Co-application of citric acid and Nocardiopsis sp. strain RA07 enhances phytoremediation potentiality of Sorghum bicolor L.

This study investigated the combined effects of citric acid (CA) and Nocardiopsis sp. RA07 on the phytoremediation potential of lead (Pb)- and copper (Cu)-contaminated soils by Sorghum bicolor L. The strain RA07 was able to tolerate Pb and Cu, and exhibited plant growth-promoting features like siderophore production, indole-3-acetic acid (IAA) synthesis, 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity and phosphate solubilization. The combined application of CA and strain RA07 significantly increased S. bicolor growth, chlorophyll content and antioxidant enzymatic activity, and decreased oxidative stress (hydrogen peroxide and malondialdehyde content) under Pb and Cu stress circumstances as compared to individual treatments (i.e., CA and strain RA07). Furthermore, the combined application of CA and RA07 significantly enhanced S. bicolor ability to accumulate Pb and Cu by 64.41% and 60.71% in the root and 188.39% and 125.56% in the shoot, respectively, as compared to the corresponding uninoculated plants. Our results indicate that inoculation of Nocardiopsis sp. together with CA could be a useful practical approach to mitigate Pb and Cu stress on plant growth and increase the effectiveness of phytoremediation in Pb- and Cu-polluted soils.

Rhodotorula mucilaginosa CAM4 improved selenium uptake in Spinacia oleracea L. and soil enzymatic activities under abiotic stresses.

This study aimed to examine selenium (Se) acquisition by spinach (Spinacia oleracea L.) plants growing under salinity and drought stress through the inoculation of Rhodotorula mucilaginosa strain CAM4. Under abiotic stress conditions, strain CAM4 with Se inoculation increased the shoot length, root length, shoot dry weight and root dry weight by 75.8-93.7%, 47.7-80.9%, 101.9-109.8% and 130.5-270.2%, respectively compared to uninoculated Se-treated plants grown under the same conditions. Under abiotic stresses, the Se-treated CAM4 inoculated plants showed a significant increase in Se concentration in the edible leaves of spinach, which was 227.3-234.5% higher than uninoculated Se-treated control plants. Likewise, strain CAM4 treatment significantly enhanced the plant nutrition of both micro and macro-nutrients. Under normal and abiotic stresses, CAM4 inoculation enhanced soil activities of acid phosphatase, alkaline phosphatase, dehydrogenase, ß-glucosidase and urease in the post harvested soil up to 28-47.5%, 62.6-121.8%, 69-177.1%, 16.2-37.9% and 19.8-41.2%, respectively over corresponding uninoculated soil.

Amelioration of aluminum phytotoxicity in Solanum lycopersicum by co-inoculation of plant growth promoting Kosakonia radicincitans strain CABV2 and Streptomyces corchorusii strain CASL5.

Aluminum (Al) toxicity is the main constraint for crop cultivation in acidic soils. In this study, Al-tolerant rhizobacteria Kosakonia radicincitans (CABV2) and actinobacteria Streptomyces corchorusii (CASL5) were isolated from Beta vulgaris rhizosphere in acidic soil. Both isolates displayed high tolerance to Al (10 mM), produce siderophores, indole-3-acetic acid, 1-aminocyclopropane-1-carboxylate and solubilize phosphate. Co-inoculation of CABV2 and CASL5 strains were significantly increased the root length (312.90%), shoot length (183.19%), fresh weight (224.82%), dry weight (309.25%) and photosynthetic pigments (chlorophyll a 279.69%, chlorophyll b 188.23% and carotenoids 158.20%) of Solanum lycopersicum plants under 300 mg Al kg-1 soil conditions as compared to uninoculated Al stressed plants. Similarly, the co-inoculation treated plants subjected to Al stress condition enhanced the uptake of essential nutrients (N 229%, P 252%, K 115%, Fe 185%, Mg 345% and Ca 202%) by plants as compared to Al stressed uninoculated plants. Under Al stress (300 mg Al kg-1 soil), co-inoculation significantly decreased malondialdehyde content (66%), and increased catalase (83%), superoxide dismutase (82%), peroxidase (89%) activities and root exudates (organic acids 6.44-12.36 fold) in S. lycopersicum as compared to uninoculated plants, indicating that the CABV2 and CASL5 strains were reduced Al-induced oxidative stress. Moreover, co-inoculation significantly reduced Al accumulation in the root (89%), stem (95%) and leaves (94%) of S. lycopersicum under Al stress at 300 mg Al kg-1 soil, compared to the uninoculated plants. This is the first report of K. radicincitans strain CABV2 and S. corchorusii strain CASL5 potentially reducing Al uptake in S. lycopersicum.

