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Is it getting crowded in here? Bacterial competition for space goes from deadly to detente

When a successful bacterium begins to outgrow its physical niche, things can get ugly. Paenibacillus dendritiformis, for instance, turns on its brothers and produces a toxic protein called Slf, which kills cells of encroaching sibling colonies. The bacterium senses when space gets tight, then deploys its toxic protein on nearby colonies so it won’t lose out in the struggle for space and nutrients.

But there’s more to this “kill or be killed” scenario, according to the authors of a study in mBio this week. P. dendritiformis is a shape-shifter that adapts to a fight for space by inducing a switch in phenotype. The Slf protein plays a different role here: at sub-lethal concentrations, Slf induces a fraction of P. dendritiformis cells to switch their phenotype from rod-shaped to coccoid. The cocci are Slf-resistant, non-motile, and have a distinct metabolic profile, so they are able to avoid lethal competition and can maintain the P. dendritiformis population by multiplying as cocci. And this switch between cell types is bi-directional: once the fight for space is alleviated and competition is reduced, the cocci switch back to motile rods.

And Slf-induced phenotypic switching might not be limited to P dendritiformis. Be’er et al. point out that genes with a high degree of homology with Slf are widespread in bacteria and yeast, indicating it could be a common mechanism for regulating population growth.

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