibition.
However, we cannot exclude that other killing factors are
responsible for these events or that both lysozyme and other
defence factors act synergically in antimicrobial defence. The
defensive role of mucus is important taking into account
that S. spallanzanii lives in eutrophic environments such as
harbours where bacteria, including pathogens to man and
marine organisms, are abundant (Barg & Phillips, 1998).
Although the worms may be aggressed by microorganisms,
they are able to survive their attack on account of the presence
of a powerful immune system which includes antimicrobial
and haemolytic activities. Thus in the studied sabellid, the
mucus not only plays an essential role in the feeding mechanisms, tube building and fertilization (Stabili et al., 2009), but is
involved in defending the worms from microbial attack. This
role has already been demonstrated for other marine invertebrates mucus (Davis & Viney, 1998; Clare, 1995).
The findings from this study not only contribute to the
limited knowledge available on the mucus composition in
invertebrates, but also have implications for future investigations related to the employment of S. spallanzanii mucus
as a source of compounds with antimicrobial activity of
pharmaceutical and marine technology interest. As regards
pharmaceuticals we have to consider that the increasing development of bacterial resistance to traditional antibiotics has
reached alarming levels, thus necessitating the strong need
to develop new antimicrobial agents. Lysozyme exhibits antimicrobial activity against different microorganisms, and was
chosen recently as a model protein to develop more potent
bactericidal agents with broader antimicrobial specificity.
Several strategies are attempting to convert lysozyme to be
active in killing Gram-negative bacteria other than Grampositive bacteria thus introducing, for the first time, a new
conceptual utilization of lysozyme which would be an important contribution for medicine and modern biotechnology
(Ibrahim et al., 2002). The utilization of S. spallanzanii
mucus to extract bioactive substances of pharmaceutical interest is encouraged also on the basis of the results obtained on
lipids as well as PCB concentrations. Notably lipids are
related to bioaccumulation of lipophilic pollutants, including
PCBs, in living substrates (Jones & de Voogt, 1999; Quinnell
et al., 2004; Brown & Bythell, 2005; Ritchie, 2006); the low
value in lipid content within the mucus of S. spallanzanii indicated the low probability of accumulation of persistent lipophilic pollutants. In addition, the estimated PCB content is
below the maximum accepted value of contamination in
pharmaceutical preparations (,0.005 mg g21).
Lastly, the antibacterial proteins of S. spallanzanii mucus
could be employed to avoid the settlement of bacteria which
is the primary colonizing process in the marine biofouling
development. Alternative marine technologies employing
biogenic compounds that function as natural anti-settlement
agents are sought, taking into account that paints containing
TBT and copper (Jelic-Mrcelic et al., 2006) and organic
biocides (Turley et al., 2005) have been banned after 2008
(e.g. Hellio et al., 2002; Stupak et al., 2003; Konstantinou &
Albanis, 2004; Ostroumov, 2008).
In conclusion Sabella spallanzanii mucus provides an
accessible, renewable resource that could reward wider
exploration. Further studies will be accomplished to isolate
and characterize the effectors responsible for the antibacterial
activity observed.
205
206
loredana stabili et al.
ACKNOWLEDGEMENT
Financial support was provided by the Project ACTIBIOMAR
(www.actibiomar.it) granted by Apulian Region.
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Correspondence should be addressed to:
L. Stabili
Dipartimento di Scienze e Tecnologie
Biologiche ed Ambientali
Università del Salento
73100 (Lecce), Italy
email: loredana.stabili@iamc.cnr.it