A novel gene from the acidophilic bacterium Leptospirillum sp. CF-1 and its role in oxidative stress and chromate tolerance

BACKGROUND: Acidophilic microorganisms like Leptospirillum sp. CF 1 thrive in environments with extremely low pH and high concentrations of dissolved heavy metals that can induce the generation of reactive oxygen species (ROS). Several hypothetical genes and proteins from Leptospirillum sp. CF 1 are known to be up regulated under oxidative stress conditions. RESULTS: In the present work, the function of hypothetical gene ABH19_09590 from Leptospirillum sp. CF 1 was studied. Heterologous expression of this gene in Escherichia coli led to an increase in the ability to grow under oxidant conditions with 5 mM K2CrO4 or 5 mM H2O2. Similarly, a significant reduction in ROS production in E. coli transformed with a plasmid carrying ABH19_09590 was observed after exposure to these oxidative stress elicitors for 30 min, compared to a strain complemented with the empty vector. A co transcriptional study using RT PCR showed that ABH19_09590 is contained in an operon, here named the "och" operon, that also contains ABH19_09585, ABH19_09595 and ABH19_09600 genes. The expression of the och operon was significantly up regulated in Leptospirillum sp. CF 1 exposed to 5 mM K2CrO4 for 15 and 30 min. Genes of this operon potentially encode a NADH:ubiquinone oxidoreductase, a CXXC motif containing protein likely involved in thiol/disulfide exchange, a hypothetical protein, and a di hydroxy acid dehydratase. A comparative genomic analysis revealed that the och operon is a characteristic genetic determinant of the Leptospirillum genus that is not present in other acidophiles. CONCLUSIONS: Altogether, these results suggest that the och operon plays a protective role against chromate and hydrogen peroxide and is an important mechanism required to face polyextremophilic conditions in acid environments.

Punica granatum L. protects mice against hexavalent chromium-induced genotoxicity

This study investigated the chemoprotective effects of Punica granatum L. (Punicaceae) fruits alcoholic extract (PGE) on mice exposed to hexavalent chromium [Cr(VI)]. Animals were pretreated with PGE (25, 50 or 75 mg/kg/day) for 10 days and subsequently exposed to a sub-lethal dose of Cr(VI) (30 mg/kg). The frequency of micronucleated polychromatic erythrocytes in the bone marrow was investigated and the Cr(VI) levels were measured in the kidneys, liver and plasm. For the survival analysis, mice were previously treated with PGE for 10 days and exposed to a single lethal dose of Cr(VI) (50 mg/kg). Exposure to a sub-lethal dose of Cr(VI) induced a significant increase in the frequency of micronucleated cells. However, the prophylactic treatment with PGE led to a reduction of 44.5% (25 mg/kg), 86.3% (50 mg/kg) and 64.2% (75 mg/kg) in the incidence of micronuclei. In addition, the 50 mg/kg dose of PGE produced a higher chemoprotective effect, since the survival rate was 90%, when compared to that of the non-treated group. In these animals, reduced amounts of chromium were detected in the biological materials, in comparison with the other groups. Taken together, the results demonstrated that PGE exerts a protective effect against Cr(VI)-induced genotoxicity.

Este estudo investigou os efeitos quimioprotetores do extrato alcoólico dos frutos da Punica granatum L. (Punicaceae) (EPG) em camundongos expostos ao cromo hexavalente [Cr(VI)]. Os animais foram pré-tratados com o EPG (25, 50 ou 75 mg/kg/dia) durante 10 dias e subsequentemente expostos a uma dose subletal de Cr(VI) (30 mg/kg). A frequência de eritrócitos policromáticos micronucleados na medula óssea foi investigada e os níveis de Cr(VI) foram quantificados nos rins, fígado e plasma. Para a análise de sobrevida, os camundongos foram previamente tratados com EPG durante 10 dias e expostos a única dose letal de Cr(VI) (50 mg/kg). A exposição à dose subletal de Cr(VI) induziu aumento significativo na frequência de células micronucleadas. Entretanto, o tratamento profilático com EPG levou à redução de 44,5% (25 mg/kg), 86,3% (50 mg/kg) e 64,2% (75 mg/kg) na incidência de micronúcleo. Além disso, a dose de 50 mg/kg de EPG produziu maior efeito quimioprotetor, uma vez que a taxa de sobrevivência foi de 90%, quando comparada àquela do grupo não tratado. Nesses animais, quantidades reduzidas de cromo foram detectadas nos materiais biológicos, em comparação com os outros grupos. Em conjunto, os resultados demonstram que o EPG exerce efeito protetor contra a genotoxicidade induzida pelo Cr(VI).