Crop productivity is affected by environmental and genetic factors. Microbes that are beneficial to plants are used to enhance the crop yield and are alternatives to chemical fertilizers and pesticides. Pseudomonas and Bacillus species are the predominant plant growth-promoting bacteria. The spore-forming ability of Bacillus is distinguished from that of Pseudomonas, and members of this genus also survive for a long time under unfavorable environmental conditions. Bacillus spp. secrete several metabolites that trigger plant growth and prevent pathogen infection. Limited studies have been conducted to understand the physiological changes that occur in crops in response to Bacillus spp. to provide protection against adverse environmental conditions. This review describes the current understanding of Bacillus-induced physiological changes in plants as an adaptation to abiotic and biotic stresses. During water scarcity, salinity and heavy metal accumulate in soil, and Bacillus spp. produce exopolysaccharides and siderophores, which prevent the movement of toxic ions and adjust the ionic balance and water transport in plant tissues while controlling the pathogenic microbial population. In addition, the synthesis of indole-3-acetic acid, gibberellic acid and 1-aminocyclopropane-1-carboxylate (ACC) deaminase by Bacillus regulates the intracellular phytohormone metabolism and increases plant stress tolerance. Cell-wall-degrading substances, such as chitosanase, protease, cellulase, glucanase, lipopeptides and hydrogen cyanide, from Bacillus spp. damage the pathogenic bacteria, fungi, nematodes, viruses and pests to control their populations in plants and agricultural lands. The normal plant metabolism is affected by unfavorable environmental stimuli, which suppress crop growth and yield. Abiotic and biotic stress factors that have detrimental effects on crops are mitigated by Bacillus-induced physiological changes, including the regulation of water transport, nutrient up-take and the activation of the antioxidant and defense systems. Bacillus association stimulates plant immunity against stresses by altering stress-responsive genes, proteins, phytohormones and related metabolites. This review describes the beneficial effect of Bacillus spp. on crop plants, which improves plant productivity under unfavorable climatic conditions, and the current understanding of the mitigation mechanism of Bacillus spp. in stress-tolerant and/or stress-resistant plants.

/pdf/bacillus-a-biological-tool-for-crop-improvement-through-bio-4uk1vfr3l3.pdf

Bacillus: A Biological Tool for Crop Improvement through Bio-Molecular Changes in Adverse Environments.

Biofertilizers consists of the microorganisms bringing about the improvement of the nutrients of the soil enhancing their accessibility to the crops. Plant nutrients form the most vital components of the sustainable agriculture. Producing healthy crops for the fulfillment of the demands of the world's growing population is completely dependent upon kind of the fertilizers being used to provide the plants with all the major nutrients but more dependability on the chemical fertilizers is destroying the environmental ecology and negatively influencing the health of humans. Thus, using microbes as bioinoculants is believed to be the best substitute of chemical fertilizers as eco-friendly manner for plant growth and soil fertility. These microbes are known to be the potent tool to provide substantial benefits to crops for sustainable agriculture. The beneficial microbes colonize the plant (epiphytic, endophytic and rhizospheric) systems of crops and plays significant role in nutrient uptake from surrounding ecosystems of plants. The plant associates microbes have ability to promote growth of plant under the natural as well as extreme conditions. These plant growth promoting microbes enhance the plant growth by various direct and indirect plant growth promoting mechanisms such as biological nitrogen fixation, the production of various plant growth hormones, siderophores, HCN, various hydrolytic enzymes and solubilization of potassium, zinc, and phosphorus. Extensive work on the biofertilizers has been done and even available which clearly reveals that these microbes possess the potential of providing the vital nutrients to the crops in adequate quantities for the enrichment of yield of the crops without disturbing the environment.

