Larval settlement and metamorphosis of the mussel Mytilus coruscus in response to natural biofilms

Settlement and metamorphosis of pediveliger larvae of Mytilus coruscus in response to natural biofilms was investigated in the laboratory. Pediveliger larvae settled and metamorphosed in response to biofilms and post-larval settlement and metamorphosis increased with biofilm age. The activity of the biofilm was positively correlated with biofilm age, dry weight, bacterial density and diatom density, but had no apparent relationship with chlorophyll a concentration. The change in bacterial community composition corresponding to biofilm age may explain differences in the age-dependent inducing activities of biofilms, which in turn may play an important role in larval settlement in this species.     

The chemical cue tetrabromopyrrole from a biofilm bacterium induces settlement of multiple Caribbean corals

Microbial biofilms induce larval settlement for some invertebrates, including corals; however, the chemical cues involved have rarely been identified. Here, we demonstrate the role of microbial biofilms in inducing larval settlement with the Caribbean coral Porites astreoides and report the first instance of a chemical cue isolated from a marine biofilm bacterium that induces complete settlement (attachment and metamorphosis) of Caribbean coral larvae. Larvae settled in response to natural biofilms, and the response was eliminated when biofilms were treated with antibiotics. A similar settlement response was elicited by monospecific biofilms of a single bacterial strain, Pseudoalteromonas sp. PS5, isolated from the surface biofilm of a crustose coralline alga. The activity of Pseudoalteromonas sp. PS5 was attributed to the production of a single compound, tetrabromopyrrole (TBP), which has been shown previously to induce metamorphosis without attachment in Pacific acroporid corals. In addition to inducing settlement of brooded larvae (P. astreoides), TBP also induced larval settlement for two broadcast-spawning species, Orbicella (formerly Montastraea) franksi and Acropora palmata, indicating that this compound may have widespread importance among Caribbean coral species.     

Metamorphosis of a Scleractinian Coral in Response to Microbial Biofilms

Microorganisms have been reported to induce settlement and metamorphosis in a wide range of marine invertebrate species. However, the primary cue reported for metamorphosis of coral larvae is calcareous coralline algae (CCA). Herein we report the community structure of developing coral reef biofilms and the potential role they play in triggering the metamorphosis of a scleractinian coral. Two-week-old biofilms induced metamorphosis in less than 10% of larvae, whereas metamorphosis increased significantly on older biofilms, with a maximum of 41% occurring on 8-week-old microbial films. There was a significant influence of depth in 4- and 8-week biofilms, with greater levels of metamorphosis occurring in response to shallow-water communities. Importantly, larvae were found to settle and metamorphose in response to microbial biofilms lacking CCA from both shallow and deep treatments, indicating that microorganisms not associated with CCA may play a significant role in coral metamorphosis. A polyphasic approach consisting of scanning electron microscopy, fluorescence in situ hybridization (FISH), and denaturing gradient gel electrophoresis (DGGE) revealed that coral reef biofilms were comprised of complex bacterial and microalgal communities which were distinct at each depth and time. Principal-component analysis of FISH data showed that the Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, and Cytophaga-Flavobacterium of Bacteroidetes had the largest influence on overall community composition. A low abundance of Archaea was detected in almost all biofilms, providing the first report of Archaea associated with coral reef biofilms. No differences in the relative densities of each subdivision of Proteobacteria were observed between slides that induced larval metamorphosis and those that did not. Comparative cluster analysis of bacterial DGGE patterns also revealed that there were clear age and depth distinctions in biofilm community structure; however, no difference was detected in banding profiles between biofilms which induced larval metamorphosis and those where no metamorphosis occurred. This investigation demonstrates that complex microbial communities can induce coral metamorphosis in the absence of CCA.     

Larval settlement of the common Australian sea urchin Heliocidaris erythrogramma in response to bacteria from the surface of coralline algae

