Privatization of Biofilm Matrix in Structurally Heterogeneous Biofilms

Abstract

The self-produced biofilm provides beneficial protection for the enclosed cells, but the costly production of matrix components makes producer cells susceptible to cheating by nonproducing individuals. Despite detrimental effects of nonproducers, biofilms can be heterogeneous, with isogenic nonproducers being a natural consequence of phenotypic differentiation processes. For instance, in Bacillus subtilis biofilm cells differ in production of the two major matrix components, the amyloid fiber protein TasA and exopolysaccharides (EPS), demonstrating different expression levels of corresponding matrix genes. This raises questions regarding matrix gene expression dynamics during biofilm development and the impact of phenotypic nonproducers on biofilm robustness. Here, we show that biofilms are structurally heterogeneous and can be separated into strongly and weakly associated clusters. We reveal that spatiotemporal changes in structural heterogeneity correlate with matrix gene expression, with TasA playing a key role in biofilm integrity and timing of development. We show that the matrix remains partially privatized by the producer subpopulation, where cells tightly stick together even when exposed to shear stress. Our results support previous findings on the existence of “weak points” in seemingly robust biofilms as well as on the key role of linkage proteins in biofilm formation. Furthermore, we provide a starting point for investigating the privatization of common goods within isogenic populations. IMPORTANCE Biofilms are communities of bacteria protected by a self-produced extracellular matrix. The detrimental effects of nonproducing individuals on biofilm development raise questions about the dynamics between community members, especially when isogenic nonproducers exist within wild-type populations. We asked ourselves whether phenotypic nonproducers impact biofilm robustness, and where and when this heterogeneity of matrix gene expression occurs. Based on our results, we propose that the matrix remains partly privatized by the producing subpopulation, since producing cells stick together when exposed to shear stress. The important role of linkage proteins in robustness and development of the structurally heterogeneous biofilm provides an entry into studying the privatization of common goods within isogenic populations.

Bacillus subtilis biofilm formation and social interactions

“…SlrR is another antagonist of SinR which is induced by threshold levels of phosphor-Spo0A 68 and promotes transcription of the epsA-O and tapA operons, thus enabling the switch from a motile state to biofilm formation 69 . As levels of phospho-Spo0A∼P are not elevated homogeneously in the population, the regulatory network heterogeneously induces expression of matrix genes, creating subpopulations of matrix producer (ON-state) and non-producer (OFF-state) cells [70][71][72] .…”

Multiscale X-ray study of Bacillus subtilis biofilms reveals interlinked structural hierarchy and elemental heterogeneity

“…An emerging perspective of biofilm development considers them as multicellular organisms, because of their ability to differentiate into subgroups of cells expressing specific set of genes. In particular, differentiation in B. subtilis biofilms has been shown to give rise to distinct subpopulations that express different sets of genes related with specific functions, such as motility, matrix production, and sporulation (20,33); Here also, heterogeneous matrix gene expression has been linked to heterogeneity in the mechanical robustness of subpopulations (34,35). Current views of differentiation of biofilms into subgroups therefore link between genetic division of labor and phenotypic heterogeneity at the single cell as well as the subpopulation level, however, it neglects a molecular view of structural heterogeneity across entire biofilms.…”

“…Heterogeneous matrix gene expression has also been linked to heterogeneity in the mechanical robustness of subpopulations 36,37 . Current views of differentiation of biofilms into subgroups therefore link genetic division of labor and phenotypic heterogeneity at the single cell as well as the subpopulation level, however, they neglect a molecular view of structural and compositional heterogeneity across entire biofilms.…”

“…In particular, differentiation in B. subtilis biofilms has been shown to give rise to distinct, function-related subpopulations, among which are motility, matrix production, sporulation 20,33 and cannibalism 34,35 . Heterogeneous matrix gene expression has also been linked to heterogeneity in the mechanical robustness of subpopulations 36,37 . Current views of differentiation of biofilms into subgroups therefore link genetic division of labor and phenotypic heterogeneity at the single cell as well as the subpopulation level, however, they neglect a molecular view of structural and compositional heterogeneity across entire biofilms.…”

Modern Methods for Researching Microbial Biofilms of the Enterobacteriaceae Family

“…Для выполнения данных методик применяют пластиковые планшеты, в которые вносят микробный инокулят. После инкубации планктон удаляют вместе с питательной средой, а сформировавшиеся BF подвергают дальнейшим исследованиям в зависимости от поставленных целей [23,24]. Преимущество динамических (открытых) систем, когда микроорганизмы циркулируют в закрытой системе в жидкой питательной среде, заключается в максимальном приближении к условиям живых систем.…”