Journal
ENVIRONMENTAL MICROBIOLOGY
Volume 19, Issue 9, Pages 3538-3550Publisher
WILEY
DOI: 10.1111/1462-2920.13847
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Funding
- U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research [DE-SC0008131]
- U.S. Army Research Office [W911NF-14-1-0411]
- Indiana University College of Arts and Sciences
- U.S. Department of Energy (DOE) [DE-SC0008131] Funding Source: U.S. Department of Energy (DOE)
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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.
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