No description available.

Species of Arthrobacter luteus, also known as Oerskovia xanthineolytica, can utilise yeast cells as a growth substrate. This unusual ability is due to the secretion of a battery of hydrolytic enzymes which degrade the yeast cell wall and thus lyse the cells. Although many hydrolytic enzymes are important in the degradation of the yeast cell wall, the key activities are endo beta--l,3-glucanases. In order to characterise components of the yeast lytic system and the genetic organisation of this little-understood organism, a molecular cloning approach was adopted. Large clones expressing beta-1,3-glucanase were isolated from a library of A. luteus DNA constructed in the positive selection vector pKGW. By a combination of subcloning, restriction mapping and Southern analysis, it was determined that the clones contained virtually the same inserts. Additional subcloning, transposon mutagenesis, deletion mapping and nucleotide sequencing were used to identify at least one glucanase gene. The predicted protein product had a molecular weight of about 46 kD. When the gene was expressed in a number of in vivo and vitro systems including E. coli minicells and a Streptomyces coupled transcription/translation system, the protein observed had a similar molecular weight. Furthermore, when the protein was produced in E. coli and run on activity stained gels, the beta-glucanase activity co-migrated with the major glucanase of A. luteus. In addition the E. coli-produced glucanase had the ability to cause limited lysis of yeast.

No description available.

During the past decade there has been an explosion in the probiotic industry due to an increase in concern for health. It is well known that these probiotic products offer consumers numerous health benefits and that viability of cultures in these products need to be maintained at high levels. It is therefore important to test for antimicrobial compounds or substances that may come into contact with probiotics and thereby negatively affect and decrease their viability. Garlic (Allium sativum) has been used as a natural medicinal remedy for thousands of years and research has shown that it has antimicrobial activity against a wide variety of microorganisms. Although it has been tested against numerous pathogenic microorganisms, there have been few studies on its effect on beneficial bacteria, specifically probiotic Bifidobacterium species. A great amount of work and money is put into preparing probiotic products with sufficient numbers of viable bacterial cells. All these are devoted to ensure that the consumers seize the optimal purported health benefits from probiotic cultures incorporated within the different products. Hence it is necessary to recognize any compound or substance that poses a threat to viability of these probiotic cells, thereby rendering them ineffective. Therefore, the current study aimed at determining whether garlic had any antibacterial activity towards selected Bifidobacterium spp. In vitro studies revealed that garlic has an inhibitory effect on these specific probiotic bacteria. The disk diffusion assay revealed antibacterial activity of garlic preparations characterized by inhibition zones ranging from 13.0 ± 1.7 to 36.7 ± 1.2 mm. Minimum inhibitory concentration (MIC) values for garlic clove extract ranged from 75.9 to 303.5 mg/ml (estimated to contain 24.84 to 99.37 μg/ml allicin) while the minimum bactericidal concentration (MBC) ranged from 10.24 to 198.74 μg/ml xix allicin. Susceptibility of the tested Bifidobacterium species to garlic varied between species as well as between strains even within a small numbers of the tested bifidobacteria. Among the tested Bifidobacterium spp., B. bifidum LMG 11041 was most susceptible to garlic, whereas B. lactis Bi-07 300B was the most resistant. These results were contrary to what has been generally published in literature, that garlic selectively kills pathogens without negatively affecting beneficial bacteria. Garlic clove, garlic powder, garlic paste and garlic spice showed varying degrees of potency, with fresh garlic clove extract and garlic paste extract having the highest and lowest antibifidobacterial activity, respectively. It became necessary to investigate the actual antibacterial mechanism of action of garlic on Bifidobacterium spp., upon realization that its extracts inhibits growth of or kills some of these bacteria, whose contribution to health and well being of consumers is to a large extent dependent on their viability. This was determined by using scanning electron microscopy (SEM) and Fourier-transform infrared (FT-IR) spectroscopy. Scanning