The complete genome sequence of the algicidal bacterium Bacillus subtilis strain JA and the use of quorum sensing to evaluate its antialgal ability.

We describe the isolation of Bacillus subtilis strain JA and demonstrate that this bacterium exhibited strong algicidal effects on the algae Alexandrium minutum with an inhibition rate exceeding 80 % within 48 h. B. subtilis JA significantly reduced the photosynthetic efficiency of A. minutum and caused extensive morphological damage to the algae. Genomic analysis of B. subtilis JA demonstrated that a putative AI-2 type quorum sensing (QS) gene (LuxS) is present in its genome cluster, which is regulate pheromone biosynthesis. Interestingly, the exogenous addition of a QS-oligopeptide (ComX-pheromone) improved the algicidal efficiency of B. subtilis JA, thus indicating that the algicidal activity of this bacterium is potentially regulated by QS. Collectively, our data describe a potential antialgal bacterium and speculated that its behavior can be modulated by QS signal. B. subtilis JA may therefore represent a valuable tool for the development of novel chemical-ecological methods with which to control harmful algae.

Complete genome sequence of Acinetobacter baumanni J1, a quorum sensing-producing algicidal bacterium, isolated from Eastern Pacific Ocean.

The Acinetobacter baumanni J1 isolated from surface water of the Eastern Pacific Ocean, demonstrated significant algicidal activity on the algae Alexandrium tamarense. Interestingly, this strain showed the ability to produce an acyl-homoserine lactone (AHL) quorum sensing molecule. To better understand its AHL producing mechanism and its ecological functions, the genome of A. baumanni strain J1 was completely sequenced. The genome contained a circular chromosome of 3,948,465 bp with an average GC content of 39.9 mol%. A total of 3707 protein coding genes, 41 tRNA genes and 16 rRNA genes were obtained. In silico genome annotation identified a LuxI putative gene located on contig 4. Subsequent thin-layer chromatography analysis indicated that C8-AHL could be produced by A. baumanni J1, which confirmed the authenticity of the LuxI gene. Taken together, this work describes an algicidal bacterium that is capable of producing an AHL molecule, which may represent a valuable tool for developing microbial methods to control harmful algae.