Compatible solutes adaptive alterations in Arthrobacter simplex during exposure to ethanol, and the effect of trehalose on the stress resistance and biotransformation performance.

Ethanol-tolerant Arthrobacter simplex is desirable since ethanol facilitates hydrophobic substrates dissolution on an industrial scale. Herein, alterations in compatible solutes were investigated under ethanol stress. The results showed that the amount of trehalose and glycerol increased while that of glutamate and proline decreased. The trehalose protectant role was verified and its concentration was positively related to the degree of cell tolerance. otsA, otsB and treS, three trehalose biosynthesis genes in A. simplex, also enhanced Escherichia coli stress tolerance, but the increased tolerance was dependent on the type and level of the stress. A. simplex strains accumulating trehalose showed a higher productivity in systems containing more ethanol and substrate because of better viability. The underlying mechanisms of trehalose were involved in better cell integrity, higher membrane stability, stronger reactive oxygen species scavenging capacity and higher energy level. Therefore, trehalose was a general protectant and the upregulation of its biosynthesis by genetic modification enhanced cell stress tolerance, consequently promoted productivity.

IrrE Improves Organic Solvent Tolerance and Δ1-Dehydrogenation Productivity of Arthrobacter simplex.

During steroid bioconversion, organic solvents are widely used for facilitating hydrophobic substrate dissolution in industry. Thus, strains that tolerate organic solvents are highly desirable. IrrE, a global transcriptional factor, was introduced into Arthrobacter simplex with Δ1-dehydrogenation ability. The results evidenced that IrrE did not affect cell biological traits and biotransformation performance under non-stress conditions. However, the recombinant strain achieved a productivity higher than that of the control strain in systems containing more ethanol and substrate, which coincided with cell viability under ethanol stress, the major stress factor during biotransformation. It also demonstrated that IrrE caused genome-wide transcriptional perturbation, and several defense proteins or systems were linked with higher organic solvent tolerance. IrrE simultaneously enhanced cell resistance to various stresses, and its horizontal impacts showed strain and stress dependence. In conclusion, the introduction of exogenous global regulators is an efficient approach to enhance organic solvent tolerance in steroid-transforming strains, resulting in higher productivity.