Jayanthi Abraham

A Biological Approach to the Synthesis of Silver Nanoparticles with Streptomyces sp JAR1 and its Antimicrobial Activity

The biological approach to synthesize metal nanoparticles is an important aspect of current nanotechnology research. Silver nanoparticles have been well-known for their inhibitory and antimicrobial effects. The ever-increasing antibiotic resistance in pathogenic and opportunistic microorganisms is a major threat to the health care industry. In the present investigation, silver nanoparticles have been successfully biosynthesized by Streptomyces sp JAR1. Biosynthesized silver nanoparticles were characterized by means of several analytical techniques including a UV-Visible spectrophotometer, Fourier transform infrared spectroscopy, X-ray diffraction pattern analysis, and atomic force microscopy. An evaluation of the antimicrobial activity of silver nanoparticles (AgNPs) was carried out against clinically important pathogenic microorganisms. The metal nanoparticles were also evaluated for their combined effects with antibiotics against the clinical pathogens. The antibacterial activities of the antibiotics increased in the presence of the biologically synthesized AgNPs against the clinically important pathogens. The highest enhancing effect was observed for erythromycin against the test pathogens.

Biosynthesis of silver and zinc oxide nanoparticles using Pichia fermentans JA2 and their antimicrobial property

The development of eco-friendly alternative to chemical synthesis of metal nanoparticles is of great challenge among researchers. The present study aimed to investigate the biological synthesis, characterization, antimicrobial study and synergistic effect of silver and zinc oxide nanoparticles against clinical pathogens using Pichia fermentans JA2. The extracellular biosynthesis of silver and zinc oxide nanoparticles was investigated using Pichia fermentans JA2 isolated from spoiled fruit pulp bought in Vellore local market. The crystalline and stable metallic nanoparticles were characterized evolving several analytical techniques including UV–visible spectrophotometer, X-ray diffraction pattern analysis and FE-scanning electron microscope with EDX-analysis. The biosynthesized metallic nanoparticles were tested for their antimicrobial property against medically important Gram positive, Gram negative and fungal pathogenic microorganisms. Furthermore, the biosynthesized nanoparticles were also evaluated for their increased antimicrobial activities with various commercially available antibiotics against clinical pathogens. The biosynthesized silver nanoparticles inhibited most of the Gram negative clinical pathogens, whereas zinc oxide nanoparticles were able to inhibit only Pseudomonas aeruginosa. The combined effect of standard antibiotic disc and biosynthesized metallic nanoparticles enhanced the inhibitory effect against clinical pathogens. The biological synthesis of silver and zinc oxide nanoparticles is a novel and cost-effective approach over harmful chemical synthesis techniques. The metallic nanoparticles synthesized using Pichia fermentans JA2 possess potent inhibitory effect that offers valuable contribution to pharmaceutical associations.

Role of Gordonia sp JAAS1 in biodegradation of chlorpyrifos and its hydrolysing metabolite 3,5,6-trichloro-2-pyridinol.

Paddy field soil with prior exposure to chlorpyrifos was chosen for the biodegradation of the pesticide by employing bacteria with special emphasis given to actinomycetes. Actinomycetes are organisms predominantly known for their bioactive compounds, but there is dearth of work pertaining to their role in bioremediation. So this work was carried out to screen for actinomycetes and assess their potential in degradation of the pesticide. Actinobacterial strains were isolated from paddy field soil, with capabilities to degrade chlorpyrifos and its major metabolite 3,5,6‐trichloro‐2‐pyridinol (TCP). Two strains were successfully isolated among which one strain was efficient and was able to tolerate high concentrations of chlorpyrifos. This strain was selected for further investigation; it was identified as Gordonia sp based on 16S rRNA analysis and designated as Gordonia sp JAAS1. The actinobacterial strain was able to degrade 110 mg l−1 of chlorpyrifos within 24 h incubation, and TCP was found to accumulate in the culture medium. However, after 72 h of incubation, TCP was degraded, and finally, diethylthiophosphoric acid (DETP) was obtained.

