Stress-tolerant Strains Research Articles

Plasmid content of salt stress-tolerant Rhizobium strains from Egyptian soils nodulating common bean (Phaseolus vulgaris L.)

Plasmid profile analysis is useful to characterize Rhizobium strains within the same species. Among the 16 Rhizobium strains examined, 14 had distinct plasmid profiles. The size of plasmids ranged from 40 to 650 kb, and three plasmids of 650, 510 and 390 kb were common to several strains. Plasmid analysis revealed that Rhizobium etli contained a mega-plasmid, similar in size to Rhizobium tropici. All the salt-tolerant strains examined had a plasmid of 250 kb, except for strain EBRI 29. This suggests that this plasmid may play an important adaptive role under salt stress conditions.

Identification of target genes conferring ethanol stress tolerance to Saccharomyces cerevisiae based on DNA microarray data analysis

During industrial production process using yeast, cells are exposed to the stress due to the accumulation of ethanol, which affects the cell growth activity and productivity of target products, thus, the ethanol stress-tolerant yeast strains are highly desired. To identify the target gene(s) for constructing ethanol stress tolerant yeast strains, we obtained the gene expression profiles of two strains of Saccharomyces cerevisiae, namely, a laboratory strain and a strain used for brewing Japanese rice wine (sake), in the presence of 5% (v/v) ethanol, using DNA microarray. For the selection of target genes for breeding ethanol stress tolerant strains, clustering of DNA microarray data was performed. For further selection, the ethanol sensitivity of the knockout mutants in each of which the gene selected by DNA microarray analysis is deleted, was also investigated. The integration of the DNA microarray data and the ethanol sensitivity data of knockout strains suggests that the enhancement of expression of genes related to tryptophan biosynthesis might confer the ethanol stress tolerance to yeast cells. Indeed, the strains overexpressing tryptophan biosynthesis genes showed a stress tolerance to 5% ethanol. Moreover, the addition of tryptophan to the culture medium and overexpression of tryptophan permease gene conferred ethanol stress tolerance to yeast cells. These results indicate that overexpression of the genes for trypophan biosynthesis increases the ethanol stress tolerance. Tryptophan supplementation to culture and overexpression of the tryptophan permease gene are also effective for the increase in ethanol stress tolerance. Our methodology for the selection of target genes for constructing ethanol stress tolerant strains, based on the data of DNA microarray analysis and phenotypes of knockout mutants, was validated.

INVERSE METABOLIC ENGINEERING BY INTEGRATION OF MULTIPLE OMICS ANALYSES

Abstract An inverse metabolic engineering method with “multiple omics analyses” was applied to creation of a stress tolerant strain of Saccharomyces cerevisiae. DNA microarray data of laboratory and brewing strains under high ethanol concentration condition (transcriptomics data) were compared and analyzed by a clustering method. Sensitivity analysis of gene knockout mutant library was further performed (phenomics data). The selection of candidate genes for conferring stress tolerance was successfully performed.

Comparative analysis of transcriptional responses to saline stress in the laboratory and brewing strains of Saccharomyces cerevisiae with DNA microarray

To construct yeast strains showing tolerance to high salt concentration stress, we analyzed the transcriptional response to high NaCl concentration stress in the yeast Saccharomyces cerevisiae using DNA microarray and compared between two yeast strains, a laboratory strain and a brewing one, which is known as a stress-tolerant strain. Gene expression dynamically changed following the addition of NaCl in both yeast strains, but the degree of change in the gene expression level in the laboratory strain was larger than that in the brewing strain. The response of gene expression to the low NaCl concentration stress was faster than that to the high NaCl concentration stress in both strains. Expressions of the genes encoding enzymes involved in carbohydrate metabolism and energy production in both strains or amino acid metabolism in the brewing strain were increased under high NaCl concentration conditions. Moreover, the genes encoding sodium ion efflux pump and copper metallothionein proteins were more highly expressed in the brewing strain than in the laboratory strain. According to the results of transcriptome analysis, candidate genes for the creation of stress-tolerant strain were selected, and the effect of overexpression of candidate genes on the tolerance to high NaCl concentration stress was evaluated. Overexpression of the GPD1 gene encoding glycerol-3-phosphate dehydrogenase, ENA1 encoding sodium ion efflux protein, and CUP1 encoding copper metallothionein conferred high salt stress tolerance to yeast cells, and our selection of candidate genes for the creation of stress-tolerant yeast strains based on the transcriptome data was validated.

Environmental factors affecting N 2 fixation in grain legumes in the tropics, with an emphasis on Brazil

Biological nitrogen (N 2) fixation is key to sustainable agricultural systems in tropical soils, which are frequently deficient in N. However, high temperature, drought and soil acidity constrain legume root-nodule formation and function in the tropics. In most cases, the microsymbiont is the more affected partner, with plants growing on mineral N usually less sensitive to these stresses. High temperature and moisture deficiency are major causes of nodulation failure, affecting all stages of the symbiosis and limiting rhizobial growth and survival in soil. They may also contribute to undesirable changes in rhizobia, including plasmid deletions, genomic rearrangements and reduced diversity. Acidity affects several steps in the development of the symbiosis, including the exchange of molecular signals between the legume and the microsymbiont. Liming is effective in overcoming soil acidity and aluminium toxicity, but in Brazil few soils are limed to near neutral pH. Selection of rhizobial inoculant strains that are genetically stable under the often harsh soil conditions of this region is essential, but that task is impaired by a lack of knowledge of tolerance in the microsymbiont. However, good results have been obtained by selecting naturally occurring rhizobia from acid tropical soils affected by water stress and high temperatures. In Brazil, increases in grain yields of common bean and soybean have resulted from inoculation with such stress-tolerant strains. Appropriate soil management practices, e.g. no-till, are other approaches that may decrease soil temperatures and preserve moisture, thereby increasing N 2 fixation.

Experimental microbiology of saturated salt solutions and other harsh environments. 3. Growth of salt-tolerant penicillium notatum in boron-rich media.

A stress-tolerant strain of Penicillium notatum, isolated by passage through a nutrient solution saturated with calcium acetate, was found to have a tolerance to boron in several states of oxidation. Growth in the presence of elementary boron, saturating amounts of boric acid, and with various concentrations of sodium borohydride was observed and mycelial mats were spectrographically analyzed for boron accumulation.