Growth capacity and biochemical mechanisms involved in rhizobia tolerance to salinity and water deficit

Abstract

The aim of the present study was to evaluate abiotic stress tolerance of rhizobial strains belonging to Mesorhizobium, Sinorhizobium, and Rhizobium genera, as well as to investigate specie specific stress response mechanisms. Effect of NaCl and PEG on growth capacity, protein, lipid peroxydation (MDA), membrane fatty acid composition and antioxidant enzymes were investigated. Growth capacity and viability of overall rhizobia strains decreased proportionally to the increase of NaCl and PEG levels in the medium. Sinorhizobium strains appeared the most tolerant, where 4H41strain was able to grow at 800 mM NaCl and 40% PEG. On the other hand, growth of R. gallicum and M. mediterraneum was inhibited by 200 mM NaCl. The content of MDA was unchanged in Sinorhizobium strains under both stresses. For Mesorhizobium, only PEG treatment increased the content of MDA. Amount of the C19:0 cyclo fatty-acid was increased in both Sinorhizobium and Mesorhizobium tolerant strains. NaCl stress increased Superoxide dismutase (SOD) activity of overall species; especially the most tolerant strain 4H41. Both treatments increased catalase (CAT) activity in 4H41, TII7, and 835 strains. Obtained results suggest that major response of tolerant Sinorhizobium and Mesorhizobium strains to NaCl and PEG stresses is a preferential accumulation of the C19:0 cyclo fatty acid within bacterial membrane as mechanism to reduce fluidity and maintain integrity. Cell integrity and functioning is also assured by maintaining and/or increasing activity of SOD and CAT antioxidant enzymes for tolerant strains to omit structural and functional damages related to reactive oxygen species overproduced under stressful conditions.

Unraveling of cross talk between Ca2+ and ROS regulating enzymes in Anabaena 7120 and ntcA mutant

“…In the present case, we found lipid peroxidation, peroxide content, GSH, SOD, and CAT levels being upregulated at higher calcium concentrations, i.e., 10 and 100 mM compared to 1 mM concentration. The obtained results thus strengthen the fact that though salinity primarily induces ionic and osmotic stress, however it may lead to oxidative stress as a secondary effect . Increased antioxidant activity may be due to membrane damage resulting in enhanced activity of NADPH oxidase which is implicated as an important producer of ROS .…”

Reorganization of Azospirillum brasilense cell membrane is mediated by lipid composition adjustment to maintain optimal fluidity during water deficit

“…Growth parameters were negatively modified in the presence of PEG. Consistent with our results, Mhamdi et al (2014) reported a progressive decrease in the number of viable cells of rhizobia strains belonging to Mesorhizobium, Sinorhizobium and Rhizobium genera with an increase in drought stress (15% to 30% of PEG). Cells cultivated in D&D medium were harvested at the late exponential phase, washed and resuspended in Tris-HCl buffer to an OD660 nm of 0Á2.…”

“…Consistent with our results, Mhamdi et al . () reported a progressive decrease in the number of viable cells of rhizobia strains belonging to Mesorhizobium , Sinorhizobium and Rhizobium genera with an increase in drought stress (15% to 30% of PEG).…”

“…Mhamdi et al . () showed that for Sinorhizobium strains, the main modification in response to osmotic stress (PEG) is preferential accumulation of the 19:0 cyclo and 18:0 SFA. When A. brasilense Az39 cells were exposed to PEG, the amount of SFA was approx.…”

“…Although FA profiles for different strains of Azospirillum have been reported (Schenk and Werner 1988), our work is the first to demonstrate that FA plays a role in the response to water deficit for this genus of bacteria and specifically for the A. brasilense Az39 strain. Mhamdi et al (2014) showed that for Sinorhizobium strains, the main modification in response to osmotic stress (PEG) is preferential accumulation of the 19:0 cyclo and 18:0 SFA. When A. brasilense Az39 cells were exposed to PEG, the amount of SFA was approx.…”