Mycoremediation of endosulfan and its metabolites in aqueous medium and soil by Botryosphaeria laricina JAS6 and Aspergillus tamarii JAS9.

Microbial degradation offers an efficient and ecofriendly approach to remove toxicants from the contaminated environments. Botryosphaeria laricina JAS6 and Aspergillus tamarii JAS9 were capable of degrading endosulfan and their metabolites which were isolated through enrichment technique. Both the strains were able to withstand an exposure of 1300 mg/L and showed luxuriant growth at 1000 mg/L of endosulfan. The change in pH in the culture broth was from 6.8 to 3.4 and 3.8 during growth kinetic studies of JAS6 and JAS9 strains, respectively upon biological degradation of endosulfan. The degradation of endosulfan by JAS6 and JAS9 strains were examined by HPLC. The biodegradation rate constant (k) and the initial concentration were reduced by 50% (DT50) which was determined by first and pseudo first order kinetic models. In the present investigation it has been revealed that Botryosphaeria laricina JAS6 and Aspergillus tamarii JAS9 possessing endosulfan degrading capability are being reported for the first time. These findings confirm the degradation of endosulfan by JAS6 and JAS9 strains which were accompanied by significant reduction in the toxicity and could be used as remedial measure in contaminated environments.

Microbial biofiltration technology for odour abatement: An introductory review

Odour is a serious complaint associated with waste air emissions that creates nuisance due to its malodorous behaviour. Its treatment process ranges from physical, chemical to biological means. A biological treatment system has several advantages over the physical and chemical technologies in being ecofriendly, more efficient with low operational cost and characterized by high flow rates of waste gas with low concentration of contaminants. Application of microorganisms in waste treatment has long been realized, especially in degrading various compounds in the waste gas that cause odour. However, the type of microorganism and its metabolism for the particular odorant are the factors crucially considered in designing a biological treatment system. Biofilters are well-known biological filtration systems that employ microorganisms for treating odours from waste gases. This report describes the generation of odorants from different sources and their possible degradation by suitable microbial cultures. In addition, comparisons among physiochemical and biological methods for odour abatement have been discussed. Nevertheless, the type of biofilter, its packing material and other reaction conditions for an effective biofiltration have also been considered.

Biodegradation of chlorpyrifos and its hydrolysis product 3,5,6-trichloro-2-pyridinol using a novel bacterium Ochrobactrum sp. JAS2: A proposal of its metabolic pathway

Biodegradation of chlorpyrifos and its major metabolite 3,5,6-trichloro-2-pyridinol (TCP) were studied with a novel bacterial strain JAS2 isolated from paddy rhizosphere soil. The molecular characterization based on 16S rRNA gene sequence homology confirmed its identity as Ochrobactrum sp. JAS2. The JAS2 strain degraded 300mgl(-1) of chlorpyrifos within 12h of incubation in the aqueous medium and it produced the TCP metabolite. However, after 72h of incubation TCP was also completely degraded by the JAS2 strain. A tentative degradation pathway of chlorpyrifos by Ochrobactrum sp. JAS2 has been proposed on basis of GC-MS analysis. The complete degradation of chlorpyrifos occurred within 24h in the soil spiked with and without addition of nutrients inoculated with Ochrobactrum sp. JAS2. TCP was obtained in both the studies which was degraded completely by 96h in the soil spiked with nutrients and whereas 120h in absence of nutrients in the soil. The mpd gene which is responsible for organophosphorus hydrolase production was identified. The isolates Ochrobactrum sp. JAS2 also exhibited a time dependent increase in the amount of tricalcium phosphate solubilization in Pikovskayas medium. Further screening of the strain JAS2 for auxiliary plant growth promoting activities revealed its remarkable capability of producing the indole acetic acid (IAA), hydrogen cyanide (HCN) and ammonia.

