From environmental signals to regulators: Modulation of biofilm development in Gram‐positive bacteria

Abstract

Bacterial lifestyle is influenced by environmental signals, and many differentiation processes in bacteria are governed by the threshold concentrations of molecules present in their niche. Biofilm is one such example where bacteria in their sessile state adapt to a lifestyle that causes several adaptive alterations in the population. Here, a brief overview is given on a variety of environmental signals that bias biofilm development in Gram-positive bacteria, including nutrient conditions, self- and heterologously produced substances, like quorum sensing and host produced molecules. The Gram-positive model organism, Bacillus subtilis is a superb example to illustrate how distinct signals activate sensor proteins that integrate the environmental signals towards global regulators related to biofilm formation. The role of reduced oxygen level, polyketides, antimicrobials, plant secreted carbohydrates, plant cell derived polymers, glycerol, and osmotic conditions are discussed during the transcriptional activation of biofilm related genes in B. subtilis.

Monitoring Spatial Segregation in Surface Colonizing Microbial Populations

“…In analogy to social insects, B. subtilis cells employ a division of labor strategy, developing subpopulations of extracellular matrix producers and cannibals, motile cells, dormant spores and other cell types 15,16 . The differentiation process is dynamic and can be altered by environmental conditions 17,18 . Strategies of surface colonization by bacteria can be easily manipulated under laboratory conditions by modifying the agar concentration in the growth media.…”

“…growth dependent population expansion facilitated by exopolysaccharide matrix and other secreted hydrophobin compounds [22][23][24] . Finally, bacteria which are capable of biofilm development form architecturally complex colonies on hard agar medium (1.2-2%) 14,17,25 . While these traits are examined in the laboratory by precisely adjusting the conditions, in natural habitats these surfacespreading strategies might transit gradually from one to another depending on the environmental conditions 26 .…”

The impact of manganese on biofilm development of Bacillus subtilis

“…The effects of signalling molecules that induce biofilm formation and sporulation in B. subtilis are often facilitated via membrane-bound histidine kinases that increase the level of phosphorylated Spo0A through a phospho-relay (Mhatre et al, 2014;Vlamakis et al, 2013). The presence of molecules such as surfactin, nystatin and their derivatives was suggested to induce pore formation in the cell membrane leading to potassium leakage, which activates the signalling domain of KinC (Gonzalez-Pastor et al, 2003;Lopez et al, 2009aLopez et al, , 2010; however, the impact of surfactin on KinC-mediated activation is debated and might be condition-or strain-specific (Devi et al, 2015;López, 2015).…”

“…The surface attachment and formation of sessile bacterial communities, yielding the so-called biofilms, are also induced by certain concentrations of nutrients and self-produced signalling molecules. Biofilm formation in Bacillus subtilis has been extensively studied, and various molecules such as self-secreted surfactin, plant polysaccharides, chlorine dioxides and combinations of glycerol and manganese have been reported to induce a cascade of reactions leading to the production of biofilm matrix components Mhatre et al, 2014;Shemesh et al, 2010;Shemesh & Chai, 2013;Vlamakis et al, 2013). These signal molecules act on distinct histidine sensor kinases and activate Spo0A, which is also required for sporulation through the phospho-relay pathway (Hoch, 1993).…”

“…While the kinases KinA and KinB are mainly important for efficient sporulation, which requires high levels of Spo0A~P (Grimshaw et al, 1998;Jiang et al, 2000), KinC and KinD play a role in the induction of biofilm development with low levels of Spo0A~P (López et al, 2009b;Vlamakis et al, 2013). During the late log phase, cells face many challenges such as depletion of nutrients, oxygen stress, production of toxins and waste molecules and the presence of surfactin-like molecules that cause membrane leakage (Mhatre et al, 2014). These molecules act as environmental cues leading to the activation of kinases that in turn facilitates the transfer of phosphate groups via Spo0F and Spo0B to Spo0A.…”