Transcriptome Profiling Reveals the Importance of Plasmid pSymB for Osmoadaptation of Sinorhizobium meliloti

Abstract

In this work, DNA microarrays were used to investigate genome-wide transcriptional responses of Sinorhizobium meliloti to a sudden increase in external osmolarity elicited by addition of either NaCl or sucrose to exponentially growing cultures. A time course of the response within the first 4 h after the osmotic shock was established. We found that there was a general redundancy in the differentially expressed genes after NaCl or sucrose addition. Both kinds of stress resulted in induction of a large number of genes having unknown functions and in repression of many genes coding for proteins with known functions. There was a strong replicon bias in the pattern of the osmotic stress response; whereas 64% of the upregulated genes had a plasmid localization, 85% of the downregulated genes were chromosomal. Among the pSymB osmoresponsive genes, 83% were upregulated, suggesting the importance of this plasmid for S. meliloti osmoadaptation. Indeed, we identified a 200-kb region in pSymB needed for adaptation to saline shock which has a high density of osmoregulated genes.

PhyR Is Involved in the General Stress Response ofMethylobacterium extorquensAM1

“…teobacteria and PhyR is restricted to this taxon, we may speculate that PhyR is important for stress resistance in other Alphaproteobacteria as well (13). The fact that phyR homologues are induced in response to various stressful conditions in other Alphaproteobacteria (9,19,20,39) is in agreement with this assumption.…”

RpoE2 of Sinorhizobium meliloti is necessary for trehalose synthesis and growth in hyperosmotic media

“…The osmotic induction of otsA, treY and treS is in agreement with the results obtained in transcriptomic work by Domínguez-Ferreras et al (2006). Our results show that the expression of treS and treY was under the control of rpoE2 during the stationary growth phase in non-stressing medium.…”

“…SMa0233, SMb20574 and SMb20099 are therefore referred to as OtsA, TreY and TreS, respectively, hereafter. These three ORFs are induced by osmotic stress, as described in the transcriptomic study by Domínguez-Ferreras et al (2006). A sequence close to the consensus of the rpoE2 promoter (ggAAC-16-17 nt-gcgTTt) proposed by Sauviac et al (2007) is located upstream of the operon they proposed, suggesting a putative rpoE2-dependent transcript ( Supplementary Fig.…”

The tRNA arg Gene and engA Are Essential Genes on the 1.7-Mb pSymB Megaplasmid of Sinorhizobium meliloti and Were Translocated Together from the Chromosome in an Ancestral Strain

“…pSymA is a self-transmissible plasmid that can also mobilize pSymB (24). The pSymB megaplasmid has several large gene clusters involved in the biosynthesis and export of surface polysaccharides (essential for nodule invasion) and in many catabolic activities and associated solute transport systems, as well as genes that contribute to osmotic tolerance of S. meliloti (15,25,26). Thus, pSymB appears to play an important role in survival under diverse nutritional conditions present in the soil and rhizospheres (21).…”