Exploring overlooked growth-promoting mechanisms by plant-associated bacteria.

Agriculture-oriented microbiome studies try to develop microbiota beneficial to their plant hosts. This positive goal extends to the soil quality driving plant growth and disease resistance. In research aimed at identifying the causes of this beneficial action, a common interpretation is that microbes will synthesize metabolites useful to their hosts. This view assumes that important microbial metabolites are exported for use by their hosts. Yet, this seems unlikely for essential metabolites, without a counterpart imported from the plants, as the corresponding syntheses would often involve the consumption of resources without explicit benefit to the microbes. Illustrating this function with the example of Bacilli of the Subtilis clade, we emphasize here that the most direct access to the contents of microbial cells is through cell lysis, a phenomenon often linked to the process of sporulation. This process also releases macromolecules that are digested in the environment, releasing key metabolites such as queuine, an important base analog present in the anticodon of some transfer RNAs. This overlooked importance of cell lysis could also be a major cause of the ubiquitous presence of bacteriophages in microbiota.