Polyhydroxybutyrate production from ultrasound-aided alkaline pretreated finger millet straw using Bacillus megaterium strain CAM12.

In this study, finger millet straw (FMS) was utilized for the production of Polyhydroxybutyrate (PHB) by Bacillus megaterium strain CAM12. Ultrasound-assisted alkaline (NaOH) pretreatment of FMS under optimized conditions followed by enzymatic saccharification resulted in the maximum delignification (72%), hydrolysis yield (84%), glucose yield (86%) and xylose yield (61%). The effects of different pH, temperature, incubation period, inoculum concentration, agitation speed and FMS enzymatic hydrolysates concentration were investigated to improve the PHB production. Under optimized conditions, strain CAM12 used the FMS hydrolysates as the sole carbon source for their growth and produced 8.31 g L-1 of PHB. The extracted polymer on Fourier transform infrared (FTIR), X-ray diffraction (XRD) and Nuclear magnetic resonance (NMR) analyses were confirmed to be PHB. These results suggest the potential of combined ultrasound and alkaline pretreated FMS hydrolysates as a promising feedstock for PHB production.

Influence of plant beneficial Stenotrophomonas rhizophila strain CASB3 on the degradation of diuron-contaminated saline soil and improvement of Lactuca sativa growth.

Diuron is one of the major hazardous pollutants which posses severe risk to the environment and human healthiness. On the other hand, salinity is the most severe environmental stressor that limits crop productivity. Therefore, it is required to address this co-existing abiotic stresses in agricultural soil. Plant growth-promoting rhizobacteria have gained an engaging role in the degradation of pesticides in agricultural soil. However, their role against the restoration of diuron-contaminated saline soil is still not known. Thus, in this study, diuron-degrading, salinity-tolerant Stenotrophomonas rhizophila strain CASB3 was isolated and characterized. Strain CASB3 showed important PGP traits under normal and diuron or salt stresses. Complete degradation of 10-50 mg L-1 diuron in the aqueous medium under normal and salinity stress conditions was achieved within 48-120 h and 48-192 h, respectively. A unique pathway for diuron biodegradation was proposed based on GC-MS analysis. In a greenhouse study, CASB3 inoculated into diuron-contaminated saline soil efficiently degraded diuron (50 mg kg-1) by 94% in 42 days and simultaneously resulted in an enhancement of root-shoot length (47.22-63.41%), fresh-dry biomass (136.36-156.66%), and photosynthetic pigments (36.93-92.28%) in Lactuca sativa plants. These results suggest the strain CASB3 could be used as a bioresource for the reclamation of diuron-contaminated saline soils.

Role of Curtobacterium herbarum strain CAH5 on aluminum bioaccumulation and enhancement of Lactuca sativa growth under aluminum and drought stresses.

Aluminum (Al) bioaccumulation by a novel Al and drought tolerant Curtobacterium herbarum strain CAH5 isolated from rhizosphere soil of Beta vulgaris grown in acidic Andisols were examined. The rhizobacterial strain also presented important plant growth promoting traits even with Al and drought stresses under in-vitro conditions in broth. In experiments with a 2-6 mM as initial Al concentrations, the percentages of Al removal by bacteria were 89-93% and 78-91% within 72 h incubation under the normal and drought conditions, respectively. Cytogenotoxicity assay revealed that the toxicity of Al was reduced after bioaccumulation process. In the greenhouse study, formulated bio-inoculant CAH5 significantly improves the Lactuca sativa growth under Al and drought stress by reducing oxidative stress, lipid peroxidation and Al accumulation in plant parts. Our results highlighted that strain CAH5 could be used as a promising bioresource for restoration of agricultural soil with presence of phytotoxic Al improving crop production even under drought conditions.

