Sangeeta Paul

Ex situ and in situ biodegradation of lindane by Azotobacter chroococcum

This study was undertaken to investigate the potential of Azotobacter chroococcum for degrading lindane. Ten cultures were screened for lindane degradation by a chloride estimation method and the best A. chroococcum culture JL 102 was selected for further studies. This strain was subjected to a lindane–tolerance experiment and based on the results obtained, 10 and 100 ppm of lindane were selected to study the potential of the A. chroococcum strain for ex situ and in situ biodegradation of lindane. The organism was grown in 2 different media viz. Jensens broth and soil extract broth and ex situ lindane degradation was studied for a period of 6 days. Maximum degradation of lindane was recorded at 10 ppm concentration. The degradation was higher in Jensens medium, compared to the soil extract broth. A pot culture experiment was conducted using both sterile and non-sterile soils supplemented with 10 ppm lindane to study in situ degradation potential of this strain for a period of 8 weeks. In both the conditions (sterile and non-sterile), the organism exhibited increased degradation over the days with maximum degradation observed on the 8th week of incubation. It could degrade most of the applied lindane by the end of the study period.

RESPONSE OF WHEAT TO INOCULATION WITH MYCORRHIZAE ALONE AND COMBINED WITH SELECTED RHIZOBACTERIA INCLUDING FLAVOBACTERIUM SP. AS A POTENTIAL BIOINOCULANT

A pot experiment was conducted to evaluate different arbuscular mycorrhiza sps. (AM) for their effect on plant growth, yield and nutrient uptake by wheat. All the AM fungal sps. significantly enhanced all the plant parameters and nutrient uptake by the plant. A positive correlation was observed between percent root colonization by AM fungi and most of the plant parameters studied. Glomus macrocarpum giving best results was selected for studying interactive effect with Azotobacter, Azospirillum (well-known PGPRs), and Flavobacterium and Proteus vulgaris (less studied PGPRs). All the PGPRs significantly increased most of the plant parameters studied and their combination with AMF had a synergistic effect. Amongst PGPRs, Flavobacterium gave best response both singly and in combination with AMF and thus, is a potential new bioinoculant for wheat. Application of 120 kg nitrogen (N) ha−1was the best treatment. Inoculation with most of the PGPRs gave better response than 60 kg N ha−1.

Exploitation of microbial antagonists for the control of postharvest diseases of fruits: a review

ABSTRACT Fungal diseases result in significant losses of fruits and vegetables during handling, transportation and storage. At present, post-production fungal spoilage is predominantly controlled by using synthetic fungicides. Under the global climate change scenario and with the need for sustainable agriculture, biological control methods of fungal diseases, using antagonistic microorganisms, are emerging as ecofriendly alternatives to the use of fungicides. The potential of microbial antagonists, isolated from a diversity of natural habitats, for postharvest disease suppression has been investigated. Postharvest biocontrol systems involve tripartite interaction between microbial antagonists, the pathogen and the host, affected by environmental conditions. Several modes for fungistatic activities of microbial antagonists have been suggested, including competition for nutrients and space, mycoparasitism, secretion of antifungal antibiotics and volatile metabolites and induction of host resistance. Postharvest application of microbial antagonists is more successful for efficient disease control in comparison to pre-harvest application. Attempts have also been made to improve the overall efficacy of antagonists by combining them with different physical and chemical substances and methods. Globally, many microbe-based biocontrol products have been developed and registered for commercial use. The present review provides a brief overview on the use of microbial antagonists as postharvest biocontrol agents and summarises information on their isolation, mechanisms of action, application methods, efficacy enhancement, product formulation and commercialisation.

