Randhir Makkar

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Recent developments in Biosurfactants

Frontiers in Microbiology, 2017

Meat production and agricultural integration

Biosurfactant—Enhanced bioremediation of hydrophobic pollutants

Journal of Biotechnology, 2008

The group IB impurities (Cu, Ag, and Au) incorporated into II-VI zinc blende hosts of ZnTe and Cd... more The group IB impurities (Cu, Ag, and Au) incorporated into II-VI zinc blende hosts of ZnTe and CdTe exhibit well resolved excitation lines followed by a photoionization continuum in their infrared absorption spectra. They are associated with transitions from a "1s-like" ground state to various "plike" excited state characteristic of a hole bound to a Coulomb center. Their spacing agree well with those predicted in the effective mass theory for single acceptors as expected for group IB elements substitutionally replacing the group IIB cations of the host. The occurrence of the simultaneous excitation of the Lyman transitions in combination with the zone center longitudinal optical phonon and hence lying in the photoionization continuum and displaying Fano-like asymmetries are features described and interpreted.

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Comparison of Synthetic Surfactants and Biosurfactants in Enhancing Biodegradation of Polycyclic Aromatic Hydrocarbons

Environmental Toxicology and Chemistry, 2003

Polycyclic aromatic hydrocarbon (PAH) contamination of the environment represents a serious threa... more Polycyclic aromatic hydrocarbon (PAH) contamination of the environment represents a serious threat to the health of humans and ecosystems. Given the human health effects of PAHs, effective and cost-competitive remediation technologies are required. Bioremediation has shown promise as a potentially effective and low-cost treatment option, but concerns about the slow process rate and bioavailability limitations have hampered more widespread use of this technology. An option to enhance the bioavailability of PAHs is to add surfactants directly to soil in situ or ex situ in bioreactors. Surfactants increase the apparent solubility and desorption rate of the PAH to the aqueous phase. However, the results with some synthetic surfactants have shown that surfactant addition can actually inhibit PAH biodegradation via toxic interactions, stimulation of surfactant degraders, or sequestration of PAHs into surfactant micelles. Biosurfactants have been shown to have many of the positive effects of synthetic surfactants but without the drawbacks. They are biodegradable and nontoxic, and many biosurfactants do not produce true micelles, thus facilitating direct transfer of the surfactant-associated PAH to bacteria. The results with biosurfactants to date are promising, but further research to elucidate surfactant-PAH interactions in aqueous environments is needed to lead to predictive, mechanistic models of biosurfactant-enhanced PAH bioavailability and thus better bioremediation design.

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Potential commercial applications of microbial surfactants

Applied Microbiology and Biotechnology, 2000

Surfactants are surface-active compounds capable of reducing surface and interfacial tension at t... more Surfactants are surface-active compounds capable of reducing surface and interfacial tension at the interfaces between liquids, solids and gases, thereby allowing them to mix or disperse readily as emulsions in water or other liquids. The enormous market demand for surfactants is currently met by numerous synthetic, mainly petroleum-based, chemical surfactants. These compounds are usually toxic to the environment and non-biodegradable. They may bio-accumulate and their production, processes and by-products can be environmentally hazardous. Tightening environmental regulations and increasing awareness for the need to protect the ecosystem have eectively resulted in an increasing interest in biosurfactants as possible alternatives to chemical surfactants. Biosurfactants are amphiphilic compounds of microbial origin with considerable potential in commercial applications within various industries. They have advantages over their chemical counterparts in biodegradability and eectiveness at extreme temperature or pH and in having lower toxicity. Biosurfactants are beginning to acquire a status as potential performance-eective molecules in various ®elds. At present biosurfactants are mainly used in studies on enhanced oil recovery and hydrocarbon bioremediation. The solubilization and emulsi®cation of toxic chemicals by biosurfactants have also been reported. Biosurfactants also have potential applications in agriculture, cosmetics, pharmaceuticals, detergents, personal care products, food processing, textile manufacturing, laundry supplies, metal treatment and processing, pulp and paper processing and paint industries. Their uses and potential commercial applications in these ®elds are reviewed.

