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.

This review followed from experiments suggesting that some fungi do not require calcium. It was found that many studies of a calcium requirement in microorganisms had assumed specificity for chelation agents such as EGTA and A23187, which the reagents did not possess. Early studies still cited today often preceded the recognition that microorganisms required manganese and zinc. As a result of both of these misunderstandings, there was rarely any attempt to replace calcium by other important trace elements. In some studies that seem to have been overlooked, the apparent requirement for calcium depended on the growth conditions used. Escherichia coli, Neurospora crassa, and Saccharomyces cerevisiae were then selected for detailed consideration and it is concluded that further experiments are needed before the involvement of calcium is proved.

The isolation, morphology, cultural characteristics and growth requirements of an autotroph which oxidizes thiocyanate are described. It is suggested that the organism be assigned to the genus Thiobacillus.The oxidation of thiocyanate by bacteria was described by Happold & Key (1937); it was not then realized that the organism was an autotroph until it was isolated in pure culture (Happold, Johnstone & Rogers, 1952). The present paper contains a fuller description of the organism. The literature will be more comprehensively reviewed in a later paper on the metabolism of the organism. Isolation of the organismMaterial for isolation was obtained from sewage effluents and also from a well water which contained thiocyanate. The cultures were enriched by percolation, in the presence of thiocyanate, through columns designed to approximate to the conditions obtaining in filter beds. The final isolation was made by the selection of single organisms, but it was first necessary to decrease the numbers of contaminating heterotrophs. The crude cultures, although maintained in a very simple medium, appeared from plate counts for heterotrophic organisms to contain heterotrophs in numbers exceeding those of the autotroph. The basal medium used for growth of the thiocyanate organisms was: Na,HPO,, 1.0 g.; KH,PO,, 0.6 g.; KCNS, 0-2 g.; distilled water to 1 1.The pH of the medium was 7-0-7-2. Contaminating heterotrophs were able to grow in these cultures even when the medium was prepared from water twice distilled from alkaline potassium permanganate and analytical grade reagents. Glassware was cleaned with aqua regia, and cotton-wool plugs were replaced by inverted glass beakers.Selection of colonies from a solid medium, prepared by addition of agar to the basal medium, failed to give any cultures which oxidized thiocyanate. Flooding of the plates with ferric nitrate reagent showed that removal of thiocyanate had rarely occurred other than in areas of confluent growth. These experiments suggested that the agar, or some contaminating material, might have an inhibitory effect on the autotroph. It therefore seemed necessary to eliminate agar from the medium and to use silica gel in its place.Silica gels were prepared by a modification of Taylor's method (Taylor, 1950)

Allomyces macrogynus plants were induced to make either zoosporangia in distilled water or resistant sporangia in a solution of glucose and glutamic acid. Analyses during the stages of developmentJ showed that plants of both series degraded nucleic acid, releasing uracil, hypoxanthine and guanin~ to the suspending medium. Plants in distilled water released inorganic phosphate to the medium while those in glucose-glutamic acid solution conserved the phosphate as bound phosphate. A. arbuscula also released the purines and pyrimidines.

No abstract