Improving stress tolerance and cell integrity of Rhodococcus ruber by overexpressing small-shock-protein Hsp16 of Rhodococcus.

Rhodococcus species have been successfully used as cell catalysts for valuable chemicals production due to their well-characterized resistance to harmful factors. An understanding of how they respond to stress is of great interest， which will enable the identification of engineering strategies for further improving their resistance and maintaining cell integrity and viability. Here， we assessed the transcriptome response of R. ruber TH3 to heat shock. Approximately， 376 genes were up-regulated in heat-shocked TH3. Among all the up-regulated functional genes， the small heat-shock-protein (Hsp16) with maximal enhanced transcript (463-fold) was identified， and its function was investigated. Results showed that overexpressed Hsp16 has no significant promotive effect on stress tolerance of in-cell enzyme. Interestingly， compared to the control TH3， a little fewer pores and folds on the surface of TH3(Hsp16) and more intact TH3(Hsp-GFP) cells under AM treatment were observed by SEM and LCSM， respectively. Moreover， survival test showed that more (about 501-700) TH3(Hsp16) colonies were observed while only 1-100 TH3 colonies after 50% AM treatment， and this trend is also found in high-temperature cultivation experiments. These results indicate that Hsp16 does great contributions to preventing cell leakage， maintaining cell integrity and viability of R. ruber under stress conditions.