Effective bioreduction of hexavalent chromium–contaminated water in fixed-film bioreactors

Hexavalent chromium (Cr6+) contamination from a dolomite stone mine in Limpopo Province, South Africa, has resulted in extensive groundwater contamination. In order to circumvent any further negative environmental impact at this site, an effective and sustainable treatment strategy for the removal of up to 6.49 mg/. Cr6+ from the groundwater was developed. Laboratory-scale, continuous up-flow bioreactors were constructed to  evaluate reduction of Cr6+, with a residence time of 24 h, an efficiency  porosity of 44% and a flow rate of 1.5 m./min. Stoichiometrically balancing terminal electron acceptors in the feed water with a selected electron donor, directed reactor balance for complete Cr6+ reduction. The microbial  community shifted in relative dominance during operation to establish an optimal metal-reducing community, including Enterobacter cloacae,  Flavobacterium sp. and Ralstonia sp., which achieved 100% reduction. Evaluation after reactor termination with SEM-EDX and XRD confirmed the establishment of biofilm on the reactor matrix, as well as trivalent  chromium (Cr3+) precipitation within the reactor. Due to gravitational force, high concentrations of Cr3+ were found in the bottom third of the reactor. Based on the results from the laboratory investigation, a 24 000 .  fixed-film pilot bioreactor was designed and constructed at this site. Influent flow rates, electron donor injection and automated sampling were remotely controlled by a programmable logic controller (PLC). Similar to the laboratory column study, steady state conditions could be achieved and successful Cr6+ reduction was evident. This is the first up-scaled, effective demonstration of a biological chromium(VI) bioremediation system in South Africa.Keywords: Bioreduction, fixed-film reactor, hexavalent chromium, microbial diversit

The Role of Physical, Chemical, and Microbial Heterogeneity on the Field-Scale Transport and Attachment of Bacteria

A field-scale bacterial transport experiment was conducted at the Narrow Channel Focus Area of the South Oyster field site located in Oyster, Virginia. The goal of the field experiment was to determine the relative influence of subsurface heterogeneity and microbial population parameters on flow direction, velocity, and attachment of bacteria at the field scale. The field results were compared with results from laboratory-scale column experiments to develop a method for predicting field-scale bacterial transport. The field site is a shallow, sandy, unconfined, aerobic aquifer that has been characterized by geophysical, sedimentological, and hydrogeological methods. Comamonas sp. strain DA001 and a conservative tracer, bromide (Br), were injected into an area of high permeability for 12 hours. The Br and bacterial concentrations in the groundwater were monitored for 1 week at 192 sampling ports spaced over a 2-m vertical zone located from 0.5 to 7 m down-gradient of the injection well. The bacterial and Br plume was observed to move past 95 sampling ports. The densely characterized field site enabled the comparison of variations in DA001 transport to the aquifer properties. The velocity of the injected plume was correlated with geophysical estimates of hydraulic conductivity. The bacterial and Br plume appeared to follow flow paths not coincident with the hydraulic gradient but through a zone of higher permeability located off the flow axis. The amount of breakthrough of the bacteria was similar in both the high and low permeability layers with only a weak correlation between the observed hydraulic conductivity and amount of bacterial breakthrough. The uniformity in the observed attachment rates across varying grain sizes could be explained by heterogeneity of microbial properties within the single strain of injected bacteria. Application of colloid filtration theory to the field data indicated that variations in the microbial population were described by a lognormal distribution of the collision efficiency (a). Core-scale studies were used to predict the a distribution and field-scale transport distances of DA001. In sandy aquifers, physical heterogeneity may play a secondary role in controlling field-scale bacterial transport, and future research should focus on the microbial factors affecting transport

Transcriptome profiling defines a novel regulon modulated by the LysR-type transcriptional regulator MexT in Pseudomonas aeruginosa

The LysR-family regulator MexT modulates the expression of the MexEF-OprN efflux system in the human pathogen Pseudomonas aeruginosa. Recently, we demonstrated that MexT regulates certain virulence phenotypes, including the type-three secretion system and early attachment independent of its role in regulating MexEF-OprN. In this study, transcriptome profiling was utilized to investigate the global nature of MexT regulation in P. aeruginosa PAO1 and an isogenic mexEF mutant. Twelve genes of unknown function were highly induced by overexpressing MexT independent of MexEF-OprN. A well-conserved DNA motif was identified in the upstream regulatory region of nine of these genes and upstream of mexE. Reporter fusion analysis demonstrated that the expression of the genes was significantly induced by MexT in P. aeruginosa and a heterogenous Escherichia coli strain and that the conserved sequence was required for this induction. The conserved DNA motif was further characterized as the MexT binding site by site-directed mutagenesis and electrophoretic mobility shift assays. Genes containing this conserved regulatory sequence were identified across other Pseudomonas species, and their expression was activated by MexT. Thus, a novel regulon directly modulated by MexT, that includes but is independent of mexEF-oprN, has been identified

Flow cytometry for microbial sensing in environmental sustainability applications: current status and future prospects

Practical and accurate microbial assessment of environmental systems is predicated on the detection and quantification of various microbial parameters in complex matrices. Traditional growth-based assays, considered to be both slow and biased, are increasingly being replaced by optical detection methods such as flow cytometry. Flow cytometry (FCM) offers high-speed multi-parametric data acquisition, compatibility with current molecular-based microbial detection technologies, and is a proven technology platform. The unique technical properties of flow cytometry have allowed the discrimination of bacteria based on nucleic acid staining, microbial identification based on genomic and immunologic characteristics, and determination of cell viability. For this technology to achieve the ultimate goal of monitoring the microbial ecology of distributed systems, it will be necessary to develop a fully functional, low cost, and networkable microsystem platform capable of rapid detection of multiple species of microorganisms simultaneously under realistic environmental conditions. One such microsystem, miniaturized and integrated in accordance with recent advances in micro-electro-mechanical systems technology, is named the Micro Integrated Flow Cytometer. This manuscript is a minireview of the current status and future prospects for environmental application of flow cytometry in general, and micro-flow cytometry in particular.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75610/1/j.femsec.2004.01.014.pd

Electroosmosis modulated peristaltic biorheological flow through an asymmetric microchannel : mathematical model

A theoretical study is presented of peristaltic hydrodynamics of an aqueous electrolytic nonNewtonian Jeffrey bio-rheological fluid through an asymmetric microchannel under an applied axial electric field. An analytical approach is adopted to obtain the closed form solution for velocity, volumetric flow, pressure difference and stream function. The analysis is also restricted under the low Reynolds number assumption and lubrication theory approximations. Debye-Hückel linearization (i.e. wall zeta potential ≤ 25mV) is also considered. Streamline plots are also presented for the different electro-osmotic parameter, varying magnitudes of the electric field (both aiding and opposing cases) and for different values of the ratio of relaxation to retardation time parameter. Comparisons are also included between the Newtonian and general non-Newtonian Jeffrey fluid cases. The results presented here may be of fundamental interest towards designing lab-on-a-chip devices for flow mixing, cell manipulation, micro-scale pumps etc. Trapping is shown to be more sensitive to an electric field (aiding, opposing and neutral) rather than the electro-osmotic parameter and viscoelastic relaxation to retardation ratio parameter. The results may also help towards the design of organ-on-a-chip like devices for better drug design