Division of labor during biofilm matrix production

Abstract

Organisms as simple as bacteria can engage in complex collective actions, such as group motility and 28 fruiting body formation. Some of these actions involve a division of labor, where phenotypically 29 specialized clonal subpopulations, or genetically distinct lineages cooperate with each other by 30 performing complementary tasks. Here, we combine experimental and computational approaches to 31 investigate any benefits arising from division of labor during biofilm matrix production. We show that 32 both phenotypic and genetic strategies for a division of labor can promote collective biofilm formation 33 in the soil bacterium Bacillus subtilis. In this species, biofilm matrix consists of two major components; 34 EPS and TasA. We observed that clonal groups of B. subtilis phenotypically segregate in three 35 subpopulations composed of matrix non-producers, EPS-producers, and generalists, which produce 36 both EPS and TasA. We further found that this incomplete phenotypic specialization was 37 outperformed by a genetic division of labor, where two mutants, engineered as strict specialists, 38 . CC-BY 4.0 International license not peer-reviewed) is the author/funder. It is made available under a The copyright holder for this preprint (which was . http://dx.doi.org/10.1101/237230 doi: bioRxiv preprint first posted online Dec. 21, 2017; 2 complemented each other by exchanging EPS and TasA. The relative fitness of the two mutants 39 displayed a negative frequency dependence both in vitro and on plant roots, with strain frequency 40 reaching an evolutionary stable equilibrium at 30% TasA-producers, corresponding exactly to the 41 population composition where group fitness is maximized. Using individual-based modelling, we could 42show that asymmetries in strain ratio can arise due to differences in the relative benefits that matrix 43 compounds generate for the collective; and that genetic division of labor can be favored when it 44 breaks metabolic constraints associated with the simultaneous production of two matrix components. Microbes can act collectively in groups, and thereby substantially influence their local environment in 62 their own benefit. Such beneficial collective actions include the secretion of nutrient-degrading 63 enzymes [1,2], iron-scavenging siderophores [3], biosurfactants for group motility [4,5], and structural 64 components for biofilm formation [6,7]. In certain cases, cooperation even involves a division of labor, 65where subpopulations of cells specialize to perform different tasks [8][9][10]. For instance, during sliding 66 colony expansion Bacillus subtilis cells phenotypically differentiate into surfactant producers and 67 matrix producers where the role of the first is to reduce surface tension, while the latter allows 68 expanding colony 'arms' to form and explore new territories [10]. Given the high relatedness between 69 cells, specialization is likely beneficial for the group as a whole [11,12], with individuals gaining an 70 inclusive fitness benefit from helping their clone ...

Evolution of specialized microbial cooperation in dynamic fluids

“…We see this in the bottom-right regions of plots in Figure 5. Wakano et al, 2009;Wilson et al, 2003), and multiple factors can couple together to influence the evolution of cooperation (Dobay, Bagheri, Messina, Kümmerli, & Rankin, 2014) and division of labour (Dragoš et al, 2018) in unexpected ways.…”

“…Since cells must be within a certain distance to exchange such services, spatial aggregation is considered a prerequisite for multicellular specialization. Spatial effects matter (Durrett & Levin, ; Fletcher & Doebeli, ; McNally et al, ; Wakano et al, ; Wilson et al, ), and multiple factors can couple together to influence the evolution of cooperation (Dobay, Bagheri, Messina, Kümmerli, & Rankin, ) and division of labour (Dragoš et al, ) in unexpected ways.…”

Fungal hyphae colonization byBacillus subtilisrelies on biofilm matrix components

“…3). Previous studies demonstrated that secreted biofilm matrix components complement pellicle biofilm formation [20,27] 9 as well as plant colonization [10,11]. Notably, mixing eps and tasA mutant B. subtilis strains results in genetic division of labor, thus increased population productivity both during pellicle biofilm formation at the air-liquid interface and during plant root colonization [11,28].…”

“…In addition, Spo0A has been later shown to impact protease secretion, toxin production, and biofilm development, thus involved in regulation of genes related to cell fate decision of the bacterium [7]. Formation of biofilm in B. subtilis requires a complex matrix composed of exopolysaccharide (EPS), TasA amyloid fiber, and a surface localized hydrophobin, BslA [8][9][10][11][12][13]. The former two matrix components are essential for the establishment of a floating biofilm on the air-medium interface (referred to as pellicle), the creation of complex vein-like structures on agar medium, or attachment to the root 3 surface of plants [8][9][10]14,15].…”

“…The ability and degree of biofilm matrix production correlates with attachment to the plant root surface in hypotonic cultures and also with the ability of the bacterial strains to protect tomato plant against wilt disease caused by Ralstonia solanacearum [10,19]. As the matrix components are secreted from the cells, mutants lacking either EPS or TasA are able to complement each other and create a functional biofilm both in vitro and on the plant root [10,11,20].…”