Microorganisms have successfully predominated deep-sea ecosystems, while we know little about their adaptation strategy to multiple environmental stresses therein, including high hydrostatic pressure (HHP). Here, we focused on the genus Halomonas, one of the most widely distributed halophilic bacterial genera in marine ecosystems and isolated a piezophilic strain Halomonas titanicae ANRCS81 from Antarctic deep-sea sediment. The strain grew under a broad range of temperatures (2 to 45°C), pressures (0.1 to 55 MPa), salinities (NaCl, 0.5 to 17.5%, wt/vol), and chaotropic agent (Mg²⁺, 0 to 0.9 M) with either oxygen or nitrate as an electron acceptor. Genome annotation revealed that strain ANRCS81 expressed potential antioxidant genes/proteins and possessed versatile energy generation pathways. Based on the transcriptomic analysis, when the strain was incubated at 40 MPa, genes related to antioxidant defenses, anaerobic respiration, and fermentation were upregulated, indicating that HHP induced intracellular oxidative stress. Under HHP, superoxide dismutase (SOD) activity increased, glucose consumption increased with less CO₂ generation, and nitrate/nitrite consumption increased with more ammonium generation. The cellular response to HHP represents the common adaptation developed by Halomonas to inhabit and drive geochemical cycling in deep-sea environments.

IMPORTANCE Microbial growth and metabolic responses to environmental changes are core aspects of adaptation strategies developed during evolution. In particular, high hydrostatic pressure (HHP) is the most common but least examined environmental factor driving microbial adaptation in the deep sea. According to recent studies, microorganisms developed a common adaptation strategy to multiple stresses, including HHP, with antioxidant defenses and energy regulation as key components, but experimental data are lacking. Meanwhile, cellular SOD activity is elevated under HHP. The significance of this research lies in identifying the HHP adaptation strategy of a Halomonas strain at the genomic, transcriptomic, and metabolic activity levels, which will allow researchers to bridge environmental factors with the ecological function of marine microorganisms.

FIG  SOD activity (A), acidogenic activity (B), glucose and N-acetylglucosamine consuming together with dissolved inorganic carbon-producing activities (C), and nitrate and nitrite consuming together with ammonia-producing activities (D) of H. titanicae ANRCS81 under four types of cultivation. (E) A conceptual model to explain the common adaptation mechanism of strain ANRCS81. Red-labeled genes indicate upregulated genes under HHP. Red squares indicate genes upregulated under e400 conditions. While blue squares indicate genes upregulated under an400 conditions. Gene names and the proteins they encode are as follows: Glu, glutamate; Asp, aspartate; narH, nitrate reductase/nitrite oxidoreductase, beta subunit; narI, nitrate reductase gamma subunit; nirB, nitrite reductase (NADH) large subunit; norB, nitric oxide reductase subunit B; norC, nitric oxide reductase subunit C; E3.5.1.49, formamidase; gudB, glutamate dehydrogenase; gltB, glutamate synthase (NADPH) large chain; gltBD, glutamate synthase (NADPH) small chain; GDH2, glutamate dehydrogenase; glnA, glutamine synthetase; pk, pyruvate kinase; FDH, formate dehydrogenase; maeA, malate dehydrogenase; aceF, pyruvate dehydrogenase E2 component; fumA, fumarate hydratase subunit alpha; fumB, fumarate hydratase subunit beta; ldh, l-lactate dehydrogenase; dld, d-lactate dehydrogenase; frdA, fumarate reductase, flavoprotein subunit; frdB, fumarate reductase, iron-sulfur subunit; acnA, aconitate hydratase; IDH3, isocitrate dehydrogenase (NAD⁺); aldh, aldehyde dehydrogenase (NAD⁺); adh, alcohol dehydrogenase; adhB, alcohol dehydrogenase (quinone), cytochrome c subunit; CS, citrate synthase; sod, superoxide dismutase; GST, glutathione S-transferase; soxR, MerR family transcriptional regulator, redox-sensitive transcriptional activator SoxR; oxyR, LysR family transcriptional regulator, hydrogen peroxide-inducible genes activator OxyR; sufBCD, Fe-S cluster assembly protein; PGD, 6-phosphogluconate dehydrogenase; gbsA, betaine-aldehyde dehydrogenase; tesA, acyl-CoA thioesterase I; znu, zinc transport system; NIT2, omega-amidase; ansAB, l-asparaginase; AGTX, alanine-glyoxylate transaminase/serine-glyoxylate transaminase/serine-pyruvate transaminase; AGTX2, alanine-glyoxylate transaminase/(R)-3-amino-2-methylpropionate-pyruvate transaminase; afuB, iron(III) transport system permease protein; afuC, iron(III) transport system ATP-binding protein; afuC, iron(III) transport system ATP-binding protein; gabD, succinate-semialdehyde dehydrogenase/glutarate-semialdehyde dehydrogenase; ald, alanine dehydrogenase; gabT, 4-aminobutyrate aminotransferase/(S)-3-amino-2-methylpropionate transaminase; ABAT, 4-aminobutyrate aminotransferase/(S)-3-amino-2-methylpropionate transaminase; POP2, 4-aminobutyrate-pyruvate transaminase.

Link: journals.asm.org/doi/10.1128/aem.01304-22