Comparative Genome Assessment of the Two Novel Poly-γ-Glutamic Acid Producing Bacillus Strains

Poly-gamma-glutamic acid (PGA) is a homopolyamide, biosynthesized mostly by Bacillus sp. Our study focuses on understanding the genetic differences between the two species of Bacillus for their capability to produce PGA. Genes related to PGA synthesis, regulation, degradation and mannitol utilization of Bacillus subtilis Natto3 (BSN3) were compared with that of B. methylotrophicus IC4 (BMIC4). These strains differed in their genome sizes and average gene lengths. BMIC4 genome size was 4,214,684 bp which was larger than BSN3 comprising of 3,601,055 bp with no plasmid found in either of them. The average gene length of BSN3 and BMIC4 were 843.33 bp and 819.82 bp, respectively with higher number of predicted genes and proteins in BMIC4 (4341 and 4223 respectively). Interestingly, BMIC4 being larger in genome size and gene number, exhibited lesser number of unique pfam results (62) compared to 389 unique pfam of BSN3. Based on 16S rRNA gene sequence, BSN3 and BMIC4 were placed distantly on the phylogenetic tree. Sequence similarity of PGA producing genes ywsC, ywtA and ywtB between BSN3 and BMIC4 was 100%, 100% and 30% respectively. We report the presence of PGA degrading gene pgdS in BMIC4 which is otherwise reportedly absent in various strains of B. methylotrophicus. Sequence variation in the genes may have an impact on the PGA chain length, produced by these strains as BMIC4 produces high molecular weight PGA than BSN3. As B. methylotrophicus is newly discovered species, our comparative study will provide insights on the genomic variability between these two novel PGA producing strains.