electron microscopy was used to investigate the effect of garlic on the morphology and cell surface properties of the tested strains while FT-IR spectroscopy was used to determine any biochemical changes taking place in garlic-treated bifidobacteria. Scanning electron microscopy showed various morphological changes such as cell elongation, distorted cells with bulbous ends and cocci-shaped cells. Behavioural changes were also observed such as swarming of cells was also observed. FT-IR spectra confirmed that garlic damaged Bifidobacterium cells by inducing biochemical changes within the cells. It identified some of the main targets sites of garlic on bifidobacteria, mainly, the nucleic acids and fatty acids (lipids) in the cell membrane. Flow cytometry analysis was used to determine the level at which the garlic decreased the viability of Bifidobacterium cells as well as the extent of damage induced by the garlic. Results revealed a drop in viability with associated decrease in stainability of some the cells, for all strains upon treatment with garlic clove extract. The inability of cells to be stained by nucleic acid stains, hence presence of cells referred to as ‘ghost cells’, has been associated with extensive damage and lysis of cellular membranes resulting in loss nucleic acids. Interestingly, re-inoculation of the cells analysed by flow cytometry into a fresh growth medium and their subsequent reanalysis using the same technique showed an increase in percentage of viable cells and a decrease in percentages of damaged, unstained and dead cells. This suggested that injured cells were able to recover and regress to their active state. Therefore, Bifidobacterium cells exposed to sub lethal amounts of garlic can repair any damage and regrow. However, it was not determined how long active compounds of garlic remain stable within the gastrointestinal tract. This study is the first, according to our knowledge, to show that garlic exhibits antibacterial activity against beneficial bacteria specifically, probiotic bifidobacteria. Furthermore, the results revealed that the mechanism of action of garlic towards bifidobacteria is similar to that which was reported for pathogenic bacteria. Bacterial death and growth inhibition occurs due to damage to the fatty acids/lipids in the cell membrane, modification of the nucleic acids (DNA and RNA). This study is of significant importance to consumers, medical practitioners as well as to the probiotic industry. It suggests that if garlic comes into contact with probiotic bifidobacteria, they die and thus become unable to deliver the promised health benefits to the consumers. Therefore, consumers should be advised against ingestion of probiotic products and garlic simultaneously, as this study reveals that garlic does indeed inhibit some probiotic Bifidobacterium spp. The probiotic industry should also consider including this information on their product labels to make consumers aware of this fact. Failure to include this information may lead to market deterioration due to loss of interest in the products as soon as consumers realize they do not get their money’s worth from the products. Lastly, medical practitioners should also be made aware of this as they also prescribe probiotics to patients for various health reasons. The effect of food matrices on the antibacterial effects, as well as determination of how long the active compounds of garlic remain within the gastrointestinal tract, in relation to levels of garlic ingested will confirm whether indeed there is concern. But for now, in light of results of the current study, caution needs to be taken in simultaneous use of probiotics and garlic, until further testing indicates otherwise. / Dissertation (MSc)--University of Pretoria, 2013. / gm2014 / Microbiology and Plant Pathology / unrestricted

Bacteriophages affect bacterial evolution, pathogenesis and global nutrient cycling. They are also the most numerous and diverse group of biological entities on the planet [1, 2, 3, 4, 5, 6]. Members of the Lambda phage family share a similar genetic organization and control early gene expression by suppressing transcription, a process known as antitermination. Transcription antitermination in Lambda is mediated by a phage-encoded protein whereas in lambdoid phage HK022, antitermination is mediated by a phage-encoded RNA molecules. Recent results suggest that another bacteriophage called HK639 also appears to use RNA-mediated antitermination. To characterize this newly identified phage we generated site directed mutations and identified where the phage integrates into the chromosome of its bacterial host.