Characterization of putative virulence factors of Serratia marcescens strain SEN for pathogenesis in Spodoptera litura

Two Serratia marcescens strains, SEN and ICC-4, isolated from diseased insect cadavers were observed to differ considerably in their virulence towards Spodoptera litura. The present study was aimed to characterize the possible virulence factors present in the virulent Serratia marcescens strain SEN. Both the S. marcescens strains were evaluated for the presence of various lytic enzymes such as chitinase, lipase, protease and phospholipase. The virulent S. marcescens strain SEN was observed to possess considerably higher activity of chitinase and protease enzymes; activity of phospholipase enzyme was also higher. Although, all the three toxin genes shlA, phlA and swr could be detected in both the S. marcescens strains, there was a higher expression of these genes in the virulent strain SEN. S. marcescens strain ICC-4 showed greater reduction in overall growth yield in the post-exponential phase in the presence of midgut juice and hemolymph of S. litura larvae, as compared to S. marcescens strain SEN. Proliferation of the S. marcescens strain SEN was also considerably higher in foregut, midgut and hemolymph of S. litura larvae, as compared to strain ICC-4. Peritrophic membrane treated with broth culture of the S. marcescens strain SEN showed higher damage as compared to strain ICC-4. The peritrophic membrane of larvae fed on diet treated with the virulent strain showed considerable damage while the peritrophic membrane of larvae fed on diet treated with the non-virulent strain showed no damage. This is the first report documenting the fate of ingested S. marcescens in S. litura gut and the relative expression of toxin genes from two S. marcescens strains differing in their virulence towards S. litura.

Greenhouse gases emission, soil organic carbon and wheat yield as affected by tillage systems and nitrogen management practices

ABSTRACT Agricultural activities are responsible for greenhouse gases (GHGs) emission in the environment. Strategies are required to enhance the soil organic carbon (SOC) and nitrogen (N) sequestration to adapt and mitigate the climate change. We investigated GHGs emission, SOC and N enhancement under conventional tillage (CT) and zero tillage (ZT) with N management in wheat (Triticum aestivum L.). Seasonal carbon dioxide (CO2) emission and global warming potential (GWP) reduced for ZT treatments over CT without residues and 100% of required N with a blanket split application (CT – R + 100N). The ZT with 5 t ha−1 maize (Zea mays L.) residues retention and 75% of required N and GreenSeekerTM (GS)-aided N management (ZT + R + 75N + GS) reduced yield-scaled GHGs emission and increased total organic carbon (C) stock over CT – R + 100N. However, nitrous oxide (N2O) emission was lower in CT. The GS-based N management saved 26–35 kg N ha−1 in different tillage systems in both years over blanket application with higher N uptake and associated reduction in N2O emission. The study recommends that ZT with residues retention and GS-based N management can minimize the GHGs emission and improve the SOC.

A modified semi-synthetic diet for bioassay of non-sporeforming entomopathogenic bacteria against Spodoptera litura

Standard semi-synthetic diet used for rearing Spodoptera litura (Fab) larvae contains many antimicrobials. This diet is not suitable for evaluating non-sporeforming bacteria. We determined the effect of antimicrobials present in S. litura semi-synthetic diet on growth of entomopathogenic Serratia marcescens. Nutrient broth supplemented with four and two times reduced doses of sorbic acid (0.15 g) and methyl parahydroxybenzoate (0.05 g) supported bacterial growth comparable to control medium. No growth could be observed even at five times reduced concentrations of formaldehyde and streptomycin sulphate. Diet for rearing S. litura was modified accordingly and validated using two S. marcescens strains. Larval mortality ranged between 20% and 30% on the standard diet and more than 90% in the modified diet.

A potential economical substrate for large-scale production of Bacillus thuringiensis var. kurstaki for caterpillar control

Abstract Bacillus thuringiensis var. kurstaki has been widely used in caterpillar control programs. Large-scale production of this bacterium is expensive because of the high cost of the raw materials used in the medium. In this study, we attempted to develop an economical medium, based on inexpensive, locally available raw materials using a 3-L fermenter. Parthenium hysterophorus L. extract based culture medium resulted in highest toxicity (LC50 14.628 µg mL–1) against 7-day-old Spodoptera litura (Fab) larvae, spore count (4.1 × 109 spores mL–1) and biomass (4.9 g L–1) within a short fermentation time of 36 h. It was 512 times cheaper than the nutrient broth (standard medium) used for B. thuringiensis production. Hence, this parthenium extract based culture medium was considered most economical with potential for the large-scale industrial production of B. thuringiensis.

Physiological studies on endorhizospheric establishment of Azotobacter chroococcum in wheat.

