Pallab Kumar Ghosh

Production and Metabolism of Indole Acetic Acid in Root Nodules and Symbiont (Rhizobium undicola) Isolated from Root Nodule of Aquatic Medicinal Legume Neptunia oleracea Lour.

Indole acetic acid is a phytohormone which plays a vital role in plant growth and development. The purpose of this study was to shed some light on the production of IAA in roots, nodules, and symbionts of an aquatic legume Neptunia oleracea and its possible role in nodular symbiosis. The symbiont (N37) was isolated from nodules of this plant and identified as Rhizobium undicola based on biochemical characteristics, 16S rDNA sequence homology, and DNA-DNA hybridization results. The root nodules were found to contain more IAA and tryptophan than root; however, no detectable amount of IAA was found in root. The IAA metabolizing enzymes IAA oxidase, IAA peroxidase (E.C.1.11.1.7), and polyphenol oxidase (E.C.1.14.18.1) were higher in root than nodule but total phenol and IAA content were reversed. The strain N37 was found to produce copious amount of IAA in YEM broth medium with tryptophan and reached its stationary phase at 20u2009h. An enrichment of the medium with mannitol, ammonium sulphate, B12, and 4-hydroxybenzaldehyde was found to promote the IAA production. The presence of IAA metabolizing enzymes and IAA production with PGPR traits including ACC deaminase activity of the symbionts was essential for plant microbe interaction and nodule function.

A halotolerant Enterobacter sp. displaying ACC deaminase activity promotes rice seedling growth under salt stress

Agricultural productivity is proven to be hampered by the synthesis of reactive oxygen species (ROS) and production of stress-induced ethylene under salinity stress. One-aminocyclopropane-1-carboxylic acid (ACC) is the direct precursor of ethylene synthesized by plants. Bacteria possessing ACC deaminase activity can use ACC as a nitrogen source preventing ethylene production. Several salt-tolerant bacterial strains displaying ACC deaminase activity were isolated from rice fields, and their plant growth-promoting (PGP) properties were determined. Among them, strain P23, identified as an Enterobacter sp. based on phenotypic characteristics, matrix-assisted laser desorption ionization-time of flight mass spectrometry data and the 16S rDNA sequence, was selected as the best-performing isolate for several PGP traits, including phosphate solubilization, IAA production, siderophore production, HCN production, etc. Enterobacter sp. P23 was shown to promote rice seedling growth under salt stress, and this effect was correlated with a decrease in antioxidant enzymes and stress-induced ethylene. Isolation of an acdS mutant strain enabled concluding that the reduction in stress-induced ethylene content after inoculation of strain P23 was linked to ACC deaminase activity.

An in silico structural, functional and phylogenetic analysis with three dimensional protein modeling of alkaline phosphatase enzyme of Pseudomonas aeruginosa

Phosphorus is a primary macronutrient required for normal plant health, metabolism and survival. It is present in soil in compound insoluble form for which plant cannot uptake it directly from the soil. Some phosphate solubilizing bacteria possess some important enzymes for phosphate solubilization as well as mineralization. Alkaline (or basic) phosphatase (EC 3.1.3.1) is a type of zinc containing dimeric hydrolase enzyme responsible for removing the phosphate groups from various kinds of molecules including nucleotides, proteins, and alkaloids. Unlike acid phosphatases alkaline phosphatases are most effective in an alkaline environment. Alkaline phosphatases (ALPs) are of immense importance in various agricultural industries including dairy industries for testing successful pasteurization process. In this present study, Pseudomonas aeruginosa phosphatase was selected for a detailed computational investigation to exploit its physicochemical characteristics, structural properties including 3D model, model quality analysis, phylogenetic assessment and functional analysis using a number of available standard bioinformatics tools. The protein having average molecular weight about 51 kDa, was found thermostable and alkaline in nature belonging to metalloenzyme superfamily. Specifically, the thermostable behavior of the protein is suitable for the dairy industry. Moreover, this theoretical overview will help researchers to get an idea about the predicted protein structure and it may also help to design genetically engineered phosphate solubilizing bacteria by designing specific primers.

