Chaitanya Kumar Jha

Isolation of Rhizobacteria from Jatropha curcas and characterization of produced ACC deaminase.

Decreased levels of ACC (1‐aminocyclopropane‐1‐carboxylic acid) result in lower levels of endogenous ethylene, which eliminate the potentially inhibitory effects of stress‐induced higher ethylene concentrations. It is worth noting the substantial ability of the bacterial species to colonize different environments, including taxonomically distinct plants cultivated in distantly separated geographical regions. For example, Enterobacter cloacae, designated as MSA1 and Enterobacter cancerogenus, designated as MSA2 were recovered from the rhizosphere of Jatropha in the present work. This study first time confirms the ACC deaminase activity in the Enterobacter cancerogenus on the preliminary basis. Several bacterial plant growth‐promoting mechanisms were analyzed and detected like phosphate solubilization, siderophore production, IAA production, GA3 (gibberellic acid) production and ACC deaminase activity in the isolated cultures. Isolates were grown until exponential growth phase to evaluate their ACC deaminase activity and the effect of pH, temperature, salt, metals and substrate concentration after the partial purification of enzyme by ion exchange chromatography. The FOURIER TRANSFORM INFRARED (FT‐IR) spectra were recorded for the confirmation of α‐ketobutyrate production. By using lineweaver Burk plot Km and Vmax value for ACC deaminase of both the organism was calculated in the different fractions. In this work, we discuss the possible implications of these bacterial mechanisms on the plant growth promotion or homeostasis regulation in natural conditions. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Combinatorial assessment on dominance and informative diversity of PGPR from rhizosphere of Jatropha curcas L.

The extensive and enduring challenges in soil microbiology depend on the development of efficient methods to be acquainted with the types of microbes present in soil, and to determine the functional performance of the overall microbial groups in situ. This study aims to investigate the combined uses of species richness and diversity as well as to estimate the combinatorial effect of species richness and diversity in order to understand their role and distribution in their habitat. To achieve this objective a study was designed targeting the rhizosphere of Jatropha curcas L. which were planted in various soil conditions on five distinctive sites of Gujarat state (India). These sites were constantly monitored and studied for the species richness and evenness (“heterogeneity”). The isolates were checked for their PGPR potentials like Phosphate solubilisation, Siderophore production, Indole acetic acid production, ACC deaminase production, HCN production, EPS production and Ammonia production. The results obtained were used to calculate richness, evenness and diversity indices. Results reveal the total heterogeneity in the site of fertile Jatropha rhizosphere (GS4) as well as sodic soil site (GS5) than other three sites. Absence of equitability under the selected and defined condition was also observed in GS4 and GS5 sites. The combinatorial estimates provide the information on their distribution and roles in the habitat. In particular, such an empirical relationship from a single rhizosphere of a distinctive species Jatropha is useful to test diversity predictions in natural sites, and further it can be applied to either by performing trials over larger spatial and temporal scales or by conducting correlational studies of biodiversity gradients. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The Role of ACC Deaminase Producing PGPR in Sustainable Agriculture

The plant rhizosphere is a multidimensional and dynamic ecological environment of complicated microbe–plant interactions for harnessing essential macro and micronutrients from a limited nutrient pool. Certain plant growth promoting rhizobacteria (PGPR) contain a vital enzyme, 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase (EC 4.1.99.4), which regulates ethylene production by metabolizing ACC (an intermediate precursor of ethylene biosynthesis in higher plants) into α-ketobutyrate and ammonia. The microbial enzyme 1-aminocyclopropane-1-carboxylate deaminase cleaves ACC irreversibly, this being the immediate precursor of ethylene in plants. ACC deaminase-expressing PGPR protect plants against the growth inhibition that might otherwise result following flooding, extremes of temperature, the presence of organic and inorganic toxicants, phytopathogens, drought or high salt concentrations. Organisms containing ACC deaminase genes have been reported to be useful in promotion of early root development from either seeds or cuttings, increasing the life of horticultural flowers, protecting plants against a wide range of environmental stresses, facilitating the production of volatile organic compounds responsible for aroma formation and phytoremediation of contaminated soils.

