Physiological adaptation of Serratia sp. AXJ-M to high temperature stress

Abstract:

[Background] The microbial treatment of paper wastewater or the polluted environment is of great practical value. However, studies remain to be carried out regarding the physiological adaption mechanisms of microorganisms to the high temperatures of paper wastewater. [Objective] To investigate the physiological response of Serratia sp. AXJ-M, a thermophilic lignin-degrading bacterial strain preserved in our laboratory, to high temperature stress. [Methods] The bacterial cells were cultured at different temperatures, and the bacterial cell morphology, cell membrane fluidity and permeability, trehalose content, and activities of antioxidant enzymes were observed and measured. Illumina HiSeq 2000 was used for the de novo sequencing of AXJ-M, and then GO, COG, KEGG, and NR were employed to annotate the functional genes in the genome. [Results] Strain AXJ-M can survive in a thermal stress environment of 50 to 80 ℃, of which 50 ℃ is the optimal growth temperature. However, its growth was significantly hindered when the temperature was rises above 70 ℃. Strain AXJ-M exhibited marked morphological differences and augmented surface roughness at high temperature stress. Strain AXJ-M cultured at 80 ℃ experienced a decline in cell membrane fluidity, an upsurge in membrane permeability, and a rise in trehalose content. Moreover, the activities of catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD) associated with oxidative stress increased by 50%–80%, 30%–47%, and 24%–31%, respectively, as the culture time was extended. By genomic analysis, strain AXJ-M contained the genes associated with the response to high temperature stress. [Conclusion] The culture at high temperatures can induce strain AXJ-M to develop heat tolerance and modify the cell morphology. Additionally, the increased trehalose content and antioxidant enzyme activities can protect the cells from external stress conditions. Moreover, a comprehensive analysis of the strain genome provides a basis for exploring the molecular response mechanism of thermophilic bacteria in high-temperature environments.