Role of plant growth-promoting rhizobacterial consortium in improving the Vigna radiata growth and alleviation of aluminum and drought stresses.

Aluminum (Al) is a major constraint for plant growth by inducing inhibition of root elongation in acid soils around the world. Besides, drought is another major abiotic stress that adversely affects growth and productivity of agricultural crops. The plant growth-promoting (PGP) rhizobacterial strains are useful choice to decrease these stressful effects and is now extensively in practice. However, the use of bacterial inoculation has not been attempted for the mitigation of Al stress in plants growing at high Al levels under drought stress. Therefore, in the present study, Al- and drought-tolerant bacterial strains were isolated from Lactuca sativa and Beta vulgaris rhizospheric soils. Among the bacterial isolates, two strains, CAM12 and CAH6, were selected based on their ability to tolerate high levels of Al (8 mM) and drought (15% PEG-6000, w/v) stresses. The bacterial strains CAM12 and CAH6 were identified as Bacillus megaterium and Pantoea agglomerans, respectively, by 16S rRNA gene sequence homology. Moreover, both strains showed multiple PGP traits even in the presence of abiotic stresses. In the pot experiments, inoculation of the strains CAM12 and CAH6 as individually or as included in a consortium improved the Vigna radiata growth under abiotic stress conditions and reduced Al uptake in plants. However, the most effective treatment was seen with bacterial consortium that allowed the plants to tolerate abiotic stress effectively and achieved better growth. These results indicate that bacterial consortium could be used as a bio-inoculant for enhancing V. radiata growth in soil with high Al levels subjected to drought conditions.

Simultaneous mitigation of aluminum, salinity and drought stress in Lactuca sativa growth via formulated plant growth promoting Rhodotorula mucilaginosa CAM4.

In the present study, a potent Aluminum (Al) resistant yeast strain CAM4 was isolated from rhizosphere soil of Rubus geoides, grown in acidic Andisols and identified as Rhodotorula mucilaginosa by 18S rRNA gene sequence analysis. The strain CAM4 was selected in terms of abiotic stress tolerance to Al, salinity and drought with multiple plant growth promoting (PGP) traits. Besides, strain CAM4 also exhibited Al removal efficiency (80-88%) from the culture medium even under combined stresses of salinity and drought. The sawdust-based formulation of strain CAM4 (sawdust-molasses 5%-PEG 1%-strain CAM4) showed higher cell viability of up to 24 weeks (8.54 log CFU g-1). Inoculation of formulated strain CAM4 significantly enhanced the various morphological and biochemical characters of Lactuca sativa grown under abiotic stress conditions. The formulated strain CAM4 also reduced the accumulation of Al in L. sativa as well that conferring Al tolerance to the plants. The study concludes that strain CAM4 could be used as a biofertilizer for healthy and safe crop production in soils, with Al toxicity as well as combined salt and drought stresses.

Evaluation of the production of exopolysaccharide by plant growth promoting yeast Rhodotorula sp. strain CAH2 under abiotic stress conditions.

The capability of plant growth promoting microbes to survive under abiotic stresses has important significance for improving plant growth and productivity. Among the various plant growth promoting biomolecules produced by microbes, exopolysaccharide (EPS) help microbes to survive in inhospitable environments and endure environmental stressful conditions. In the present study, a yeast strain CAH2 was isolated from Beta vulgaris rhizosphere soil and identified as Rhodotorula sp., based on the partial 18S rRNA gene sequence analysis. Rhodotorula sp. strain CAH2 was found to tolerate higher concentrations of Al (6 mM), NaCl (150 mM) and PEG-6000 (15%, w/v). The strain CAH2 was shown to produce 7.5 g L-1 of EPS in the production medium with sucrose and yeast extract as a carbon and nitrogen sources, respectively. The EPS yield was increased constantly with increasing concentrations of Al, NaCl and PEG-6000. The structural feature of EPS studied through FT-IR and NMR spectral analysis confirmed the presence of glucose, mannose and galactose. The yeast strain CAH2 was produced multiple plant growth promoting traits in the presence and absence of abiotic stresses. Finally, these results indicate that the production of EPS could be safeguard the plant growth promoting Rhodotorula sp. strain CAH2 from unfavourable environmental conditions.