Enhancing the Adaptability of the Deep-Sea Bacterium Shewanella piezotolerans WP3 to High Pressure and Low Temperature by Experimental Evolution under H2O2 Stress

The oxidative stresses commonly exist in natural environments and microbes have developed variety of defensive systems to counteract such events. Although increasing evidence has shown that high-hydrostatic pressure (HHP) and low temperature (LT) induce the antioxidant defense responses in cells, there is no direct evidence to prove the connection between antioxidant defense mechanism and adaptation of bacteria to HHP/LT. In this study, using the wild-type strain (WT) of a deep-sea bacterium Shewanella piezotolerans WP3 as an ancestor, we obtained a mutant, OE100, with enhanced antioxidant defense capacity by experimental evolution under H 2 O 2 stress. Notably, OE100 exhibited better tolerance not only to H 2 O 2 stress but also to HHP/LT (20 MPa/4°C). Whole-genome sequencing identified deletion mutation in the gene oxyR , which encodes the transcription factor that controls oxidative stress response. Comparative transcriptome analysis showed that the genes associated with oxidative stress defense, anaerobic respiration, DNA repair, flagella and bacteriophage synthesis were differentially expressed in OE100 compared with the WT at 20 MPa/4°C. Genetic analysis of oxyR and ccpA2 indicated the OxyR-regulated cytochrome c peroxidase CcpA2 significantly contributed to the adaptation of WP3 to HHP/LT. Taken together, these results confirmed the inherent relationship between antioxidant defense mechanism and HHP/LT adaptation in benthic microorganism. IMPORTANCE The oxidative stress exists in various niches including the deep-sea ecosystem, which is an extreme environment with conditions of HHP, and predominantly LT. Although previous studies have shown that HHP and LT induce antioxidant defense response in cells, the direct evidence to prove the connection between antioxidant defense mechanism and adaptation of bacteria to HHP/LT is lacking. In this work, using the deep-sea bacterium Shewanella piezotolerans WP3 as a model, we proved that enhancement of the adaptability of WP3 to HHP/LT can benefit from its antioxidant defense mechanism, which provided useful insight into the ecological roles of antioxidant genes in benthic microorganism, and contributed to an improved understanding of microbial adaptation strategies in deep-sea environments.