Recruiting: Bacterial Genes Needed!

Recruiting: Bacterial Genes Needed!

Most benthic marine organisms have a planktonic larval phase in their life-cycle and, as a consequence, larval settlement is an important factor determining distribution patterns of benthic marine organisms.  Biofilms (defined as a community of organisms on the surface of an inanimate object or living organism) provide chemical cues for settling larvae and are therefore markedly important in the marine environment. Biofilms are also particularly relevant in the commercial sector where bio“fouling” can be economically expensive. Given the financial incentive from the commercial sector; research to increase the understanding of biofilms has exploded, with over 1000 published papers on the topic to date. Despite much speculation, the role of bacterial cues in biofilms and recruitment is unknown. Furthermore the role of molecular inducers in general is poorly understood. Huang et al. (2012) aimed to fill the described knowledge gap by investigating the molecular cues and mechanisms in which an important marine tube worm larvae (Hydroides elegans) is induced to settle on bacterial biofilms of the abundant Pseudoaltermonas luteoviolacea.

Wilde-type P.luteoviolacea is known to induce the settlement of H.elegans, however the mechanisms of induction are unstudied. Huang et al. created mutants of P.luteoviolacea via random transposon insertion and screened for non-inducing strains. Two strains which did not induce the settlement of H.elegans were isolated for further investigation (Plm9 and Plm45). Analysis of the isolated mutant’s Open Reading Frames (ORFs) revealed possible genes important for settlement induction. Using the isolated mutants, deletion mutants were created (strain with deletion of the genes in which the transposon was inserted), allowing the confirmation that the genes disrupted by transposon insertion were responsible for the lack of induction.  The growth rate of mutants was compared to that of wild-type cells to confirm lack of induction was not simply down to reduced mutant growth rate. In addition, phenotypic parameters such as biofilm cell density, thickness and exopolymeric substance biomass were not different in mutant and wild-types biofilms. The lack of induction by deletion mutants suggests that the deleted gene products are important and in some way provide cues for settlement. BLAST analysis of the deleted ORFs revealed some putative information about the potential function of protein products, of particular interest was a gene coding for Type VI secretion systems (secretion in bacteria means the transport or translocation of effector molecules).

The reviewed study represents the first evidence that bacterial genes are important in the settlement of macrofaunal marine organisms. Whilst the paper is in no way conclusive, it does provide a solid preliminary understanding into the possible role of molecular cues in settlement. Increasing our understanding of bacterial biofilm induction cues is not only important in the broad areas of benthic ecology and micro-macro interactions, but is also potentially important for the development of solutions to biofouling.

Huang, Y., Callahan, S., & Hadfield, M. G. (2012). Recruitment in the sea: bacterial genes required for inducing larval settlement in a polychaete worm. Scientific reports, 2, 228.

http://www.nature.com/srep/2012/120118/srep00228/full/srep00228.html