Inherent tendency of and heterotrophic bacteria for mutualism on long-term coexistence despite environmental interference.

Mutualism between and heterotrophic bacteria has been found to support their prolonged survival in nutrient-depleted conditions. However, environmental interference on the fate of their mutualism is not understood. Here, we show that exogenous nutrients disrupt their established mutualism. Once the exogenous nutrients were exhausted, and heterotrophic bacteria gradually reestablished their metabolic mutualism during 450 days of culture, which revived unhealthy cells. Using metagenomics, metatranscriptomics, and the N tracer method, we reveal that the associated bacterial nitrogen fixation triggered the reestablishment of the mutualism and revival of health. During this process, bacterial community structure and functions underwent tremendous adjustments to achieve the driving effect, and a cogeneration of nitrogen, phosphorus, iron, and vitamin by the heterotrophic bacteria sustained 's prolonged healthy growth. Our findings suggest that and heterotrophic bacteria may have an inherent tendency toward mutualism despite environmental interference. This may exhibit their coevolutionary adaptations in nutrient-deficient environments.