ABSTRACT
Oxidative stresses commonly exist in natural environments, and microbes have developed a variety of defensive systems to counteract such events. Although increasing evidence has shown that high hydrostatic pressure (HHP) and low temperature (LT) induce antioxidant defense responses in cells, there is no direct evidence to prove the connection between antioxidant defense mechanisms and the adaptation of bacteria to HHP and LT. In this study, using the wild-type (WT) strain of a deep-sea bacterium,
Shewanella piezotolerans
WP3, as an ancestor, we obtained a mutant, OE100, with an 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 and LT (20 MPa and 4°C, respectively). Whole-genome sequencing identified a deletion mutation in the
oxyR
gene, which encodes the transcription factor that controls the oxidative stress response. Comparative transcriptome analysis showed that the genes associated with oxidative stress defense, anaerobic respiration, DNA repair, and the synthesis of flagella and bacteriophage were differentially expressed in OE100 compared with the WT at 20 MPa and 4°C. Genetic analysis of
oxyR
and
ccpA2
indicated that the OxyR-regulated cytochrome
c
peroxidase CcpA2 significantly contributed to the adaptation of WP3 to HHP and LT. Taken together, these results confirmed the inherent relationship between antioxidant defense mechanisms and the adaptation of a benthic microorganism to HHP and LT.
IMPORTANCE
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 responses in cells, direct evidence to prove the connection between antioxidant defense mechanisms and the adaptation of bacteria to HHP and 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 and LT can benefit from its antioxidant defense mechanism, which provided useful insight into the ecological roles of antioxidant genes in a benthic microorganism and contributed to an improved understanding of microbial adaptation strategies in deep-sea environments.
Enhancing the Adaptability of the Deep-Sea Bacterium
Shewanella piezotolerans
WP3 to High Pressure and Low Temperature by Experimental Evolution under H
2
O
2
Stress