Characterization of dual bacteriocins producing Bacillus subtilis SC3.7 isolated from fermented food.

The thermostable antimicrobial peptide with broad-spectrum inhibitory activity is of great interest due to its
potential application as a biopreservative agent. In the present study, we characterized a Bacillus spp. isolated
from fermented foods of Northeast region, India. The selective screening of bacteriocins producers was carried
out using B. subtilis based whole-cell biosensors BSF2470 and BS168.BS2. Among 12 isolates showing bacteriocin
production, culture with high antibacterial activity was subjected to whole-genome sequencing and referred to as
B. subtilis strain SC3.7. Through genome annotation, two bacteriocin genes spaS and sboA, responsible for the
synthesis of sublichenin and subtilosin A were identified. Further, mass spectrometric analysis confirmed the
secretion of sublichenin (3346 Da), its succinylated form (3446 Da), and subtilosin A (3399 Da). Interestingly, a
unique acyclic variant of subtilosin A (3417 Da) was also determined. The purified peptides were effective
against various indicator strains at lower concentrations. Overall, the study reports a B. subtilis strain that produces
two bacteriocins sublichenin and subtilosin A. This new combination of bacteriocins can be an effective
biopreservative in the food industry.