Simple and Rapid Cell Growth Estimation Method for Thiobacillus ferrooxidans and the Growth Rate in the Presence of Polyoxyethylenes

摘要

Conventional turbidity method can not be used to estimate the cell growth of Thiobacillus ferrooxidans, be-cause ferric precipitates (ferric hydroxide and jarosites) are formed in the medium due to bacterial oxidation of ferrous ions. In this paper, a modified turbidity method is proposed and demonstrated. The microorganisms were grown in 9K medium and the culture medium was sampled periodically. The sample medium was mixed with equal volumes of 6N HCI to dissolve ferric precipitates. The precipitates dissolved completely after 10 minutes. The turbidity of the mixed solution was measured by nephelometer after the dissolution. During the culture, the turbidity increased exponentially, then reached a constant value, corresponding to exponential and stationary phases on the growth curve. The specific growth rate obtained from the turbidity curve agreed with the rate from the direct cell counting. The proposed method is more simple and rapid than the direct cell counting and protein assay that are usually used to estimate the cell growth of Thio bacillus ferrooxidans.Using the modified turbidity method, the growth rates of Thiobacillus ferrooxidans in 9K medium containing 0 to 1,000 g/m~3 of Tween20, Brij35, or polyethyleneglycol were investigated. With addition of 1,000 g/m~3, all three polyoxyrthylenes markedly suppressed the bacterial ferrous oxidation and cell growth.