Whole genome sequence analysis of an environmental isolate Bacillus subtilis K3C: Genome plasticity and acquisition of hyaluronic acid capsule traits through horizontal multigene transfer

Abstract

B. subtilis K3C was isolated from an environmental sample. Genomic analysis revealed that the GRAS strain harbors a circular chromosome of 4,120,051 bp composed of 4361 protein coding sequences with a GC content of 43.4 %, 80 tRNA, and 3 rRNA genes. Two regions containing complete assembly of prophages encoded by 83 prophage genes were present suggesting the role of bacteriophage infection in evolutionary accumulation of strain-specific genes contributing towards strain diversification. Strong recombination, repair, transfer and competence systems were identified, suggesting their role in strain fitness and evolutionary process. Pan-genomic analysis revealed 3824 protein homologs as the bacterial core genome shared among different strains and 390 singletons in the pan-genome orthologous groups. The hyaluronic acid capsule trait in the isolate seems to be acquired through selective pressure to adapt in environmentally stressed niches. Phyloproteomic analysis showed that the acquired genes responsible for HA production were phylogenetically closer to Streptococcal clade, evidencing the role of horizontal gene transfer. The bacterial genome showed the presence of multiple HA genes translating HasB and HasC proteins suggesting gene dosage in the strain. However, no gene rearrangement events seem to have taken course as the HA genes were integrated in different contigs of the genome.