Quorum sensing, a population density-dependent mechanism for bacterial communication and gene regulation, plays a crucial role in the symbiosis between alfalfa and its symbiont Sinorhizobium meliloti. The Sin system, one of three quorum sensing systems present in S. meliloti, controls the production of the symbiotically active exopolysaccharide EPS II. Based on DNA microarray data, the Sin syst...

The plant symbiotic α-proteobacterium Sinorhizobium meliloti has two RpoH-type sigma factors, RpoH1 and RpoH2. The former induces the synthesis of heat shock proteins and optimizes interactions with the host. Using a Western blot analysis, we examined time course changes in the intracellular contents of these factors upon a temperature upshift. The RpoH1 level was relatively high and constant, ...

During development of the symbiotic soil bacterium Sinorhizobium meliloti into nitrogen-fixing bacteroids, DNA replication and cell division cease and the cells undergo profound metabolic and morphological changes. Regulatory genes controlling the early stages of this process have not been identified. As a first step in the search for regulators of these events, we report the isolation and char...

Hemoglobins (Hbs) have been characterized from a wide variety of eubacteria, but not from nitrogen-fixing rhizobia. Our search for Hb-like sequences in the Sinorhizobium meliloti genome revealed that a gene coding for a flavohemoglobin (fHb) exists in S. meliloti (SmfHb). Computer analysis showed that SmfHb and Alcaligenes eutrophus fHb are highly similar and could fold into the same tertiary s...

A novel gene (pdxP) encoding a pyridoxine 5'-phosphate (PNP) phosphatase involved in the last step of pyridoxine biosynthesis was cloned from Sinorhizobium meliloti IFO 14782 on the basis of the peptide sequences of the natural enzyme. The pdxP gene is an open reading frame (708 bp) encoding 235 amino acid residues with a calculated molecular weight of 26,466. From its deduced amino acid sequen...

Structural variation, including variation in gene copy number and presence or absence of genes, is a widespread and important source of genomic variation. We used whole-genome DNA sequences from 48 strains of Sinorhizobium (recently renamed Ensifer), including 20 strains of Sinorhizobium meliloti and 12 strains of S. medicae that were the focus of the analyses, to study the fitness effects of n...

We constructed a stable, low-copy-number plasmid containing a fusion between a Sinorhizobium meliloti rRNA promoter and gfp(mut3). When transformed into S. meliloti the resulting strain, Rm1021/pKW1, fluoresced in proportion to its growth rate during balanced growth. This strain also showed an unexpected behavior when grown to stationary phase in TY medium: the average cellular fluorescence inc...

We studied the genetic structure of 176 bacterial isolates from nodules of Medicago sativa, M. lupulina and M. polymorpha in fifteen sites distributed in three localities in Mexico. The strains were characterized by multilocus enzyme electrophoresis, plasmid profiles, PCR restriction fragment length polymorphism of 16S rRNA genes and of the intergenic spacer between 16S and 23S rRNA genes, and ...