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

• Published in: Shigen to sozai Vol. 112; no. 3; pp. 171 - 175
• Main Authors: HIROYOSHI, Naoki, ITO, Mayumi, TSUNEKAWA, Masami, HIRAJIMA, Tsuyoshi
• Format: Journal Article
• Language: Japanese; English
• Published: The Mining and Materials Processing Institute of Japan 1996
• Subjects: Growth Rate; Polyoxyethylenes; Thiobacillus ferrooxidans; Turbidity
• ISSN: 0916-1740; 1880-6244
• DOI: 10.2473/shigentosozai.112.171

Conventional turbidity method can not be used to estimate the cell growth of Thiobacillus ferrooxidans, because 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 HC1 to dissolve ferric precipitates. The precipitates dissolved completely after 30 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 Thiobacillus ferrooxidans. Using the modified turbidity method, the growth rates of Thiobacillus ferrooxidans in 9K medium containing 0 to 1, 000g/m3 of Tween 20, Brij 35, or polyethyleneglycol were investigated. With addition of 1, 000g/m3, all three polyoxyethylenes markedly suppressed the bacterial ferrous oxidation and cell growth.