Airborne exposure of Rhizobium leguminosarum strain E20-8 to volatile monoterpenes: Effects on cells challenged by cadmium

Rhizobium etli CFN42 proteomes showed isoenzymes in free-living and symbiosis with a different transcriptional regulation inferred from a transcriptional regulatory network

A comparative proteomic study at 6 h of growth in minimal medium (MM) and bacteroids at 18 days of symbiosis of Rhizobium etli CFN42 with the Phaseolus vulgaris leguminous plant was performed. A gene ontology classification of proteins in MM and bacteroid, showed 31 and 10 pathways with higher or equal than 30 and 20% of proteins with respect to genome content per pathway, respectively. These pathways were for energy and environmental compound metabolism, contributing to understand how Rhizobium is adapted to the different conditions. Metabolic maps based on orthology of the protein profiles, showed 101 and 74 functional homologous proteins in the MM and bacteroid profiles, respectively, which were grouped in 34 different isoenzymes showing a great impact in metabolism by covering 60 metabolic pathways in MM and symbiosis. Taking advantage of co-expression of transcriptional regulators (TF’s) in the profiles, by selection of genes whose matrices were clustered with matrices of TF’s, Transcriptional Regulatory networks (TRN´s) were deduced by the first time for these metabolic stages. In these clustered TF-MM and clustered TF-bacteroid networks, containing 654 and 246 proteins, including 93 and 46 TFs, respectively, showing valuable information of the TF’s and their regulated genes with high stringency. Isoenzymes were specific for adaptation to the different conditions and a different transcriptional regulation for MM and bacteroid was deduced. The parameters of the TRNs of these expected biological networks and biological networks of E. coli and B. subtilis segregate from the random theoretical networks. These are useful data to design experiments on TF gene–target relationships for bases to construct a TRN.

Effects of volatile sulfur compounds on growth and oxidative stress of Rhizobium leguminosarum E20-8 exposed to cadmium

Volatile sulfur compounds (VSCs) have been reported to be produced by many bacterial species. Depending on the compound, they can negatively influence some organisms (fungi, nematodes and insects) or promote plant growth. Some of these compounds have also been hypothesized to play a role in bacterial response to cadmium (Cd) induced stress. This study aimed to assess the potential effects of four VSCs (dimethyl sulfide - DMS, dimethyl disulfide - DMDS, dimethyl trisulfide - DMTS and methyl thioacetate - MTA) on the growth and oxidative status of Rhizobium sp. strain E20-8 via airborne exposure, in order to test the hypothesis that these volatile compounds can influence growth and tolerance to cadmium. Our results show that, overall, the tested compounds triggered similar antioxidant mechanisms in Rhizobium in the presence of Cd. The protective effect at the membrane level by DMDS and DMTS particularly demonstrates the antioxidant effect of these volatiles, with reductions of up to 50% (DMS) and 80% (DMTS) in lipid peroxidation levels. Due to the volatile nature of these compounds, the low concentrations tested (1 nM to 100 mM), and considering that they are released by bacteria and other organisms such as plants, it is possible that these effects also occur in the soil ecosystem.