Bioaccumulation of cadmium by Enterobacter sp. and enhancement of rice seedling growth under cadmium stress

Bacteria-mediated plant growth promotion and bioremediation of heavy metal containing soil is a widely accepted eco-friendly method. The present study is aimed to screen out cadmium resistant bacterial strain from metal contaminated rice rhizosphere and evaluate its effects on the growth of rice seedlings under cadmium stress. Among four different isolates (designated as S1, S2, S3 and S5), the S2 isolate was screened on the basis of different PGP traits and multi heavy metal resistance (minimum inhibitory concentration for cadmium, lead and arsenic were 3500, 2500 and 1050u202fµg/ml respectively). The selected S2 strain has ability to produce ACC deaminase (236.11u202fng α-keto-butyrate/mg protein/h), IAA (726u202fµg/ml), solubilize phosphate (73.56u202fppm) and fix nitrogen (4.4u202fµg of nitrogen fixed/h/mg protein). The selected strain was identified as Enterobacter sp. on the basis of phenotypic characterization, MALDI-TOF MS analysis of ribosomal proteins, FAME analysis and 16u202fS rDNA sequence homology. The high cadmium removal efficiency (>u202f95%) of this strain from the growth medium was measured by Atomic Absorption Spectrophotometer and it was due to intracellular cadmium accumulation evidenced by SEM-EDX-TEM-EDX study. SEM analysis also revealed no distortion of surface morphology of this strain even grown in the presence of high cadmium concentration (3000u202fµg/ml). Inoculation of this strain with rice seedlings significantly enhanced various morphological, biochemical characters of seedling growth compared with un-inoculated seedlings under Cd stress. The strain also exhibited alleviation of cadmium-induced oxidative stress, reduction of stress ethylene and decreased the accumulation of cadmium in seedlings as well that conferred cadmium tolerance to the plant. Thus the S2 strain could be considered as a potent heavy metal resistant PGPR applicable in heavy metal contaminated agricultural soil for bioremediation and plant growth promotion as well.nnnMAIN FINDINGnA cadmium resistant plant growth promoting Enterobacter sp. was isolated that accumulated cadmium evidenced by SEM-TEM-EDX study. It reduced Cd uptake and enhanced growth in rice seedlings.

Computational elucidation of phylogenetic, structural and functional characteristics of Pseudomonas Lipases

Lipase (triacylglycerol acylhydrolase, EC 3.1.1.3) catalyzes tri-, di-, and monoacyl glycerol of fat into glycerol and fatty acids. It has important roles in the digestion of lipids in living organisms and industrially as laundry detergents along with proteases. The microbial lipases are more stable, active and economically feasible compared to plant and animal sources. Hence, much attention was given to the maximum production of the enzyme from the microbial sources. The phylogenetic analysis revealed that the amino acid sequence of lipase protein and their corresponding cDNA of Pseudomonas aeruginosa clustered with Pseudomonas stutzeri among different species of Pseudomonas, while P. aeruginosa PA1 clustered with P. aeruginosa SJTD-1 among different strains of P. aeruginosa. The lipase of P. aeruginosa PA1 was a monomeric, acidic and thermostable protein having a molecular weight ranging in between 32.72 to 34.89u202fkDa. The protein was abundant with random coils and alpha helices in its secondary structure. The tertiary model showed 96.310 score as an overall quality factor. Hence, this in silico study gives some useful information about the lipase protein without performing crystal structure assessment by X-ray Crystallography or NMR study in wet lab experiments which could be helpful for isolation and characterization of the enzyme in vitro.

Pseudomonas: A Quorum Sensing System for Improved Crop Production

The soil is a unique and ultimate home of the variety of beneficial and biotechnologically important inhabitant microorganisms. These microorganisms comply such a best services especially beneficial agriculture in turn farmers benefitted. Effective management of agriculture ecosystem and proper use of microorganisms such as Pseudomonas and Pseudomonas-like can improve crop health, increase crop yield and productivity, maintain the health of soil over a period of long time span. Bacterium Pseudomonas associated species in the six groups in the Pseudomonadaceae family capable of sensing and generating biomolecules having short and long chains. These include quorum sensing (QS) molecules, hydrolytic enzymes, proteins, siderophores, antibiotics and much many antibacterial and antifungal compounds under various environmental situations such as high or low temperature, high or low salt concentrations, in the presence and absence of contaminants (chemicals, bio-chemicals and hydrocarbons), in response to specific ions and in response to specific signalling molecules. All these characteristics possessed and activities carried out by Pseudomonas have biotechnological applications especially in agriculture. Pseudomonas have major application in crop production by acting as biocontrol agent due to its infection ability, recognising and sending QS molecules, as an antagonistic, as phytopathogens, as plant growth promoting (PGP) agent in the form of individual cell (solid, liquid, spray), in mixed culture and co-culture, as individual or mixed culture inoculums etc. All these characteristics of genus Pseudomonas make a suitable and biotechnologically important cellular model for the variety of application in agriculture and horticulture.

