Complete genome sequence of Shewanella marisflavi ECSMB14101, a red pigment synthesizing bacterium isolated from the East China Sea.

Bacteria of the genus Shewanella have been studied for their versatile electron-accepting abilities, particularly for extracellular electron transfer via minerals. Shewanella marisflavi ECSMB14101 was isolated from naturally formed biofilms in the East China Sea. The genome of S. marisflavi ECSMB14101 encodes 3891 genes with a total size of 4,343,492 bp in one chromosome. Its GC content is 49.89%. S. marisflavi ECSMB14101 is able to synthesize a red pigment, which may be achieved through Cytochrome c3 and electron transfer to reduce Fe(III) oxide. The genomic data presented here could provide fundamental insights to better understand the physiological characteristics of S. marisflavi, the ecological significance of red pigment synthesis, and its inductive effects on the settlement of marine invertebrate larvae.

Deep-sea bacteria trigger settlement and metamorphosis of the mussel Mytilus coruscus larvae.

Bacteria from coast seawaters are widely known to induce larval recruitment of many invertebrates. However, whether and how deep-sea bacteria, that play crucial roles in the ecological and biogeochemical cycles, promote larval recruitment remains little known. Here, the interaction between deep-sea bacterial biofilms (BFs) and Mytilus coruscus larvae was tested. All these nine deep-sea bacterial isolates triggered planktonic-sessile transition, and the highest percentage of post-larvae was observed in Virgibacillus sp. 1 BF. Except for Pseudomonas sp. 3, Pseudoalteromonas sp. 32 and Bacillus sp. 13, other BF cell  densities were significantly related to their corresponding inductive efficiency. The deep-sea Virgibacillus sp. 1 BF's cue that triggers planktonic-sessile transition was uncovered. Treating Virgibacillus sp. 1 BFs through physic-chemical approaches reduced inducing impact and cell survival. The conditioned water collaborated with formalin-fixed Virgibacillus sp. 1 BF hoisted planktonic-sessile transition efficiency in comparison to each one alone. Thus, two signals derived from deep-sea bacteria trigger planktonic-sessile transition in M. coruscus. This finding firstly demonstrates that deep-sea bacteria has good potential for application in the mussel seed production and provides novel insight to clarify the bacteria-mussel interaction.

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

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.