Bacillus subtilis biofilm formation and social interactions

Abstract

Biofilm formation is a process in which microbial cells aggregate to form collectives that are embedded in a self-produced extracellular matrix. Bacillus subtilis is a Gram-positive bacterium that is used to dissect the mechanisms controlling matrix production and the subsequent transition from a motile planktonic cell state to a sessile biofilm state. The collective nature of life in a biofilm allows emergent properties to manifest, and B. subtilis biofilms are linked with novel industrial uses as well as probiotic and biocontrol processes. In this Review, we outline the molecular details of the biofilm matrix and the regulatory pathways and external factors that control its production. We explore the beneficial outcomes associated with biofilms. Finally, we highlight major advances in our understanding of concepts of microbial evolution and community behaviour that have resulted from studies of the innate heterogeneity of biofilms.

Cryptic surface-associated multicellularity emerges through cell adhesion and its regulation

“…Theoretical models on surface growth are paralleled by a large body of empirical literature where surface-associated organisms are studied by either growing collectives in isolation (e.g., biofilms, colonies, pellicles, swarms, fruiting bodies) [110][111][112][113], thereby focusing on their multicellular organization [36,[114][115][116][117][118], or by competing several genotypes against each other on a surface [30,[119][120][121][122][123][124]. Competition experiments revealed that spatial interactions can strongly affect the outcome of competition, oftentimes leading to the coexistence of multiple genotypes [43,120,125].…”

Diversification ofB. subtilisduring experimental evolution onA. thalianaand the complementarity in root colonization of evolved subpopulations

“…The PGPR B. subtilis is a promising sustainable alternative to traditionally used agrochemicals, as it harbors many important plant growth-promoting and biocontrol properties while having reduced negative effects on biodiversity and the environment (Blake et al ., 2021; Arnaouteli et al ., 2021). Even though its potential seems immense under laboratory conditions and in greenhouse trials, the success varies greatly when applied in fields (Peng et al ., 2011; Bardin et al ., 2015; Moreira & de Mio, 2015; Wei et al ., 2016).…”

Deletion of Rap‐Phr systems in Bacillus subtilis influences in vitro biofilm formation and plant root colonization

“…Matrix production is well known to be required for the formation of architecturally complex biofilms under laboratory conditions (Arnaouteli et al, 2021; Branda et al, 2006). Moreover, matrix production and localized cell death are responsible for the formation of wrinkles during biofilm development (Asally et al, 2012; Branda et al, 2006; Gallegos‐Monterrosa et al, 2017).…”

“…The variation in environmental conditions throughout the biofilm (Costerton et al, 1994) thereby leads to a heterogeneous population with different cell types performing distinct tasks and occupying different micro‐niches. The extracellular signals triggering cell differentiation include quorum‐sensing molecules, natural products, and nutrient availability that activate a set of sensor kinases (Arnaouteli et al, 2021; Mhatre et al, 2014). Once activated, the sensor kinases phosphorylate their respective master transcriptional regulators, Spo0A, DegU, and ComA, each of which activates different sets of genes (López & Kolter, 2010).…”

“…Bacillus subtilis can easily be isolated from the rhizosphere of plants (Fall et al, 2004), and a study performed by Chen et al (2013) showed that the majority of natural strains isolated from the rhizosphere formed architecturally complex biofilms under laboratory conditions, indicating that biofilm formation is an important trait for B. subtilis to thrive in its natural habitat. In the laboratory, B. subtilis has long been studied using different kinds of biofilm models including colonies at the air-agar interface and floating biofilms formed at the air-liquid interface, termed pellicles (Arnaouteli et al, 2021).…”