Water pollution, especially caused due to the indiscriminate release of heavy metals as a result of anthropogenic activities is a major concern worldwide. Chromium, a heavy metal, regardless of its commercial importance has found to be a potent water pollutant. Chromium generally exist as hexavalent (Cr(VI)) and trivalent (Cr(III)) chromium in the environment. Cr(VI) is ascertained to be more toxic compared to Cr(III) and the former is identified as a carcinogen by the World Health Organisation (WHO). Some of the conventional methods currently available for chromium pollution mitigation are not cost effective and most importantly lead to secondary pollution in the form of sludge. Bioremediation is a promising alternative technique which is also ecofriendly. The bioremediation process utilises biological materials such as microorganisms and agricultural byproducts. Biosorption is a bioremediation process that is a surface related phenomenon involving adsorption of contaminant chromium ions onto the binding sites of the biosorbents. In addition to the efforts made to the remediation of chromium, continuous monitoring of chromium contaminant level in polluted water bodies becomes imperative. The present research study encompasses findings related to bioremediation and detection of chromium ions using bacterial cells. The first part of the dissertation involves studies pertaining to the bioremediation of chromium ions using different bacterial strains as biosorbent. For the study, bacterial strains procured from a microbial culture collection bank as well as those isolated from chromium polluted water samples collected from an industrial site were assessed for their ability to remediate chromium. The next aim of the study was to elucidate the mechanisms involved in the bioremediation of chromium ions by the bacterial cells for which the different characterisation methods such as, Fourier Transform Infrared (FTIR) spectroscopy, Energy Dispersive Spectroscopy (EDS), X-ray Photoelectron Spectroscopy (XPS) and zeta potential measurements which enabled to throw light on the reactions occurring at the bacterial cell surface-chromium solution interface. The later part of the study examines the capability of the bacterial strains used in the bioremediation studies as sensors for the detection of Cr(VI) and Cr(III) ions by adopting electroanalytical techniques, such as, Cyclic Voltammetry (CV) and Cathodic Stripping Voltammetry (CSV), wherein a microbe-modified Carbon Paste Electrode (CPE) was used as the working electrode in a typical three electrode electrochemical cell with Saturated Calomel Electrode (SCE) and platinum wire used as the reference and auxiliary electrodes respectively. The key objectives of the present study are as follows: (i) To study the bioremediation of Cr(VI) and Cr(III) ions present in aqueous solutions using two bacterial strains procured from a microbial culture collection bank as biosorbents. The bacterial strains used were Corynebacterium paurometabolum (Cp), a Gram positive bacterium and Citrobacter freundii (Cf), a Gram negative bacterium. The various factors affecting the biosorption process are to be investigated. (ii) To isolate and identify bacterial strains from water samples collected from chromium contaminated mining site in Sukinda, Odisha, India, by adopting appropriate microbiological and molecular biological procedures. (iii) To study the various factors affecting bioremediation of Cr(VI) using the mine isolates (Chromobacterium sp. (Cb) and Sphingopyxis sp. (Sp)) both Gram negative, as biosorbents. (iv) To elucidate the mechanisms adopted by the chosen bacterial cells in the bioremediation of chromium. (v) To develop an electrochemical-microbial sensor by modifying the Carbon Paste Electrode (CPE) using the bacterial strains for the detection of Cr(VI) and Cr(III) ions present in aqueous solutions. (vi) To determine the capability of the developed sensor in the detection of Cr ions in mine water samples collected from Sukinda chromite mine in Odisha, India. (vii) To elucidate the mechanisms occurring at the bio-modified electrode–solution interface. A compendious description of the findings from the present work is given below: The capability of two bacterial strains procured from a microbial culture collection bank (MTCC), Corynebacterium paurometabolum (Gram positive bacterium) and Citrobacter freundii (Gram negative bacterium) as biosorbents for Cr (VI) and Cr(III) ions was assessed. Further, it became of interest to translate the studies related to bioremediation to an industrial situation. For this, bacterial strains were isolated from chromium