Qualitative and quantitative determination of a humic model compound in microbial cultures by cyclic voltammetry

Enhancement of anaerobic degradation of petroleum hydrocarbons by electron intermediate: Performance and mechanism

A quinone-respiring strain capable of degrading multitudinous petroleum hydrocarbons was isolated by selective medium and identified as Bacillus sp. (named as C8). Maximum 76.7% of total petroleum hydrocarbons (TPH) were degraded by the biosurfactant-mediated C8 with the aid of nitrate and electron intermediate (anthraquinone-2,6-disulphonate, AQDS). The quantitative real-time PCR results of several intracellular key functional genes suggested that AQDS could participate in the transformation of intermediates and accelerate the electron transfer in the degradation of TPH and nitrate, thereby eliminating the accumulation of nitrite and increasing the degradation efficiency of TPH. A strengthening mechanism, which promoted electron transport in the anaerobic denitrification degradation of petroleum hydrocarbons by quinone-respiring strain with the aid of electron intermediate, was proposed. The influencing factors were evaluated by using response surface methodology, and the TPH removal was positively related to temperature but negatively to pH.

Inhibitory effects of quinoid redox mediators on a denitrifying culture

Denitrification with p-cresol as the electron source was studied in the presence of three quinones at different molar concentrations (0-2 mM): menadione (MEN), alizarine (ALZ) and anthraquinone-2,6-disulfonate (AQDS). Results showed that denitrifying yields were not altered (0.9), but the substrates' consumption efficiency was mainly affected when adding MEN. In the presence of ALZ and MEN, specific consumption rates decreased 40% for p-cresol and 90% for nitrate. The sludge previously exposed to quinones was submitted to recovering denitrifying studies using acetate and p-cresol. After exposing to AQDS and ALZ, the metabolic activity of denitrifying sludge was completely recovered. The previous exposition to any MEN concentration resulted in a very low metabolic recuperation. The results show that MEN and ALZ have a marked inhibitory effect on substrates' consumption and the AQDS does not affect at all. The evidence suggests that MEN modifies the transport system of substrates and ALZ forms a complex with molybdenum. A model based on oxido-reduction potentials of the enzymes involved points out that the influence of quinones tested appears to be more associated with quinone moiety structural properties and hydrophobicity.

Dying for Good: Virus-Bacterium Biofilm Co-evolution Enhances Environmental Fitness

Commonly used in biotechnology applications, filamentous M13 phage are non-lytic viruses that infect E. coli and other bacteria, with the potential to promote horizontal gene transfer in natural populations with synthetic biology implications for engineering community systems. Using the E. coli strain TG1, we have investigated how a selective pressure involving elevated levels of toxic chromate, mimicking that found in some superfund sites, alters population dynamics following infection with either wild-type M13 phage or an M13-phage encoding a chromate reductase (Gh-ChrR) capable of the reductive immobilization of chromate (ie, M13-phage_Gh-ChrR). In the absence of a selective pressure, M13-phage infection results in a reduction in bacterial growth rate; in comparison, in the presence of chromate there are substantial increases in both cellular killing and biomass formation following infection of E. coli strain TG1with M13-phage_Gh-ChrR that is dependent on chromate-reductase activity. These results are discussed in terms of community structures that facilitate lateral gene transfer of beneficial traits that enhance phage replication, infectivity, and stability against environmental change.

Cathodes as electron donors for microbial metabolism: which extracellular electron transfer mechanisms are involved?

This review illuminates extracellular electron transfer mechanisms that may be involved in microbial bioelectrochemical systems with biocathodes. Microbially-catalyzed cathodes are evolving for new bioprocessing applications for waste(water) treatment, carbon dioxide fixation, chemical product formation, or bioremediation. Extracellular electron transfer processes in biological anodes, were the electrode serves as electron acceptor, have been widely studied. However, for biological cathodes the question remains: what are the biochemical mechanisms for the extracellular electron transfer from a cathode (electron donor) to a microorganism? This question was approached by not only analysing the literature on biocathodes, but also by investigating known extracellular microbial oxidation reactions in environmental processes. Here, it is predicted that in direct electron transfer reactions, c-type cytochromes often together with hydrogenases play a critical role and that, in mediated electron transfer reactions, natural redox mediators, such as PQQ, will be involved in the bioelectrochemical reaction. These mechanisms are very similar to processes at the bioanode, but the components operate at different redox potentials. The biocatalyzed cathode reactions, thereby, are not necessarily energy conserving for the microorganism.