Bacterial biofilms are increasingly seen as important for the successful settlement of marine invertebrate larvae. Here we tested the effects of biofilms on settlement of the sea urchin Heliocidaris erythrogramma. Larvae settled on many surfaces including various algal species, rocks, sand and shells. Settlement was reduced by autoclaving rocks and algae, and by treatment of algae with antibiotics. These results, and molecular and culture-based analyses, suggested that the bacterial community on plants was important for settlement. To test this, approximately 250 strains of bacteria were isolated from coralline algae, and larvae were exposed to single-strain biofilms. Many induced rates of settlement comparable to coralline algae. The genus Pseudoalteromonas dominated these highly inductive strains, with representatives from Vibrio, Shewanella, Photobacterium and Pseudomonas also responsible for a high settlement response. The settlement response to different bacteria was species specific, as low inducers were also dominated by species in the genera Pseudoalteromonas and Vibrio. We also, for the first time, assessed settlement of larvae in response to characterised, monospecific biofilms in the field. Larvae metamorphosed in higher numbers on an inducing biofilm, Pseudoalteromonas luteoviolacea, than on either a low-inducing biofilm, Pseudoalteromonas rubra, or an unfilmed control. We conclude that the bacterial community on the surface of coralline algae is important as a settlement cue for H. erythrogramma larvae. This study is also an example of the emerging integration of molecular microbiology and more traditional marine eukaryote ecology.     

Metamorphosis of a scleractinian coral in response to microbial biofilms

Microorganisms have been reported to induce settlement and metamorphosis in a wide range of marine invertebrate species. However, the primary cue reported for metamorphosis of coral larvae is calcareous coralline algae (CCA). Herein we report the community structure of developing coral reef biofilms and the potential role they play in triggering the metamorphosis of a scleractinian coral. Two-week-old biofilms induced metamorphosis in less than 10% of larvae, whereas metamorphosis increased significantly on older biofilms, with a maximum of 41% occurring on 8-week-old microbial films. There was a significant influence of depth in 4- and 8-week biofilms, with greater levels of metamorphosis occurring in response to shallow-water communities. Importantly, larvae were found to settle and metamorphose in response to microbial biofilms lacking CCA from both shallow and deep treatments, indicating that microorganisms not associated with CCA may play a significant role in coral metamorphosis. A polyphasic approach consisting of scanning electron microscopy, fluorescence in situ hybridization (FISH), and denaturing gradient gel electrophoresis (DGGE) revealed that coral reef biofilms were comprised of complex bacterial and microalgal communities which were distinct at each depth and time. Principal-component analysis of FISH data showed that the Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, and Cytophaga-Flavobacterium of Bacteroidetes had the largest influence on overall community composition. A low abundance of Archaea was detected in almost all biofilms, providing the first report of Archaea associated with coral reef biofilms. No differences in the relative densities of each subdivision of Proteobacteria were observed between slides that induced larval metamorphosis and those that did not. Comparative cluster analysis of bacterial DGGE patterns also revealed that there were clear age and depth distinctions in biofilm community structure; however, no difference was detected in banding profiles between biofilms which induced larval metamorphosis and those where no metamorphosis occurred. This investigation demonstrates that complex microbial communities can induce coral metamorphosis in the absence of CCA.     

High bacterial diversity in nearshore and oceanic biofilms and their influence on larval settlement by Hydroides elegans (Polychaeta)

Settlement of many benthic marine invertebrates is stimulated by bacterial biofilms, although it is not known if patterns of settlement reflect microbial communities that are specific to discrete habitats. Here, we characterized the taxonomic and functional gene diversity (16S rRNA gene amplicon and metagenomic sequencing analyses), as well as the specific bacterial abundances, in biofilms from diverse nearby and distant locations, both inshore and offshore, and tested them for their ability to induce settlement of the biofouling tubeworm Hydroides elegans, an inhabitant of bays and harbours around the world. We found that compositions of the bacterial biofilms were site specific, with the greatest differences between inshore and offshore sites. Further, biofilms were highly diverse in their taxonomic and functional compositions across inshore sites, while relatively low diversity was found at offshore sites. Hydroides elegans settled on all biofilms tested, with settlement strongly correlated with bacterial abundance. Bacterial density in biofilms was positively correlated with biofilm age. Our results suggest that the localized distribution of H. elegans is not determined by ‘selection’ to locations by specific bacteria, but it is more likely linked to the prevailing local ecology and oceanographic features that affect the development of dense biofilms and the occurrence of larvae.     

Biofilm history and oxygen availability interact to affect habitat selection in a marine invertebrate

In marine systems, oxygen availability varies at small temporal and spatial scales, such that current oxygen levels may not reflect conditions of the past. Different studies have shown that marine invertebrate larvae can select settlement sites based on local oxygen levels and oxygenation history of the biofilm, but no study has examined the interaction of both. The influence of normoxic and hypoxic water and oxygenation history of biofilms on pre-settlement behavior and settlement of the bryozoan Bugula neritina was tested. Larvae used cues in a hierarchical way: the oxygen levels in the water prime larvae to respond, the response to different biofilms is contingent on oxygen levels in the water. When oxygen levels varied throughout biofilm formation, larvae responded differently depending on the history of the biofilm. It appears that B. neritina larvae integrate cues about current and historical oxygen levels to select the appropriate microhabitat and maximize their fitness.     