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Reductive dechlorination of tetrachloroethene by a stepwise catalysis of different organohalide respiring bacteria and reductive dehalogenases

Biodegradation, 2011

The enrichment culture SL2 dechlorinating tetrachloroethene (PCE) to ethene with strong trichloro... more The enrichment culture SL2 dechlorinating tetrachloroethene (PCE) to ethene with strong trichloroethene (TCE) accumulation prior to cis-1,2dichloroethene (cis-DCE) formation was analyzed for the presence of organohalide respiring bacteria and reductive dehalogenase genes (rdhA). Sulfurospirillum-affiliated bacteria were identified to be involved in PCE dechlorination to cis-DCE whereas ''Dehalococcoides''-affiliated bacteria mainly dechlorinated cis-DCE to ethene. Two rdhA genes highly similar to tetrachloroethene reductive dehalogenase genes (pceA) of S. multivorans and S. halorespirans were present as well as an rdhA gene very similar to the trichloroethene reductive dehalogenase gene (tceA) of ''Dehalococcoides ethenogenes'' strain 195. A single strand conformation polymorphism (SSCP) method was developed allowing the simultaneous detection of the three rdhA genes and the estimation of their abundance. SSCP analysis of different SL2 cultures showed that one pceA gene was expressed during PCE dechlorination whereas the second was expressed during TCE dechlorination. The tceA gene was involved in cis-DCE dechlorination to ethene. Analysis of the internal transcribed spacer region between the 16S and 23S rRNA genes revealed two distinct sequences originating from Sulfurospirillum suggesting that two Sulfurospirillum populations were present in SL2. Whether each Sulfurospirillum population was catalyzing a different dechlorination step could however not be elucidated.

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$Research paper thumbnail of Synthesis of enhanced biosurfactant by Bacillus subtilis MTCC 2423 at 45°C by foam fractionation$

Synthesis of enhanced biosurfactant by Bacillus subtilis MTCC 2423 at 45°C by foam fractionation

Production of a lipopeptide surfactant in a 6.5-L batch fermentor was carried out using Bacillus ... more Production of a lipopeptide surfactant in a 6.5-L batch fermentor was carried out using Bacillus subtilis MTCC 2423 at 45°C. A good yield was obtained from sucrose (2%) substrate fermentation by continuous removal of the product by foam fractionation. The biosurfactant was recovered from collapsed foam by acid precipitation. The biosurfactant yield (4.5 g/L) was about 4.5 times higher than the yield (ca. 1 g/L) obtained by shake-flask fermentation. Surface activity of the collapsed foam was very high, and total surface activity was observed in the collapsed foam. The structural characterization of this biosurfactant produced at 45°C by the strain used in this study was recently reported. The biosurfactant was analyzed by thin-layer chromatography, infrared, 1H nuclear magnetic resonance, and mass spectroscopy and was found to be identical to surfactin, a lipopeptide surfactant.

Anaerobic electron acceptor amendment for aromatic pollutant biodegradation in sediments

Recent studies in our laboratory and others have demonstrated conclusively that polycyclic aromat... more Recent studies in our laboratory and others have demonstrated conclusively that polycyclic aromatic hydrocarbons (PAHs) and other unsubstituted aromatics are biodegradable under anaerobic conditions. This important result suggests that PAH contamination in anaerobic environments (such as sediments) may be more amenable to biological treatment than once thought. In previous work, we postulated that the availability of anaerobic electron acceptors limits degradation of aromatic pollutants in sediment systems and that amendment with anaerobic electron acceptors could be exploited to remediate contaminated sediments. We termed this the Anaerobic Electron Acceptor Amendment (AEAA) process. This research consisted of two phases: Phase 1 was to quantify nitrate and sulfate reduction rates for test sediments from the study sites. These experiments consisted of incubations with test sediments amended with varying levels of nitrate or sulfate and incubated under field temperatures. In Phase 2 we amended sediment from the field sites with nitrate or sulfate and incubated them in the field over time to assess electron acceptor, sediment organic matter (SOM), and pollutant transformations. Electron acceptor utilization and SOM degradation rates were measured at temperatures that represented a year round range: 4° C (winter), 15° C (fall/spring), and 22° C (summer) to determine the temperature dependence for electron acceptor utilization coupled to SOM degradation. Concurrent with this work, we developed a diffusive flux model of electron acceptor transport in sediments. These results were used to develop comparisons of cost effectiveness between the AEAA process and other treatment technologies. The diffusive flux model of nitrate and sulfate release from the microcosms showed that the process of bioturbation has a dramatic effect on the loss of electron acceptor out of the cap due to the greatly increased advective flux. Preliminary cost analysis suggests that SOM-degradation related electron acceptor utilization does not represent an insurmountable cost barrier. Costs based on utilization rates predicted in this study suggest that the AEAA process may be competitive with existing sediment treatment technologies.

