Soma Barman

Sunlight-induced rapid and efficient biogenic synthesis of silver nanoparticles using aqueous leaf extract of Ocimum sanctum Linn. with enhanced antibacterial activity

Background Nanotechnology is now regarded as a distinct field of research in modern science and technology with multifaceted areas including biomedical applications. Among the various approaches currently available for the generation of metallic nanoparticles, biogenic synthesis is of increasing demand for the purpose of green nanotechnology. Among various natural sources, plant materials are the most readily available template-directing matrix offering cost-effectiveness, eco-friendliness, and easy handling. Moreover, the inherent pharmacological potentials of these medicinal plant extracts offer added biomedical implementations of the synthesized metal nanoparticles. Results A robust practical method for eco-friendly synthesis of silver nanoparticles using aqueous leaf extract of Ocimum sanctum (Tulsi) as both reducing and capping agent, under the influence of direct sunlight has been developed without applying any other chemical additives. The nanoparticles were characterized with the help of UV-visible spectrophotometer and transmission electron microscopy (TEM). The prepared silver nanoparticles exhibited considerable antibacterial activity. The effects were more pronounced on non-endospore-forming Gram-positive bacteria viz., Staphylococcus aureus, Staphylococcus epidermidis, and Listeria monocytogenes than endospore-forming species Bacillus subtilis. The nanoparticles also showed prominent activity on Gram-negative human pathogenic Salmonella typhimurium, Escherichia coli, Pseudomonas aeruginosa, and plant pathogenic Pantoea ananatis. A bactericidal mode of action was observed for both Gram-positive and Gram-negative bacteria by the nanoparticles. Conclusions We have developed a very simple, efficient, and practical method for the synthesis of silver nanoparticles using aqueous leaf extract of O. sanctum under the influence of direct sunlight. The biosynthesis of silver nanoparticles making use of such a traditionally important medicinal plant without applying any other chemical additives, thus offers a cost-effective and environmentally benign route for their large-scale commercial production. The nanoparticles dispersed in the mother solution showed promising antibacterial efficacy.Graphical Abstract Sunlight-induced rapid and efficient biogenic synthesis of silver nanoparticles using aqueous leaf extract of Ocimum sanctum Linn. with enhanced antibacterial activity. Electronic supplementary material The online version of this article (doi:10.1186/s13588-014-0018-6) contains supplementary material, which is available to authorized users.

Role of phosphate solubilizing Burkholderia spp. for successful colonization and growth promotion of Lycopodium cernuum L. (Lycopodiaceae) in lateritic belt of Birbhum district of West Bengal, India

Profuse growth of Lycpodium cernuum L. was found in phosphate deficient red lateritic soil of West Bengal, India. Interaction of vesicular-arbuscular mycorrhiza (VAM) with Lycopodium rhizoids were described earlier but association of PGPR with their rhizoids were not studied. Three potent phosphate solubilizing bacterial strains (P4, P9 and P10) associated with L. cernuum rhizoids were isolated and identified by 16S rDNA homologies on Ez-Taxon database as Burkholderia tropica, Burkholderia unamae and Burkholderia cepacia respectively. Day wise kinetics of phosphate solubilization against Ca3(PO4)2 suggested P4 (580.56±13.38 μg ml(-1)) as maximum mineral phosphate solubilizer followed by P9 (517.12±17.15 μg ml(-1)) and P10 (485.18±14.23 μg ml(-1)) at 28 °C. Release of bound phosphates by isolated strains from ferric phosphate (FePO4), aluminum phosphate (AlPO4) and four different complex rock phosphates indicated their very good phosphate solubilizng efficacy. Nitrogen independent solubilizition also supports their nitrogen fixing capabilities. Inhibition of P solubilization by calcium salts and induction by EDTA suggested pH dependent chelation of metal cations by all of the isolates. Rhizoidal colonization potentials of Burkholderia spp. were confirmed by in planta experiment and also using scanning electron microscope (SEM). Increases of total phosphate content in Lycopodium plants upon soil treatment with these isolates were also recorded. In addition siderophore production on CAS agar medium, tryptophan dependent IAA production and antifungal activities against pathogenic fungi by rhizospheric isolates deep-rooted that they have definite role in nutrient mobilization for successful colonization of L. cernuum in nutrient deficient lateritic soil.

A new pentacyclic triterpene with potent antibacterial activity from Limnophila indica Linn. (Druce)

A new pentacyclic triterpenoid constituent, characterized as 3-oxo-olean-12(13),18(19)-dien-29α-carboxylic acid (1) on the basis of detailed spectral studies, was isolated from the aerial parts and roots of Limnophila indica (Scrophulariaceae). Compound 1 exhibited considerable antibacterial activity against three Gram-positive bacteria viz. Bacillus subtilis, Staphylococcus aureus and Listeria monocytogenes (MICs within a range of 25-30 μg/ml) and moderate activity against four Gram-negative bacteria Salmonella typhimurium, Escherichia coli, Pseudomonas aeruginosa, and Pantoea ananatis (MICs within a range of 30-100 μg/ml). The plant pathogenic bacterium P. ananatis and human pathogenic S. typhimurium responded at comparatively higher concentrations of the compound 1, which were 75 and 100 μg/ml respectively. The compound inhibited the growth of Gram-positive B. subtilis and Gram-negative P. aeruginosa completely with a clear bactericidal mode of action at their MIC values. The compound upon treatment on both B. subtilis and P. aeruginosa released substantial amount of nucleic acid in the external medium and also effected the change of morphology towards pleomorphicity, thereby indicating its probable action on cell membrane. Furthermore, the triterpenoid 1 was found not to inhibit a probiotic lactic acid bacterium Lactococcus lactis subsp. lactis LABW4 under in vitro condition and to possess no toxicity in Swiss albino mice.

