Readiness to utilize alternative carbon substrates
In contrast to previous studies on microbial physiology under carbon limitation, where chemostats were run at growth rates of 0.01 h−1 and above , the current study investigated the physiology of G. metallireducens at growth rates below 0.003 h−1 , which might be more relevant for carbonlimited environments . It was expected that such low growthrates might induce an energy-saving mode in G. metallireducens and prevent expression of many alternative catabolic pathways when their substrates are not readily available. Instead, G. metallireducens expressed key proteins related to utilization of nearly 50% of the carbon sources (Fig. 4) it could use . During carbon limitation, G. metallireducens seemed
to employ a strategy where some preferred metabolic pathways were de-repressed while others needed specific induction (e.g. the toluene-degrading pathway). Thus, G. metallireducens appears to be adapted to typical anoxic habitats where primary fermenting microorganisms deplete sugars and proteins, and release alcohols and fatty acids as fermentation products.