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Production of biosurfactant at mesophilic and thermophilic conditions by a strain of Bacillus subtilis

Journal of Industrial Microbiology & Biotechnology, 1998

The ability of a Bacillus subtilis strain to grow and produce biosurfactant on different carbon a... more The ability of a Bacillus subtilis strain to grow and produce biosurfactant on different carbon and nitrogen sources under thermophilic conditions (45°C) was studied. The strain was able to reduce surface tension to 34 dynes cm−1 on 2% sucrose, and 32 dynes cm−1 on starch after 96 h of growth. The biosurfactant was stable at 100°C and within a wide pH range (3.0–11.0). Biosurfactant formation at mesophilic conditions (30°C) was also studied. The organism was able to produce the maximum amount of biosurfactant when nitrate ions were supplied as the nitrogen source. The potential application of the biosurfactant in oil recovery from desert oil fields, acidic and alkaline environments is demonstrated. The biosurfactant was identical to surfactin as confirmed by TLC and IR analysis.

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Biodegradation of soil‐applied endosulfan in the presence of a biosurfactant

Journal of Environmental Science and Health Part B-pesticides Food Contaminants and Agricultural Wastes, 1999

Biodegradation of endosulfan isomers in soil‐applied and flask‐coated conditions was studied, by ... more Biodegradation of endosulfan isomers in soil‐applied and flask‐coated conditions was studied, by an isolated bacterial coculture. The degradation in soil‐applied form was 20–30% slower than in flask‐coated condition. Addition of a biosurfactant, isolated from Bacillus subtilis MTCC 1427, enhanced the rate of biodegradation by 30–45% in both the conditions. It also mobilized the residual endosulfan towards biodegradation, that otherwise remains undegraded.

Recent applications of biosurfactants as biological and immunological molecules

Current Opinion in Microbiology, 2004

The interest in microbial biosurfactants has steadily increased during the past decade. In additi... more The interest in microbial biosurfactants has steadily increased during the past decade. In addition to the classical application as emulsifiers of hydrocarbons, they can be used in environmental protection, crude-oil recovery, food-processing industries and in various fields of biomedicine. Biosurfactants have several advantages over chemical surfactants including lower toxicity and higher biodegradability, and are likely to become molecules of the future in areas such as biomedicine and therapeutics. Here, we discuss the role and applications of biosurfactants (mainly glycolipids and lipopeptides) focusing on medicinal and therapeutic perspectives.

Effects of various nutritional supplements on biosurfactant production by a strain of Bacillus subtilis at 45°C

Journal of Surfactants and Detergents, 2002

Effects of various factors on growth and biosurfactant production by Bacillus subtilis MTCC 2423 ... more Effects of various factors on growth and biosurfactant production by Bacillus subtilis MTCC 2423 were studied. Sucrose (2%) and potassium nitrate (0.3%) were the best carbon and nitrogen sources. The addition of various metal supplements (magnesium, calcium, iron, and trace elements) greatly affected growth and biosurfactant production. The effect of the metal cations, used together, is greater than when they are used individually. The biosurfactant production increased considerably (almost double) by addition of metal supplements. Very high concentrations of metal supplements, however, inhibited biosurfactant production. Amino acids such as aspartic acid, asparagine, glutamic acid, valine, and lysine increased the final yield of biosurfactant by about 60%. The organism could produce biosurfactant at 45°C and within the pH range of 4.5–10.5. The biosurfactant was thermostable and pH stable (from 4.0 to 12.0). The capability of the organism to produce biosurfactant under thermophilic...

Electricity generation by thermophilic microorganisms from marine sediment

The search for microorganisms that are capable of catalyzing the reduction of an electrode within... more The search for microorganisms that are capable of catalyzing the reduction of an electrode within a fuel cell has primarily been focused on bacteria that operate mesobiotically. Bacteria that function optimally under extreme conditions are beginning to be examined because they may serve as more effective catalysts (higher activity, greater stability, longer life, capable of utilizing a broader range of fuels) in microbial fuel cells. An examination of marine sediment from temperate waters (Charleston, SC) proved to be a good source of thermophilic electrodereducing bacteria. Electric current normalized to the surface area of graphite electrodes was approximately ten times greater when sediment fuel cells were incubated at 60°C (209 to 254 mA/m 2) vs 22°C (10 to 22 mA/m 2). Electricitygenerating communities were selected in sediment fuel cells and then maintained without sediment or synthetic electroncarrying mediators in single-chambered fuel cells. Current was generated when cellulose or acetate was added as a substrate to the cells. The 16S ribosomal ribonucleic acid genes from the heavy biofilms that formed on the graphite anodes of acetate-fed fuel cells were cloned and sequenced. The preponderance of the clones (54 of 80) was most related to a Gram-positive thermophile, Thermincola carboxydophila (99% similarity). The remainder of clones from the community was most related to T. carboxydophila, or uncultured Firmicutes and Deferribacteres. Overall, the data indicate that temperate aquatic sediments are a good source of thermophilic electrode-reducing bacteria.

