Inhibition of biological TCE and sulphate reduction in the presence of iron nanoparticles.

Iron (Fe) nanoparticles are increasingly being employed for the remediation of Chlorinated Aliphatic Hydrocarbon (CAH) contaminated sites. However, these particles have recently been reported to be cytotoxic to bacterial cells, and may therefore have a negative impact on exposed microbial communities. The overall objective of this study was to investigate the impact of Fe nanoparticles on the biodegradation of CAHs by an indigenous dechlorinating bacterial community. Also, to determine the most appropriate combination and/or application of bimetallic (Ni/Fe) nanoparticles and dechlorinating bacteria for the remediation of CAH contaminated sites. Addition of Fe nanoparticles to groundwater collected from a CAH contaminated site in Derby, UK, led to a decrease in the oxidation-reduction potential (ORP) and an increase in pH. The biological degradation rate of TCE was observed to progressively decrease in the presence of increasing Fe nanoparticle concentrations; which ranged from 0.01 to 0.1 gL(-1), and cease completely at concentrations of 0.3 gL(-1) or above. Concentrations greater than 0.3 gL(-1) led to a decline in viable bacterial counts and the inhibition of biological sulphate reduction. The most appropriate means of combining bimetallic (Ni/Fe) nanoparticles and indigenous dechlorinating bacteria was to employ a two step process: initially stimulating the biodegradation of TCE using acetate, followed by the addition of bimetallic nanoparticles to degrade the remaining cis-1,2-DCE and VC.

Optimization of nano-scale nickel/iron particles for the reduction of high concentration chlorinated aliphatic hydrocarbon solutions.

The use of nano-scale particles as a means of environmental remediation still provides a comparatively novel approach for the treatment of contaminated waters. The current study compares the reactivity of micro-scale Fe, nano-scale Fe and nano-scale Ni/Fe (nickel/iron) particles specifically for dechlorination of solutions containing 350 mg L(-1) of TCE (concentration measured at a contaminated site in Derbyshire, UK). The results indicated that employing 1 g L(-1) of reactive material for dechlorination in the monometallic form (both micro- and nano-scale) exhibited very little reduction capability compared with the bimetallic Ni/Fe nano-scale particles, containing 28.9% Ni (in molar), which achieved complete dechlorination of the TCE in solution within 576 h. Experiments were also performed to determine the optimum bimetallic composition of the Ni/Fe particles for TCE reduction. This revealed that 3.2% Ni was the optimum Ni/Fe molar ratio for both maximum dehalogenation performance and minimum release of Ni into solution. Using particles of the most effective bimetallic composition, experiments were carried out to determine the concentration required for optimal TCE reduction. Over the range of nano-scale particle concentrations tested (0.1-9 g L(-1)), reduction rates of TCE increased with greater TCE:nano-scale particle ratios. However, a concentration range of 1-3 g L(-1) was selected as the most appropriate for site remediation, since more concentrated solutions demonstrated only small increases in rates of reaction. Finally, in order to test the long term performance and reactivity of the 3.2% Ni/Fe bimetallic nano-scale particles, weekly spikes of 350 mg L(-1) TCE were injected into a 3 g L(-1) nano-scale particle batch reactor. Results showed that the bimetallic nano-scale particles had the ability to reduce 1750 mg L(-1) TCE and remained active for at least 13 weeks.

Evolution of compatible replicons of the related IncQ-like plasmids, pTC-F14 and pTF-FC2.

Two closely related but compatible plasmids of the IncQ-2alpha and IncQ-2beta groups, pTF-FC2 and pTC-F14, were discovered in two acidiphilic chemolithotrophic bacteria. Cross-complementation and cross-regulation experiments by the replication proteins were carried out to discover what changes were necessary when the plasmids evolved to produce two incompatibility groups. The requirement of a pTC-F14 oriV for a RepC DNA-binding protein was plasmid specific, whereas the requirement for the RepA helicase and RepB primase was less specific and could be complemented by the IncQ-2alpha plasmid pTC-FC2, and the IncQ-1beta plasmid pIE1108. None of the IncQ-1alpha plasmid replication proteins could complement the pTC-F14 oriV, and pTC-F14 and RSF1010 were incompatible. This incompatibility was associated with the RepC replication protein and was not due to iteron incompatibility. Replication of pTC-F14 took place from a 5.7 kb transcript that originated upstream of the mobB gene located within the region required for mobilization. A pTC-F14 mobB-lacZ fusion was regulated by the pTC-F14 repB gene product and was plasmid specific, as it was not regulated by the RepB proteins of pTF-FC2 or the IncQ-1alpha and IncQ-1beta plasmids. Plasmid pTC-F14 appears to have evolved independently functioning iterons and a plasmid-specific RepC-binding protein; it also has a major replication transcript that is independently regulated from that of pTF-FC2. However, the RepA and RepB proteins have the ability to function with either replicon.