Abstract
Colonies are an abundant form of bacterial multicellularity; however, relatively little is known about the initial stages of their construction. We have previously described that colony development of the soil bacterium Bacillus subtilis is a highly ordered process, typically initiating with the formation of extending cell chains arranged in a Y shape structure. Furthermore, we demonstrated that Y arm extension is a key for defining the size of the future colony. Here we conducted a genetic screen surveying for mutants deficient in these early developmental stages, and revealed LtaS, the major lipoteichoic acid (LTA) synthase, to be crucial for execution of these events. We found that the ltaS mutant fails to produce proper Y shape structures, forming extremely elongated chains of cells with no evidence of chain breakage, necessary for Y shape formation. Furthermore, we show that frequent cell death at the tips of the cell chains is a major cause in limiting arm extension. Collectively, these perturbations lead to the production of a small sized colony by the mutant. Thus, deficiency in LTA synthesis causes a mechanical failure in executing the colony developmental program.
Highlights
Bacteria are highly adaptable organisms capable of living in a vast variety of niches, either as planktonic single cells, or in large bacterial communities
Cross-sectioned inspection of aging Escherichia coli (E. coli) colonies revealed that inner regions are characterized by cells producing amyloidic curli fibers, whereas the bottom zone of the macrocolonies is comprised of dividing cells encased within tight flagella mesh
The investigated mutants exhibited an array of various growth rates (Figure 2B; Figure S1B), ; only the ltaS mutant showed clear abnormal developmental patterns, failing to form either the typical Y shape or significantly extending arm chains (Figure 2C; Figure S2A). ltaS mutant displayed an extended lag phase, its growth rate was only slightly perturbed in comparison to wild type at 37◦C, but the change was more significant at lower temperatures (Figure S2B)
Summary
Bacteria are highly adaptable organisms capable of living in a vast variety of niches, either as planktonic single cells, or in large bacterial communities. Accumulating evidence highlights that living in large bacterial assemblies is beneficial for exploiting a wide variety of nutrients and withstanding harsh environmental conditions, such as antibiotic assault (Gilbert and Mcbain, 2001; Lewis, 2001; Stickler, 2002; Anderson and O’toole, 2008). Bacterial assemblies provide shelter and a steadier environment, conditions that are rarely achieved during the bacterium planktonic life. Bacterial multicellularity has several forms starting from relatively simple chains of cells up to biofilms, structured macrocolonies and fruiting bodies. A key feature in various forms of bacterial multicellularity is division of labor which is achieved through differentiation into subpopulations that execute distinct activities. Cross-sectioned inspection of aging Escherichia coli (E. coli) colonies revealed that inner regions are characterized by cells producing amyloidic curli fibers, whereas the bottom zone of the macrocolonies is comprised of dividing cells encased within tight flagella mesh
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