Proteome analysis demonstrates complex replicon and luteolin interactions in pSyma-cured derivatives of Sinorhizobium
H Chen1, J Higgins, I J Oresnik
1Genomic Interaction Group, Research School of Biological Sciences, ANU, Canberra, Australia.
Abstract:
Sinorhizobium meliloti was studied by proteomic analysis to investigate the contribution made by plasmid-encoded functions on the intracellular regulation of this bacterium. Protein profiles of strain 2011 were compared with those from its mutant strains which were either cured of their pRme2011a (also called pSyma) plasmid (strain 818), or contained an extensive deletion of this plasmid (strain SmA146). Plasmid pSyma contains the nodulation and nitrogen fixation genes and is 1.4 Mbp with an estimated coding potential of 1,400 proteins. However, under the growth conditions used we could detect 60 differences between the parent strain and its pSyma-cured derivative, strain 818. While the majority of these differences were due to regulatory changes, such as up- and downregulation, some proteins were totally missing in some strains. These 60 proteins were classified into 21 subgroups, A to U, based on their measured protein levels when the cells were grown in the presence or absence of luteolin. Comparisons were made between the different strains to assess the possible interactions of the different proteins of the subgroups and plasmid pSyma. These results suggest that pSyma has a role in the regulation of the expression of genes from the other replicons (3.5 Mbp chromosome and the 1.7 Mbp pSymB plasmid) present in the S. meliloti cells. Proteome analysis provides a sensitive tool to examine the functional organisation of the S. meliloti genome and the intracellular gene interactions between replicons and will provide a powerful analytical tool to complement the genome sequencing of strain 1021.
Insights
Sinorhizobium meliloti
Area of Science:
- Microbiology
- Proteomics
- Genomics
Background:
- Sinorhizobium meliloti is a soil bacterium crucial for legume symbiosis.
- Understanding its intracellular regulation is key to optimizing nitrogen fixation.
- Plasmids play a significant role in bacterial physiology and adaptation.
Purpose of the Study:
- To investigate the role of plasmid-encoded functions in Sinorhizobium meliloti intracellular regulation.
- To identify proteins affected by the presence or absence of the pSyma plasmid.
- To explore the regulatory interactions between different replicons within S. meliloti.
Main Methods:
- Comparative proteomic analysis of S. meliloti strains.
- Utilizing wild-type, plasmid-cured, and plasmid-deleted mutant strains.
- Protein profiling under varying growth conditions (with and without luteolin).
Main Results:
- Sixty protein expression differences were detected between parent and pSyma-cured strains.
- These differences included up/downregulation and complete absence of certain proteins.
- Proteins were categorized into 21 subgroups based on expression patterns.
- pSyma influences the expression of genes located on the chromosome and pSymB plasmid.
Conclusions:
- The pSyma plasmid significantly contributes to the intracellular regulatory network of S. meliloti.
- Proteome analysis is a powerful tool for dissecting bacterial genome organization and inter-replicon gene interactions.
- These findings complement genome sequencing efforts and enhance understanding of S. meliloti functional genomics.