The effect of bacterial and diatom biofilms on the settlement of the bryozoan Bugula neritina

Biofilms of marine bacteria and diatoms and their combinations were examined in laboratory choice assays to determine their effects on the attachment and successful metamorphosis of the larvae of the bryozoan Bugula neritina (Linnéus). The larval settlement in response to unfilmed surfaces, a natural biofilm (NBF) and adsorbed cells of three strains of bacteria, five strains of pennate diatoms and combinations of the two at different densities. Bacterial and diatom strains showed different effects on the larval settlement of B. neritina. Bacterial monospecific strains of an unidentified α-Proteobacterium and Vibrio sp. mediated the same percentage of settlement as a filtered seawater control. Biofilms of Pseudoalteromonas sp. caused significantly lower larval settlement. Larval settlement of B. neritina was negatively correlated with increasing densities of Pseudoalteromonas sp. The highest percentages of settlement were mediated by the biofilms of the diatom species Achnanthes sp., Amphora cofeaeformis, Amphora tenerrima, Nitzschia constricta and a 5-day-old natural biofilm, while the lowest settlement was found on a N. frustulum film. A three-way analysis of variance demonstrated that the density of bacteria and the presence of particular species of diatoms and bacteria in combined biofilms, significantly affected the settlement of B. neritina larvae. High settlement of larvae (50-90%) at all treatments indicated that B. neritina larvae are much more indiscriminate settlers than previously expected. Hence, using this species as a monitoring organism to trace ecologically relevant subtle changes of settlement cues in the natural environment should be carefully re-examined.     

Larval development and post-settlement metamorphosis of the barnacle Balanus albicostatus Pilsbry and the serpulid polychaete Pomatoleios kraussii Baird: Impact of a commonly used antifouling biocide,Irgarol 1051

Abstract

The impact of a commonly-used antifouling algicide, Irgarol 1051, on the larval development and post-settlement metamorphosis of the barnacle, Balanus albicostatus Pilsbry (Crustacea: Cirripedia), and the larval metamorphosis of a serpulid polycheate, Pomatoleios kraussii Baird, was evaluated. In the case of B. albicostatus, larval mortality increased with an increase in the concentration of Irgarol 1051, and there was a shift in the larval stage targeted from advanced instars to early instars. Nauplii that survived to the cyprid instar stage when reared in the presence of Irgarol 1051 showed prolonged instar and total naupliar duration when compared to the controls. The post-settlement metamorphosis of cyprids significantly varied with Irgarol concentration and also with biofilm age. One and 2-d-old untreated biofilms showed higher metamorphosis when compared to 5-d-old biofilms. However, when the biofilms that promoted cyprid metamorphosis were treated with Irgarol 1051 at low concentrations, metamorphosis rates decreased. Cyprids were prevented from metamorphosing completely by biofilms treated at the highest concentration of Irgarol 1051. Inhibition of metamorphosis was also observed in the case of competent polychaete larvae when exposed to Irgarol 1051 compared to those exposed to metamorphosis inducers such as 3-iso-butyl-1-methylxanthine (IBMX) and natural biofilms. Identification of the pathway(s) that caused the promotory biofilms to become toxic when exposed to Irgarol 1051 is discussed.     

Impact of Irgarol 1051 on the larval development and metamorphosis of Balanus amphitrite Darwin,the diatom Amphora coffeaformis and natural biofilm

The effect of Irgarol 1051 on the biofilm-forming diatom, Amphora coffeaformis, and on natural biofilm (NBF) was assessed. A reduction in the number of A. coffeaformis cells within a biofilm was observed after treatment with Irgarol 1051, confirming its role as an inhibitor of photosynthetic activity. The impact of this compound on the development of nauplii of Balanus amphitrite was evaluated through its impact on Chaetoceros calcitrans, which was provided as food for the larvae. A reduction in the number of cells of C. calcitrans was observed when treated with Irgarol 1051. When larvae of B. amphitrite were reared using C. calcitrans in the presence of Irgarol 1051, their mortality increased with an increase in the concentration of Irgarol 1051 (13% at 1 µg l^?1 to 40% at 1000 µg l^?1) compared with the control (6%). Nauplii reared in the presence of Irgarol 1051 developed more slowly (6–7 days) compared with control larvae (4–5 days). Cyprid bioassay results indicated an increase in percentage metamorphosis (76%) when NBFs were treated with the highest concentration of Irgarol 1051, compared with untreated biofilm (28%). The enhanced rate of metamorphosis appeared to be related to an increase in bacterial numbers in the biofilm, which may have been due to lysis of diatoms caused by Irgarol 1051. A. coffeaformis biofilms grown in the presence of antibiotics showed a significant reduction in cell numbers, which on further treatment with Irgarol 1051 showed an increase in cell numbers. Thus, it can be hypothesised that A. coffeaformis cells that were subjected to stress twice may have expressed resistant genes. Furthermore, if plasmids are present in the biofilms, they may enhance transfer to the surviving cells making them more resistant to hostile conditions.     

