Bacterial endophytes modulates the withanolide biosynthetic pathway and physiological performance in Withania somnifera under biotic stress.

Despite the vast exploration of endophytic microbes for growth enhancement in various crops, knowledge about their impact on the production of therapeutically important secondary metabolites is scarce. In the current investigation, chitinolytic bacterial endophytes were isolated from selected medicinal plants and assessed for their mycolytic as well as plant growth promoting potentials. Among them the two most efficient bacterial endophytes namely Bacillus amyloliquefaciens (MPE20) and Pseudomonas fluorescens (MPE115) individually as well as in combination were able to modulate withanolide biosynthetic pathway and tolerance against Alternaria alternata in Withania somnifera. Interestingly, the expression level of withanolide biosynthetic pathway genes (3-hydroxy-3-methylglutaryl co-enzyme A reductase, 1-deoxy-D-xylulose-5-phosphate reductase, farnesyl di-phosphate synthase, squalene synthase, cytochrome p450, sterol desaturase, sterol Δ-7 reductase and sterol glycosyl transferases) were upregulated in plants treated with the microbial consortium under A. alternata stress. In addition, application of microbes not only augmented withaferin A, withanolide A and withanolide B content (1.52-1.96, 3.32-5.96 and 12.49-21.47 fold, respectively) during A. alternata pathogenicity but also strengthened host resistance via improvement in the photochemical efficiency, normalizing the oxidized and non-oxidized fraction, accelerating photochemical and non-photochemical quantum yield, and electron transport rate. Moreover, reduction in the passively dissipated energy of PSI and PSII in microbial combination treated plants corroborate well with the above findings. Altogether, the above finding highlights novel insights into the underlying mechanisms in application of endophytes and emphasizes their capability to accelerate biosynthesis of withanolides in W. somnifera under biotic stress caused by A. alternata.

Tailoring shape and size of biogenic silver nanoparticles to enhance antimicrobial efficacy against MDR bacteria.

Spherical, rectangular, penta, and hexagonal silver nanoparticles of different dimensions were biosynthesized in an eco-friendly manner by biocontrol agent, Trichoderma viride by manipulating physical parameters, pH, temperature, and reaction time. The particles were characterized by UV-vis spectroscopy; Dynamic Light Scattering (DLS), Transmission Electron Microscopy (TEM) and Fourier Transform Infra-red Spectroscopy (FTIR). Shape and size dependent antimicrobial activity of nanoparticles against human pathogens was observed. Maximum inhibition was found with spherical nanoparticles (2-5 nm) showing 40, 51, 43, 53.9 and 55.8% against Shigella sonnei, Escherichia coli, Serratia marcescens, Staphylococcus. aureus and Pseudomonas aeruginosa respectively, where as pentagonal and hexagonal nanoparticles (50-100 nm) demonstrated 32, 41, 31, 42.84 and 42.80% of inhibition as compared to control. Nanoparticles of different geometry and dimension established enhanced antagonistic activity against pathogens with all the tested antibiotics. Excellent antimicrobial efficacy was obtained with spherical nanoparticles of 2-5 nm with ampicillin and penicillin. Shape and size played major role in enhancing antimicrobial potential of silver nanoparticles, both singly and synergistically with antibiotics which can be exploited to combat the spread of multidrug resistant pathogens.

Constructed wetland as an ecotechnological tool for pollution treatment for conservation of Ganga river.

With aim to develop an efficient and ecofriendly approach for on-site treatment of sewage, a sub-surface flow constructed wetland (CW) has been developed by raising potential aquatic macrophytes; Typha latifolia, Phragmites australis, Colocasia esculenta, Polygonum hydropiper, Alternanthera sessilis and Pistia stratoites in gravel as medium. Sewage treatment potential of CW was evaluated by varying retention time at three different stages of plant growth and stabilization. After 6 months, monitoring of fully established CW indicated reduction of 90%, 65%, 78%, 84%, 76% and 86% of BOD, TSS, TDS, NO3-N, PO4-P and NH4-N, respectively in comparison to inlet after 36 h of retention time. Sewage treatment through CW also resulted in reduction of heavy metal contents. Thus, CW proved an effective method for treatment of wastewater and may be developed along river Ganga stretch as an alternative technology. Treated water may be drained into river to check further deterioration of Ganga water quality.