Ten strains of Azotobacter chroococcum were studied for their ability to invade the endorhizosphere of wheat. Strain W‐5 exhibited ability to invade endorhizosphere as shown in the microscopic observations. This strain was compared with the strain OA‐3 which did not invade the endorhizosphere zone. Strain W‐5 showed higher production of cellulase and pectinase than OA‐3. Both the strains induced defense enzymes in the host plant. However, induction of peroxidase and phenylalanine ammonia lyase activities (PAL) was higher in OA‐3 than W‐5. Quantitative differences in flavonoid like compounds obtained from root extracts and root exudates of plants inoculated with these strains were observed. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Isolation and Screening of Osmotolerant Endophytic Bacteria from Succulent and Non-Succulent Drought Tolerant plants for water stress alleviation in Cluster Bean (Cyamopsis tetrogonoloba)

In the present investigation endophytic bacteria were isolated from succulent (Nagphani) and non-succulent (mustard) plants growing in drought prone regions of Rajasthan. Out of the sixty eight endophytic bacteria, twenty six were highly osmotolerant and in presence of 30% PEG 6000 showed 50% or higher growth as compared to that obtained under control conditions. Effect of osmotic stress on their growth was determined. Although, at concentrations higher than 30% PEG 6000, growth of most of the selected endophytes was reduced, however, these were observed to be able to grow even in presence of 50% PEG 6000. Inoculation with most of the isolates from both the sources improved fresh and dry weight of shoot, number of flowers and pods formed and dry weight of roots. On the basis of most of the parameters studied, two promising isolates were identified, which can be used as biofertilizers to improve productivity of Cluster bean in arid and semi-arid regions of the country.

An Environmentally Friendly Engineered Azotobacter Strain That Replaces a Substantial Amount of Urea Fertilizer while Sustaining the Same Wheat Yield

ABSTRACT In our endeavor to improve the nitrogen fixation efficiency of a soil diazotroph that would be unaffected by synthetic nitrogenous fertilizers, we have deleted a part of the negative regulatory gene nifL and constitutively expressed the positive regulatory gene nifA in the chromosome of Azotobacter chroococcum CBD15, a strain isolated from the local field soil. No antibiotic resistance gene or other foreign gene was present in the chromosome of the engineered strain. Wheat seeds inoculated with this engineered strain, which we have named Azotobacter chroococcum HKD15, were tested for 3 years in pots and 1 year in the field. The yield of wheat was enhanced by ∼60% due to inoculation of seeds by A. chroococcum HKD15 in the absence of any urea application. Ammonium only marginally affected acetylene reduction by the engineered Azotobacter strain. When urea was also applied, the same wheat yield could be sustained by using seeds inoculated with A. chroococcum HKD15 and using ∼85 kg less urea (∼40 kg less nitrogen) than the usual ∼257 kg urea (∼120 kg nitrogen) per hectare. Wheat plants arising from the seeds inoculated with the engineered Azotobacter strain exhibited far superior overall performance, had much higher dry weight and nitrogen content, and assimilated molecular 15N much better. A nitrogen balance experiment also revealed much higher total nitrogen content. Indole-3-acetic acid (IAA) production by the wild type and that by the engineered strain were about the same. Inoculation of the wheat seeds with A. chroococcum HKD15 did not adversely affect the microbial population in the field rhizosphere soil. IMPORTANCE Application of synthetic nitrogenous fertilizers is a standard agricultural practice to augment crop yield. Plants, however, utilize only a fraction of the applied fertilizers, while the unutilized fertilizers cause grave environmental problems. Wild-type soil diazotrophic microorganisms cannot replace synthetic nitrogenous fertilizers, as these reduce atmospheric nitrogen very inefficiently and almost none at all in the presence of added nitrogenous fertilizers. If the nitrogen-fixing ability of soil diazotrophs could be improved and sustained even in the presence of synthetic nitrogenous fertilizers, then a mixture of the bacteria and a reduced quantity of chemical nitrogenous fertilizers could be employed to obtain the same grain yield but at a much-reduced environmental cost. The engineered Azotobacter strain that we have reported here has considerably enhanced nitrogen fixation and excretion abilities and can replace ∼85 kg of urea per hectare but sustain the same wheat yield, if the seeds are inoculated with it before sowing.