| Microbes may co-occur with the other microbes in natural conditions,which can lead to various interactions between them.These microbial interactions are important points for biological researchers.Bacteria and algae in the biosphere play important roles in energy flow and nutrient cycles,when they coexist in the same habitat they may have different forms of interspecies interactions.These interactions can have deep effects on their physiological condition or the ecological effect,but there is still a lack of understanding in the form and mechanism behind these interactions.Therefore,it is of great scientific significance to explore the molecular mechanism of the interaction between bacteria and algae by using a multidisciplinary approach.Previous studies have shown that certain vitamin B12(VB12)-producing bacteria(for example,Rhizobium bacteria)can significantly enhance the heat resistance of Chlamydomonas by secreting VB12 when co-cultured with Chlamydomonas reinhardtii,which means that the bacteria can by interspecies interaction regulate the response of algae to environmental factors.However,the regulatory mechanism of global gene expression and the functions of key genes in this interaction are still less known.To solve these problems,we used the co-culture with Sinorhizobium meliloti 1021(Sm1021)and Chlamydomonas reinhardtii 21gr and adopted label-free quantitative proteomics technology to examine the proteomics profiles in this bacteria-algal interaction.We analyzed the Sm 1021’s differentially expressed proteins under the tested conditions,and performed molecular experiments to study the functions of certain selected genes.The main results are as follows:(1)Acquisition of proteomic data.The proteome of Sm 1021 cells grown with or without 21 gr at normal and high temperature were determined by label-free proteomics,at different time points.dNSAF algorithm was used to quantify these data and obtain the proteome expression data of Sm 1021 under various conditions.(2)Analysis of bacteria Sm 1021’s proteome.After cluster analysis,we found that the co-culture conditions had a great influence on the proteome expression of Sm1021 bacteria.Through statistical analysis,we obtained differentially expressed proteins of Sm1021 under different conditions(such as high temperature,co-culture,etc.).In this experiment,we also found that the differentially expressed protein numbers increased gradually after the temperature increased.(3)Differential proteins involved in the process of enhancing the heat resistance of algae.This study focused on the proteins of bacteria Sm1021 highly expressed in the co-cultures with 21gr at high temperature.The results indicated that certain proteins related to the synthesis of cell membrane,cell components,VB12 biosynthesis,metabolic processes,amino acids and lipid synthesis were significantly upregulated,while some protein expression in lipid metabolism,capacity metabolism and carbon cycle was reduced.These results suggested that a comprehensive gene expression regulation happened in bacterial signal transduction and substance transport processes during its interactions with algae.(4)Function studies of some genes.In this study,four candidate differentially expressed proteins were investigated by means of molecular biology.The corresponding genes of these four proteins were hemB,a ubiquitin-specific protein(SMa1231).A gene whose function is unknown(SM_b20173).It was preliminarily found that the mutation of hemB or SMa1231 resulted in a weak enhancement of the heat tolerance,which suggested they may play important roles in the Sm 1021-21gr interactions.In summary,we investigated the proteomic expression profiles and the functions of some differentially expressed genes of VB12-producing bacteria Sm1021 in its enhancement of the heat resistance of Chlamydomonas reinhardtii.Our data not only shed new insights in the key genes involved in bacteria-algal interaction,but.provide a useful technical reference for the interspecific relationship between microbial species. |
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