Lagerstroemia speciosa fruit extract modulates quorum sensing-controlled virulence factor production and biofilm formation in Pseudomonas aeruginosa.

Lagerstroemia speciosa (Lythraceae) is a south-east Asian tree more commonly known as 'Jarul'. Research on health benefits suggests that the L. speciosa plant contains phytomolecules that may have antioxidant, anti-diabetic and anti-obesity properties. However, antimicrobial activities have not been reported for this plant. The ability of L. speciosa fruit extract (LSFE) to antagonize cell-to-cell communication, expression of virulence genes and factors, and biofilm formation was evaluated in Pseudomonas aeruginosa strain PAO1. Our results suggested that LSFE caused downregulation of quorum sensing (QS)-related genes (las and rhl) and their respective signalling molecules, N-acylhomoserine lactones, without affecting the growth of P. aeruginosa PAO1. Significant inhibition of virulence factors: LasA protease, LasB elastase, and pyoverdin production, was also recorded. Application of LSFE to P. aeruginosa PAO1 biofilms increased bacterial susceptibility to tobramycin. These data suggest a possible role for quorum-quenching mechanisms unrelated to static or cidal effects, and also suggest that L. speciosa could serve as a cost-effective source in the development of new QS-based antibacterial drugs.

Paenibacillus lentimorbus enhances growth of chickpea (Cicer arietinum L.) in chromium-amended soil.

Chromium (Cr), with its great economic importance in industrial use, is a major metal pollutant of the environment. It affects soil microbial activity and soil fertility, resulting in losses in yield of plants. Paenibacillus lentimorbus B-30488(r) (B-30488(r)) tolerated 200 µg ml(-1) of Cr under in vitro conditions and produced the plant growth promoting substance indole acetic acid in the presence of Cr. Our in vitro study indicates enhancement in B-30488(r) biofilm formation by sodium alginate (SA) and calcium chloride (CaCl(2)) both in absence and presence of supplemented Cr(VI) as compared to unsupplemented control. The plant growth promoting effects caused by the B-30488(r) biofilm in rhizosphere of chickpea under Cr(VI) stress suggests a phytoprotective role of B-30488(r) biofilm. Our study reflects the multifarious role of strain B-30488(r) and presents it as a potent plant growth promoting and bioremediation agent useful in Cr-contaminated rhizosphere soil, whereby the SA and CaCl(2) induced B-30488(r) biofilm on plant root acts as a shield in preventing the direct access of toxic Cr to plant tissues, thus reducing its uptake in plants.

Crossing the limits of Rhizobium existence in extreme conditions.

An ecological survey was conducted to characterize 5000 Rhizobium sp. sesbania strains of diverse geographical origin, isolated from the root nodules of Sesbania aculeata growing in neutral (pH 7) and alkaline (pH 8.5 and above) soils. The rhizobia from the alkaline soil showed significantly higher salt tolerance than those isolated from neutral soil. Upper limits of stress survival of rhizobial isolates, Rhizobium sp. NBRI0102 sesbania selected from neutral soil, and Rhizobium sp. NBRI2505 sesbania selected from alkaline soil, were studied under free living conditions. Rhizobium sp. NBRI0102 sesbania and Rhizobium sp. NBRI2505 sesbania tolerated yeast extract mannitol broth (YEB) containing 10% and 28% salt (NaCl, wt/vol) for up to 18 h of incubation at 30 degrees C. Growth of Rhizobium sp. NBRI0102 sesbania and Rhizobium sp. NBRI2505 sesbania at pH 7, 11, and 12 was identical, except for a lag period of about 10 h in the growth of Rhizobium sp. NBRI0102 sesbania at pH 11 and 12, as compared with pH 7. Rhizobium sp. NBRI0102 sesbania and Rhizobium sp. NBRI2505 sesbania survived at 50 degrees C and 65 degrees C, in YEB at pH 7 for up to 4 and 2 h, respectively. To our knowledge, this is the first report of rhizobia demonstrating survival of Rhizobium sp. NBRI2505 sesbania, estimated by counting viable cells, to such extreme conditions of salt and temperature, individually. In contrast to Rhizobium sp. NBRI0102 sesbania, high temperature was tolerated efficiently by Rhizobium sp. NBRI2505 sesbania, in the presence of salt at higher pH. Our results suggest that the possession of the trait of high salt tolerance might be of some evolutionary significance for the survival of rhizobia in alkaline soils, at high pH and temperature.