Algal epibiosis on Megabalanus tintinnabulum and its role in segregation of the Balanus amphitrite population

Ulva sp. and Gracilaria sp. were found colonizing shell surfaces of an acorn barnacle, Megabalanus tintinnabulum. However, this association was not noticed in the case of Balanus amphitrite, which was a co‐inhabitant. Such a difference in intergeneric interactions with the algae was examined in laboratory experiments. For this, the influence that extracts of algae, extracts of algae‐associated bacteria and natural leachants from M. tintinnabulum exerted on cyprid metamorphosis of B. amphitrite was examined. Extracts of algae and associated bacteria showed no effect on the metamorphosis of B. amphitrite. This may be attributed to absence of cue‐specific sugars in the exopolysaccharides and culture supernatants of bacteria. On the other hand, natural leachants of M. tintinnabulum, which showed the presence of N‐acetyl‐d ‐glucosamine, a known algal spore attractant, also inhibited metamorphosis of B. amphitrite. Thus, hosting specific epibionts could have important roles in the segregation of barnacle population.     

Significance of biofilm proteins in modulating cyprid metamorphosis of Balanus amphitrite (Cirripedia: Thoracica)

The role of biofilm proteins in modulating cyprid metamorphosis is not well understood. In the present investigation this possibility was explored by disrupting biofilm proteins using commercially available protease. The influence of natural biofilm and artificial biofilms of Aeromonas salmonicida salmonicida and Bacillus brevis and their culture supernatants and exopolysaccharides obtained under different nutritional conditions was evaluated. Natural biofilm facilitated cyprid metamorphosis in Balanus amphitrite, whereas monospecies biofilms did not. The treatment of biofilms with protease resulted in a decline in metamorphosis, except in B. brevis, where although metamorphosis was negated initially, it increased with the protease concentration and observation days. As the response of cyprids to exopolysaccharides produced by A. salmonicida salmonicida was dependent on protein concentration, protease treatment resulted in a decrease in metamorphosis, whereas in case of B. brevis biofilms, protease hydrolysis products could be important in providing settlement cues. Thus, biofilm bacterial components play an important role in the cyprid metamorphosis of Balanus amphitrite.     

Phylogenetic diversity of carbohydrate degrading culturable bacteria from Mandovi and Zuari estuaries,Goa, west coast of India

Coastal and estuarine waters are highly productive and dynamic ecosystems. The complex carbohydrate composition of the ecosystem would lead to colonisation of microbial communities with abilities to produce an array of complex carbohydrate degrading enzymes. We have examined the abundance and phylogenetic diversity of culturable bacteria with abilities to produce complex carbohydrate degrading enzymes in the Mondovi and Zuari eustauri. It was interesting to note that 65% of isolated bacteria could produce complex carbohydrate degrading enzymes. A majority of these bacteria belonged to Bacillus genera followed by Vibrio, Marinobacter, Exiquinobacterium, Alteromonas, Enterobacter and Aeromonas. Most abundant bacterial genus to degrade hemicellulose and cellulose were Bacillus and Vibrio respectively. Most abundant bacterial genus to degrade hemicellulose and cellulose were Bacillus and Vibrio respectively. It was seen that 46% of Bacillus had ability to degrade both the substrate while only 14% of Vibrio had bifunctionality.     

Influence of Bacterial Exopolymers, Conspecific Adult Extract and Salinity on the Cyprid Metamorphosis of Balanus amphitrite Cirripedia: Thoracica

Abstract. The influence of bacterial exopolymers and conspecific adult extract of Balanus amphitrite on metamorphosis of cyprid larvae at different salinities has been evaluated through laboratory assay. The bacterial exopolymers epm extracted from Pseudomonas, Acinetobacter and Enterobacteriaceae strains, isolated from the shell surface of Balanus amphitrite , were examined for their influence on metamorphosis, both individually and in combination with conspecific adult extract at 15, 25, 35 and 45% salinities. The epm extracted from the pool of these three strains mixed culture was also tested similarly.
The influence of epm varied with the strain of bacteria and salinity. The surface condition and time interval significantly influenced the metamorphosis rate. The interaction between these two variables, however, did not change in any combination, irrespective of the bacterial strain used. The Pseudomonas epm promoted metamorphosis at 15%, but was inhibitory at 45%. The Acinetobacter epm induced metamorphosis to a level of 71 ± 15% at 15%. No such metamorphosis promotion was observed with the epm of this strain at higher salinities and the influence was less than the conspecific adult extract. The epm of Enterobacteriaceae and mixed culture epm did not promote metamorphosis. There was no appreciable change in the metamorphic rate in the control conditions at 25%, 35% and 45% salinities and the rate was much lower than that obtained with conspecific adult extract. At 15%, however, the influence of adult extract was closer to that of the control condition. This shows that even in the absence of any attractant, the settlement intensity is positively influenced at mid-salinity of the barnacles' natural distributional range.     

Epibiotic community on the acorn barnacle (Balanus amphitrite) from a monsoon‐influenced tropical estuary

The epibiotic communities (diatoms and metazoans) on the outer surfaces of the shell of the barnacle Balanus amphitrite (BSh) and its opercular valves (the scutum and tergum; BST) were investigated on a monthly basis for 1 year in a tropical monsoon‐influenced estuary and compared with that of the surrounding rock biofilm. BSh and BST were rich in the diatoms Achnanthes longipes and Melosira nummuloides and amongst the invertebrates, nematodes and tardigrades were abundant. To the best of our knowledge, this is the first report of epibiosis on the acorn barnacle. Diatom abundance was at its maximum during the monsoon season on all the inter‐tidal substrata i.e. BSh, BST and rock. A significant correlation was found between the density of diatoms and invertebrates associated with the BSh and BST, possibly because of the trophic relationship between them or the suitability of the physical environment. The possible role of these epibionts on the settlement of this barnacle species is currently unknown and needs further investigation.     

Interactions of bacteria with diatoms: influence on natural marine biofilms

Interactions between microfouling components influence the biofilm community and the cascading events, thus playing an important role in the biofouling process. Bacteria and diatoms are among the dominant forms reported in biofilms. Experiments were carried out with natural marine biofilms from a tropical monsoon‐influenced environment to evaluate the interactions between bacteria and diatoms through application of antibiotics (streptomycin and chloramphenicol). Overall, chloramphenicol inhibited diatom communities, whereas streptomycin did not. These antibiotic‐mediated changes in the fouling diatom community were consistent across the seasons. However, the rates at which the fouling communities changed depended on the initial species composition. It was also observed that elevated nutrient concentrations overrode the inhibitory effect of chloramphenicol. Maximum Vibrio enhancement was observed in the enriched conditions during the pre‐monsoon and unenriched conditions during the monsoon (with naturally elevated background nutrient concentrations), highlighting the relevance of nutrient concentrations for Vibrio spp. This has interesting implications for antibiotic‐mediated interactions between fouling diatom and bacterial communities under differing nutrient regimes. Although this study indicates the relevance of ‘cross‐talk’ at the microfouling level, understanding the effects of additional microbial products (e.g. bacteriocins and peptidoglycan) on these community‐level interactions will represent a step forward.