Anjana K. Vala

Antibacterial activity of silver: the role of hydrodynamic particle size at nanoscale.

Silver shows the highest antimicrobial activities amongst all metals. It is better than many first line antibiotics. The antimicrobial properties of silver can be tuned by altering its physical and surface properties. Researchers have demonstrated enhancement in the antibacterial properties of silver with decreasing particle size from bulk to nano. In the present article, we study the effect of particle size of silver at nanoscale on their antimicrobial properties. Two samples of silver nanoparticles (SNPs) of same physical size (≈8 nm) but different hydrodynamic size (59 and 83 nm) are prepared by chemical reduction of AgNO3 with oleylamine followed by phase transfer with triblock copolymer Pluronic F-127. Their antimicrobial properties are investigated by microdilution method against clinically important strains of gram positive (S. aureus and B. megaterium) and gram negative (P. vulgaris and S. sonnei) bacteria. Nearly 38-50% enhancement in the antibacterial action of SNPs was observed when their hydrodynamic size was reduced to 59 nm from 83 nm. It has been observed that the antibacterial action of SNPs was governed by their hydrodynamic size and not by their crystallite and physical size. The phenomenological model was also proposed which makes an attempt to explain the microscopic mechanism responsible for the size dependent antibacterial activities of silver.

Tolerance and removal of arsenic by a facultative marine fungus Aspergillus candidus

The objective of the work was to investigate tolerance to and removal of arsenic by a facultative marine fungus Aspergillus candidus. The fungus showed luxuriant growth in different concentrations (25 and 50mg/L) of trivalent and pentavalent forms of arsenic. Biomass accumulation data substantiate tolerance of A. candidus towards the test concentrations of trivalent and pentavalent forms of arsenic. Highest arsenic removal (mg/g) was recorded on day 3. As removal increased with an increase in concentration. Hence, the test fungus A. candidus is a promising candidate for arsenic remediation.

Biogenesis of Silver Nanoparticles by Marine- Derived Fungus Aspergillus flavus from Bhavnagar Coast, Gulf of Khambhat, India

Biogenesis of Silver Nanoparticles by Marine- Derived Fungus Aspergillus flavus from Bhavnagar Coast, Gulf of Khambhat, India Despite the fact that researches on nanobiotechnology in future may increasingly depend on marine microbes, they are quite under explored for biosynthesis of nanoparticles. The present work was carried out with a view to examine silver nanoparticle biosynthesis potential of a marine-derived fungus Aspergillus flavus. The test fungus could synthesize silver nanoparticles intracellularly at different silver nitrate concentrations within 24h.

Influence of antibiotic adsorption on biocidal activities of silver nanoparticles.

Excessive use of antibiotics has posed two major challenges in public healthcare. One of them is associated with the development of multi-drug resistance while the other one is linked to side effects. In the present investigation, the authors report an innovative approach to tackle the challenges of multi-drug resistance and acute toxicity of antibiotics by using antibiotics adsorbed metal nanoparticles. Monodisperse silver nanoparticles (SNPs) have been synthesised by two-step process. In the first step, SNPs were prepared by chemical reduction of AgNO3 with oleylamine and in the second step, oleylamine capped SNPs were phase-transferred into an aqueous medium by ligand exchange. Antibiotics - tetracycline and kanamycin were further adsorbed on the surface of SNPs. Antibacterial activities of SNPs and antibiotic adsorbed SNPs have been investigated on gram-positive (Staphylococcus aureus, Bacillus megaterium, Bacillus subtilis), and gram-negative (Proteus vulgaris, Shigella sonnei, Pseudomonas fluorescens) bacterial strains. Synergistic effect of SNPs on antibacterial activities of tetracycline and kanamycin has been observed. Biocidal activity of tetracycline is improved by 0-346% when adsorbed on SNPs; while for kanamycin, the improvement is 110-289%. This synergistic effect of SNPs on biocidal activities of antibiotics may be helpful in reducing their effective dosages.

Intra- and Extracellular Biosynthesis of Gold Nanoparticles by a Marine-Derived Fungus Rhizopus oryzae

Gold nanoparticles (GNPs) production by the green chemistry approach was examined using a marine-derived fungus Rhizopus oryzae. The test fungi revealed production of gold nanoparticles both, extra and intracellularly. Extracellular biosynthesis was found at the gold chloride concentration 0.25 mM, as evidenced by lavender-purple color of the solution. At other concentrations, intense coloration in biomass was observed indicating intracellular biosynthesis of gold nanoparticles. To the best of the authors knowledge, this is first ever report on extracellular biosynthesis of GNPs by R. oryzae under static condition.

