Ramkrishna Sen

Antimicrobial potential of a lipopeptide biosurfactant derived from a marine Bacillus circulans

Aims:  To isolate the biologically active fraction of the lipopeptide biosurfactant produced by a marine Bacillus circulans and study its antimicrobial potentials.

Enhancement of tensile strength of lignocellulosic jute fibers by alkali-steam treatment.

The physico-chemical properties of jute fibers treated with alkali (NaOH) solution have been investigated in this study. The treatments were applied under ambient and elevated temperatures and high pressure steaming conditions. To the knowledge of these authors the influence of alkali-steam treatment on the uniaxial tensile strength of natural ligno-cellulosic fibers, such as jute, has not been investigated earlier. The results from this investigation indicate that a 30 min dipping of the fibers in 0.5% alkali solution followed by 30 min alkali-steam treatment leads to an increase in the tensile strength of up to 65%. The increase appears to be due to fiber separation and removal of non-cellulosic materials, which, in turn, resulted in an increased crystallinity.

Improved bioavailability and biodegradation of a model polyaromatic hydrocarbon by a biosurfactant producing bacterium of marine origin.

Polyaromatic hydrocarbons (PAHs) are organic pollutants mostly derived from the processing and combustion of fossil fuels and cause human health hazards. In the present study a marine biosurfactant producing strain of Bacillus circulans was used to increase the bioavailability and consequent degradation of a model polyaromatic hydrocarbon, anthracene. Although the organism could not utilize anthracene as the sole carbon source, it showed better growth and biosurfactant production in an anthracene supplemented glycerol mineral salts medium (AGlyMSM) compared to a normal glycerol mineral salts medium (GlyMSM). The biosurfactant product showed high degree of emulsification of various hydrocarbons. Analysis by gas chromatography (GC), high performance thin layer chromatography (HPTLC) and Fourier transform infrared spectroscopy (FTIR) showed that the biosurfactant could effectively entrap and solubilize PAH. Thin layer chromatographic analysis showed that anthracene was utilized as a carbon substrate for the production of biosurfactant. Thus organic pollutant anthracene was metabolized and converted to biosurfactants facilitating its own bioremediation.

Application of response-surface methodology to evaluate the optimum environmental conditions for the enhanced production of surfactin

Abstract Response-surface methodology was applied to determine the effect of the fermentation process conditions, namely pH, temperature, rates of agitation and aeration, on surfactin production. The effects of the mutual interactions between these parameters were extensively studied to optimize the process conditions for the maximum production of surfactin. With a view to simultaneously reducing the number of experiments and obtaining the mutual interactions between the variables required for achieving the optimal experimental conditions, a 24 full-factorial central composite design followed by multi-stage Monte-Carlo optimization was employed for experimental design and analysis of the results. The optimum process conditions for the enhanced production of surfactin were as follows: pH = 6.755, temperature = 37.4 °C, agitation = 140 rpm and aeration = 0.75 vvm. Relative surfactin concentrations were denoted by the reciprocal of the critical micelle concentrations.

Response Surface Optimization of the Critical Media Components for the Production of Surfactin

Optimization of the fermentation media for maximization of surfactin production was carried out. The carbon source (glucose), the nitrogen source (ammonium nitrate) and the mineral salts ferrous and manganous sulphates were the critical components of the medium optimized. A 2 4 full factorial central composite experimental design followed by multi-stage Monte-Carlo optimization was used in the design of experiments and in the analysis of results. This procedure limited the number of actual experiments performed while allowing for possible interactions between the four components. The optimum values for the tested variables for the maximal production of surfactin were (in g dm -3 ): glucose = 36.5; NH 4 NO 3 = 4.5; FeSO 4 = 4 x 10 -3 and MnSO 4 = 27.5 x 10 -2 . Relative surfactant concentrations were expressed as the reciprocal of the critical micelle concentration (CMC -1 ) and the maximum predicted yield of surfactin in terms of CMC -1 was 45.5.

Potential therapeutic applications of biosurfactants.

