Growth and metabolism of the obligate photolithotroph Chlorobium thiosulfatophilum in the presence of added organic nutrients

Growth of Chlorobium vibrioforme f. thiosulfatophilum NCIB 8327 could be monitored by measurement of turbidity (E₆₀₀); absorbance at 745 and 665 nm; increase in methanol-extractable pigment (E₆₆₀); fixation of ¹⁴CO₂; and titration of thiosulphate and sulphide in the medium. Growth could be inhibited by formate, methionine, tryptophan, tyrosine, threonine, serine and glycine, but not by 14 other amino acids, shikimic acid, some alcohols, sugars or acetate. Inhibition could some-times be relieved by the presence of other amino acids. This was probably partly due to restoration of normal internal amino acid requirements by “feeding”, and partly because uptake of amino acids appeared to show some competition for two or more low specificity uptake systems. Numerous ¹⁴C-labelled amino acids, formate and glucose were shown to be photoassimilated by Chlorobium, and the labelling patterns obtained provided information on its pathways of intermediary biosynthesis. Growth inhibition by threonine could be related to the probable presence of a normal branched pathway for the synthesis of the aspartate family of amino acids, with an aspartokinase enzyme subject to strong inhibition by threonine and lysine, separately and in combination.