Quantifying nutrient colimitation of microbial growth

Resource availability dictates how fast and how much microbial populations grow. Quantifying the relationship between microbial growth and resource concentrations makes it possible to promote, inhibit, and predict microbial activity. Microbes require many resources, including macronutrients (e.g., carbon and nitrogen), micronutrients (e.g., metals), and complex nutrients like vitamins and amino acids. When multiple resources are scarce, as occurs in nature, microbes may experience resource colimitation in which more than one resource limits growth simultaneously. Despite growing evidence for colimitation, the data is difficult to interpret and compare due to a lack of quantitative measures of colimitation and systematic tests of resource conditions. We hypothesize that microbes experience a continuum of nutrient limitation states and that nutrient colimitation is common in the laboratory and in nature. To address this, we develop a quantitative theory of resource colimitation that captures the range of possible limitation states and describes how they can change dynamically with resource conditions. We apply this approach to clonal populations of Escherichia coli to show that colimitation occurs in common laboratory conditions. We also show that growth rate and growth yield are colimited differently, reflecting their different underlying biology. Finally, we analyze environmental data to provide intuition for the continuum of limitation and colimitation conditions in nature. Altogether our results provide a quantitative framework for understanding and quantifying colimitation of microbes in biogeochemical, biotechnology, and human health contexts.