-
The effects of eighteen L-amino acids and two peptides, added individually to an otherwise autotrophie medium, on the growth of Thiobacillus thioparus, Thiobacillus neapolltanus and Thiobacillus thiooxidans were tested. Under these conditions, specific L-amino acids, which differed for each of the thiobacilli, inhibited growth.
-
All inhibitory effects were reversed, completely or in part, in the presence of non-inhibitory concentrations of casein hydrolysate.
-
L-tyrosine or x.-tryptophane reversed the L-phenylalanine inhibition of T. thioparus and T. nealoolitanus; L-serine inhibition of T. thiooxidans was partially reversed by x.-threonine and completely by L-valine plus L-leucine; and L-valine inhibition of T. thiooxidans was similarly reversed by T.-leucine or L-isoleucine.
-
In cell-free systems derived from T. thiooxidans, L-valine or L-isoleucine inhibited the activity of acetolactate-forming enzyme. Repression of synthesis of this enzyme by L-valine, L-isoleucine and L-leucine could not be demonstrated.
-
D-valine and D-isoleucine were also inhibitory to T. thioparus. The inhibition by D-valine was not reversed in the presence of any combination of the x.-isomers of valine, isoleucine and leucine.
-
It is concluded that inhibition of growth of these three obligately chemolithotrophic thiobacilli by L-amino acids is due to amino acid imbalances that derange normal regulatory processes as also occurs in chemoorganotrophic bacteria.
Ever since the studies of Winogradsky and Omeliansky (1899), which showed that nitrifying bacteria were inhibited by certain organic compounds, it has been widely believed that obligately ehemolithotrophic bacteria are generally and uniquely inhibited by organic matter. In fact, subsequent work (Nathanson, 1902;Fred and Davenport, 1921;Jensen, 1950; 1V[eike]john, 1954; and others) has shown that a general toxicity does not exist, and that species and strains of these organisms differ qualitatively and quantitatively in the sensitivities to organic matter that they do exhibit. * Taken in part from a dissertation submitted by M. C. L. to the University of California in partial fulfillment of the requirements for a Master's degree in Microbiology.