Pyrroloquinoline-quinone: a reactive oxygen species scavenger in bacteria

Engineering of Deinococcus radiodurans R1 for bioprecipitation of uranium from dilute nuclear waste

Genetic engineering of radiation-resistant organisms to recover radionuclides/heavy metals from radioactive wastes is an attractive proposition. We have constructed a Deinococcus radiodurans strain harboring phoN, a gene encoding a nonspecific acid phosphatase, obtained from a local isolate of Salmonella enterica serovar Typhi. The recombinant strain expressed an approximately 27-kDa active PhoN protein and efficiently precipitated over 90% of the uranium from a 0.8 mM uranyl nitrate solution in 6 h. The engineered strain retained uranium bioprecipitation ability even after exposure to 6 kGy of 60Co gamma rays. The PhoN-expressing D. radiodurans offers an effective and eco-friendly in situ approach to biorecovery of uranium from dilute nuclear waste.

An exonuclease I-sensitive DNA repair pathway in Deinococcus radiodurans: a major determinant of radiation resistance

Deinococcus radiodurans R1 recovering from acute dose of gamma radiation shows a biphasic mechanism of DNA double-strand break repair. The possible involvement of microsequence homology-dependent, or non-homologous end joining type mechanisms during initial period followed by RecA-dependent homologous recombination pathways has been suggested for the reconstruction of complete genomes in this microbe. We have exploited the known roles of exonuclease I in DNA recombination to elucidate the nature of recombination involved in DNA double-strand break repair during post-irradiation recovery of D. radiodurans. Transgenic Deinococcus cells expressing exonuclease I functions of Escherichia coli showed significant reduction in gamma radiation radioresistance, while the resistance to far-UV and hydrogen peroxide remained unaffected. The overexpression of E. coli exonuclease I in Deinococcus inhibited DNA double-strand break repair. Such cells exhibited normal post-irradiation expression kinetics of RecA, PprA and single-stranded DNA-binding proteins but lacked the divalent cation manganese [(Mn(II)]-dependent protection from gamma radiation. The results strongly suggest that 3' (rho) 5' single-stranded DNA ends constitute an important component in recombination pathway involved in DNA double-strand break repair and that absence of sbcB from deinococcal genome may significantly aid its extreme radioresistance phenotype.

PprA: A protein implicated in radioresistance of Deinococcus radiodurans stimulates catalase activity in Escherichia coli

PprA: a pleiotropic protein promoting DNA repair, role in radiation resistance of Deinococcus radiodurans was demonstrated. In this study, the effect of radiation and oxidative stress on transgenic Escherichia coli expressing pprA has been studied. The pprA gene from D. radiodurans KR1 was cloned and expressed in E. coli. Transgenic E. coli cells expressing PprA showed twofold to threefold higher tolerance to hydrogen peroxide as compared to control. The 2.8-fold in vivo stimulation of catalase activity largely contributed by KatE was observed as compared to nonrecombinant control. Furthermore, the purified PprA could stimulate the E. coli catalase activity by 1.7-fold in solution. The effect of PprA on catalase activity observed both in vivo and in vitro was reverted to normal levels in the presence of PprA antibodies. The results suggest that enhanced oxidative stress tolerance in E. coli expressing PprA was due to the PprA stimulation of catalase activity, perhaps through the interaction of these proteins.

Pyrroloquinoline quinone modulates mitochondrial quantity and function in mice

When pyrroloquinoline quinone (PQQ) is added to an amino acid-based, but otherwise nutritionally complete basal diet, it improves growth-related variables in young mice. We examined PQQ and mitochondrial function based on observations that PQQ deficiency results in elevated plasma glucose concentrations in young mice, and PQQ addition stimulates mitochondrial complex 1 activity in vitro. PQQ-deficient weanling mice had a 20-30% reduction in the relative amount of mitochondria in liver; lower respiratory control ratios, and lower respiratory quotients than PQQ-supplemented mice (2 mg PQQ/kg diet). In mice from dams fed a conventional laboratory diet, but switched at weaning to the basal diet, plasma glucose, Ala, Gly, and Ser concentrations were elevated at 4 wk (PQQ- vs. PQQ+), but not at 8 wk. The relative mitochondrial content (ratio of mtDNA to nuclear DNA) also tended (P<0.18) to be lower (PQQ- vs. PQQ+) at 4 wk, but not at 8 wk. PQQ also counters the mitochondrial complex 1 inhibitor, diphenylene iodonium (DPI). Mice were gavaged with 0, 0.4, or 4 microg PQQ/g body weight (BW) daily for 14 d. At each PQQ level, DPI was injected (i.p.) at 0, 0.4, 0.8, or 1.6 microg DPI/g BW. The PQQ-deficient mice exposed to 0.4 or 4.0 microg DPI/g lost weight and had lower plasma glucose levels than PQQ-supplemented mice (P<0.05). In addition, fibroblasts took up (3)H-PQQ added to cell cultures, and cultured hepatocytes maintained mitochondrial PQQ concentrations similar to those observed in vivo. Collectively, these results indicate that dietary PQQ can influence mitochondrial amount and function, particularly in perinatal and weanling mice.