Antioxidant pathways are up-regulated during biological nitrogen fixation to prevent ROS-induced nitrogenase inhibition in Gluconacetobacter diazotrophicus

Gluconacetobacter diazotrophicus, an endophyte isolated from sugarcane, is a strict aerobe that fixates N2. This process is catalyzed by nitrogenase and requires copious amounts of ATP. Nitrogenase activity is extremely sensitive to inhibition by oxygen and reactive oxygen species (ROS). However, the elevated oxidative metabolic rates required to sustain biological nitrogen fixation (BNF) may favor an increased production of ROS. Here, we explored this paradox and observed that ROS levels are, in fact, decreased in nitrogen-fixing cells due to the up-regulation of transcript levels of six ROS-detoxifying genes. A cluster analyses based on common expression patterns revealed the existence of a stable cluster with 99.8% similarity made up of the genes encoding the α-subunit of nitrogenase Mo–Fe protein (nifD), superoxide dismutase (sodA) and catalase type E (katE). Finally, nitrogenase activity was inhibited in a dose-dependent manner by paraquat, a redox cycler that increases cellular ROS levels. Our data revealed that ROS can strongly inhibit nitrogenase activity, and G. diazotrophicus alters its redox metabolism during BNF by increasing antioxidant transcript levels resulting in a lower ROS generation. We suggest that careful controlled ROS production during this critical phase is an adaptive mechanism to allow nitrogen fixation

Alterações hepáticas em trabalhadores de uma refinaria de petróleo e em uma população de referência no Estado da Bahia, Brasil Liver changes in workers at an oil refinery and in a reference population in the state of Bahia, Brazil

OBJETIVO: Determinar a prevalência de alterações nas enzimas hepáticas de trabalhadores de uma refinaria de petróleo localizada no Estado da Bahia em comparação a uma população de referência não ocupacionalmente exposta a produtos químicos, e descrever os fatores associados à variação nessa prevalência. MÉTODO: Foram avaliados os trabalhadores da refinaria e os funcionários do escritório da gerência administrativa da empresa, situada em Salvador, capital do Estado da Bahia. Estudaram-se amostras de sangue de 692 trabalhadores da refinaria e de 377 trabalhadores da população de referência. Classificaram-se como casos de alterações hepáticas indivíduos que apresentaram valores acima dos padrões de referência simultaneamente para gama-glutamiltransferase (GGT) (>50 U/L para o sexo masculino e >32 U/L para o sexo feminino) e alanina aminotrans- ferase (ALT) (>50 U/L). Foram coletadas informações sobre idade, sexo, peso, altura, tempo de serviço, uso de álcool, hábito de fumar, exercício físico, exposição ocupacional a produtos químicos, uso de equipamento de proteção individual e antecedentes médicos de hepatite, icterícia e obesidade. RESULTADOS: A prevalência de alterações hepáticas na refinaria foi de 15,3% (IC95%: 12,5 a 18,1), contra 3,8% (IC95%: 1,8 a 5,8) na população de referência. A análise de regressão logística múltipla estimou que os trabalhadores da refinaria apresentavam uma prevalência de alterações hepáticas 3,56 vezes maior (IC95%: 1,99 a 6,38) do que a prevalência observada na população de referência, independentemente de outras covariáveis relevantes, como obesidade, prática de exercícios físicos, fumo e bebida alcoólica. CONCLUSÕES: Os resultados sugerem que a exposição ocupacional desempenha um papel importante na determinação das alterações hepáticas nos trabalhadores dessa refinaria de petróleo.<br>OBJECTIVE: To determine the prevalence of liver changes in workers at an oil refinery located in the state of Bahia, Brazil, as compared to a reference population with no occupational exposure to chemical products, and to describe the factors associated with the observed differences in prevalence. METHODS: We studied workers at the refinery and at the company's central management office located in the city of Salvador, which is the state capital. Blood samples of 692 refinery workers and 377 workers from the reference population were analyzed. Cases were defined as individuals presenting high serum levels of both gamma-glutamyltransferase (GGT) and alanine aminotransferase (ALT) (GGT > 50 U/L for males and > 32 U/L for females; ALT > 50 U/L). Data were collected on age, sex, weight, height, years working for the company, use of alcohol, smoking habits, physical exercise, occupational exposure to chemical products, use of personal safety equipment, and medical history of hepatitis, jaundice, and obesity. RESULTS: The prevalence of liver changes among refinery workers was 15.3% (95% CI: 12.5 to 18.1), vs. 3.8% (95% CI: 1,8 to 5,8) in the reference population. According to multiple logistic regression analysis, the prevalence of liver changes among refinery workers was 3.56 times greater (95% CI: 1,99 to 6,38) than in the reference population, regardless of the presence of other relevant co-variables, such as obesity, exercise, smoking, and alcohol consumption. CONCLUSIONS: These results suggest that occupational exposure may play a major role in the development of liver changes among workers at the oil refinery where the study was carried out

Complete genome sequence of the sugarcane nitrogen-fixing endophyte gluconacetobacter diazotrophicus PAL5

17 p. : il.Background: Gluconacetobacter diazotrophicus Pal5 is an endophytic diazotrophic bacterium that lives in association with sugarcane plants. It has important biotechnological features such as nitrogen fixation, plant growth promotion, sugar metabolism pathways, secretion of organic acids, synthesis of auxin and the occurrence of bacteriocins. Results: Gluconacetobacter diazotrophicus Pal5 is the third diazotrophic endophytic bacterium to be completely sequenced. Its genome is composed of a 3.9 Mb chromosome and 2 plasmids of 16.6 and 38.8 kb, respectively. We annotated 3,938 coding sequences which reveal several characteristics related to the endophytic lifestyle such as nitrogen fixation, plant growth promotion, sugar metabolism, transport systems, synthesis of auxin and the occurrence of bacteriocins. Genomic analysis identified a core component of 894 genes shared with phylogenetically related bacteria. Gene clusters for gum-like polysaccharide biosynthesis, tad pilus, quorum sensing, for modulation of plant growth by indole acetic acid and mechanisms involved in tolerance to acidic conditions were identified and may be related to the sugarcane endophytic and plant-growth promoting traits of G. diazotrophicus. An accessory component of at least 851 genes distributed in genome islands was identified, and was most likely acquired by horizontal gene transfer. This portion of the genome has likely contributed to adaptation to the plant habitat. Conclusion: The genome data offer an important resource of information that can be used to manipulate plant/bacterium interactions with the aim of improving sugarcane crop production and other biotechnological applications