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An update on the use of unconventional substrates for biosurfactant production and their new applications

Applied microbiology and biotechnology, 2002

Biosurfactants are valuable microbial amphiphilic molecules with effective surface-active and bio... more Biosurfactants are valuable microbial amphiphilic molecules with effective surface-active and biological properties applicable to several industries and processes. Microbes synthesize them, especially during growth on water-immiscible substrates, providing an alternative to chemically prepared conventional surfactants. Because of their structural diversity (i.e., glycolipids, lipopeptides, fatty acids, etc.), low toxicity, and biodegradability, these molecules could be widely used in cosmetic, pharmaceutical, and food processes as emulsifiers, humectants, preservatives, and detergents. Moreover, they are ecologically safe and can be applied in bioremediation and waste treatments. They can be produced from various substrates, mainly renewable resources such as vegetable oils, distillery and dairy wastes, which are economical but have not been reported in detail. In this review, we report advances made in using renewable substrates for biosurfactant production and their newer applications.

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Advances in utilization of renewable substrates for biosurfactant production

AMB Express, 2011

Biosurfactants are amphiphilic molecules that have both hydrophilic and hydrophobic moieties whic... more Biosurfactants are amphiphilic molecules that have both hydrophilic and hydrophobic moieties which partition preferentially at the interfaces such as liquid/liquid, gas/liquid or solid/liquid interfaces. Such characteristics enable emulsifying, foaming, detergency and dispersing properties. Their low toxicity and environmental friendly nature and the wide range of potential industrial applications in bioremediation, health care, oil and food processing industries makes them a highly sought after group of chemical compounds. Interest in them has also been encouraged because of the potential advantages they offer over their synthetic counterparts in many fields spanning environmental, food, biomedical, petrochemical and other industrial applications. Their large scale production and application however are currently restricted by the high cost of production and by the limited understanding of their interactions with cells and with the abiotic environment. In this paper, we review the current knowledge and latest advances in the search for cost effective renewable agro industrial alternative substrates for their production.

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Microbial production of surfactants and their commercial potential

Microbiology and Molecular Biology …, 1997

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Synthesis of biosurfactants in extreme conditions

Applied microbiology and biotechnology, 1998

The interest in industrial biotechnology and its importance opens up challenging possibilities of... more The interest in industrial biotechnology and its importance opens up challenging possibilities of research in this area. Surfactants have long been among the most versatile of process chemicals. Their market is extremely competitive and manufacturers will have to expand their arsenal to develop products for the year 2000 and beyond. Biosurfactants are one of the most promising compounds in this regard. A review of the literature reveals that studies on oil-degrading and biosurfactantproducing microorganisms deal almost exclusively with their synthesis in moderate environments. Biosurfactants and the microbes that produce them have numerous industrial, medical and environmental applications, which frequently involve exposure to extremes of temperatures, pressure, ionic strength, pH and organic solvents. Hence, there is a continuing need to isolate microbes that are able to function under extreme conditions. There is an urgent need to explore these extremophiles for their ability to produce biosurfactants that can function suitably under the conditions prevailing when they are applied.

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Potential commercial applications of microbial surfactants

Applied Microbiology and Biotechnology, 2000

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Effects of various nutritional supplements on biosurfactant production by a strain of Bacillus subtilis at 45°C

Journal of Surfactants and Detergents

Detection of Bacillus anthracis Spores from Environmental Water Using Bioluminescent Reporter Phage

Journal of applied microbiology, Jan 18, 2017

We investigated the ability of a temperate B. anthracis reporter phage (Wβ::luxAB-2), which trans... more We investigated the ability of a temperate B. anthracis reporter phage (Wβ::luxAB-2), which transduces bioluminescence to infected cells, to detect viable spores from deliberately contaminated environmental water samples. Environmental water was inoculated with spores and assayed with Wβ::luxAB-2. Bioluminescent signals directly correlated with input phage and spore concentrations. A limit of detection of 10(1) and 10(2) CFU mL(-1) within 8 hours was achieved from pond and lake water, respectively. Detection was greatly simplified by minimizing sample processing steps without spore extraction. The complex endogenous microbial flora and salt content of brackish water challenged the assay, extending the detection time to 12 hours for a sensitivity of 10(2) CFU mL(-1) . Phage-mediated bioluminescence was strictly dependent on bacterial physiology, being significantly reduced in mid/late log phase cells. This was shown to be due to an inability of the phage to adsorb. The reporter phage...

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