Biomineralization and formulation of endosulfan degrading bacterial and fungal consortiums

Microbial degradation offers an effective approach to remove toxicants and in this study, a microbial consortium consisting of bacterial strains and fungal strains were originally obtained from endosulfan contaminated agricultural soils. Identification of the bacterial isolates by 16S rRNA sequences revealed the isolates to be Halophilic bacterium JAS4, Klebsiella pneumoniae JAS8, Enterobacter asburiae JAS5, and Enterobacter cloacae JAS7, whereas the fungal isolates were identified by 18S rRNA sequences and the isolates were Botryosphaeria laricina JAS6, Aspergillus tamarii JAS9 and Lasiodiplodia sp. JAS12. The biodegradation of endosulfan was monitored by using HPLC and FTIR analysis. The bacterial and fungal consortium could degrade 1000 mg l(-1) of endosulfan efficiently in aqueous medium and in soil. The infrared spectrum of endosulfan degraded samples in the aqueous medium by bacterial and fungal consortium showed bands at 1400 and 950 cm(-1) which are the characteristics of COOH group and acid dimer band respectively. In the present investigation, low cost solid materials such as sawdust, soil, fly ash, molasses and nutrients were used for the formulation of microbial consortium and to achieve greater multiplication and survival of the microbial strains.

Efficacy of Ganoderma sp. JAS4 in bioremediation of chlorpyrifos and its hydrolyzing metabolite TCP from agricultural soil.

A novel fungal strain JAS4 was isolated from agricultural soil and was found to be highly effective in degrading chlorpyrifos and its major degradation product 3,5,6‐trichloro‐2‐pyridinol (TCP). The molecular characterization based on 18S rRNA sequence analysis, revealed strain JAS4 as Ganoderma sp. which could able to degrade chlorpyrifos and its metabolite in an aqueous medium with rate constant of 0.8460 day−1, following first order rate kinetics, and the time in which the initial insecticide concentration was reduced by 50% (DT50) was 0.81 days. Studies on biodegradation in soil with nutrients showed that JAS4 strain exhibited efficient degradation of insecticide with a rate constant of 0.9 day−1, and DT50 was 0.73 day. In contrast, degradation of insecticide in soil without nutrients was characterized by a rate constant of 0.7576 day−1 and the DT50 was 0.91 day.

Antimicrobial properties of hemoglobin.

Hemoglobin consists of a heme containing component and a globin unit. It exists as a tetramer with 2 α subunits and 2 β subunits in adults and with 2 α subunits and 2 γ chains in infants. On proteolytic cleavage, hemoglobin breaks down to produce many biologically active compounds, among which are hemocidins, those which exhibit antimicrobial property. The generation of these peptides does not depend on the blood group, Rhesus factor, age and sex of the healthy donors. The microbicidal activity has been observed against a variety of gram positive and Gram-negative bacteria, and against filamentous fungi, yeast and even certain parasites. The discovery of hemocidins opens a new field for research into the details of the peptides acting as second line of defence in boosting the innate immune system of the organisms.

Ribosomally synthesized peptides from natural sources

There are many antibiotic-resistant microbial pathogens that have emerged in recent years causing normal infections to become harder and sometimes impossible to treat. The major mechanisms of acquired resistance are the ability of the microorganisms to destroy or modify the drug, alter the drug target, reduce uptake or increase efflux of the drug and replace the metabolic step targeted by the drug. However, in recent years, resistant strains have been reported from almost every environment. New antimicrobial compounds are of major importance because of the growing problem of bacterial resistance, and antimicrobial peptides have been gaining a lot of interest. Their mechanism of action, however, is often obscure. Antimicrobial peptides are widespread and have a major role in innate immunity. An increasing number of peptides capable of inhibiting microbial growth are being reviewed here. In this article, we consider the possible use of antimicrobial peptides against pathogens.