Bioaccumulation Of Cadmium By Rhodopseudomonas Palustris And Its Proteomics Profiling

Excessive cadmium can cause serious harm in human body,animals and plants.Cadmium pollution was a hot issue at environmental pollution treatment.Microbial bioaccumulation of heavy metal ions is a promising research because microbes have strong tolerance and high accumulation capacity,and it is of low cost and environmentfriendly.We investigated the optimal bioaccumulation conditions and the release of Cd2+ in Rhodopseudomonas palustris(R.palustris).Proteomics was used to analyze the differentially expressed proteins in the three groups: wild strain in blank medium(WB),first-generation in cadmium medium(WC)and multi-generation in cadmium medium(TC).Finally,proteins with large differential expression were selected for quantitative real-time PCR.The biomass of R.palustris and the bioaccumulation efficiency of Cd2+ were investigated with the pH from 3.5 to 8.5.Results showed that the bioaccumulation efficiency was between 88.9 % and 91.5 %.Strains had excellent biomass and strong Cd2+ bioaccumulation within the pH=6.0-7.0.Effect on the biomass and Cd2+ bioaccumulation was investigated in concentration of Cd2+ from 40 to 200 mg/L.It was found that Cd2+ could inhibit the growth of R.palustris.Bioaccumulation efficiency was respectively up to 90.3 % and 80.2 % at the Cd2+ concentration of 80 and 120 mg/L.When the concentration of Cd2+ was 120 mg/L,biomass and Cd2+ bioaccumulation was significantly inhibited.The results of coexisting ion showed that K+,Ca2+,Zn2+,Co2+ and Cu2+ had little effect on the Cd2+ bioaccumulation.The pseudo-first-order kinetic model was better fit for the bioaccumulation,with a correlation coefficient R2= 0.862-0.9474.R.palustris was examined by X-ray diffraction analysis.There was no obvious peak in the control group,and the Cd2+-bioaccumulated strains had diffraction peaks.Comparing with XRD standards,it was corresponded to cadmium carbonate.Cd2+ release showed that only a small amount of Cd2+ was released in 30 days.A total of 2670 proteins were identified by total protein TMT quantitative proteomics profiling.The repeatability test showed that Pearson coefficients were respectively 0.81,0.88 and 0.94,which was good enough to perform further analysis.Subcellular structural localization analysis found that most of the differentially expressed proteins were located in the cytoplasm.Among these,ribosomal S8 and L6 subunit proteins were respectively up-regulated 2.261-fold and 1.651-fold in the WC: WB.S5,L10 and L19 subunit proteins were respectively up-regulated 8.198-fold,1.478-fold and 1.395-fold in the TC: WC.These results indicated that Cd2+ bioaccumulation has a great effect on the stability of ribosome and the accuracy of transcription and translation.GO analysis showed that Cd2+ affected mitochondria to produce more ROS at first-generation and multi-generation,which led to disorders in intracellular energy metabolism and electron transport chains.SOD and Trx R were respectively up-regulated 7.1-fold and 5.308-fold in the WC: WB.And,SOD and Trx R were respectively down-regulated 0.019-fold and 0.484-fold in the TC: WC,Ahp was up-regulated 16.089-fold.We speculated that the strain mainly removed excess ROS by SOD and Trx R in WC: WB,and ROS is mainly removed by the synergism of Trx R and Ahp in the TC: WC.MCP sensor was also down-regulated to reduce the Cd2+ toxicity and to enhance the bioaccumulation capacity.COG classification analysis showed that proteins associated with energy metabolism and gene expression were severely affected at first-generation and multi-generation.Amino acid metabolism and fatty acid metabolism were mainly affected in energy metabolism.While in gene expression,structure and transcription and translation of ribosomes were mainly affected.Fatty acid metabolism had revealed R.palustris tended to synthesize long-chain fatty acids at multi-generation culture.In PPIs analysis,we chose 75 proteins in WC: WB and 77 proteins in TC: WC to construct the protein-protein interaction network.Ribosome S12 subunit protein was selected as central protein for further study.The result found that most of these proteins were ribosomal subunit protein(S3,S8,S9,L6,L10,L13,L17).Signal transduction histidine kinase was selected as central protein.The result showed that 6 proteins were receptor proteins.Down-regulated of receptor proteins and histidine kinase would inhibit intracellular stimuli response mechanisms.The m RNA was respectively extracted at Cd2+ concentration of 80 mg/L in TC and WC,and c DNA was obtained by reverse transcription.Ahp and SOD were detected by fluorescence quantitative PCR.The results showed that the expression difference of ahp was 17.02-fold in WC: WB,and the expression difference of SOD protein reached 28.6-fold in TC: WC.These were consistent with the quantitative results of protein,and it indicated that Ahp and SOD proteins are important for the bioaccumulation of Cd2+ in R.palustris.