Swaranjit Singh Cameotra

Potential commercial applications of microbial surfactants.

Abstract 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 effectively 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 effectiveness at extreme temperature or pH and in having lower toxicity. Biosurfactants are beginning to acquire a status as potential performance-effective molecules in various fields. At present biosurfactants are mainly used in studies on enhanced oil recovery and hydrocarbon bioremediation. The solubilization and emulsification 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 fields are reviewed.

Advances in utilization of renewable substrates for biosurfactant production

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.

Cost effective technologies and renewable substrates for biosurfactants’ production

Diverse types of microbial surface active amphiphilic molecules are produced by a range of microbial communities. The extraordinary properties of biosurfactant/bioemulsifier (BS/BE) as surface active products allows them to have key roles in various field of applications such as bioremediation, biodegradation, enhanced oil recovery, pharmaceutics, food processing among many others. This leads to a vast number of potential applications of these BS/BE in different industrial sectors. Despite the huge number of reports and patents describing BS and BE applications and advantages, commercialization of these compounds remain difficult, costly and to a large extent irregular. This is mainly due to the usage of chemically synthesized media for growing producing microorganism and in turn the production of preferred quality products. It is important to note that although a number of developments have taken place in the field of BS industries, large scale production remains economically challenging for many types of these products. This is mainly due to the huge monetary difference between the investment and achievable productivity from the commercial point of view. This review discusses low cost, renewable raw substrates, and fermentation technology in BS/BE production processes and their role in reducing the production cost.

Interaction of Al2O3 nanoparticles with Escherichia coli and their cell envelope biomolecules

The aim of this study is to investigate the antibacterial activity of aluminium oxide nanoparticles (Al2O3 NPs) against multidrug‐resistant clinical isolates of Escherichia coli and their interaction with cell envelope biomolecules.

Interaction of silver nanoparticles with Escherichia coli and their cell envelope biomolecules

The antibacterial effect of AgNPs was investigated by determining MIC/MBC and growth kinetics assay. The lowest MIC/MBC was found to be in the range of 11.25–22.5u2009µgu2009ml−1. The growth kinetics curve shows that 25u2009µgu2009ml−1 AgNPs strongly inhibits the bacterial growth. Confocal laser scanning electron microscopy (CLSM) shows that as the concentration of NPs increases, reduction in the number of cells was observed and at 50u2009µgu2009ml−1 of NPs, 100% death was noticed. Scanning electron microscopy (SEM) shows cells were severely damaged with pits, multiple depressions, and indentation on cell surface and original rod shape has swollen into bigger size. High resolution‐transmission electron microscopic (HR‐TEM) micrograph shows that cells were severely ruptured. The damaged cells showed either localized or complete separation of the cell membrane. The NPs that anchor onto cell surface and penetrating the cells may cause membrane damage, which could result in cell lysis. The interaction of AgNPs to membrane biomolecules; lipopolysaccharide (LPS) and L‐α‐phosphatidyl‐ethanolamine (PE) were investigated by attenuated total reflectance–fourier transform infrared (ATR–FTIR) spectroscopy. LPS and PE showed IR spectral changes after AgNPs exposure. The O‐antigen part of LPS was responsible for interaction of NPs through hydrogen bonding. The phosphodiester bond of PE was broken by AgNPs, forming phosphate monoesters and resulting in the highly disordered alkyl chain. The AgNPs‐induced structural changes in phospholipid may lead to the loss of amphiphilic properties, destruction of the membrane and cell leaking. The biomolecular changes in bacterial cell envelope revealed by ATR–FTIR provide a deeper understanding of cytotoxicity of AgNPs.