Microbial biofertilizers: Bioresources and eco-friendly technologies for agricultural and environmental sustainability

Plant growth promoting rhizobacteria (PGPRs) are very effective in immobilization of heavy metals and reducing their translocation in plants via precipitation, complex formation and adsorption. The present study was therefore designed to understand the role of Pseudomonas aeruginosa and Burkholderia gladioli in mitigation of Cd stress (0.4 mM) in 10-days old L. esculentum seedlings. The present work investigated growth characteristics, photosynthetic pigments, metal tolerance index, metal uptake and the contents of metal chelating compounds (protein bound and non-protein bound thiols, total thiols) in microbes inoculated Cd treated L. esculentum seedlings. The gene expression profiling of different metal transporters was conducted in order to investigate the quantitative analysis. Our results revealed Cd generated toxicity in seedlings in terms of reduced growth (root length, shoot length and fresh weight) and photosynthetic pigments (chlorophyll, carotenoid and xanthophyll) which enhanced upon inoculations of P. aeruginosa and B. gladioli. Further, the metal uptake along with levels of protein and non-protein bound thiols was also enhanced in Cd-treated seedlings. Gene expression studies suggested enhanced expression in the metal transporter genes which were further declined in the microbe supplemented seedlings. Therefore, micro-organisms possess growth promoting traits that enable them to reduce metal toxicity in plants.

/pdf/metal-resistant-pgpr-lowered-cd-uptake-and-expression-of-3g3r637355.pdf

Metal resistant PGPR lowered Cd uptake and expression of metal transporter genes with improved growth and photosynthetic pigments in Lycopersicon esculentum under metal toxicity.

Gamma-aminobutyric acid (GABA) is a ubiquitous four-carbon, non-protein amino acid. GABA has been widely studied in animal central nervous systems, where it acts as an inhibitory neurotransmitter. In plants, it is metabolized through the GABA shunt pathway, a bypass of the tricarboxylic acid (TCA) cycle. Additionally, it can be synthesized through the polyamine metabolic pathway. GABA acts as a signal in Agrobacterium tumefaciens-mediated plant gene transformation and in plant development, especially in pollen tube elongation (to enter the ovule), root growth, fruit ripening, and seed germination. It is accumulated during plant responses to environmental stresses and pathogen and insect attacks. A high concentration of GABA elevates plant stress tolerance by improving photosynthesis, inhibiting reactive oxygen species (ROS) generation, activating antioxidant enzymes, and regulating stomatal opening in drought stress. The transporters of GABA in plants are reviewed in this work. We summarize the recent research on GABA function and transporters with the goal of providing a review of GABA in plants.

https://www.tandfonline.com/doi/pdf/10.1080/15592324.2020.1862565

The versatile GABA in plants.

Supplementation with plant growth promoting rhizobacteria (PGPR) alleviates cadmium toxicity in Solanum lycopersicum by modulating the expression of secondary metabolites.

This study aimed to elucidate the role played by Enterobacter asburiae KE17 in the growth and metabolism of soybeans during copper (100 μm Cu) and zinc (100 μm Zn) toxicity. When compared to controls, plants grown under Cu and Zn stress exhibited significantly lower growth rates, but inoculation with E. asburiae KE17 increased growth rates of stressed plants. The concentrations of plant hormones (abscisic acid and salicylic acid) and rates of lipid peroxidation were higher in plants under heavy metal stress, while total chlorophyll, carotenoid content and total polyphenol concentration were lower. While the bacterial treatment reduced the abscisic acid and salicylic acid content and lipid peroxidation rate of Cu-stressed plants, it also increased the concentration of photosynthetic pigments and total polyphenol. Moreover, the heavy metals induced increased accumulation of free amino acids such as aspartic acid, threonine, serine, glycine, alanine, leucine, isoleucine, tyrosine, proline and gamma-aminobutyric acid, while E. asburiae KE17 significantly reduced concentrations of free amino acids in metal-affected plants. Co-treatment with E. asburiae KE17 regulated nutrient uptake by enhancing nitrogen content and inhibiting Cu and Zn accumulation in soybean plants. The results of this study suggest that E. asburiae KE17 mitigates the effects of Cu and Zn stress by reprogramming plant metabolic processes.

Enterobacter asburiae KE17 association regulates physiological changes and mitigates the toxic effects of heavy metals in soybean

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Enterobacter asburiae KE17 association regulates physiological changes and mitigates the toxic effects of heavy metals in soybean