Role of ACC Deaminase as a Stress Ameliorating Enzyme of Plant Growth-Promoting Rhizobacteria Useful in Stress Agriculture: A Review

The crop production is inhibited by a large number of both biotic and abiotic stresses. These stresses include presence of toxic heavy metals, high salt, flood, drought, temperature, wounding, various pathogens, etc. The agricultural production was intensified by management of these stresses with increased use of chemicals, and it needs more attention for incoming population explosion. These chemical inputs caused several harmful effects on the environment and sustainable agriculture. It is ne3cessary to decrease dependence of chemical input for sustainable agriculture with a holistic approach and also essential for environmental protection. One such possible approach is the use of 1-aminocyclopropane-1-carboxylate (ACC) deaminase-producing plant growth-promoting rhizobacteria (PGPR) to protect the crop plants from the harmful effects of both biotic and abiotic stresses. The enzyme ACC deaminase (EC 4.1.99.4) regulates stress ethylene production by catalysing ACC into α-ketobutyrate and ammonia. Various research works have documented the application of ACC deaminase-producing PGPR under both normal and stressed conditions responsible for the increased growth, health and productivity of crop plant. These beneficial rhizobacteria may decrease the dependence on agrochemicals (fertilizer and pesticides) to stabilize the agroecosystems and maintained sustainable agriculture. Different biochemical and biophysical properties of this enzyme and its regulation have been briefly described. This review also describes the role of ACC deaminase enzyme in plant growth and production by ameliorating different stress conditions including heavy metal, salinity, drought, flood, temperature, etc. Finally, the latest paradigms for useful application of ACC deaminase-containing plant growth-promoting rhizobacteria in different agroecosystems have been discussed comprehensively under stress conditions to highlight the recent scenario with the aim to develop future insights.

Characterization of Cd-resistant Klebsiella michiganensis MCC3089 and its potential for rice seedling growth promotion under Cd stress

Application of heavy metal resistant plant growth promoting rhizobacteria has an important role as they help to evade metal-induced toxicity in plants on one hand and enhance plant growth on the other. The present study is therefore focused on the characterization of a cadmium resistant bacterial strain isolated from heavy metal contaminated rhizospheric soil designated as S8. This S8 strain was selected in terms of cadmium resistance and plant growth promoting traits. Moreover, it also showed resistance to lead and arsenic to a considerable extent. The selected strain S8 was identified as Klebsiella michiganensis by modern approaches of bacterial taxonomy. The plant growth promoting traits exhibited by the strain include 1-aminocyclopropane-1-carboxylic acid deaminase activity (58.33u202fng α-keto butyrate/mg protein/h), Indole-3-acetic acid production (671u202fμg/ml), phosphate solubilization (71.98u202fppm), nitrogen fixation (3.72u202fμg of nitrogen fixed/h/mg protein) etc. Besides, the strain also exhibited high cadmium removal efficiency (73-97%) from the medium and intracellular accumulation as well. Its efficiency to alleviate cadmium-induced toxicity was determined against a rice cultivar in terms of morphological and biochemical changes. Enhanced growth and reduced oxidative stress were detected in presence of the bacterium. On the basis of these results, it can be concluded that K. michiganensis strain S8 is cadmium accumulating plant growth promoting rhizobacterium that can be applied in cadmium contaminated agricultural soil to achieve better productivity of rice.

The role of arsenic resistant Bacillus aryabhattai MCC3374 in promotion of rice seedlings growth and alleviation of arsenic phytotoxicity

The biological agents have been utilized as an affordable alternative to conventional costly metal remediation technologies for last few years. The present investigation introduces arsenic (As) resistant plant growth promoting rhizobacteria (PGPR) isolated from the As-contaminated agricultural field of West Bengal, India that alleviates arsenic-induced toxicity and exhibited many plant growth promoting traits (PGP). The isolated strain designated as AS6 has identified as Bacillus aryabhattai based on phenotypic characteristics, physio-biochemical tests, MALDI-TOFMS bio-typing, FAME analysis and 16S rDNA sequence homology. The strain found to exhibit five times more resistance to arsenate than arsenite with minimum inhibitory concentrations (MIC) being 100u202fmM and 20u202fmM respectively. The result showed that accumulation of As was evidenced by SEM- EDAX, TEM-EDAX studies. The intracellular accumulation of arsenic was also confirmed as in bacterial biomass by AAS, FTIR, XRD and XRF analyses. The increased rate of As (V) reduction by this strain found to be exploited for the remediation of arsenic in the contaminated agricultural field. The strain also found to exhibit important PGP traits viz., ACC deaminase activity (2022u202fnmol α-ketobutyrate/mg protein/h), IAA production (166u202fμg/ml), N2 fixation (0.32u202fμgN fixed/h/mg proteins) and siderophore production (72%) etc. Positive influenced of AS6 strain on rice seedlings growth promotion under As stress was observed considering the several morphological, biochemical parameters including antioxidants activities as compared with an uninoculated set. Thus this strain might be exploited for stress amelioration and plant growth enhancement of rice cultivar under arsenic spiked agricultural soil.