Effect of biofilm age on settlement of Mytilus edulis

Biofilm ageing is commonly assumed to improve mussel settlement on artificial substrata, but the structure and taxonomic composition of biofilms remains unclear. In the present study, multi-species biofilms were characterized at different ages (1, 2, and 3 weeks) and their influence on settlement of the blue mussel, Mytilus edulis, was tested in the field. As biofilms can constitute a consistent food resource for larvae, the lipid quality, defined as the proportion of related essential fatty acids, may be a selection criterion for settlement. Overall mussel settlement increased on biofilms older than 1 week, and the enhanced settlement corresponded to the abundance and composition of the biofilm community, rather than to essential fatty acid levels. However, during a pulse of phytoplankton, the positive influence of biofilm was not detected, suggesting that pelagic cues overwhelmed those associated with biofilms. The influence of biofilms on mussel settlement could be more crucial when planktonic resources are limited.     

Settlement of Pomatoceros lamarkii (Serpulidae) larvae on biofilmed surfaces and the effect of aerial drying

The settlement responses of Pomatoceros lamarkii (Polychaeta: Serpulidae) larvae to biofilms of varying age on slate surfaces and to dried biofilms on slate surfaces were investigated in the laboratory. Settlement experiments were performed as multi-treatment, still water assays. Larvae did not settle on clean, non-biofilmed slates but settled on biofilms up to 28 days old. Settlement intensity was closely related to the bacterial density of a biofilm. Drying a biofilmed surface for 1-2 h at 20 degrees C to simulate a single tidal emersion completely negated the former inductive effect of the biofilm. Drying also negated the larval settlement-inducing effect that normally results from the presence of conspecific adults. The settlement inhibition lasted for approximately 5 days following a single drying event. Larvae settled readily on biofilms exposed to formalin and antibiotics. Treating biofilms with formalin or antibiotics before or after drying had no effect upon larval avoidance of dried biofilms. Freeze-drying a biofilm had the same effect as aerial drying. The biofilm drying effect could not be mimicked by exposing biofilms to hyper-saline seawater. The finding that P. lamarkii larvae do not settle on dried biofilms could have significance in explaining the natural distribution of this species in the intertidal.     

The interplay of substrate nature and biofilm formation in regulating Balanus amphitrite Darwin, 1854 larval settlement

The settlement of marine larvae is influenced by a wide range of physical and biological factors. It is still poorly known how the nature of substrate and the biofilm can interact in regulating settlement patterns of invertebrate larvae. Here we use laboratory experiments focused on settlement behaviour of the barnacle Balanus amphitrite. The aim of this work is to understand whether: (i) the nature of substratum can affect biofilm formation and its structure, (ii) the nature of substratum can affect B. amphitrite larval settlement, (iii) the age of the biofilms and the nature of substrate can interact in influencing larval settlement.Four kinds of substrata (marble, quartz, glass, and cembonit) were biofilmed under laboratory conditions for 5, 10 and 20 days at the temperature of 28 °C. Settlement response was investigated with 5-day-old cyprids. Biofilms were quantitatively and qualitatively analysed by scanning electron microscopy. The settlement of B. amphitrite larvae significantly differed among substrata; also, the patterns of development of biofilm assemblages changed with substrate. In addition, the larval attractiveness of different substrates tends to disappear with biofilm age.     