Longterm storage of post-packaged bread by controlling spoilage pathogens using Lactobacillus fermentum C14 isolated from homemade curd.

One potent lactic acid bacterial strain C14 with strong antifungal activity was isolated from homemade curd. Based on morphological as well as biochemical characters and 16S rDNA sequence homology the strain was identified as Lactobacillus fermentum. It displayed a wide antimicrobial spectrum against both Gram-positive and Gram-negative pathogenic bacteria, and also against number of food spoilage, plant and human pathogenic fungi. The cell free supernatant (CFS) of the strain C14 was also effective against the fungi tested. Inhibition of radial growth of Penicillium digitatum, Trichophyton rubrum and Mucor sp. was noticed in the presence of CFS of C14 even at low concentration (1%). More than 94.3 ± 1.6% and 91.5 ± 2.2% inhibition of conidial germination of P. digitatum and Mucor sp. were noticed in the presence of 10-fold-concentrated CFS of C14. Massive deformation of the fungal mycelia was observed by SEM studies, and losses of cellular proteins and DNA are also evident upon its treatment with C14. HPLC analysis revealed the presence of phenyl lactic acid, lactic acid along with some unidentified compounds in the antifungal extract. Challenge experiment showed immense potential of the strain C14 in preventing the spoilage of bread samples caused by Mucor sp. and Bacillus subtilis. The bread samples remained fresh upto 25 days even after inoculation with Mucor sp. (3.7 × 104 spores /ml) and B. subtilis (4.6 × 104 CFU /ml). Along with the antifungal properties, the isolated lactic acid bacterial strain also showed very good antioxidant activities. Unchanged level of liver enzymes serum glutamic pyruvic transaminase and serum glutamic oxaloacetic transaminase in albino mice upon feeding with C14 also suggested non-toxic nature of the bacterial isolate.

Suppression of Leaf Blight of Ocimum sanctum L. Using Lactic Acid Bacteria as Novel Bio-control Agent

Fungal pathogens causing leaf blight of Ocimum sanctum L. have been isolated from the lateritic belt of Birbhum district of West Bengal, India and were identified as species of Alternaria. The pathogen not only destroys the mesophyll tissues of the leaves but also decreases the antibacterial potential and antioxidant activity of Ocimum plants. Two strains of Lactococcus lactis subsp. hordniae, viz., LABW1, LABW3 and a strain of Lactococcus lactis subsp. lactis LABW4, isolated from high quality fermented milk product (homemade buttermilk), were able to produce significant zones of inhibition against the pathogen on dual culture overlay plates. A maximum of 4.5xa0±xa00.2xa0cm zone of inhibition was produced by LABW4. Cell free supernatant of LABW4 (50%) was also effective to inhibit more than 89% of conidial germination of Alternaria sp. VBOS17. Antifungal action of LABW4 was responsible for prominent mycelial deformations and breakages of pathogen as evident from scanning electron microscopic studies. During in vivo greenhouse experiment only 14.57xa0±xa01.99% leaf blight was noticed after 60xa0days of bacterial application even upon treatment with high concentration of Alternaria conidia (1.6xa0×xa0104 conidia/ml), as compared to pathogen treated set (87.95xa0±xa02.14%). Efficacy of LABW4 to control the disease was also noticed during field experiment. In addition, LABW4 also increased the antibacterial and antioxidant potentials of the plant. L. lactis subsp. lactis LABW4 can be used as a prospective agent to control leaf blight disease of Ocimum plant and to increase its medicinal properties.

A comparative antibacterial evaluation of raw and processed Guñjā (Abrus precatorius Linn.) seeds

Background: Seed of Guñjā (Abrus precatorius Linn.), a known poisonous drug, is used extensively in various ayurvedic formulations with great therapeutic significance. Ayurveda recommends the administration of Guñjā in diseases like Indralupta (alopecia), Śotha (edema), Kṛmi (helminthes), Kuṣṭha (skin diseases), Kaṇḍu (itching), Prameha (urinary disorders) etc., after being treated with specific Śodhana (purification) procedures. Objective: To assess the antimicrobial action of of raw and Śhodhita (Processed) Guñjā seeds Methods: Guñjā seeds after being processed with Godugdha (cows milk), Nimbu swarasa (Lemon juice), Kāñjī (Sour gruel) and water, as the media, were evaluated for its antibacterial effect against clinically important bacterial strains using agar well diffusion method. Results: Aqueous extracts of raw seeds of Guñjā exert its antibacterial effect on both Gram positive, as well as Gram negative bacteria but none of the Śodhita Guñjā seeds showed any bactericidal effect on any bacterial strains. Chloroform extracts of all the Śodhita Guñjā seed extracts could inhibit bacterial growth but with variations Conclusion: The study displayed that chloroform extracts of raw and śodhita samples for bacterial study were much sensitive than the aqueous extracts.