contaminated water samples collected from surface water of Sukinda chromite mine in Odisha, India. Based on detailed microbiological and molecular biological protocols, two strains of bacteria were identified and characterised as Chromobacterium sp. and Sphingopyxis sp. The bioremediation efficiency of the strains was evaluated taking into consideration the various factors such as effect of contact time of bacterial cells with the chromium ions, pH of the chromium ion solution, biomass loading and initial chromium ion concentration. The Cr(VI) biosorption efficiency obtained for C. freundii was found to be about 59 %, followed by Sphingopyxis sp. and C. paurometabolum ≈ Chromobacterium sp. in the range of 50 % to 55 %. Subsequent to interaction of the bacterial cells with the Cr(VI) solution, the residual chromium was found to be in the form of Cr(III) ions. Hence, complete bioremediation of Cr(VI) could be achieved in terms of both biosorption and bioreduction processes using all the bacterial strains. It was found that the bioreduction process occurring in conjunction with the biosorption process resulted in nil concentration of Cr(VI) ions in the bulk solution. Similarly, studies related to bioremediation of Cr(III) using C. paurometabolum and C. freundii bacterial strains were also performed with higher biosorption efficiency achieved for the former, 50 % compared to 30 % obtained for C. freundii bacterial cells. The bioremediation of Cr(III) ions by the bacterial cells is achieved by the biosorption process. Biosorption of Cr ions by all the bacterial strains were found to follow a typical Langmuirian behaviour. The bioremediation process by the bacterial strains was also evaluated using suitable kinetic models and the results indicated that the bioremediation of Cr(VI) and Cr(III) by C. paurometabolum and C. freundii respectively followed pseudo first order kinetics, while the bioremediation of Cr(VI) by C. freundii, Chromobacterium sp. and Sphingopyxis sp. followed pseudo second order kinetics. It becomes of importance to ascertain the mechanisms of bioremediation of chromium ions by the bacterial cells and for this, different characterisation methods were adopted that helped in deducing the reactions occurring at the bacterial cell surface-chromium solution interface. The involvement of chemical forces in the bioremediation process was corroborated by the achievement of only partial desorption of chromium ions from the biosorbed bacterial cells. This was further confirmed by the Gibbs free energy (∆G) values, which were found to be in the range of -25 to -30 kJ/mol. FTIR spectral studies provided evidence in support of the key functional groups present on the bacterial cell surface such as, –OH, -COOH and –NH, which facilitated the binding with chromium. The EDS data for chromium biosorbed bacterial cells showed peaks corresponding to chromium, thereby confirming the binding of chromium by the bacterial cells. The redox state of chromium bound on the bacterial cell surface was determined with the help of XPS analysis. In the Cr2p XPS spectra obtained for the bacterial cells interacted with Cr(VI), it was interesting to observe a peak corresponding to Cr(III) in addition to Cr(VI), unequivocally indicating that the Cr(III) formed via bioreduction was not only released into the bulk solution but also got biosorbed on the bacterial cell surface. Apparent shifts in the binding energy values for the bacterial cells interacted with chromium were observed in the spectra recorded corresponding to C1s, O1s, N1s, P2p and S2p as compared to the spectra obtained for the bacterial cells alone. This attests to the fact that the functional groups corresponding to the elements mentioned are involved in chemical interaction with the chromium ions or are involved in the donation of electrons to bring about reduction of Cr(VI) to the less toxic Cr(III). The variation in the charge of the bacterial cell surface before and after interaction with chromium ions was monitored by performing zeta potential measurements as a function of pH. The surface charge of the bacterial cells alone was found to be negative over a wide range of pH. Subsequent to interaction of the bacterial cells with the negatively charged oxyanions of Cr(VI) ions, the surface charge was observed to be less electronegative, which further confirmed the binding of the positively charged Cr(III) ions formed via bioreduction on the bacterial cell surface. Similar results were also observed in the case when cells were allowed to interact with Cr(III) ions. The shifts in the iso-electric point for bacterial cells interacted with