Studies on the Metabolism of Thiobacillus thiocyanoxidans

Abstract

SUMMARY: The investigation of the metabolism of thiocyanate by pure cultures of Thiobacillws thiocyanoxidans was complicated by the fact that thiocyanate serves both as source of energy and as source of carbon and nitrogen. It was, therefore, difficult to separate oxidation from carbon dioxide fixation. The equation which best represented the resulkant of these two processes was:Thiocyanate was first hydrolysed to cyanate and sulphide. Cyanate was further hydrolysed to carbon dioxide and ammania and sulphide was oxidized to sulphate.The oxidation of sulphide approximated to the equation : NqS + 20, = NqSO, . Gas uptakes were lower than would be expected from this equation, although special precautions were taken to prevent loss of sulphide.Thiosulphate was oxidized to sulphate according to the equation: Na,S,O, + H,O + 2 0 , = Na,S04 + HzS04.Fixation of carbon dioxide after the oxidation of thiosulphate was shown, but the efficiency of energy utilization appeared lower than during the oxidation of thiocyanate. Thioacetamide and thioacetic acid were oxidized to sulphate but this was believed to be preceded by a chemical breakdown to sulphide. Sulphite, metabisulphite, dithionite, dithionate, tetrathionate, trithionate, thiourea and cysteine were tested ; no evidence was obtained of their utilization.The presence of thiocyanate in gas works liquors led to early experiments on the biological oxidation of the compound. Sludges were activated by exposure to the compound until they were metabolizing 400 p.p.m. thiocyanate ion/ 24 hr. The products, ammonia and sulphate, appeared in amounts which suggested the equation : NH4CNS + 2H,O + 202 = (NH4),S0, + CO, for the reaction.

Thiocyanate degradation by pure and mixed cultures of microorganisms

“…The mixed culture ( Fig.1-a) and the BMV8 isolated strain (Fig.1-b) were able to degrade thiocyanate heterotrophically using this compound as a nitrogen source. Most of the thiocyanate-utilizing microbes reported in the literature are autotrophs, and only few heterotrophs with ability to degrade thiocyanate have been described (1,16,18,19). In the noninoculated control medium (M9), the levels of thiocyanate did not decrease during the incubation period.…”

Anaerobic growth of the haloalkaliphilic denitrifying sulfur-oxidizing bacterium Thialkalivibrio thiocyanodenitrificans sp. nov. with thiocyanate

“…The ability to grow with thiocyanate as an electron donor for energy generation and CO 2 fixation is restricted to a few strains of neutrophilic thiobacilli (De Kruyff et al, 1957;Happold et al, 1954Happold et al, , 1958Katayama & Kuraishi, 1978;Smith & Kelly, 1988;Youatt, 1954). Recently, we described several new thiocyanate-oxidizing bacteria capable of chemolithoautotrophic growth with thiocyanate at high pH and salt concentration (Sorokin et al, 2001a).…”

“…Initial cleavage of the C-S bond results in the formation of the intermediate cyanate (N;C-O 2 ) which, in the presence of bicarbonate, is converted further to ammonia and CO 2 by the enzyme cyanase (Happold et al, 1958;Youatt, 1954). The alternative pathway is based on the initial hydrolytic cleavage of the nitrile bond (N;C), resulting in the formation of carbonyl sulfide (S=C=O) and ammonia (Katayama et al, 1992(Katayama et al, , 1993(Katayama et al, , 1998.…”

Thioalkalivibrio thiocyanoxidans sp. nov. and Thioalkalivibrio paradoxus sp. nov., novel alkaliphilic, obligately autotrophic, sulfur-oxidizing bacteria capable of growth on thiocyanate, from soda lakes.

“…The ability to use thiocyanate (SCN − ) as a single energy substrate is limited to few strains of neutrophilic, obligately autotrophic, sulfur-oxidizing bacteria such as Thiobacillus thioparus (Happold et al, 1954(Happold et al, , 1958Youatt, 1954 ;Katayama & Kuraishi, 1978 ;Smith & Kelly, 1988) and Thiobacillus denitrificans (De Kruyff et al, 1957), and the facultatively autotrophic Paracoccus thiocyanatus (Katayama et al, 1995). Recently, a large number of alkaliphilic, obligately autotrophic, sulfur-oxidizing isolates belonging to two new genera, namely Thioalkalimicrobium and Thioalkalivibrio, in the γ-Proteobacteria have been obtained from soda lakes (Sorokin et al, 2000(Sorokin et al, , 2001a.…”