Algumas exigências metabólicas de Pseudomonas denitrificans

Para estudos da bioquímica da desnitrificação os desnitrificadores são cultivados em meio parcialmente sintético, com extrato de levedura ou de carne ou ainda peptona. Procurou-se então um meio de cultura completamente sintético no qual P. denitrificans pudesse desenvolver-se e fazer desnitrificação. Para tanto, células de um "strain" dessa bactéria foram crescidas durantes, 24 e 48 horas em tubos de ensaio contendo 10 ml de meio de cultura consistindo de succinato de sódio, nitrato de potássio, extrato de levedura o tampão de fosfato 1M, valôr pH 6,8. Dêsse meio (controle) 0,1 ml foi inoculado em 10 ml do meio de cultura em estudo, mantido então em condições parcialmente anaeróbicas. Após 24 horas uma alíquota foi retirada e suspensa em água destilada e a turbidês lida em espectrofotômetro Beckman, a 420 my. Os dados obtidos após longa série de ensaios permitiram concluir que a fim de se obter em 48 horas um crescimento da mesma ordem que o obtido com o meio controle, o meio de cultura sintético deve conter micronutrientes (Zn, Fe, Mn, Cu, Co, B e Mo, em EDTA), sulfato de sódio, sulfato de magnésio e ácido glutâmico, além de KNO3, succinato e tampão de fosfato.

Aplicação de técnicas eletroquímicas no estudo da dissolução oxidativa da covelita (CuS) por Thiobacillus ferrooxidans

Among the copper sulphides, chalcopyrite (CuFeS2), covellite (CuS) and chalcocite (Cu2S) are the most important source of minerals for copper mining industry. The acknowledge of behaviour of these sulphides related with bacterial leaching process are essential for optimization procedures. Despite of its importance, covellite has not deserved much interest of researchers regarding this matter. In this work it was studied the oxidation of covellite by the chemolithotrophic bacterium Thiobacillus ferrooxidans by using electrochemical techniques, such as open circuit potentials with the time and cyclic voltammetry. The experiments were carried out in acid medium (pH 1.8), containing or not Fe2+ as additional energy source, and in different periods of incubation; chemical controls were run in parallel. The results showed that a sulphur layer is formed spontaneously due the acid attack, covering the sulphide in the initial phase of incubation, blocking the sulphide oxidation. However, the bacterium was capable to oxidize this sulphur layer. In the presence of Fe2+ as supplemental energy source, the corrosion process was facilitated, because ocurred an indirect oxidation of covellite by Fe3+, which was produced by T. ferrooxidans oxidation of the Fe2+ added in the medium.

Sulfur in agriculture

Sulfur (S) deficiency in soils is becoming increasingly common in many areas of the world as a result of agronomic practices, high biomass exportation and reduced S emissions to the atmosphere. In this review, the incidence and commercial exploitation of S pools in nature are discussed, as well as the importance of S for plants and the organic and inorganic S forms in soil and their transformations, especially the process of microbiological oxidation of elemental sulfur (S0) as an alternative to the replenishment of S levels in the soil. The diversity of S0-oxidizing microorganisms in soils, in particular the genus Thiobacillus, and the biochemical mechanisms of S0 oxidation in bacteria were also addressed. Finally, the main methods to measure the S0 oxidation rate in soils and the variables that influence this process were revised.