Plant Polysaccharides Modulate Biofilm Formation and Insecticidal Activities of Bacillus thuringiensis Strains

Pectic homogalacturonan sensed by Bacillus acts as host associated cue to promote establishment and persistence in the rhizosphere

Bacillus velezensis isolates are among the most promising plant-associated beneficial bacteria used as biocontrol agents. However, various aspects of the chemical communication between the plant and these beneficials, determining root colonization ability, remain poorly described. Here we investigated the molecular basis of such interkingdom interaction occurring upon contact between Bacillus velezensis and its host via the sensing of pectin backbone homogalacturonan (HG). We showed that B. velezensis stimulates key developmental traits via a dynamic process involving two conserved pectinolytic enzymes. This response integrates transcriptional changes leading to the switch from planktonic to sessile cells, a strong increase in biofilm formation, and an accelerated sporulation dynamics while conserving the potential to efficiently produce specialized secondary metabolites. As a whole, we anticipate that this response of Bacillus to cell wall-derived host cues contributes to its establishment and persistence in the competitive rhizosphere niche and ipso facto to its activity as biocontrol agent.

Microbially-derived cocktail of carbohydrases as an anti-biofouling agents: a 'green approach'

Enzymes, also known as biocatalysts, display vital properties like high substrate specificity, an eco-friendly nature, low energy inputs, and cost-effectiveness. Among their numerous known applications, enzymes that can target biofilms or their components are increasingly being investigated for their anti-biofouling action, particularly in healthcare, food manufacturing units and environmental applications. Enzymes can target biofilms at different levels like during the attachment of microorganisms, formation of exopolymeric substances (EPS), and their disruption thereafter. In this regard, a consortium of carbohydrases that can target heterogeneous polysaccharides present in the EPS matrix may provide an effective alternative to conventional chemical anti-biofouling methods. Further, for complete annihilation of biofilms, enzymes can be used alone or in conjunction with other antimicrobial agents. Enzymes hold the promise to replace the conventional methods with greener, more economical, and more efficient alternatives. The present article explores the potential and future perspectives of using carbohydrases as effective anti-biofilm agents.

Glucose-Induced Biofilm Formation in Bacillus thuringiensis KPWP1 is Associated with Increased Cell Surface Hydrophobicity and Increased Production of Exopolymeric Substances

Bacillus thuringiensis is an agriculturally and medically important bacteria as it produces insecticidal Cry proteins and can form biofilm on different plant surfaces. Previous studies reported that the ubiquitous carbon source glucose could induce restricted motility and fractal pattern formation in the growing colonies of pH, salt and arsenate tolerant Bacillus thuringiensis KPWP1. As bacteria are evolved with the ability to exhibit multicellular behavior and biofilm formation under limiting conditions for survival, the present study was focused on exploring the effect of glucose in biofilm formation by Bacillus thuringiensis KPWP1. A significant rise in biofilm loads was observed with increased glucose concentrations in growth media. Compared to control, six times more biofilm load was marked in presence of 2% of glucose. Interestingly, it was observed that the effect was glucose specific and also not due to any change in the sugar-induced physicochemical property of the growth media as the addition of galactose or arabinose could not induce any significant increase in KPWP1 biofilm load. Scanning electron-, confocal laser scanning-microscopic studies and biochemical tests revealed that increased concentrations of glucose could induce increased production of exopolymeric substances, increased number of densely-packed micro-colonies in KPWP1 biofilm and increased hydrophobicity and adherence properties in KPWP1cells.