Gopal Reddy

Effect of plant growth promoting Pseudomonas spp. on compatible solutes, antioxidant status and plant growth of maize under drought stress

Drought is one of the major abiotic stresses affecting yield of dryland crops. Rhizobacterial populations of stressed soils are adapted and tolerant to stress and can be screened for isolation of efficient stress adaptive/tolerant, plant growth promoting rhizobacterial (PGPR) strains that can be used as inoculants for crops grown in stressed ecosystems. The effect of inoculation of five drought tolerant plant growth promoting Pseudomonas spp. strains namely P.entomophila strain BV-P13, P. stutzeri strain GRFHAP-P14, P. putida strain GAP-P45, P. syringae strain GRFHYTP52, and P. monteilli strain WAPP53 on growth, osmoregulation and antioxidant status of maize seedlings under drought stress conditions was investigated. Drought stress induced by withholding irrigation had drastic effects on growth of maize seedlings. However seed bacterization of maize with Pseudomonas spp. strains improved plant biomass, relative water content, leaf water potential, root adhering soil/root tissue ratio, aggregate stability and mean weight diameter and decreased leaf water loss. The inoculated plants showed higher levels of proline, sugars, free amino acids under drought stress. However protein and starch content was reduced under drought stress conditions. Inoculation decreased electrolyte leakage compared to uninoculated seedlings under drought stress. As compared to uninoculated seedlings, inoculated seedlings showed significantly lower activities of antioxidant enzymes, ascorbate peroxidase (APX), catalase (CAT), glutathione peroxidase (GPX) under drought stress, indicating that inoculated seedlings felt less stress as compared to uninoculated seedlings. The strain GAP-P45 was found to be the best in terms of influencing growth and biochemical and physiological status of the seedlings under drought stress. The study reports the potential of rhizobacteria in alleviating drought stress effects in maize.

Drought-tolerant plant growth promoting Bacillus spp.: effect on growth, osmolytes, and antioxidant status of maize under drought stress

Abstract In present study Bacillus spp. screened for drought tolerance could tolerate minimal water potential (-0.73 MPa) were evaluated for plant growth promoting properties at –0.73 MPa. Drought stress affected growth of isolates as indicated by increased intracellular free amino acids, proline, total soluble sugars, and exopolysaccharides. Drought-tolerant Bacillus spp. HYD-B17, HYTAPB18, HYDGRFB19, BKB30, RMPB44 identified as Bacillus amyloliquefaciens, Bacillus licheniformis, Bacillus thuringiensis, Paenibacillus favisporus, Bacillus subtilis based on 16S rDNA gene sequence were used to study the effect of inoculation on growth, osmolytes, antioxidant status. Inoculation increased plant biomass, relative water content, leaf water potential, root adhering soil/root tissue ratio, aggregate stability, decreasing leaf water loss. Bacillus spp. effect on osmoregulation increased proline, sugars, free amino acids and decreased electrolyte leakage. Inoculation reduced the activity of antioxidant enzymes ascorbate peroxidase, catalase, glutathione peroxidase. As a result, Bacillus spp. inoculated maize seedlings showed physiological response that could alleviate drought stress negative effects.

Application of plant growth-promoting bacteria associated with composts and macrofauna for growth promotion of Pearl millet (Pennisetum glaucum L.)

Plant growth-promoting bacteria (PGPB) were reported to influence the growth, yield, and nutrient uptake by an array of mechanisms. We selected seven different plant growth-promoting traits and antagonistic ability to screen 207 bacteria isolated from composts. Fifty-four percent of PGPB were from farm waste compost (FWC), 56% from rice straw compost (RSC), 64% from Gliricidia vermicompost (GVC), and 41% from macrofauna associated with FWC. Twelve isolates based on different plant growth-promoting traits and seed vigor index were evaluated at glasshouse for plant growth-promoting activity on pearl millet. Seven isolates significantly increased shoot length and ten isolates showed significant increase in leaf area, root length density, and plant weight. Maximum increase in plant weight was by Serratia marcescens EB 67 (56%), Pseudomonas sp. CDB 35 (52%), and Bacillus circulans EB 35 (42%). Plant growth-promoting activity of composts and bacteria (EB 35, EB 67, and CDB 35) was studied together. All the three composts showed significant increase in growth of pearl millet, which was 77% by RSC, 55% by GVC, and 30% by FWC. Application of composts with bacteria improved plant growth up to 88% by RSC with EB 67, 83% with GVC and EB 67. These results show the synergistic effect of selected bacteria applied with composts on growth of pearl millet.

Direct fermentation of various pure and crude starchy substrates to L(+) lactic acid using Lactobacillus amylophilus GV6

Lactobacillus amylophilus GV6 fermented a variety of pure and natural starches directly to L(+) lactic acid. Starch to lactic acid conversion efficiency was more than 90% by strain GV6 at low substrate concentrations with all starches. The strain GV6 produced high yields of lactic acid per g of substrate utilized with pure starches such as soluble starch, corn starch, and potato starch, yielding 92–96% at low substrate concentrations in 2 days and 78–89% at high substrate (10%) concentrations in 4–6 days. Strain GV6 also produced high yields of lactic acid per g of substrate utilized with crude starchy substrates such as wheat flour, sorghum flour, cassava flour, rice flour and barley flour yielding 90–93% at low substrate concentrations in 2 days and 80% or more at high substrate concentrations in 6–7 days. Lactic acid yields by L. amylophilus GV6 with pure starches were comparable when low cost crude starchy substrates were used. Lactic acid productivity by strain GV6 is higher than for any other previously reported strains of L. amylophilus.

