Factors inducing transition from growth to dormancy in rhizobacteria Azospirillum brasilense

The factors suppressing division of the cells of the rhizobacterium Azospirillum brasilense and inducing their transition to a dormant state were analyzed. These included the presence of hexylresorcinol or heavy metals (Cu and Co) in the medium, oxygen stress, and transfer of the cells into the physiological saline or phosphate buffer solution. The results were used to develop a protocol for obtaining of nonculturable cells of A. brasilense Sp245, a natural symbiont of wheat. The cells lost their ability to grow on synthetic agar medium, but could revert to growth when incubated in freshly prepared liquid medium. Needle-shaped crystals differing from struvite, which has been previously reported for this strain, were found in the dormant culture of A. brasilense Sp245.     

Biological oxidation of sulfide raw material using a culture of Thiobacillus ferrooxidans under various conditions of leaching

Major parameters of the first stage of leaching of a copper-zinc sulfide product by a culture of Thiobacillus ferrooxidans have been studied, including the effects of solid phase concentration, Fe2+ and Fe3+ ions, pH, and the intensity of mixing. The first stage of leaching of the sulfide raw material is optimum under the following conditions: pH of the original leaching solution equal to 1.6; Fe3+ concentration of order of 10 g/l; and vigorous mixing of the suspension at solid phase concentrations of 30-35%. A theoretical substantiation of the observed dependences is proposed.     

Biological Oxidation of Sulfide Raw Material Using a Culture of Thiobacillus ferrooxidans under Various Conditions of Leaching

Major parameters of the first stage of leaching of a copper–zinc sulfide product (raw material) by a culture of Thiobacillus ferrooxidans have been studied, including the effects of solid-phase concentration, Fe²⁺ and Fe³⁺ ions, pH, and the intensity of mixing. The first stage of leaching of the sulfide raw material is optimum under the following conditions: pH of the original leaching solution equal to 1.6; Fe³⁺ concentration of the order of 10 g/l; and vigorous mixing of the suspension at solid-phase concentrations of 30–35%. A theoretical substantiation of the observed dependences is proposed.