Poly Γ-glutamic Acid Production Research Articles

Production and molecular weight variation of poly-γ-glutamic acid using a recombinant Bacillus subtilis with various pgs-component ratios.

Poly-γ-glutamic acid (PGA) has been of interest as a sustainable biopolymer in industrial applications. PGA biosynthesis in Bacillus subtilis is catalyzed by a transmembrane protein complex comprising PgsB, PgsC, and PgsA. To determine the Pgs component responsible for PGA overproduction, we constructed recombinants in which the promoter of the host-derived pgs gene was replaced with another host-derived gene promoter. These recombinants were then transformed using high-copy-number plasmids with various pgs-gene combinations to enhance Pgs component in different ratios. Subsequently, PGA production was investigated in batch cultures with l-glutamate supplemented medium. The recombinant strain enhanced with pgsB alone significantly overproduced PGA (maximum production 35.8 gL-1) than either the pgsC- or pgsA-enhanced strain. The molecular weight of the PGA produced with pgsB-enhanced strain was also greater than the pgsC- or pgsA-enhanced strain (approximately 10-fold). Hence, PgsB enhancement alone contributes to PGA overproduction with increased molecular weight.

Density and temperature controlled fluid extraction in a bacterial biofilm is determined by poly-γ-glutamic acid production

A hallmark of microbial biofilms is the self-production of an extracellular molecular matrix that encases the resident cells. The matrix provides protection from the environment, while spatial heterogeneity of gene expression influences the structural morphology and colony spreading dynamics. Bacillus subtilis is a model bacterial system used to uncover the regulatory pathways and key building blocks required for biofilm growth and development. In this work, we report on the emergence of a highly active population of bacteria during the early stages of biofilm formation, facilitated by the extraction of fluid from the underlying agar substrate. We trace the origin of this fluid extraction to the production of poly-γ-glutamic acid (PGA). The flagella-dependent activity develops behind a moving front of fluid that propagates from the boundary of the biofilm towards the interior. The extent of fluid proliferation is controlled by the presence of extracellular polysaccharides (EPS). We also find that PGA production is positively correlated with higher temperatures, resulting in high-temperature mature biofilm morphologies that are distinct from the rugose colony biofilm architecture typically associated with B. subtilis. Although previous reports have suggested that PGA production does not play a major role in biofilm morphology in the undomesticated isolate NCIB 3610, our results suggest that this strain produces distinct biofilm matrices in response to environmental conditions.

Expression dynamics of the poly-γ-glutamic acid biosynthesis genes of Bacillus subtilis in response to glucose and glutamic acid-a pilot study.

Poly-γ-glutamic acid (PGA) is biosynthesized by various Bacillus species through PGA synthetase, encoded by the PGA operon comprised of the ywsC and ywtABC genes. Due to the minimal available knowledge, understanding the expression pattern of PGA operon genes is pivotal. In this study, the effect of glucose and glutamic acid on the global gene expression profile of Bacillus subtilis Natto3 was investigated using high throughput microarray, with an emphasis on the PGA operon and genes influencing PGA production. Two treatment groups (set1-in the presence of glutamic acid and set2-in the presence of glutamic acid+glucose) were analyzed against the control (in the presence of glucose). In the microarray, both the groups showed a trend of up-regulation for ywsC and ywtA genes (log2 fold change of 0.55, P=0.0194, 0.92, P=0.0069 in set1 and 0.78, P=0.0023, 0.59, P=0.0172 in set2, respectively) and down-regulation of ywtB and ywtC genes (log2 fold change of -1.83, P=0.0001, -1.42, P=0.0017 in set1 and -1.52, P=0.0012, -0.55, P=0.1112 in set2, respectively), supporting the indispensability of the ywsC and ywtA genes in PGA production. Interestingly, the ywtB and ywtC genes, belonging to the same operon, were down-regulated in both the conditions (set1 and set2). To the best of our knowledge, this expression pattern of PGA operon genes is a unique observation.