Exploring potential soybean bradyrhizobia from high trehalose-accumulating soybean genotypes for improved symbiotic effectiveness in soybean / Exploración de bradirizobios potenciales de la soja a partir de genotipos de soja con alto contenido de trehalosa para mejorar la eficacia simbiótica en la soja

Drought is the most important factor limiting the activity of rhizobia during N-fixation and plant growth. In the present study, we isolated Bradyrhizobium spp. from root nodules of higher trehalose-accumulating soybean genotypes and examined for moisture stress tolerance on a gradient of polyethylene glycol (PEG 6000) amended in yeast extract mannitol (YEM) broth. In addition, the bradyrhizobial strains were also evaluated for symbiotic effectiveness on soybean. Based on 16S rDNA gene sequences, four bradyrhizobial species were recovered from high trehalose-accumulating genotypes, i.e., two Bradyrhizobium liaoningense strains (accession number KX230053, KX230054) from EC 538828 and PK-472, respectively, one Bradyrhizobium daqingense (accession number KX230052) from PK-472, and one Bradyrhizobium kavangense (accession number MN197775) from Valder genotype having low trehalose. These strains, along with two native strains, viz., Bradyrhizobium japonicum (JF792425), Bradyrhizobium liaoningense (JF792426), and one commercial rhizobium, were studied for nodulation, leghaemoglobin, and N-fixation abilities on soybean under sterilized sand microcosm conditions in a completely randomized design. Among all the strains, D-4A (B. daqingense) followed by D-4B (B. liaoningense) was found to have significantly higher nodulation traits and acetylene reduction assay (ARA) activity when compared to other strains and commercial rhizobia. The bradyrhizobia isolates showed plant growth promotion traits such as indole acetic acid (IAA), exopolysaccharide (EPS), and siderophore production, phosphate-solubilizing potential, and proline accumulation. The novel species B. daqingense was reported for the first time from Indian soil and observed to be a potential candidate strain and should be evaluated for conferring drought tolerance in soybean under simulated stress conditions.(AU)

Analysis of validamycin as a potential antifungal compound against Candida albicans

Validamycin A has been successfully applied in the fight against phytopathogenic fungi. Here, the putative antifungal effect of this pseudooligosaccharide against the prevalent human pathogen Candida albicans was examined. Validamycin A acts as a potent competitive inhibitor of the cell-wall-linked acid trehalase (Atc1p). The estimated MIC50 for the C. albicans parental strain CEY.1 was 500 mg/l. The addition of doses below MIC50 to exponentially growing CEY.1 cells caused a slight reduction in cell growth. A concentration of 1 mg/ml was required to achieve a significant degree of cell killing. The compound was stable as evidenced by the increased reduction of cell growth with increasing incubation time. A homozygous atc1delta/atc1delta mutant lacking functional Atc1p activity showed greater resistance to the drug. The antifungal power of validamycin A was limited compared with the drastic lethal action caused by exposure to amphotericin B. The endogenous content of trehalose rose significantly upon validamycin and amphotericin B addition. Neither serum-induced hypha formation nor the level of myceliation recorded in macroscopic colonies were affected by exposure to validamycin A. Our results suggest that, although validamycin A cannot be considered a clinically useful antifungal against C. albicans, its mechanism of action and antifungal properties provide the basis for designing new, clinically interesting, antifungal-related compounds (AU)

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Osmoadaptation mechanisms in prokaryotes: distribution of compatible solutes

Microorganisms respond to osmotic stress mostly by accumulating compatible solutes, either by uptake from the medium or by de novo synthesis. These osmotically active molecules preserve the positive turgor pressure required for cell division. The diversity of compatible solutes is large but falls into a few major chemical categories; they are usually small organic molecules such as amino acids or their derivatives, and carbohydrates or their derivatives. Some are widely distributed in nature while others seem to be exclusively present in specific groups of organisms. This review discusses the diversity and distribution of known classes of compatible solutes found in prokaryotes as well as the increasing knowledge of the genes and pathways involved in their synthesis. The alternative roles of some archetypal compatible solutes not subject to osmoregulatory constraints are also discussed (AU)

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Diversity and biosynthesis of compatible solutes in hyper/thermophiles / Diversidad y biosíntesis de solutos compatibles en hiper/termófilos

