Preliminary screening of poly-γ-glutamic acid-associated genes in Bacillus strains isolated from Thai fermented soybean

Thua Nao is a traditional Thai fermented soybean product in which Bacillus species play a dominant role during fermentation. Poly-γ-glutamic acid (PGA), a biopolymer responsible for the viscous texture characteristic of several fermented soybean foods, is widely associated with Bacillus species; however, molecular information on PGA-associated genes in Thua Nao remains limited. This study aimed to perform a preliminary screening of PGA-related genes in Bacillus isolates obtained from Thua Nao. A total of 24 isolates were examined for the presence of the pgsC gene, involved in PGA biosynthesis, and the pgdS gene, associated with PGA degradation, using polymerase chain reaction. Strain TN51, previously identified as a potential PGA-producing strain based on the formation of a slime-like mucous substance, was included as a reference. Our findings showed that only five isolates yielded amplification products for one or both target genes. Among these, strains TN14 and TN51 carried both pgsC and pgdS , whereas strains TN01 and TN20 were positive only for pgdS , and strain TN02 was positive only for pgsC . The limited distribution of PGA-associated genes among the isolates indicates genetic diversity within the Thua Nao Bacillus population. Overall, this study represents the first screening of the PGA-associated genes pgsC and pgdS in Bacillus strains isolated from Thua Nao and provides a molecular basis for future studies investigating PGA metabolism in this traditional fermented food.