Direct conversion of starch to L(+) lactic acid by amylase producing Lactobacillus amylophilus GV6

Abstract Lactobacillus amylophilus strain GV6, isolated from corn starch processing industrial wastes, was amylolytic and produced 0.96 g L(+) lactic acid per gram of soluble starch. The optimum temperature and pH for growth and L(+) lactic acid production were 37 °C and 6.5, respectively. At low substrate concentrations, the lactic acid production on corn starch was almost similar to soluble starch. The strain is fermenting various naturally available starches directly to lactic acid. The total amylase activity of the strain is 0.59 U/ml/min. The strain produced 49 and 76.2 g/l L(+) lactic acid from 60 g/l corn starch and 90 g/l soluble starch, respectively. This is the highest L(+) lactic acid among the wild strains of L. amylophilus reported so far.

An economic approach for l-(+) lactic acid fermentation by Lactobacillus amylophilus GV6 using inexpensive carbon and nitrogen sources

Aims:  Development of cost‐effective production medium by applying statistical designs for single‐step fermentation of starch (corn flour – CF) to l‐(+) lactic acid, using inexpensive nitrogen sources as substitutes for peptone and yeast extract in MRS medium by amylolytic Lactobacillus amylophilus GV6.

Production of thermostable pullulanase by Clostridium thermosulfurogenes SV2 in solid-state fermentation: optimization of enzyme leaching conditions using response surface methodology.

Abstract The optimization of parameters for the effective leaching of thermostable pullulanase from Clostridium thermosulfurogenes SV2-fermented bran was carried out using response surface methodology based on the central composite rotatable design. The design contains a total of 54 experimental trials with the first 32 organized in a fractional factorial design and experimental trials from 33–40 and 51–54 involving the replication of the central points. The design was employed by selecting solvent to wheat bran ratio (S/BB), process temperature, solvent pH, shaking (RPM) and contact time (h) as model factors. Among the five independent variables studied, the S/BB, solvent pH and shaking were found to be significant. S/BB ratio of 9.0, 200 RPM shaking and solvent pH 6.0 were identified as optimum for the leaching of thermostable pullulanase from the strain SV2-fermented bran.

Production of thermostable pullulanase by Clostridium thermosulfurogenes SV2 in solid-state fermentation: optimization of nutrients levels using response surface methodology

Abstract The optimization of nutrient levels for the production of thermostable pullulanase by Clostridium thermosulfurogenes SV2 in solid-state fermentation (SSF) was carried out using response surface methodology based on the central composite rotatable design. The design contains a total of 54 experimental trials with the first 32 organized in a fractional factorial design and experimental trials from 33–40 and 51–54 involving the replication of the central points. The design was employed by selecting potato starch, magnesium chloride, ferrous sulfate, corn steep liquor and pearl millet flour as model factors. Among the five independent variables studied, except magnesium chloride, all the nutrients were found significant. 16.5% potato starch, 2.5% corn steep, 0.015% ferrous sulfate and 14% pearl millet flour have been found optimal for the production of thermostable pullulanase. The strain SV2 produced 10% more pullulanase in the nutritionally optimized solid-state fermentation medium containing only four nutrients.

Production of ethanol from cellulosic biomass by Clostridium thermocellum SS19 in submerged fermentation: screening of nutrients using Plackett-Burman design.

Plackett-Burman design, a statistical methodology, was used to screen 23 nutrients belonging to three categories—carbon, nitrogen, and salt/mineral sources—for the production of ethanol from cellulosic biomass by Clostridium thermocellum SS19 in an aerobic submerged fermentation. In this design, just n number of experiments is required for screening n=1 variables. The experimental data were subjected to statistical analysis for calculating the regression coefficients and t-values. Filter paper, Solka Floc, corn steep liquor (CSL), cysteine HCl, magnesium chloride, and ferrous sulfate showed relatively higher regression coefficients on ethanol production and growth. Among the 23 nutrients screened, based on their performance in terms of product-promoting ability, availability, and cost, filter paper, CSL, cysteine HCl, magnesium chloride, and ferrous sulfate were identified as the most effective and, therefore, selected for inclusion in further optimization studies.

Effect of various flours on the production of thermostable β-amylase and pullulanase by Clostridium thermosulfurogenes SV2

The effects of various flours on production of thermostable beta-amylase and pullulanase using Clostridium thermosulfurogenes SV2 was studied in submerged fermentation. Among the flours added to PYE basal medium, potato flour was the best substrate for enzyme production, and under optimal conditions C. thermosulfurogenes SV2 produced 0.87 and 0.98 U of thermostable beta-amylase and pullulanase, respectively, per ml culture broth.