Characterisation of a gene encoding a membrane protein that affects exopolysaccharide production and intracellular Mg2+ concentrations in Ensifer meliloti

Abstract

Exopolysaccharides play an important role in the physiology of a bacterial cell. Ensifer meliloti is capable of producing at least two types of exopolysaccharides (EPS): succinoglycan and galactoglucan. In E. meliloti, EPS are best known for their role in mediating interaction with its symbiotic hosts. It was previously shown that high concentrations of Mg2+ or K+ were capable of suppressing the mucoid phenotype associated with galactoglucan production in an expR+ derivative of Rm1021. In an attempt to determine how Mg2+ regulates galactoglucan production, SRmD363 was mutagenised and screened for mutants which were visibly mucoid at high concentrations of magnesium. Tn5 mutations in genes exoX, emmB, phoC and SMc00722 were isolated. SMc00722 is annotated as a hypothetical transmembrane protein that is conserved in the α-proteobacteria. Characterisation of SMc00722 in Rm1021 showed that the increased mucoidy was due to succinoglycan. Strains carrying mutations in SMc00722 showed increased biofilm production, and were more sensitive to high Mg2+ concentrations and deoxycholate. In addition, we show that strains carrying a mutation in SMc00722 have elevated intracellular Mg2+ concentrations. Taken together, the data are consistent with the hypothesis that SMc0722 may play a role in maintaining intracellular magnesium concentration, and we suggest that this gene be tentatively annotated as mhrA (magnesium homeostasis related).

Novel Genes and Regulators That Influence Production of Cell Surface Exopolysaccharides in Sinorhizobium meliloti

“…Mutant SMc00722-38 has its insertion in mhrA. A recent study also showed DOC sensitivity when mhrA was mutated; furthermore, those mutants overproduced EPS-I, made more biofilm than the wild type, and were defective in maintaining intracellular Mg 2ϩ levels, suggesting that MhrA plays a role in magnesium homeostasis (61).…”

Structural and Functional Properties, Biosynthesis, and Patenting Trends of Bacterial Succinoglycan: A Review

“…ion or deoxycholate. Magnesium homeostasis related mhrA are tentatively behind this action [8]. Apart from this, exoR produces a negative biosynthesis regulator too, genetically attached with ChvG/ChvI system.…”

“…Later, the name is changed to succinoglycan as one galactose residue per seven glucose residues are also present in the structure along with some non-carbohydrate substituents, namely pyruvate, succinate and acetate [2,3]. So far yield of bacterial succinoglycan up to 13.7 g/l [4] has only been reported from soil inhabiting bacteria like Agrobacterium tumefaciens, Agrobacterium radiobacter, Agrobacterium rhizogenes [5], Rhizobium radiobacter [6], Sinorhizobium meliloti [7], Ensifer meliloti [8] and Pseudomonas sp. [9].…”

Preparation and Gut Microbiota Modulatory Property of the Oligosaccharide Riclinoctaose

“…Succinoglycan is a bacterial extracellular polysaccharide secreted by some soil microbes. − Succinoglycan from different sources has a standard structural unit, consisting of one galactose (Gal) and seven glucose (Glc) residues, and the pyruvate group is attached to the terminal glucose residue of the side chain . Some of the succinoglycan also contains non-carbohydrate substitutions of acetate on the backbone and succinate on the branch. , However, the molecular weight and the nature of the substitution of succinoglycan may vary from source to source .…”