Development of tolerance to aldehyde-based inhibitors of pretreated lignocellulosic biomass sugars in E. coli MG1655 by sequential batch adaptive evolution

Aim: The current study involved carrying out adaptive evolution to inculcate tolerance to hydrolysate-derived aldehyde-based inhibitors, furfural, vanillin, syringaldehyde and 4-hydroxybenzaldehyde (4-HB) for the valorization of pretreated lignocellulosic biomass. Methodology: The growth-inhibitory effects of the aforementioned inhibitors on E. coli MG1655 were investigated. The percentage of inhibition was calculated from the initial growth, followed by extrapolating the IC values for each inhibitor. Based on these findings, adaptation experiments were conducted for individual inhibitors at a concentration lesser than or closer to IC50. Results: The specific growth rate of cells was lowered by 2.2-, 3-, 1.3- and 5- fold when grown in the presence of furfural, vanillin, syringaldehyde and 4-hydroxybenzaldehyde (4-HB), respectively. The adapted strains which were grown in the presence of furfural (9mM), vanillin (9mM), syringaldehyde (8mM) and 4- HB (6mM) individually showed around 1.5 -2.5- fold increase in the specific growth rate as compared to the wild-type with decreased lag phases and increased final cell densities. Interpretation: The strains, subjected to adaptive evolution, resulted in increased tolerance to single inhibitors and these will further be sequentially adapted to other three inhibitors for their utilization in the valorization of pretreated lignocellulosic biomass.