An analysis of genes in the marine bacterium Pseudoalteromonas luteoviolacea underlying its capacity to induce larval settlement in the polychaete Hydroides elegans

Abstract

Competent larvae of serpulid polychaete Hydroides elegans can be induced to settle and metamorphose by single or multiple-species of bacterial biofilms. Previous experiment showed that Pseudoalteromonas luteoviolacea (HI1) is one of very good inductive strains. Total 4 open reading frames (ORFs) in the genome of P. luteoviolacea (HI1) were identified to be essential for the inductive capacity of P. luteroviolacea (HI1) by transposon mutagenesis or allelic replacement. These 4 ORFs were clustered in a very long operon containing at least 7 ORFs and a length of 16, 622bp. Quantitative real time reverse transcription PCR (q-RT-PCR) was applied to compare the expression of the identified ORFs between planktonic and biofilm phases of P. luteoviolacea (HI1). None of the inductive ORFs exhibited differential expression between biofilm and planktonic phases. To understand the function of genes that confer larval settlement-inducing capacity to biofilms of P. luteoviolacea (HI1), major biofilm characteristics, such as biofilm bacterial density, biofilm thickness, biofilm biomass and EPS biomass, were investigated in biofilms composed of P. luteoviolacea (HI1) and seven deletion mutants made from this species. The results showed that there are not significantly different between biofilm of wild type P. luteroviolacea (HI1) and its 7 deletion mutants in the characteristics invested above, suggesting that physical characteristics of biofilms are not critical to the inductive capacity of P. luteoviolacea (HI1), and that essential inductive molecular components are missing in the non-inductive deletion mutant strains.