Growth‐independent cross‐feeding modifies boundaries for coexistence in a bacterial mutualism

Nutrient cross‐feeding can stabilize microbial mutualisms, including those important for carbon cycling in nutrient‐limited anaerobic environments. It remains poorly understood how nutrient limitation within natural environments impacts mutualist growth, cross‐feeding levels and ultimately mutualism dynamics. We examined the effects of nutrient limitation within a mutualism using theoretical and experimental approaches with a synthetic anaerobic coculture pairing fermentative Escherichia coli and phototrophic Rhodopseudomonas palustris. In this coculture, E. coli and R. palustris resemble an anaerobic food web by cross‐feeding essential carbon (organic acids) and nitrogen (ammonium) respectively. Organic acid cross‐feeding stemming from E. coli fermentation can continue in a growth‐independent manner during nitrogen limitation, while ammonium cross‐feeding by R. palustris is growth‐dependent. When ammonium cross‐feeding was limited, coculture trends changed yet coexistence persisted under both homogenous and heterogenous conditions. Theoretical modelling indicated that growth‐independent fermentation was crucial to sustain cooperative growth under conditions of low nutrient exchange. In contrast to stabilization at most cell densities, growth‐independent fermentation inhibited mutualistic growth when the E. coli cell density was adequately high relative to that of R. palustris. Thus, growth‐independent fermentation can conditionally stabilize or destabilize a mutualism, indicating the potential importance of growth‐independent metabolism for nutrient‐limited mutualistic communities.     

Exploiting Quorum Sensing To Confuse Bacterial Pathogens

SUMMARY

Cell-cell communication, or quorum sensing, is a widespread phenomenon in bacteria that is used to coordinate gene expression among local populations. Its use by bacterial pathogens to regulate genes that promote invasion, defense, and spread has been particularly well documented. With the ongoing emergence of antibiotic-resistant pathogens, there is a current need for development of alternative therapeutic strategies. An antivirulence approach by which quorum sensing is impeded has caught on as a viable means to manipulate bacterial processes, especially pathogenic traits that are harmful to human and animal health and agricultural productivity. The identification and development of chemical compounds and enzymes that facilitate quorum-sensing inhibition (QSI) by targeting signaling molecules, signal biogenesis, or signal detection are reviewed here. Overall, the evidence suggests that QSI therapy may be efficacious against some, but not necessarily all, bacterial pathogens, and several failures and ongoing concerns that may steer future studies in productive directions are discussed. Nevertheless, various QSI successes have rightfully perpetuated excitement surrounding new potential therapies, and this review highlights promising QSI leads in disrupting pathogenesis in both plants and animals.