Vijayalakshmi Muvva

Optimization of Culture Conditions for Enhanced Antimicrobial Activity of Rhodococcus erythropolis VLK-12 Isolated from South Coast of Andhra Pradesh, India.

Aims: To Isolate and characterize the antimicrobial actinomycetes from the marine habitats of south coast of Andhra Pradesh, India. Place and Duration of the Study: Marine habitats of south coast of Andhra Pradesh, India, between June 2011 and July 2012. Methodology: The soil samples were collected, pre-treated and plated on yeast extractmalt extract dextrose agar medium. Identification of the strain was carried out by employing the polyphasic taxonomical studies including the 16S rRNA sequence based analysis. Phylogenetic tree was constructed using the Molecular Evolutionary Genetic Analysis (MEGA) version 5. The influence of culture conditions and the effect of environmental factors on the biomass and antimicrobial activy\ity of the strain was the focus of this study. Results: A total of 20 actinobacteria were isolated from the marine habitats of south coast of Andhra Pradesh, India, and screened for antimicrobial activity against test bacteria and fungi. The potent bioactive metabolite producing strain was designated as VLK-12. Research Article British Microbiology Research Journal, 4(1): 63-79, 2014 64 Further polyphasic studies revealed that the Isolate VLK-12 belongs to the genera Rhodococcus. Phylogenetic analysis of 16S rRNA sequencing studies revealed that the strain is closely related to Rhodococcus erythropolis. The crude ethyl acetate extract obtained by culturing the strain on YMD inhibited Gram positive and Gram negative bacteria along with fungi. Conclusion: Rhodococcus erythropolis isolated from the marine habitats of south coast of Andhra Pradesh exhibited antimicrobial activity against pathogens.

Optimization of process parameters for improved production of bioactive metabolites by Streptomyces tritolerans DAS 165T.

Aims: To optimize the process parameters for enhanced production of bioactive metabolites by Streptomyces tritolerans DAS 165. Place and Duration of Study: Department of Botany and Microbiology, April 2012 to August 2012. Methodology: Agar well diffusion assay was employed to study the effect of environmental parameters such as incubation period, pH, temperature and salt concentration and influence of various nutrients such as carbon and nitrogen sources and minerals on the bioactive metabolite production by Streptomyces tritolerans DAS 165.  Results: The production of antimicrobial metabolite was high when the strain was cultured for six days at 35oC in medium (pH 7.5) with sucrose at the concentration of 2% (carbon source), soya peptone at the concentration of 1% (nitrogen source) and sodium chloride at the concentration of 5%.  Conclusion: This is the first report on the optimization of bioactive metabolite production Original Research Article British Microbiology Research Journal, 4(4): 428-442, 2014 429 by Streptomyces tritolerans DAS 165. As the strain exhibited potent antimicrobial activity, it may be explored for biotechnological purposes. 

Bioactive natural products from Pseudonocardia endophytica VUK-10

Two proline containing cyclic dipeptides (CDPs), cyclo (L-Pro-L-Tyr) (1) and cyclo (L-Pro-L-Phe) (2) were isolated from the fermentation broth of Pseudonocardia endophytica VUK-10 originating from the Nizampatnam mangrove ecosystem on the south coast of Andhra Pradesh, India. The structures of the compounds were established by 1H NMR and 13C NMR spectroscopy, FTIR and EIMS. The antimicrobial and cytotoxic activities of the compounds were tested against a variety of medicinally and agriculturally important bacteria and fungi as well as on the MDA-MB-231, OAW-42, HeLa and MCF-7 human cell lines. Xanthomonas malvacearum was most sensitive toward 1 (MIC 4 μg/ml), whereas compound 2 had good antibacterial activity against Xanthomonas campestris (MIC 8 μg/ml). Fusarium solani was highly sensitive toward 1 (MIC 16 μg/ml). The compounds were cytotoxic against the human cell lines at micro molar concentrations; the highest activity (IC50 < 10 μM) of 1 was recorded against the MDA-MB-231 cancer cell line.

Production of Antimicrobial Metabolites by Streptomyces lavendulocolor VHB-9 Isolated from Granite Mines

The actinobacterial strain Streptomyces lavendulocolor VHB-9 was isolated from granite mine soil samples of Khammam district, Telangana state, India. The strain was identified based on detailed microorphological, cultural and phylogenetic analysis. Bioactive guided isolation of the secondary metabolites of the strain was carried out by growing the strain in optimized medium (0.5% lactose, 0.5% peptone, 0.05% K2HPO4, 0.2% CaCO3 with pH adjusted to 7.0). Separation and purification of the active fractions from the crude ethyl acetate extract was carried out by silica gel column chromatography and resulted in the isolation of two active fractions. Structural elucidation of the two (B2 and B3) active compounds was carried out by FT-IR, Mass and NMR spectroscopy and were identified as Bis (7-methyloctyl) phthalate and (Z)-3-aminoacrylic acid. The antimicrobial activity of the bioactive compounds produced by S. lavendulocolor VHB-9 was expressed in terms of minimum inhibitory concentration against opportunistic pathogenic bacteria and fungi. Both fractions exhibited good antimicrobial potential against the bacteria and fungi tested.

