evolution strategy of Clostridium ljungdahlii on iron is to slow down its growth and produce electron resovior chemicals

Evolution is a powerful tool to comprehend how the given environments have effects on microorganisms. This study aimed to unvail the influence of microbial electrosynthesis on acetogens. Clostridium ljungdahlii is a type acetogen used for gas fermentation and microbial electrosynthesis. C. ljungdahlii was cultivated long-term on iron as the sole electron source in 38 serial two-week batch cultures to drive mutations for increased fitness on iron. 95% of the culture was replaced with fresh medium to retain iron-attached C. ljungdahlii at the end of each cycle. At the last batch, 10- and 6.5-fold higher acetate production rates than the first batches were achieved. Multiple mutants were isolated to investigate the influence of long-term cultivation on iron. The mutants showed similar growth rate on fructose to the wild-type, but much slower on H2 and CO2, with only marginal differences between isolates. The selected mutants produced much less acetate than wild-type. 16 mutations were identified from whole-genome sequencing of the mutants, while seven mutations were found to all isolates. This work provides how C. ljungdahlii evolved on iron to improve fitness in an electron-limiting environment.