chromium ions further testified to the involvement of chemical binding forces in the bioremediation process. The findings obtained from the different characterisation methods enabled in understanding the reactions that are occurring at the bacterial cell surface-Cr solution interface. Initially, biosorption via electrostatic interaction of negatively charged oxyanions of Cr(VI) with the positively charged amino groups present on the bacterial cell surface takes place. Subsequent to the biosorption of Cr(VI) ions, the adjacent electron donating functional groups containing ligands present on the bacterial cell surface reduce Cr(VI) to Cr(III) via the reactions shown below: Bioreduction involving –OH group Bioreduction involving –SH group It can be seen that, the reactions involving bioreduction of Cr(VI) in the form of chromate oxyanion to Cr(III) involving hydroxyl and thiol group present on the bacterial cell surface result in the formation of intermediates, chromate-oxy and chromate-thio ester respectively. These intermediates facilitate the transfer of electrons from oxygen/sulphur donor centers to Cr(VI) acceptor molecule, thereby resulting in the reduction of Cr(VI) to Cr(III). The Cr(III) ions thus formed are then either released into the bulk solution or get complexed with the binding groups present on the bacterial cell surface. The next objective was to explore the potential of bacterial strains as sensors for the detection of Cr(VI) and Cr(III) ions. The chromium ions were detected using CV and CSV, both of which are electroanalytical techniques. For this, CPE was coated with the bacterial strains, C. paurometabolum, C. freundii, Chromobacterium sp. and Sphingopyxis sp., and the modified electrode was used as the working electrode in a typical three electrode electrochemical cell. These biosensors developed using each of the aforementioned strains resulted in a ~ 2 to 2.5 fold improved performance compared to the bare CPE for the detection of Cr(VI) ions, due to the binding ability of the various functional groups present on the bacterial cell surface. The lower limit of detection (LLOD) obtained for Cr(VI) and Cr(III) ions using CV technique was found to be 1x10-4 M and 5x10-4 M respectively. The LLOD was further improved to 1x10-9 M and 1x10-7 M for Cr(VI) and Cr(III) respectively using CSV. From the voltammograms obtained, it was postulated that the different functional groups present on the bacterial cell surface facilitate the detection of the chromium ions. Additionally, the developed microbial sensors were also found to be capable of detecting Cr(VI) ions in mine water samples collected from Sukinda chromite mine Odisha, India. In summary, the mechanisms of bioremediation of toxic Cr(VI) ions have been delineated as comprising of both biosorption and bioreduction processes. The residual Cr(VI) concentration subsequent to the treatment of the Cr(VI) aqueous solution with the bacterial cells was found to be nil, which meets the regulatory limit of 0.05 mg L-1 put forward by the US-Environmental Protection Agency (EPA) for a safe effluent discharge. Moreover, it has also been demonstrated that the chosen bacterial strains could be used as sensors for the detection of upto nanomolar concentration of Cr(VI) ions, under optimum conditions.

Heavy metals are released into the environment either by natural processes or by anthropogenic activities. Industries such as leather tanning, textiles, metallurgical, electroplating and mining activities discharge the chromium along with other heavy metals, which causes water pollution and environmental degradation. There are many conventional methods to overcome this problem such as chemical precipitation, ion exchange, reverse osmosis, etc but, these methods have certain drawbacks like generation of secondary sludge, inefficient removal of metal ions of low concentration, high cost etc. To overcome these limitations by conventional methods, an environmental friendly method, namely bioremediation has been adopted. Bioremediation uses microorganisms, biodegradable industrial wastes, or plants to mitigate this problem. In this investigation, bacterial strains have been isolated from the soil and water samples collected from a chromite mine in Karnataka. The capability of these bacterial strains have been assessed to remediate Cr (VI) in batch experiments in order to achieve the prescribed standards of regulatory agencies, and to elucidate the mechanisms of bioremediation of Cr (VI). Additionally, using these bacterial strains, biosensors have been developed to detect Cr (VI) ions in the solution by electroanalytical techniques. The