Characterisation of the DNA gyrase from the thermophilic eubacterium Thermus thermophilus

Production of a Natural Dihydropteroate Synthase and Development of a Signal-Amplified Pseudo-Immunoassay for the Determination of Sulfonamides in Pork

In this study, a type of magnetic photoaffinity-labeled activity-based protein profiling probe for sulfonamide drugs was first synthesized for the purpose of capturing the natural dihydropteroate synthase of Escherichia coli by using simple incubation and magnetic separation. After characterization of its identity with LC-ESI-MS/MS, this enzyme was used as a recognition reagent to develop a direct competitive pseudo-ELISA for the determination of the residues of 40 sulfonamides in pork. Because of the use of streptavidin-horseradish peroxidase and biotinylated horseradish peroxidase as a signal-amplified system, the limits of detection for the 40 drugs were in the range of 0.001-0.016 ng/mL. Compared to the steps in a conventional assay formation, the operation steps were the same, but the sensitivities increased 32-88-fold. Furthermore, the assay performances were better than the previously reported immunoassays performances for sulfonamides. Therefore, this method could be used as a practical tool for multiscreening the trace levels of sulfonamides residues in food samples.

Resistance to UV Irradiation Caused by Inactivation of nurA and herA Genes in Thermus thermophilus

NurA and HerA are thought to be essential proteins for DNA end resection in archaeal homologous recombination systems. Thermus thermophilus, an extremely thermophilic eubacterium, has proteins that exhibit significant sequence similarity to archaeal NurA and HerA. To unveil the cellular function of NurA and HerA in T. thermophilus, we performed phenotypic analysis of disruptant mutants of nurA and herA with or without DNA-damaging agents. The nurA and herA genes were not essential for survival, and their deletion had no effect on cell growth and genome integrity. Unexpectedly, these disruptants of T. thermophilus showed increased resistance to UV irradiation and mitomycin C treatment. Further, these disruptants and the wild type displayed no difference in sensitivity to oxidative stress and a DNA replication inhibitor. T. thermophilus NurA had nuclease activity, and HerA had ATPase. The overexpression of loss-of-function mutants of nurA and herA in the respective disruptants showed no complementation, suggesting their enzymatic activities were involved in the UV sensitivity. In addition, T. thermophilus NurA and HerA interacted with each other in vitro and in vivo, forming a complex with 2:6 stoichiometry. These results suggest that the NurA-HerA complex has an architecture similar to that of archaeal counterparts but that it impairs, rather than promotes, the repair of photoproducts and DNA cross-links in T. thermophilus cells. This cellular function is distinctly different from that of archaeal NurA and HerA.IMPORTANCE Many nucleases and helicases are engaged in homologous recombination-mediated DNA repair. Previous in vitro analyses in archaea indicated that NurA and HerA are the recombination-related nuclease and helicase. However, their cellular function had not been fully understood, especially in bacterial cells. In this study, we performed in vivo analyses to address the cellular function of nurA and herA in an extremely thermophilic bacterium, Thermus thermophilus As a result, T. thermophilus NurA and HerA exhibited an interfering effect on the repair of several instances of DNA damage in the cell, which is in contrast to the results in archaea. This finding will facilitate our understanding of the diverse cellular functions of the recombination-related nucleases and helicases.

Marine extremophiles: a source of hydrolases for biotechnological applications

The marine environment covers almost three quarters of the planet and is where evolution took its first steps. Extremophile microorganisms are found in several extreme marine environments, such as hydrothermal vents, hot springs, salty lakes and deep-sea floors. The ability of these microorganisms to support extremes of temperature, salinity and pressure demonstrates their great potential for biotechnological processes. Hydrolases including amylases, cellulases, peptidases and lipases from hyperthermophiles, psychrophiles, halophiles and piezophiles have been investigated for these reasons. Extremozymes are adapted to work in harsh physical-chemical conditions and their use in various industrial applications such as the biofuel, pharmaceutical, fine chemicals and food industries has increased. The understanding of the specific factors that confer the ability to withstand extreme habitats on such enzymes has become a priority for their biotechnological use. The most studied marine extremophiles are prokaryotes and in this review, we present the most studied archaea and bacteria extremophiles and their hydrolases, and discuss their use for industrial applications.