Polyglutamic acid (PGA), a protein in the mucilage of PGA-producing Bacillus spp., has expected applications in medical and biotechnological industries. Although the Bacillaceae family contains over 100 genera, research on bacterial PGA has exclusively focused on the genus Bacillus, especially B. subtilis var. natto and B. licheniformis. In the present study, indigenous Bacillaceae family strains were isolated from withered leaves and soil samples and screened for PGA production. As a result of the screening, the strain 8h was found to produce a mucilage possessing greater viscosity than PGA of B. subtilis var. natto (natto PGA). Biochemical analyses revealed that the 8h mucilage contains 63% protein and 37% polysaccharide, while mucilage of B. subtilis var. natto is composed of 61% protein and 39% polysaccharide. The most plentiful amino acid in 8h mucilage protein was glutamate (43%, mol/mol), which is similar to that of natto PGA, suggesting that it possesses characteristics of PGA. Although natto mucilage contains fructan, glucan was found as the polysaccharide of 8h mucilage. While phylogenetic studies indicated that the strain 8h belongs to Peribacillus simplex, the yield of the viscous mucilage by strain 8h was significantly higher than P. simplex type strain, suggesting that 8h is a mucilage-overproducing strain of P. simplex. Interestingly, 8h mucilage protein was found to contain more hydrophobic amino acid residues than natto PGA, suggesting that its amphiphilicity is suitable as a drug carrier and adjuvant. The present study is the first report of viscous mucilage and PGA-like protein produced by the genus Peribacillus.
Keywords: Bacillaceae; Mucilage protein; Peribacillus simplex; Polyglutamic acid; Soil bacteria.
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