major objectives of this research investigation are: a) Isolation, characterization and identification of bacterial strains from water and soil samples obtained from a chromite mine in Karnataka. b) To study the ability of three isolated bacterial strains namely Arthrobacter sp, Exiguobacterium sp. and Micrococcus sp. to remediate Cr (VI) during growth in media, amended with different concentrations of Cr (VI) c) Delineation of the probable mechanisms of bioremediation of Cr (VI) by three bacterial strains with the aid of proteomic and metabolomic studies d) Optimization of factors influencing the bioremoval of Cr (VI) using the isolated bacterial strains as biosorbents in batch experiments. c) Elucidation of mechanisms of bioremoval of Cr (VI) at the microbe – metal interface for all three bacterial strains, adopting characterization techniques like FTIR, XPS, SEM – EDS and zeta potential measurements. d) Micrococcus sp. was chosen for the fabrication of biomodified carbon paste electrode (CPE) to sense the Cr (VI) ions using voltammetric techniques, namely cyclic voltammetry (CV) and differential pulse cathodic stripping voltammetry (DPCSV). The salient findings of this research work are highlighted as follows: Firstly, bioremediation experiments were carried out using the bacterial strains isolated from soil and water samples collected from the chromite mines of Mysore Minerals Limited, Hassan district, Karnataka, India. Initially, the characterisation of the isolated bacterial strains were carried out with respect to their biochemical aspects, antibiotic susceptibility, morphology using scanning electron microscopy and cell wall nature by Gram’s staining. The identification of the three isolated bacterial strains were accomplished by 16S rRNA method and the three bacterial strains have been identified as Arthrobacter sp., Exiguobacterium sp. and Micrococcus sp.. The experiments were conducted to assess the potential of the isolated bacterial strains namely, Arthrobacter sp., Exiguobacterium sp. and Micrococcus sp., for the remediation at two different concentrations of 10 mg/L and 30 mg/L of Cr (VI) ions, during cell growth i.e. using metabolically active cells of bacteria. It was found that the three bacterial strains could bioreduce toxic Cr (VI) to the less toxic Cr (III) form, by 95% to 99%, within a time span of 12 h to 120 h. In the experiment with sulphate as the competitive ion in the growing mode of the bacterial strains Arthrobacter sp., Exiguobacterium sp. and Micrococcus sp., the percentage bioreduction of Cr (VI) to Cr (III) was not hampered. Scanning electron microscopic studies on the bacterial cells of Arthrobacter sp., Exiguobacterium sp. and Micrococcus sp., before and after interaction with Cr (VI) showed the morphological changes after interaction with Cr (VI), as an adaptive strategy to counter the toxic effect of Cr (VI). Further, to elucidate the mechanisms of bioreduction of Cr (VI) to Cr (III) by the three bacterial strains, the proteins and metabolites were isolated from the pristine bacterial cells and Cr (VI) interacted bacterial cells. The proteins were isolated from different parts of the cells and assessed for the differential expression of proteins under Cr (VI) stress. It was found that, seven differentially expressed protein bands were observed on SDS PAGE profile of Arthrobacter sp. interacted with Cr (VI), from the soluble protein isolated from the crude extract, devoid of cell membrane. A single band of differentially expressed protein was observed in the extracellular secretion in Exiguobacterium sp. and in the case of Micrococcus sp. four differentially expressed proteins were observed in the membrane fraction of proteins. The mass spectrometry data of the differentially expressed proteins were used to identify the probable protein candidates using MASCOT search in NCBIr database. It was found that some of these proteins were a class of transport proteins and a few belong to the reactive oxygen species scavengers. These findings suggested that the bioreduction of Cr (VI) to Cr (III) involved the efflux mechanism and ROS scavenger production, to resist the toxicity of Cr (VI). The metabolite concentration profile was studied for the all three bacterial cells in the absence and presence of Cr (VI) using NMR spectroscopy. The results of this study showed an increase and decrease in the concentration of various metabolite components after interaction with Cr (VI), and this was observed in all the three bacterial strains. Some of the metabolites identified using Chenomx 8.1 metabolite library, were found to be osmoprotectants like betaine, proline