Adaptation of <Emphasis Type="Italic">Lactobacillus acidophilus</Emphasis> to Thermal Stress Yields a Thermotolerant Variant Which Also Exhibits Improved Survival at pH 2

Loss in probiotic viability upon exposure to stressful storage and transport conditions has plagued the probiotic market worldwide. Lactobacillus acidophilus is an important probiotic that is added to various functional foods. It is known to be fairly labile and susceptible to temperature variations that it encounters during processing and storage which increases production cost. It has been repeatedly demonstrated that pre-exposure to sub-lethal doses of stress, particularly, temperature and pH, leads to improved survival of various probiotics when they subsequently encounter the same stress of a much greater magnitude. Attempts to adapt L. acidophilus to temperatures as high as 65 °C to arrive at a thermotolerant variant have not been reported previously. To improve viability at elevated temperatures, we gradually adapted the L. acidophilus NCFM strain to survival at 65 °C for 40 min. Following adaptation, the variant showed a 2-log greater survival compared to wild-type at 65 °C. Interestingly, this thermotolerant variant also demonstrated a 2-log greater stability compared to wild-type at pH 2.0. The improved pH and temperature stress tolerance exhibited by this variant remained unaltered even when the strain was lyophilized. Moreover, the thermotolerant variant demonstrated improved stability compared to wild-type when stored for up to a week at 37 and 42 °C. Probiotic properties of the variant such as adherence to epithelial cells and antibacterial activity remained unaltered. This strain can potentially help address the issue of significant loss in viable cell counts of L. acidophilus which is typically encountered during probiotic manufacture and storage.     

Changes in net photosynthetic rate and chlorophyll fluorescence in potato leaves induced by water stress

Net rates of photosynthesis (PN) saturated by irradiance of >500 mol m-2 s-1 (PAR) significantly decreased in water-stressed potato (Solanum tuberosum L. cv. Kufri Sindhuri) plants. The quantum yield of photochemical energy conversion (Fv/Fm), relative electron transport rate (ETR), and photochemical quenching (Qp) exhibited a parallel decline at high irradiance. A slight decrease in relative water content (RWC) was accompanied by a drastic decline in leaf water potential (w) from -0.2 to -1.0 MPa. Dehydrated leaves showed an increase in the amount of total soluble sugars per unit leaf area which inhibited the photosynthesis in a feedback manner. After rewatering, PN and Fv/Fm were restored to the values of control plants within 24 h, and the restoration was accompanied by a proportionate lowering of content of total soluble sugars in the leaves.     

Engineered silver nanoparticles are sensed at the plasma membrane and dramatically modify the physiology of Arabidopsis thaliana plants

Silver nanoparticles (Ag NPs) are the world's most important nanomaterial and nanotoxicant. The aim of this study was to determine the early stages of interactions between Ag NPs and plant cells, and to investigate their physiological roles. We have shown that the addition of Ag NPs to cultivation medium, at levels above 300 mg L^?1, inhibited Arabidopsis thaliana root elongation and leaf expansion. This also resulted in decreased photosynthetic efficiency and the extreme accumulation of Ag in tissues. Acute application of Ag NPs induced a transient elevation of [Ca²⁺]_cyt and the accumulation of reactive oxygen species (ROS; partially generated by NADPH oxidase). Whole‐cell patch‐clamp measurements on root cell protoplasts demonstrated that Ag NPs slightly inhibited plasma membrane K⁺ efflux and Ca²⁺ influx currents, or caused membrane breakdown; however, in excised outside‐out patches, Ag NPs activated Gd³⁺‐sensitive Ca²⁺ influx channels with unitary conductance of approximately 56 pS. Bulk particles did not modify the plasma membrane currents. Tests with electron paramagnetic resonance spectroscopy showed that Ag NPs were not able to catalyse hydroxyl radical generation, but that they directly oxidized the major plant antioxidant, l ‐ascorbic acid. Overall, the data presented shed light on mechanisms of the impact of nanosilver on plant cells, and show that these include the induction of classical stress signalling reactions (mediated by [Ca²⁺]_cyt and ROS) and a specific effect on the plasma membrane conductance and the reduced ascorbate.     

A src-related kinase in the brush border membranes of gastrointestinal cells is regulated by c-met.

