On the other hand, spatial demixing (here referred to as a ‘segregated pattern’) can stabilize intransitive interactions among antibiotic-producing, -sensitive, and -resistant species ( 10), and also protects cells from contact-dependent killing by their competitors ( 11). For example, spatial mixing of different interacting cells (here referred to as a ‘mixed pattern’) benefits their metabolic exchanges ( 8) and alleviates antibiotic stress ( 9).
Spatial patterns of a community reflect the distribution of different populations across the habitat, and this distribution profoundly influences the interactions that occur among these populations. Biofilms are spatially well-organized, with different populations interacting with each other, arranging themselves nonrandomly across space, and ultimately developing well-organized spatial patterns (here referred to as ‘spatial self-organization’) ( 6, 7). These surface-attached communities play important roles in ecosystem processes ( 3), pollutant removal ( 4), and human health ( 5).
In addition to the planktonic lifestyle, microorganisms also form intricate multispecies communities on surfaces ( 1, 2). This novel insight assists our understanding of the ecological processes of surface-attached microbial communities and suggests a potential strategy for engineering high-performance synthetic microbial communities. Here, we report that in a cross-feeding consortium, the type IV pilus affects the spatial intermixing of interacting populations involved in pattern formation and ultimately influences overall community productivity and robustness. The type IV pilus is commonly found to mediate surface-associated behaviors of microorganisms, but its role on pattern formation within microbial communities is unclear. The development of these patterns is affected by several drivers, including cell-cell interactions, nutrient levels, density of founding cells, and surface properties. These patterns can significantly affect the overall properties of the community, enabling otherwise impermissible metabolic functions to occur as well as driving the evolutionary and ecological processes acting on communities. IMPORTANCE When growing on surfaces, multispecies microbial communities form biofilms that exhibit intriguing spatial patterns. These insights provide tangible clues for the engineering of synthetic microbial systems that perform highly in spatially structured environments. Our findings show that the type IV pilus plays a role in mitigating spatial intermixing of different populations in surface-attached microbial communities, with consequences for governing community-level properties. The intermixed pattern was maintained in a robust manner across a wide range of initial ratios between the two strains. Interestingly, when the genes encoding type IV pili were deleted from both strains, a highly intermixed spatial pattern developed and increased the productivity of the entire community. We found that the consortium self-organizes across space to form a previously unreported spatial pattern (here referred to as a ‘bubble-burst’ pattern) that exhibits a low level of intermixing. Here, we investigated the spatial patterning and intermixing of an engineered synthetic consortium composed of two mutualistic Pseudomonas stutzeri strains that degrade salicylate via metabolic cross-feeding. However, the precise factors that determine spatial patterns and intermixing remain unclear. The specific levels of spatial intermixing critically contribute to how the dynamics and functioning of such communities are governed.
Spatial intermixing emerging from microbial interaction is one of the best-studied characteristics of spatial patterns. Spatial patterns of populations within biofilms can be important determinants of community-level properties. Microbes are social organisms that commonly live in sessile biofilms.
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