海假交替单胞菌fliC-02330基因缺失影响生物被膜形成及厚壳贻贝幼虫附着变态

【背景】假交替单胞菌属是一种广泛分布于海洋环境的革兰氏阴性细菌,存在于海底沉积物中,能分泌大量的胞外产物形成海洋微生物被膜,从而诱导海洋无脊椎动物的附着。【目的】探究海假交替单胞菌鞭毛蛋白fliC基因对生物被膜形成及厚壳贻贝诱导活性的影响。【方法】通过基因敲除构建海假交替单胞菌fliC-02330基因缺失突变菌,研究突变菌和野生菌菌落形态、生物被膜形成能力、胞外物质以及对厚壳贻贝幼虫附着变态的诱导能力等的差异性。【结果】与野生菌相比,突变菌菌落表型出现褶皱,运动能力下降,形成被膜膜厚增加,以及对幼虫附着变态诱导活性下降。共聚焦扫描发现,fliC-02330基因缺失突变菌胞外多糖含量下降,而蛋白含量上升。【结论】海假交替单胞菌鞭毛蛋白fliC-02330基因缺失促进生物被膜形成,但抑制厚壳贻贝幼虫附着变态。本研究为探究细菌鞭毛蛋白基因与厚壳贻贝幼虫的作用机制,以及后续进一步探索微生物参与海洋无脊椎动物附着变态提供一定的理论依据。     

Copper affects biofilm inductiveness to larval settlement of the serpulid polychaete Hydroides elegans (Haswell)

Copper (Cu) contamination is a potential threat to the marine environment due to the use of Cu-based antifouling paints. Cu stress on larval settlement of the polychaete Hydroides elegans was investigated, and this was linked to Cu stress on biofilms and on the biofilm development process. The inductiveness of young biofilms was more easily altered by Cu stress than that of old biofilms, indicating the relative vulnerability of young biofilms. This might result from changes in bacterial survival, the bacterial community composition and the chemical profiles of young biofilms. Cu also affected biofilm development and the chemical high performance liquid chromatograph fingerprint profile. The results indicate that Cu affected larval settlement mainly through its effect on the process of biofilm development in the marine environment, and the chemical profile was crucial to biofilm inductiveness. It is strongly recommended that the effects of environmentally toxic substances on biofilms are evaluated in ecotoxicity bioassays using larval settlement of invertebrates as the end point.     

Facilitation and inhibition of larval attachment of the bryozoan Bugula neritina in association with mono-species and multi-species biofilms

In this study, we investigated the effect of mono-species and multi-species biofilms on larval attachment of the bryozoan Bugula neritina. The effect of biofilms was examined through a double-dish choice bioassay in which larvae were given the choice of attaching either to a clean surface of a container or to surfaces covered with biofilms. Larvae attached in response to mono-species biofilms of 5 out of 7 bacterial isolates from a subtidal region, but they avoided surfaces covered by biofilms of 7 out of 8 isolates obtained from an intertidal region. In the follow-up choice experiments with multi-species biofilms developed for 2 days, 7 days, 14 days, 28 days and 30 days, larvae preferentially attached to filmed surfaces over the unfilmed surfaces. When biofilms from 2 different tidal regions (intertidal and subtidal) were offered as choices in the double-dish bioassay, larvae in all cases attached on the subtidal biofilms. Two-day-old subtidal biofilms with low densities of bacteria induced significantly higher (p < 0.05) attachment than did 30- day-old intertidal biofilms, which had high bacterial density. Terminal Restriction Fragment Polymorphism (T-RFLP) analysis revealed that the bacterial communities were substantially different in the subtidal and intertidal regions during all periods of the experiment. Attachment of B. neritina on subtidal biofilms did not depend on the bacterial density but rather was negatively correlated with diatom density, thickness of the exopolysaccharide layer and biofilm age. Our results suggest that the larvae of B. neritina can discriminate between biofilmed and clean surfaces and between biofilms developed under different tidal zones.     

Induction of larval metamorphosis of the coral Acropora millepora by tetrabromopyrrole isolated from a Pseudoalteromonas bacterium

