Palashpriya Das

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.

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.

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.

Antiadhesive action of a marine microbial surfactant

The antiadhesive action of a lipopeptide biosurfactant from a marine bacterium was investigated. The effect of cultivation conditions on the adhesion property of few bacterial strains was studied. It was observed that the static cultures showed greater adhesion due to scarcity of oxygen. The biosurfactant upon surface conditioning was found to be effective in removal of the microbial adhesion at a concentration as low as 0.1 g L(-1). The percentages of inhibition of adhesion against different test bacterial strains ranged from 15 to 89% using 0.1-10 g L(-1) of purified biosurfactant. These percentages of adhesion inhibition were found to be significantly higher than the previously reported values. The antiadhesive efficacy of the biosurfactant was also evident from confocal laser scanning microscopy studies.

Genetic regulations of the biosynthesis of microbial surfactants: an overview.

Abstract Microbial biosurfactants are surface active metabolites synthesized by microbes growing on a variety of substrates. In spite of having great potential for commercial, therapeutic and environmental applications, industrial level production has not been realized for their low yields and productivities. One vital factor determining their biosynthesis is the genetic makeup of the producer organisms. Studies on molecular genetics and biochemistry of the synthesis of several biosurfactants have revealed the operons, the enzymes and the metabolic pathways required for their extracellular production. Surfactin, a cyclic lipopeptide biosurfactant is a potent antimicrobial agent and is produced as a result of non-ribosomal biosynthesis catalyzed by a large multienzyme peptide synthetase complex called the surfactin synthetase. Pathways for the synthesis of other lipopeptides such as iturin, lichenysin and arthrofactin are also mediated by similar enzyme complexes. These non-ribosomal peptide synthetases (NRPSs) responsible for lipopeptide biosynthesis display a high degree of structural similarity among themselves even from distant microbial species. Plasmid-encoded- rhlA, B, R and I genes of rhl quorum sensing system are required for production of glycolipid biosurfactants by Pseudomonas species. Molecular genetics of biosynthesis of alasan and emulsan by Acinetobacter species and of the fungal biosurfactants such as mannosylerythritol lipids (MEL) and hydrophobins have been deciphered. However, limited genetic information is available about biosynthesis of other biosurfactants such as viscosin, amphisin and synthesized counterparts. As these molecules have emerged as potential agents in many industrial and environmental processes as well as in biomedical and therapeutic applications, it is essential to make them cost competitive. Genetically engineered hyper producing organisms giving high yields can bring the real breakthrough in the production process. This is possible only if the genetics of the microbial surfactant production is known in details. It is therefore desirable that the future research on biosurfactants be focused on the development and use of hyperproducers. The detailed knowledge of the genetics of microbial surfactant production should be used to produce organisms giving higher production with better product characteristics. With a better knowledge of the genes involved in this process, biosurfactant production can be realized in non-pathogenic industrial strains. The knowledge of expression of genes of a particular biosurfactant producer in a particular habitat will also throw light upon substrate dependence of production and preference for a particular substrate. Detailed description of the genetics of production of the newly identified biosurfactants like flavolipids, tensin and lokisin is not available. Efforts should be made by investigators to develop high yielding strains of microorganisms producing strong biosurfactants such as arthrofactin and lichenysin. A few marine biosurfactants have been discovered (Kalinovskaya et al. 2004) and there is high possibility of finding many other novel surface active compounds from the marine sources. Many of these are expected to possess interesting properties as pharmaceuticals and biomedical agents. The knowledge of molecular genetics of microbial surfactant production and its subsequent use to produce hyperproducers will determine the fate of biosurfactant industry.

Antimicrobial biosurfactants from marine Bacillus circulans: extracellular synthesis and purification

Aims:  To purify the biosurfactant produced by a marine Bacillus circulans strain and evaluate the improvement in surface and antimicrobial activities.

Rapid quantification of a microbial surfactant by a simple turbidometric method

Quantification of the biosurfactants produced by a variety of microorganisms is a time taking and difficult task due to the lack of rapid, efficient and accurate methods. This work presents a simple turbidometric method for quantification of crude biosurfactants based on their property to become insoluble at low pH values. Biosurfactants obtained from a Bacillus sp. using different carbon substrates showed a good linear correlation (R(2)>0.99) between biosurfactant concentrations and turbidity in the range of 1 to 10 g L(-1) of crude biosurfactants. The substrate specific equations (SSE) and generalized equations (GE) developed in this work effectively predicted the amount of crude biosurfactant produced in different sets of fermentation experiments validating the method. A similar linear correlation was also observed with biosurfactants obtained from two other strains, Bacillus circulans and Pseudomonas sp. This simple method may prove to be effective in fast, accurate and inexpensive quantification of crude biosurfactants produced by diverse bacteria.

Microbial Surfactants of Marine Origin: Potentials and Prospects

Marine environment occupies the vast majority of the earths surface and is a rich source of highly potent and active compounds. In recent years, microbial surfactants and emulsifiers have been reported from marine microflora. Surfactant and emulsifier molecules having diverse chemical nature such as exopolysaccharides, carbohydrate-lipid-protein complexes or glycolipopeptide, glycolipids, lipopeptides, phospholipids and ornithine lipids have been reported from various marine bacteria. These surface-active agents have been found to possess good emulsification and stabilization potentials for various lipophilic compounds such as aliphatic, aromatic and polyaromatic hydrocarbons and their uptake and degradation by the microorganisms. Few biosurfactant types such as glycolipids and lipopeptides have also been found to possess valuable biological activities. Surface-active agents from marine environments thus have tremendous potential to be used in industrial processes, for environmental remediation and as drugs.

Green surfactant of marine origin exerting a cytotoxic effect on cancer cell lines

The present work reveals the efficacy of a marine antimicrobial lipopeptide biosurfactant in blocking proliferation of breast cancer and colon cancer cell lines, without displaying any significant antioxidant activity. A novel isoform of 1382 Da played the key role, in sharp contrast to proliferation-blocking marine biosurfactant isoforms detected earlier in the range of 996–1077 Da and 1470–1509 Da. Inhibition of cancer cells was promoted by nanomolar concentrations of the test compound whereas much higher concentrations were reported for a few biosurfactants of marine origin as well as those of terrestrial origin like surfactin and rhamnolipids. Dual staining with annexin V and propidium iodide followed by FACS analysis showed an increased population of cancer cells at the sub G0/G1 phase indicative of the programmed cell death after treatment. Although in vivo studies are yet to be done, the results of the in vitro studies displaying the cytotoxicity of this non-hemolytic marine biosurfactant product advocates for its exploitation as a potential drug candidate in anticancer chemotherapy.