Enterobacter : Role in Plant Growth Promotion

It is believed that inoculation with rhizobacteria containing plant growth promoting (PGP) characteristics consequently promote root and shoot growth. Further evaluation of these bacteria exhibiting multiple PGP traits on soil–plant system is needed to uncover their efficacy as effective PGP rhizobacteria (PGPR) or PGP bacteria (PGPB) depending upon their nature. The genera within the family Enterobacteriaceae that feature members described as PGPB are Citrobacter, Enterobacter, Erwinia, Klebsiella, Kluyvera, Pantoea and Serratia, although some of these genera also contain species reported to be plant pathogens. Genus Enterobacter is a Gram-negative, straight rod which is motile with peritrichous flagella and is facultatively anaerobic. Enterobacter spp. are known to have a wide range of PGP characteristics involving in nitrogen fixation, soil phosphorus solubilisation, production of antibiotics, having ability to secrete siderophore produce, chitinase, ACC deaminase, hydrolytic enzymes besides exopolysaccharides and in the enhancement of soil porosity. Numerous Enterobacter strains express these activities which promote plant growth and suppress soilborne plant pathogens. These PGP abilities of Enterobacter can make them a potential candidate suitable for plant growth and development. Due to their multifarious role in crop growth, a number of these strains have been developed commercially as plant growth promoters and biocontrol agents.

Bacilli and Agrobiotechnology

Development of value-added products from renewable supplies is attracting more and more attention due to the fossil fuel resource depletion and environmental concerns. Bacillus species show distinctive benefits as hosts for production of industrially important enzymes and biochemical compounds. They are also improved through metabolic engineering techniques for efficient production of fuels, microbial enzymes, and fine and bulk chemicals. In this chapter, recent findings about Bacillus spp. and their usage as microbial factories are summarized.

Hormonal Signaling by PGPR Improves Plant Health Under Stress Conditions

Changes in climate and/or resource management will mean that future crops, either unintentionally or deliberately, will receive insufficient irrigation necessarily drying the soil as well as limiting leaf expansion and gas exchange and, consequently, yield. The soil environment is a complex and highly heterogeneous system with its chemical, physical, and biological characteristics that vary significantly with location and time. Several chemical changes in soil are associated with plant-growth-promoting rhizobacteria (PGPRs). Some bacterial strains directly regulate plant physiology by mimicking synthesis of plant hormones, whereas others increase mineral and nitrogen availability in the soil as a way to augment growth. Such bacteria have been applied to a wide range of agricultural species for the purposes of growth enhancement, including increased seed emergence, plant weight, crop yields, and disease control. Various types of stress, including chilling, heat, wounding, pathogen infection, salt, metals, and nutritional stress, with increased damage, have been documented. However, the defined mechanisms involved in the use of PGPR which decrease the damage to plants that occurs under stress conditions is a potentially important adjuvant to agricultural practice in locales where stress is a major constraint. Of particular significance to the discussion here are rhizobacteria that can impact on plant hormone signaling pathways either by producing ABA (abscisic acid), auxins, gibberellin, and cytokinins or by mediating plant ethylene levels by producing ACC deaminase. Coinoculation of different rhizobacterial strains (that alter different signaling pathways) also may provide a ready-made solution. Depending on inoculum’s persistence, PGPRs may also provide an opportunity to target alterations in plant hormone status to specific growth stages or under particular stress conditions, under specific environmental conditions.

Rhizobacteria for Management of Nematode Disease in Plants

Plant-parasitic nematodes are considered worst enemies of mankind because of devastation they cause to crops. There is hardly any crop which is not affected by nematodes. Management of the nematode disease appears to be less straightforward than one might anticipate. Therefore, it is fundamental to have prior knowledge of the interactions involved, as even low densities of nematode can result in a disease of significant importance. One of the solutions is to use chemicals to control the interacting microorganisms and thus preventing the formation of disease-like complexes. However, potential threat to environment, their harmful effects on nontarget species, including human, as well as their residual effects on climax communities, the time required for the development of nematode-resistant host cultivars, and high costs of chemical control agents possess a serious problem in their wide application. An alternative to chemicals that fulfill all requirements and brings sustainability of agricultural crops is the range of rhizospheric microorganisms which attack the plant-parasitic nematodes. Hence, nematode management strategies using biological microorganisms have gained considerable interest. As a group of important natural enemies of nematode disease, microorganisms exhibit diverse modes of action: these include parasitizing; producing toxins, antibiotics, or enzymes; competing for nutrients; inducing systemic resistance of plants; and promoting plant health. They act synergistically on plants through the direct suppression of nematodes, promoting plant growth and facilitating the rhizospheric colonization and activity of microbial antagonists.