etc, which combat the stress of Cr (VI). Therefore, the overall bioremediation of Cr (VI) by metabolically active bacterial cells is through bioreduction of toxic Cr (VI) to the less toxic Cr (III) form and the resistance mechanisms to overcome the toxic effect of Cr (VI) is by the efflux mechanism, production of osmoprotectants and expression of ROS scavengers. In the third part of investigation, the bioremoval of Cr (VI) ions in batch experiments using metabolically inactive cells as biosorbents, for all the three bacterial strains, were studied. The bioremediation efficiency of each bacterial strain was evaluated, considering the various parameters like effect of contact time of bacterial cells with the Cr (VI) ions, pH of Cr ion solution, biomass loading and initial concentration of Cr (VI) ion. The Cr (VI) biosorption efficiency obtained for the bacterial strains Arthrobacter sp., Exiguobacterium sp. and Micrococcus sp. was found to be 93 %, 85 % and 100 % respectively. Apart from the biosorption of Cr (VI) by bacterial cells, the residual Cr was found to be in the form of Cr (III) ions. Therefore, complete bioremoval of Cr (VI) ions could be achieved as a combined process of biosorption and bioreduction, for all three bacterial strains, meeting the acceptable limits prescribed for Cr (VI) ion for drinking water, by regulatory agencies i.e. 0.05 mg/L of Cr (VI) ions. The biosorption of Cr ions by all the three bacterial strains were found to follow a typical Langmurian behaviour. The bioremediation process by the bacterial strains was also evaluated using suitable kinetic models and the results indicated that the bioremoval of Cr (VI) by Arthrobacter sp., Exiguobacterium sp. and Micrococcus sp. followed pseudo second order kinetics. The next aim was to ascertain the mechanism of bioremoval of Cr (VI) ions by the metabolically inactive cells. For this, different characterisation techniques were adopted that aided in the elucidation of reactions occurring at the interface of bacterial cell surface and Cr solution. The nature of interacting forces in bioremoval process was found out by desorption studies, and it was observed that only partial desorption of Cr ions was achieved from the biosorbed bacterial cells. This was further confirmed, by calculation of Gibbs free energy and the values were found to be in the range of – 25 to -32 kJ/mol, thus indicating that the process of bioremoval of Cr (VI) ions by the bacterial cells, is by chemisorption process. The variation in the charge of the bacterial cell surface, before and after interaction with chromium ions, was studied by performing zeta potential measurements as a function of pH. The surface charge of the bacterial cells alone was found to be negatively charged over a wide range of pH. Subsequent to interaction of the bacterial cells with the negatively charged oxyanions of Cr (VI) ions, the surface charge was observed to be less electronegative, which further confirmed the binding of the positively charged Cr (III) ions, formed via bioreduction on the bacterial cell surface. FTIR spectral studies revealed the functional groups involved, in bioremoval of Cr ions, present on bacterial cell surface. The functional group facilitating the bioremoval of Cr ions are –NH, -COOH and phosphate. EDS studies confirmed the Cr peak for the bacterial cells interacted with Cr ions. The oxidation state of Cr ion bound to the bacterial cell surface was determined with the help of XPS analysis. It was interesting to observe the Cr (III) peaks along with their Cr (VI) peaks. These studies provided evidence in support of the bioreduction of Cr (VI) to Cr (III) and biosorption of bioreduced Cr (III) ions onto the surface of bacterial cells, apart from the fraction present in bulk solution. The next objective was to assess the potential of Micrococcus sp. as sensor for the detection of Cr (VI) ions, using electroanalytical techniques such as, cyclic voltammetery (CV) and differential pulse cathodic stripping voltammetry (DPCSV). For this, Carbon Paste Electrode (CPE) was coated with the bacterial strain namely, Micrococcus sp and the modified electrode was used as the working electrode in a three electrode system. The developed biomodified electrode showed an approximately 3-fold increase in the sensing of Cr (VI) ion in comparison with the unmodified electrode CPE, which is attributed to the binding of Cr (VI) ions to functional groups present on the bacterial cell surface. The lower limit of detection obtained for Cr (VI) ions using CV was found to be 1 x10-4 M. The lower limit of detection was improved to 1 x 10-9 M of Cr (VI) using DPCSV.