Characterization of L-asparaginase from marine-derived Aspergillus niger AKV-MKBU, its antiproliferative activity and bench scale production using industrial waste

L-asparaginase (LA), an enzyme with anticancer activities, produced by marine-derived Aspergillus niger was subjected to purification and characterization. The purified enzyme was observed to have molecular weight ∼90KDa. The enzyme retained activity over a wide range of pH, i.e. pH 4-10. The enzyme was quite stable in temperature range 20-40°C. Tween 80 and Triton X-100 were observed to enhance LA activity while inhibition of LA activity was observed in presence of heavy metals. The values for Km was found to be 0.8141 mM and Vmax was 6.228μM/mg/min. The enzyme exhibited noteworthy antiproliferative activity against various cancer cell lines tested. Successful bench scale production (in 5L bioreacator) of LA using groundnut oil cake as low cost substrate has also been carried out.

Isolation and Investigation of Biodegradation Potential of Multiple Polycyclic Aromatic Hydrocarbons (PAHs) Degrading Marine Bacteria near Bhavnagar Coast, India

Present work deals with modified isolation methods for indigenous microorganisms with a capability to use both low molecular weight (LMW) and high molecular weight (HMW)PAHs, which are pervasive recalcitrant pollutants. Methods such as biphasic enrichment, and specific isolation methods has resulted in the isolation of organisms such as Sphingomonas, Pseudomonas, Mycobacterium, Achromobacter, and Streptomyces species with efficacy to degrade majority of LMW PAHs up to 85% after four days of experiments, which is substantially rapid rate of degradation attributed by microorganisms. Moreover, the organisms had shown up to 30% degradation of HMW PAHs within the same time frame, making the isolation strategies more credible. The study thus, holds prime importance of conquering the difficulties in the isolation of multiple hydrocarbons degrading microorganisms, which can be further applied for the successful application for bioremediation of hydrocarbon impacted environments.

Marine-Derived Fungi: Potential Candidates for Fungal Nanobiotechnology

Due to unique properties, gold and silver nanoparticles (GNPs and AgNPs, respectively) have wide applications in diverse fields like biomedicine, catalysis, imaging and photonics, solar energy conversion and nanoelectronics etc. and hence, are in great demand. Available physicochemical synthesis protocols generally face limitations like high cost, polluting nature, and also have restricted use in clinical and pharma applications. In order to overcome these limitations, biosynthesis of nanoparticles could be a promising alternative. While it has been suggested that initiatives should be taken for exploitation of marine microbial resources in the area of nanobiotechnology, despite the unique traits of marine-derived fungi, they are comparatively less explored for biosynthesis of GNPs and AgNPs. Though a few, available reports suggest marine-derived fungi as promising candidates for such purpose. Recent reports on observation of the laser speckle pattern and weak localization of light by AgNPs and GNPs biosynthesized by marine-derived fungi assert their novel application potentialities.

Observation of weak localization of light in gold nanofluids synthesized using the marine derived fungus Aspergillus niger

We have observed weak localization of light for the first time in gold nanofluids synthesized using the marine derived fungus Aspergillus niger. Coherent backscattering of waves by a disordered scattering medium is responsible for weak localization of light. We have directly observed this effect using polarized visible light and for different sized gold nanoparticles in nanofluids. The localization parameter kl* obtained from the observation is 1 < kl* < 5, which is the precondition for the weak localization of light. The kl* is controlled by the size and concentration of the particles in the nanofluids. Quadratic scaling is used to study the localization transition. The localization length obtained is nearly 225 nm. Gold nanoparticles have potential applications in biomedicine, imaging, catalysis and photonics.

Marine-Derived Fungi: Prospective Candidates for Bioremediation

With increased industrialization and urbanization, there has been an increased level of pollutants in the environment. It is imperative to reduce concentration of toxic compounds in the effluent to meet ever-increasing legislative standards. While in most of the cases physicochemical treatments of wastes suffer from one or the other limitation, bioremediation is a promising alternative. Fungi, with their unique traits like their greater growth capacity, reach by virtue of mycelial branching, ability to produce a number of enzymes and metal accumulation potential, etc., are very well suited for bioremediation processes. Marine-derived fungi, being able to grow under extreme conditions (like high salinity and pH), are even better candidates for such purposes as their traits may especially be useful in the treatment of industrial effluent. The role of marine-derived fungi in general, and those screened along Gujarat coast, India, in particular, for removal of some pollutants, is discussed. Based on the findings, marine-derived fungi are envisioned as prospective bioremediation candidates.