Phenyl aldehyde and propanoids exert multiple sites of action towards cell membrane and cell wall targeting ergosterol in Candida albicans

In the present study, two phyto-compounds phenyl aldehyde (cinnamaldehyde) and propanoid (eugenol) were selected to explore their modes of action against Candida albicans. Electron microscopy, flow cytometry and spectroscopic assays were employed to determine the targets of these compounds. Treatment of C. albicans (CA04) with sub-MICs of cinnamaldehyde (50xa0μg/mL) and eugenol (200xa0μg/mL) indicated multiple sites of action including damages to cell walls, cell membranes, cytoplasmic contents and other membranous structures as observed under electron microscopy. Concentration and time dependent increase in the release of cytoplasmic contents accompanied with change in extracellular K+ concentration was recorded. Exposure of Candida cells at 4u2009×u2009MIC of cinnaamldehyde and eugenol resulted in 40.21% and 50.90% dead cells, respectively as revealed by flow cytometry analysis. Treatment of Candida cells by cinnamaldehyde and eugenol at 0.5u2009×u2009MIC showed 67.41% and 76.23% reduction in ergosterol biosynthesis, respectively. The binding assays reflected the ability of compounds to bind with the ergosterol. Our findings have suggested that the membrane damaging effects of phenyl aldehyde and propanoids class of compounds is attributed to their ability to inhibit ergosterol biosynthesis and simultaneously binding with ergosterol. Indirect or secondary action of these compounds on cell wall is also expected as revealed by electron microscopic studies.

Gum arabic capped-silver nanoparticles inhibit biofilm formation by multi-drug resistant strains of Pseudomonas aeruginosa

Clinical isolates (nu2009=u200955) of Pseudomonas aeruginosa were screened for the extended spectrum β‐lactamases and metallo‐β‐lactamases activities and biofilm forming capability. The aim of the study was to demonstrate the antibiofilm efficacy of gum arabic capped‐silver nanoparticles (GA‐AgNPs) against the multi‐drug resistant (MDR) biofilm forming P. aeruginosa. The GA‐AgNPs were characterized by UV‐spectroscopy, X‐ray diffraction, and high resolution‐transmission electron microscopy analysis. The isolates were screened for their biofilm forming ability, using the Congo red agar, tube method and tissue culture plate assays. The biofilm forming ability was further validated and its inhibition by GA‐AgNPs was demonstrated by performing the scanning electron microscopy (SEM) and confocal laser scanning microscopy. SEM analysis of GA‐AgNPs treated bacteria revealed severely deformed and damaged cells. Double fluorescent staining with propidium iodide and concanavalin A‐fluorescein isothiocyanate concurrently detected the bacterial cells and exopolysaccharides (EPS) matrix. The CLSM results exhibited the GA‐AgNPs concentration dependent inhibition of bacterial growth and EPS matrix of the biofilm colonizers on the surface of plastic catheters. Treatment of catheters with GA‐AgNPs at 50u2009µgu2009ml−1 has resulted in 95% inhibition of bacterial colonization. This study elucidated the significance of GA‐AgNPs, as the next generation antimicrobials, in protection against the biofilm mediated infections caused by MDR P. aeruginosa. It is suggested that application of GA‐AgNPs, as a surface coating material for dispensing antibacterial attributes to surgical implants and implements, could be a viable approach for controlling MDR pathogens after adequate validations in clinical settings.

Antibiofilm efficacy of silver nanoparticles against biofilm of extended spectrum β-lactamase isolates of Escherichia coli and Klebsiella pneumoniae

