Poly-γ-Glutamic Acids Contribute to Biofilm Formation and Plant Root Colonization in Selected Environmental Isolates of Bacillus subtilis

Abstract

Bacillus subtilis is long known to produce poly-γ-glutamic acids (γ-PGA) as one of the major secreted polymeric substances. In B. subtilis, the regulation of γ-PGA production and its physiological role are still unclear. B. subtilis is also capable of forming structurally complex multicellular communities, or biofilms, in which an extracellular matrix consisting of secreted proteins and polysaccharides holds individual cells together. Biofilms were shown to facilitate B. subtilis–plant interactions. In this study, we show that different environmental isolates of B. subtilis, all capable of forming biofilms, vary significantly in γ-PGA production. This is possibly due to differential regulation of γ-PGA biosynthesis genes. In many of those environmental isolates, γ-PGA seems to contribute to robustness and complex morphology of the colony biofilms, suggesting a role of γ-PGA in biofilm formation. Our evidence further shows that in selected B. subtilis strains, γ-PGA also plays a role in root colonization by the bacteria, pinpointing a possible function of γ-PGA in B. subtilis–plant interactions. Finally, we found that several pathways co-regulate both γ-PGA biosynthesis genes and genes for the biofilm matrix in B. subtilis, but in an opposing fashion. We discussed potential biological significance of that.

Influence ofl-amino acids on aggregation and biofilm formation inAzotobacter chroococcumandTrichoderma viride

“…Glutamic acid is associated with production of polymeric substances, biofilm formation and subsequent root colonization by B. subtilis (Yu et al . ). Glutamine, in addition to its role in the synthesis of nucleotides and participation in metabolism, also functions as a signalling molecule in micro‐organisms (Kan et al .…”

“…In A. vinelandii, Glu has been suggested as a primary intermediate in the utilization of nitrogen either as NH 3 or molecular N 2 , with active participation of glutamic dehydrogenase (Burma and Burris 1957). Glutamic acid is associated with production of polymeric substances, biofilm formation and subsequent root colonization by B. subtilis (Yu et al 2016). Glutamine, in addition to its role in the synthesis of nucleotides and participation in metabolism, also functions as a signalling molecule in micro-organisms (Kan et al 2015).…”

Role of Bacillus species in biofilm persistence and emerging antibiofilm strategies in the dairy industry

“…7,65,66 Moreover, B. subtilis produces other extracellular polymeric substances, including γ-poly-DL-glutamic acid (PGA), which can predominantly enhance the formation of submerged biofilms. 67,68 Moreover, the hydrophobic BslA protein was also shown to be abundantly present in the biofilm matrix of B. subtilis. 39 69 BslA proteins localize to the outer surface of the biofilms and provide strong surface hydrophobicity.…”

“…In this bacterium, the matrix has two main components: exopolysaccharides synthesized by the products of the epsA‐O operon and amyloid‐like fibers encoded by tasA located in the tapA‐sipW‐tasA operon . Moreover, B. subtilis produces other extracellular polymeric substances, including γ ‐poly‐ dl ‐glutamic acid (PGA), which can predominantly enhance the formation of submerged biofilms . Moreover, the hydrophobic BslA protein was also shown to be abundantly present in the biofilm matrix of B. subtilis .…”

Social behaviours by Bacillus subtilis: quorum sensing, kin discrimination and beyond

“…In many cases, a buffered defined medium using glutamic acid, as the sole nitrogen source, and glycerol, as the sole carbon source, is used to trigger production of the biofilm matrix (Branda et al, ). A few studies have also examined biofilm formation of model strains in different growth conditions (Dogsa et al, ; Ma et al, ), while limited insights into the diversity of biofilm regulation and biofilm properties of different B. subtilis isolates have been acquired (Oslizlo et al, ; Sanchez‐Vizuete et al, ; Yu et al, ).…”