Bioactive-guided fractionation of diols from Streptomyces sp. MSL

An actinomycete strain with a great potential to produce bioactive compounds isolated from a laterite soil was identified as Streptomyces sp. MSL based on 16S rDNA sequence analysis. Secondary metabolites produced by the strain in optimized nutrient broth were extracted and analyzed by chromatographic and spectroscopic techniques. Among the different fractions, four diols, viz., (1) (2R,3R)-2,3-Butanediol, (2) (2R,3S)-2,3-Butanediol, (3) 2,3-dimethyl-2,3-butanediol (Pinacol), and (4) (3R)-1,3-Butanediol exhibited good antimicrobial activity. These compounds inhibited growth of both Gram-positive and Gram-negative bacteria as well as fungi tested. Minimum inhibitory concentration of these compounds was also determined against test micro-organisms in vitro. This is the first report on the occurrence of 2,3-dimethyl-2,3-butanediol (Pinacol) in the genus Streptomyces. This paper also reports the extraction, purification, and antimicrobial spectrum of diols fractionated from the culture filtrate of Streptomyces sp. MSL.

Pullulan-Stabilized Silver Nanoparticles -Their Synthesis, Characterization and Application as Bactericidal Agents.

A rapid method for Pullulan-stabilized silver nanoparticles (PuAgNPs) synthesis has been developed. Different concentrations of Pullulan and Silver nitrate and effects of reaction time, pH was used to investigate the synthesis of silver nanoparticles. The synthesized Pu-AgNPs were first screened and identified using surface plasmon peaks of UV–VIS spectroscopy.The research results indicated that the surface plasmon resonance peaks were observed between 410–460 nm wavelengths in UV-VIS spectroscopy studies.The morphology of the synthesized AgNPs proved a variation in spherical shape and polydispersed with an averagesize of 10-55 nm, using TEM. Further, five characteristic peaksconfirmed the presence of elemental silver and the crystalline structure of silver nanoparticles from XRD analysis. From FTIR spectra, stretching vibrations of hydroxyl (O-H), carbonyl (C=O) and C=C stretches exhibits the reduction and stabilization of AgNPs. Further, clear zones of inhibition (about 10-25 mm) against four bacterial pathogens obtained in the antibacterial studies for the synthesized PuAgNPs.The experimental results demonstrated that pullulan could be used as reducing and stabilizing agentfor formation of AgNPs and can be used as redoubtablebactericidal agents.

Screening and antimicrobial activity of actinomycetes isolated from the rhizosphere of Clitoria ternatea

The air dried rhizosphere soil samples pretreated with calcium carbonate was employed for the isolation of actinomycete strains. Serial dilution plate technique was used for the isolation of actinomycetes. A total of 20 actinomycete strains designated as BS1 -BS20 were isolated from the rhizosphere of medicinal plant Clitoria ternatea. All the 20 strains were subjected to primary screening for antimicrobial activity. Among the 20 strains screened, 10 strains exhibited high antimicrobial spectrum against Staphylococcus aureus, Escherichia coli and Candida albicans.

Antimicrobial profile of Arthrobacter kerguelensis VL-RK_09 isolated from Mango orchards

An actinobacterial strain VL-RK_09 having potential antimicrobial activities was isolated from a mango orchard in Krishna District, Andhra Pradesh (India) and was identified as Arthrobacter kerguelensis. The strain A. kerguelensis VL-RK_09 exhibited a broad spectrum of in vitro antimicrobial activity against bacteria and fungi. Production of bioactive metabolites by the strain was the highest in modified yeast extract malt extract dextrose broth, as compared to other media tested. Lactose (1%) and peptone (0.5%) were found to be the most suitable carbon and nitrogen sources, respectively, for the optimum production of the bioactive metabolites. The maximum production of the bioactive metabolites was detected in the culture medium with an initial pH of 7, in which the strain was incubated for five days at 30 °C under shaking conditions. Screening of secondary metabolites obtained from the culture broth led to the isolation of a compound active against a wide variety of Gram-positive and negative bacteria and fungi. The structure of the first active fraction was elucidated using Fourier transform infrared spectroscopy, electrospray ionization mass spectrometry, 1H and 13C nuclear magnetic resonance spectroscopy. The compound was identified as S,S-dipropyl carbonodithioate. This study is the first report of the occurrence of this compound in the genus Arthrobacter.