Murugesan Chandrasekaran

Spore Associated Bacteria (SAB) of Arbuscular Mycorrhizal Fungi (AMF) and Plant Growth Promoting Rhizobacteria (PGPR) Increase Nutrient Uptake and Plant Growth Under Stress Conditions

Microorganisms present in the rhizosphere soil plays a vital role in improving the plant growth and soil fertility. Many kinds of fertilizers including chemical and organic has been approached to improve the productivity. Though some of them showed significant improvement in yield, they failed to maintain the soil properties. Rather they negatively affected soil eventually, the land became unsuitable for agricultural. To overcome these problems, microorganisms have been used as effective alternative. For past few decades, plant growth promoting rhizobacteria (PGPR) and arbuscular mycorrhizal fungi (AMF) have been used as effective inoculants to enhance the plant growth and productivity. PGPR improves the plant growth and helps the plant to withstand biotic and abiotic stresses. AM fungi are known to colonize roots of plants and they increase the plant nutrient uptake. Spore associated bacteria (SAB) are attached to spore wall or hyphae and known to increase the AMF germination and root colonization but their mechanism of interaction is poorly known. Better understanding the interactions among AMF, SAB and PGPR are necessary to enhance the quality of inoculants as a biofertilizers. In this paper, current knowledge about the interactions between fungi and bacteria are reviewed and discussed about AMF spore associated bacteria.

Investigation of role of aspartame on apoptosis process in HeLa cells

Aspartame is an artificial sweetener used as an alternate for sugar in several foods and beverages. The study reports that consumption of aspartame containing product could lead to cancer. However, the effect of aspartame on apoptosis process in cancer is not yet understood clearly. HeLa cells were exposed to different concentrations (0.01–0.05 mg/ml) of aspartame for 48 h. Cytotoxicity of aspartame on cancer cells was determined by SRB assay. The result indicates no significant changes on cell viability. Aspartame suppresses apoptosis process in cancer cells by down-regulation of mRNA expression of tumor suppressor gene p53, and pro-apoptotic gene bax. It up-regulates anti-apoptotic gene bcl-2 mRNA expression. In addition, Ki 67 and PCNA mRNA, and protein expressions were determined. Taking all these together, we conclude that aspartame may be a potent substance to slow-down the apoptosis process in HeLa cells. Further works are ongoing to understand the biochemical and molecular mechanism of aspartame in cancer cells.

Proteases from phytopathogenic fungi and their importance in phytopathogenicity

Phytopathogenic fungi, causal agents of some of the world’s most serious plant diseases, can significantly reduce yields during large-scale agricultural production. Among the numerous hydrolytic enzymes they produce for nutritional and/or pathogenicity purposes, hydrolases and proteases are required for their growth and survival. The present review focuses on extracellular and/or secretory proteases from phytopathogenic fungi. Several extracellular proteases have been identified that contribute to fungal growth, infection structure formation, cell wall degradation, proteolytic processing of pathogenesis-related proteins and that act as elicitors of defense responses. In this review, the positive correlation between protease secretion and disease aggressiveness and/or necrosis is highlighted. The involvement of various fungal proteases in pathogenic mechanisms makes them potential targets for designing protease inhibitors that may provide an improved way to combat plant diseases, which in turn will reduce dependence on fungicides.

Meta-analysis Reveals That the Genus Pseudomonas Can Be a Better Choice of Biological Control Agent against Bacterial Wilt Disease Caused by Ralstonia solanacearum

Biological control agents (BCAs) from different microbial taxa are increasingly used to control bacterial wilt caused by Ralstonia solanacearum. However, a quantitative research synthesis has not been conducted on the role of BCAs in disease suppression. Therefore, the present study aimed to meta-analyze the impacts of BCAs on both Ralstonia wilt disease suppression and plant (host) growth promotion. The analysis showed that the extent of disease suppression by BCAs varied widely among studies, with effect size (log response ratio) ranging from −2.84 to 2.13. The disease incidence and severity were significantly decreased on average by 53.7% and 49.3%, respectively. BCAs inoculation also significantly increased fresh and dry weight by 34.4% and 36.1%, respectively on average. Also, BCAs inoculation significantly increased plant yield by 66%. Mean effect sizes for genus Pseudomonas sp. as BCAs were higher than for genus Bacillus spp. Among antagonists tested, P. fluorescens, P. putida, B. cereus, B. subtilis and B. amyloliquefaciens were found to be more effective in general for disease reduction. Across studies, highest disease control was found for P. fluorescens, annual plants, co-inoculation with more than one BCA, soil drench and greenhouse condition were found to be essential in understanding plant responses to R. solanacearum. Our results suggest that more efforts should be devoted to harnessing the potential beneficial effects of these antagonists, not just for plant growth promoting traits but also in mode of applications, BCAs formulations and their field studies should be considered in the future for R. solanacearum wilt disease suppression.

Induction of defence-related enzymes in tomato (Solanum lycopersicum) plants treated with Bacillus subtilis CBR05 against Xanthomonas campestris pv. vesicatoria

ABSTRACT Bacterial spot disease caused by Xanthomonas campestris pv. vesicatoria is one of the most important destructive diseases of tomato in many parts of the agricultural world. Therefore, the present study aims to determine the effects of Bacillus subtilis CBR05 inoculation on bacterial spot disease severity and the induction of defence-related enzymes response in tomato. Tomato leaves were evaluated to determine the activities of antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and polyphenol oxidase (PPO)) and the content of malondialdehyde (MDA). A reduction in bacterial spot severity was observed in plants inoculated with B. subtilis, compared with those of uninoculated controls. A significant increase in SOD, CAT, POD, and PPO activities was observed in plants treated with B. subtilis after 24 h inoculation compared with non-inoculated pathogen control and mock-inoculated controls. Moreover, the MDA content was induced by pathogen infection, and its amount in B. subtilis inoculated plants was significantly lower than that in pathogen control. Our results suggest that early increases in antioxidant enzymes and the reduction in MDA content with B. subtilis inoculation may play a pivotal role in mitigating oxidative stress, thereby induced systemic resistance against bacterial spot disease in tomato.