The ability of bacteria to develop antibiotic resistance and colonize abiotic surfaces by forming biofilms is a major cause of medical implant-associated infections and results in prolonged hospitalization periods and patient mortality. Different approaches have been used for preventing biofilm-related infections in health care settings. Many of these methods have their own demerits that include chemical-based complications; emergent antibiotic-resistant strains, and so on. Silver nanoparticles (AgNPs) are renowned for their influential antimicrobial activity. We demonstrate the biofilm formation by extended spectrum β-lactamases-producing Escherichia coli and Klebsiella spp. by direct visualization applying tissue culture plate, tube, and Congo red agar methods. Double fluorescent staining for confocal laser scanning microscopy (CLSM) consisted of propidium iodide staining to detect bacterial cells and concanavalin A-fluorescein isothiocyanate staining to detect the exopolysaccharides matrix were used. Scanning electron microscopy observations clearly indicate that AgNPs reduced the surface coverage by E. coli and Klebsiella spp. thus prevent the biofilm formations. Double-staining technique using CLSM provides the visual evidence that AgNPs arrested the bacterial growth and prevent the exopolysaccharides formation. The AgNPs-coated surfaces effectively restricted biofilm formation of the tested bacteria. In our study, we could demonstrate the complete antibiofilm activity AgNPs at a concentration as low as 50xa0μg/ml. Our findings suggested that AgNPs can be exploited towards the development of potential antibacterial coatings for various biomedical and environmental applications. These formulations can be used for the treatment of drug-resistant bacterial infections caused by biofilms, at much lower nanosilver loading with higher efficiency.

Antibacterial potential of Al2O3 nanoparticles against multidrug resistance strains of Staphylococcusaureus isolated from skin exudates

To date very little studies are available in the literature on the interaction of Al2O3 nanoparticles with multidrug-resistant strains of Staphylococcusaureus. Considering the paucity of earlier reports the objective of present study was to investigate the antibacterial activity of Al2O3 NPs (<50xa0nm) against methicillin-resistant S. aureus and methicillin-resistant coagulase negative staphylococci by various methods. Al2O3 NPs were characterized by scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray diffraction. The MIC was found to be in the range of 1,700–3,400xa0μg/ml. Almost no growth was observed at 2,000xa0μg/ml for up to 10xa0h. SEM micrograph revealed that the treated cells were significantly damaged, showed indentation on cell surface and clusters of NPs on bacterial cell wall. HR-TEM micrograph shows disruption and disorganization of cell membrane and cell wall. The cell membrane was extensively damaged and, most probably, the intracellular content has leaked out. Al2O3 NPs not only adhered at the surface of cell membrane, but also penetrated inside the bacterial cells, cause formation of irregular-shaped pits and perforation on their surfaces and may also interact with the cellular macromolecules causing adverse effect including cell death. The data presented here are novel in that Al2O3 NPs are effective bactericidal agents regardless of the drug resistance mechanisms that confer importance to these bacteria as an emergent pathogen. Therefore, in depth studies regarding the interaction of Al2O3 NPs with cells, tissues, and organs as well as the optimum dose required to produce therapeutic effects need to be ascertained before we can expect a more meaningful role of the Al2O3 NPs in medical application.

Efficient biotransformation of herbicide diuron by bacterial strain Micrococcus sp. PS-1

A Gram-positive, Micrococcus sp. strain PS-1 capable of utilizing phenylurea herbicide diuron as a sole carbon source at a high concentration (up to 250xa0ppm) was isolated from diuron storage site by selective enrichment study. The taxonomic characterization with 16S rRNA gene sequencing (1,477xa0bp) identified PS-1 as a member of Micrococcus sp. It was studied for the degradation of diuron and a range of its analogues (monuron, linuron, monolinuron, chlortoluron and fenuron). The shake flasks experiments demonstrated fast degradation of diuron (up to 96% at 250xa0ppm within 30xa0h incubation) with the addition of small quantity (0.01%) of non-ionic detergent. The relative degradation profile by the isolate was in the order of fenuronxa0>xa0monuronxa0>xa0diuronxa0>xa0linuronxa0>xa0monolinuronxa0>xa0chlortoluron. Further, the biochemical characterization of catabolic pathway by spectroscopic and chromatographic techniques demonstrated that the degradation proceeded via formation of dealkylated metabolites to form 3,4-dichloroaniline (3,4-DCA). It was the major metabolite formed, associated with profound increase in degradation kinetics in presence of appropriate additive.