The induction of larval attachment and metamorphosis of benthic marine invertebrates is widely considered to rely on habitat specific cues. While microbial biofilms on marine hard substrates have received considerable attention as specific signals for a wide and phylogenetically diverse array of marine invertebrates, the presumed chemical settlement signals produced by the bacteria have to date not been characterized. Here we isolated and fully characterized the first chemical signal from bacteria that induced larval metamorphosis of acroporid coral larvae (Acropora millepora). The metamorphic cue was identified as tetrabromopyrrole (TBP) in four bacterial Pseudoalteromonas strains among a culture library of 225 isolates obtained from the crustose coralline algae Neogoniolithon fosliei and Hydrolithon onkodes. Coral planulae transformed into fully developed polyps within 6 h, but only a small proportion of these polyps attached to the substratum. The biofilm cell density of the four bacterial strains had no influence on the ratio of attached vs. non-attached polyps. Larval bioassays with ethanolic extracts of the bacterial isolates, as well as synthetic TBP resulted in consistent responses of coral planulae to various doses of TBP. The lowest bacterial density of one of the Pseudoalteromonas strains which induced metamorphosis was 7,000 cells mm(-2) in laboratory assays, which is on the order of 0.1-1% of the total numbers of bacteria typically found on such surfaces. These results, in which an actual cue from bacteria has been characterized for the first time, contribute significantly towards understanding the complex process of acroporid coral larval settlement mediated through epibiotic microbial biofilms on crustose coralline algae.     

The effect of carbon nanotubes and titanium dioxide incorporated in PDMS on biofilm community composition and subsequent mussel plantigrade settlement

This study investigated the effect of carbon nanotubes (CNTs) and titanium dioxide (TiO₂) incorporated in PDMS on biofilm formation and plantigrade settlement of Mytilus coruscus. TiO₂ increased bacterial density, and CNTs also increased bacterial density but reduced diatom density in biofilms after 28 days. Further analysis was conducted between bacterial communities on glass, PDMS, CNTs (0.5 wt%) and TiO₂ (7.5 wt%). ANOSIM analysis revealed significant differences (R > 0.9) between seven, 14, 21 and 28 day-old bacterial communities. MiSeq sequencing showed that CNTs and TiO₂ impacted the composition of 28 day-old bacterial communities by increasing the abundance of Proteobacteria and decreasing the abundance of Bacteroidetes. The maximum decreased settlement rate in 28 day-old biofilms on CNTs and TiO₂ was > 50% in comparison to those on glass and PDMS. Thus, CNTs and TiO₂ incorporated in PDMS altered the biomass and community composition of biofilms, and subsequently decreased mussel settlement.     

CHEMICAL MEDIATION OF COLONIZATION OF SEAWEED SURFACES1

The surfaces of macroalgal thalli are colonized by planktonic propagules (larvae, spores, cells, etc.) from a wide diversity of eukaryotes and prokaryotes. Colonization (here defined broadly to include processes such as settlement, attachment, metamorphosis, biofilm formation, and infection) of seaweed surfaces can be both induced and inhibited by metabolites produced at those surfaces. However, detailed examples of chemically mediated interactions at seaweed surfaces for which chemical cues have been characterized, quantified in situ, a biological effect determined, and the consequences to the demography of the seaweeds or colonizers demonstrated are very rare. Here we briefly review the literature on both deterrents (“natural antifoulants”) and inducers of colonization and on interactions at seaweed surfaces between the hosts and associated bacterial biofilms. One theme that emerges is the strong need to integrate ecology, cell biology, and chemistry to understand the distribution of surface‐active molecules in situ and their ecological consequences. This multidisciplinary approach is further emphasized for research on biofilms on seaweeds, where recently developed molecular tools for characterizing bacterial communities are opening up an entire new area of marine chemical ecology. Finally, we emphasize an integrated approach to the topic, as we believe that many aspects of somewhat disparate fields including, for example, induction of larval settlement, algal pathogenesis, and the molecular biology of bacterial signaling can be usefully viewed within the overall framework of chemical mediation of surface colonization.     

A bacterial polysaccharide biosynthesis-related gene inversely regulates larval settlement and metamorphosis of Mytilus coruscus

Abstract

Larval settlement and metamorphosis is essential for the development of marine invertebrates. Although polysaccharides are involved in larval settlement and metamorphosis of Mytilus coruscus, the molecular basis of polysaccharides underlying this progression remains largely unknown. Here, the roles of the polysaccharide biosynthesis-related gene 01912 of Pseudoalteromonas marina ECSMB14103 in the regulation of larval settlement and metamorphosis were examined by gene-knockout technique. Compared with biofilms (BFs) of the wild-type P. marina, Δ01912 BFs with a higher colanic acid (CA) content showed a higher inducing activity on larval settlement and metamorphosis. Deletion of the 01912 gene caused an increase in c-di-GMP levels, accompanied by a decrease in the motility, an increase in cell aggregation, and overproduction of CA. Thus, the bacterial polysaccharide biosynthesis-related gene 01912 may regulate mussel settlement by producing CA via the coordination of c-di-GMP. This work provides a deeper insight into the molecular mechanism of polysaccharides in modulating mussel settlement.