Hepatocyte growth factor (HGF) elicits pleiotropic cellular responses by binding to c-met, a PTK transmembrane receptor. The recent identification of HGF in fluids which enter the gut lumen suggests a mechanism by which c-met molecules are accessible to ligand that is present near the apical surfaces of polarized enterocytes. A subset of c-met molecules was detected, by confocal and immunoelectron microscopic analysis, which colocalizes with a recently identified src-related gastrointestinal tyrosine kinase (gtk) in the brush border membranes of enterocytes. Furthermore, treatment of c-met/gtk-transfected cells with a chemical cross-linking agent revealed that c-met forms a physical complex with gtk, in vivo. Not surprisingly, activation of the receptor molecules with HGF rapidly stimulated gtk enzymatic activity. Similarly, the stimulation of gtk activity occurred when nontransfected primary hepatocytes were exposed to ligand. These findings suggest a model in which HGF binding to luminally accessible c-met stimulates gtk activity. This brush border-associated c-met-linked pathway may be associated with a defined set of epithelial cell responses.     

Expression of cold and drought regulatory protein (CcCDR) of pigeonpea imparts enhanced tolerance to major abiotic stresses in transgenic rice plants

Main conclusion

Transgenic rice expressing pigeonpea Cc CDR conferred high-level tolerance to different abiotic stresses. The multiple stress tolerance observed in CcCDR -transgenic lines is attributed to the modulation of ABA-dependent and-independent signalling-pathway genes.

Stable transgenic plants expressing Cajanus cajan cold and drought regulatory protein encoding gene (CcCDR), under the control of CaMV35S and rd29A promoters, have been generated in indica rice. Different transgenic lines of CcCDR, when subjected to drought, salt, and cold stresses, exhibited higher seed germination, seedling survival rates, shoot length, root length, and enhanced plant biomass when compared with the untransformed control plants. Furthermore, transgenic plants disclosed higher leaf chlorophyll content, proline, reducing sugars, SOD, and catalase activities, besides lower levels of MDA. Localization studies revealed that the CcCDR-GFP fusion protein was mainly present in the nucleus of transformed cells of rice. The CcCDR transgenics were found hypersensitive to abscisic acid (ABA) and showed reduced seed germination rates as compared to that of control plants. When the transgenic plants were exposed to drought and salt stresses at vegetative and reproductive stages, they revealed larger panicles and higher number of filled grains compared to the untransformed control plants. Under similar stress conditions, the expression levels of P5CS, bZIP, DREB, OsLEA3, and CIPK genes, involved in ABA-dependent and-independent signal transduction pathways, were found higher in the transgenic plants than the control plants. The overall results amply demonstrate that the transgenic rice expressing CcCDR bestows high-level tolerance to drought, salt, and cold stress conditions. Accordingly, the CcCDR might be deployed as a promising candidate gene for improving the multiple stress tolerance of diverse crop plants.

     

Choice of topology estimators in Bayesian phylogenetic analysis

Wheeler WC and Pickett KM (2008. Topology-Bayes versus clade-Bayesin phylogenetic analysis. Mol Biol Evol. 25:447–453.)discuss two ways of summarizing the posterior probability distributionof a Bayesian phylogenetic analysis, which they refer to as"topology-Bayes" and "clade-Bayes." They claim that the clade-Bayesapproach leads to problems such as "exaggerated clade support,inconsistently biased priors, and the impossibility of topologyhypothesis testing," which are not problems for the topology-Bayesapproach. However, their argument for topology-Bayes over clade-Bayesis based on errors in the interpretation of summary statisticsassociated with Bayesian phylogenetic analysis. Although thereis a well-documented difference between the maximum posteriorprobability topology and the majority-rule consensus topology(the established terms for topology-Bayes and clade-Bayes summaries,respectively), both have a place in phylogenetic analysis. Choiceof summarization strategy should be driven by choice of parametersthat need to be estimated versus those to be marginalized giventhe evolutionary questions being asked or hypotheses being tested.     

Genome sequences of Salmonella enterica serovar typhimurium, Choleraesuis, Dublin, and Gallinarum strains of well- defined virulence in food-producing animals

Salmonella enterica is an animal and zoonotic pathogen of worldwide importance and may be classified into serovars differing in virulence and host range. We sequenced and annotated the genomes of serovar Typhimurium, Choleraesuis, Dublin, and Gallinarum strains of defined virulence in each of three food-producing animal hosts. This provides valuable measures of intraserovar diversity and opportunities to formally link genotypes to phenotypes in target animals.