The accumulation of compatible solutes, either by uptake from the medium or by de novo synthesis, is a general response of microorganisms to osmotic stress. The diversity of compatible solutes is large but falls into a few major chemical categories, such as carbohydrates or their derivatives and amino acids or their derivatives. This review deals with compatible solutes found in thermophilic or hyperthermophilic bacteria and archaea that have not been commonly identified in microorganisms growing at low and moderate temperatures. The response to NaCl stress of Thermus thermophilus is an example of how a thermophilic bacterium responds to osmotic stress by compatible solute accumulation. Emphasis is made on the pathways leading to the synthesis of mannosylglycerate and glucosylglycerate that have been recently elucidated in several hyper/thermophilic microorganisms. The role of compatible solutes in the thermoprotection of these fascinating microorganisms is also discussed (AU)

La acumulación de solutos compatibles por incorporación del medio o mediante síntesis de novo es una respuesta general de los microorganismos al estrés osmótico. La diversidad de solutos compatibles es grande pero cae en unas pocas categorías químicas importantes tales como carbohidratos o sus derivados y aminoácidos o sus derivados. Esta revisión trata de los solutos compatibles encontrados en bacterias y en arqueas termófilas o hipertermófilas y que no se han identificado en microorganismos que viven a temperaturas bajas y moderadas. La respuesta de Thermus thermophilus al estrés causado por el NaCl es un ejemplo de cómo responde una bacteria termófila al estrés osmótico mediante la acumulación de solutos compatibles. Se destacan las vías que conducen a la síntesis del manosilglicerato y del glucosilglicerato que se han descubierto recientemente en varios microorganismos hiper/thermófilos. Se describe también la función de los solutos compatibles en la termoprotección de estos apasionantes microorganismos (AU)

Trehalose accumulation induced during oxidative stress response is independent of TPS1 mRNA levels in Candida albicans / La acumulación de trehalosa inducida durante la respuesta al estrés oxidativo es independiente de los niveles de mRNA de TPS1 en Candida albicans

Growing cells of the Candida albicans trehalose-deficient mutant tps1/tps1 were extremely sensitive to severe oxidative stress exposure (H2O2). However, their viability was not affected after saline stress or heat-shock treatments, being roughly equivalent to that of the parental strain. In wild-type cells, these adverse conditions induced the intracellular accumulation of trehalose together with activation of trehalose-6P synthase, whereas the endogenous trehalose content and the corresponding biosynthetic activity were barely detectable in the tps1/tps1 mutant. The addition of cycloheximide did not prevent the marked induction of trehalose-6P synthase activity. Furthermore, the presence of H2O2 decreased the level of TPS1 mRNA expression. Hence, the conspicuous trehalose accumulation in response to oxidative stress is not induced by increased transcription of TPS1. Our results are consistent with a specific requirement of trehalose in order to withstand a severe oxidative stress in C. albicans, and suggest that trehalose accumulation observed under these conditions is a complex process that most probably involves post-translational modifications of the trehalose synthase complex (AU)

Células en crecimiento de Candida albicans tps1/tps1, mutantes deficientes en trehalosa, demostraron ser muy sensibles a un intenso estrés oxidativo (H2O2). No obstante, su viabilidad no se vio afectada tras un estrés salino ni por tratamientos de choque térmico, siendo equivalente a la de la cepa parental. Estas condiciones adversas inducen en las células salvajes la acumulación intracelular de trehalosa junto con la activación del enzima trehalosa-6P sintasa, mientras que en los mutantes tps1/tps1 el contenido de trehalosa y la activación de este enzima eran prácticamente indetectables. El añadido de cicloheximida no impedía una marcada inducción de la actividad trehalosa-6P sintasa. Asimismo, la presencia de H2O2 hacía disminuir el nivel de expresión de mRNA de TPS1. Por lo tanto, la acumulación abundante de trehalosa en respuesta al estrés oxidativo no es inducida por un aumento de la transcripción del gen TPS1. Nuestros resultados concuerdan con una demanda específica de trehalosa que necesita Candida albicans para resistir el estrés oxidativo severo, y sugieren que la acumulación de trehalosa observada en estas condiciones es un proceso complejo que muy probablemente implica modificaciones postraduccionales del sistema de trehalosa sintasa (AU)