Biosurfactants have recently emerged as promising molecules for their structural novelty, versatility, and diverse properties that are potentially useful for many therapeutic applications. Mainly due to their surface activity, these molecules interact with cell membranes of several organisms and/or with the surrounding environments, and thus can be viewed as potential cancer therapeutics or as constituents of drug delivery systems. Some types of microbial surfactants, such as lipopeptides and glycolipids, have been shown to selectively inhibit the proliferation of cancer cells and to disrupt cell membranes causing their lysis through apoptosis pathways. Moreover, biosurfactants as drug delivery vehicles offer commercially attractive and scientifically novel applications. This review covers the current state-of-the-art in biosurfactant research for therapeutic purposes, providing new directions towards the discovery and development of molecules with novel structures and diverse functions for advanced applications.

Artificial neural network modeling and genetic algorithm based medium optimization for the improved production of marine biosurfactant.

A nonlinear model describing the relationship between the biosurfactant concentration as a process output and the critical medium components as the independent variables was developed by artificial neural network modeling. The model was optimized for the maximum biosurfactant production by using genetic algorithm. Based on a single-factor-at-a-time optimization strategy, the critical medium components were found to be glucose, urea, SrCl(2) and MgSO(4). The experimental results obtained from a statistical experimental design were used for the modeling and optimization by linking an artificial neural network (ANN) model with genetic algorithm (GA) in MATLAB. Using the optimized concentration of critical elements, the biosurfactant yield showed close agreement with the model prediction. An enhancement in biosurfactant production by approximately 70% was achieved by this optimization procedure.

Antioxidant and free radical scavenging activities of an exopolysaccharide from a probiotic bacterium.

Probiotic bacteria synthesize extracellular polysaccharides (EPSs) with commercially significant physiological and therapeutic activities. This important class of biomolecules is also characterized by their ability to remove reactive oxygen species (ROS) that are formed in the intestine by various metabolic reactions; hence, they exhibit antioxidant activities. Our probiotic bacterium, Bacillus coagulans RK‐02, produces an EPS during the exponential and stationary growth phases when grown in a glucose mineral salts medium. The time course of EPS synthesis was studied with respect to biomass growth. The antioxidant and free radical scavenging potential of isolated EPS were studied by various methods, including the β‐carotene‐linoleic acid model system, a superoxide radical scavenging assay using the PMS‐NADH‐nitroblue tetrazolium system, the 1,1‐diphenyl‐2‐picrylhydrazyl radical scavenging activity, a hydroxyl radical scavenging assay using the ascorbic acid‐Cu2+‐cytochrome c system and an in vitro microsome peroxidation inhibition study using a thiobarbituric acid assay. The antioxidant activities were compared to known antioxidants vitamin C and E, which were used as reference standards. The results showed that the EPS, which is a heteropolymer composed of four monosaccharides, produced by B. coagulans RK‐02 had significant antioxidant and free radical scavenging activities.

Biosurfactant of marine origin exhibiting heavy metal remediation properties

The present study was aimed at elucidating the role of biosurfactant product isolated from a marine bacterium in removing heavy metals from heavy metal containing solutions. In this study, metal removal was biosurfactant-mediated. Efficiency of metal removal depended on the concentration of the metal as well as that of the biosurfactant. At a concentration 5x, the critical micelle concentration (CMC), almost complete removal of 100 ppm of lead and cadmium occurred. Atomic absorption spectroscopy (AAS) studies also showed metal removal at a concentration less than the CMC in contrast to earlier findings that only micelles are involved in metal removal. Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM) equipped with energy dispersive X-ray spectroscopy (EDS) further substantiated these findings.

Substrate dependent production of extracellular biosurfactant by a marine bacterium

The potential of a marine microorganism to utilize different carbon substrates for the production of an extracellular biosurfactant was evaluated. Among the several carbon substrates tested for this purpose, production of the crude biosurfactant was found to be highest with glycerol (2.9+/-0.11 g L(-1)) followed by starch (2.5+/-0.11 g L(-1)), glucose (1.16+/-0.11 g L(-1)) and sucrose (0.94+/-0.07 g L(-1)). The crude biosurfactant obtained from glycerol, starch and sucrose media had significantly higher antimicrobial action than those obtained from glucose containing medium. RP-HPLC resolved the crude biosurfactants into several fractions one of which had significant antimicrobial action. The antimicrobial fraction was found in higher concentrations in biosurfactant obtained using glycerol, starch and sucrose as compared to the biosurfactants from glucose medium, thereby explaining higher antimicrobial activity. The carbon substrate was thus found to affect biosurfactant production both in a qualitative and quantitative manner.