HCO 3 − Fixation by Naturally Occurring Tufts and Pure Cultures of Thiothrix nivea

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Abstract
Naturally occurring tufts of the mixotroph Thiothrix nivea blanketed the East Everglades (Dade County, Fla.) Chekika artesian well and runoff areas. The rate of HCO3− fixation by these Thiothrix tufts was determined to be 14.0 ± 5.4 nmol of HCO3− per min per mg of dry weight, which reflected a growth rate of 5.0%/h. The addition of 10 mM glucose, ribose, acetate, or pyruvate or 0.05% Casamino Acids (Difco Laboratories, Detroit, Mich.) did not appear to alter the HCO3− fixation rate. Whereas 1 mM acetate or 10 mM lactate, ethanol, glycerol, α-ketoglutarate, succinate, fumarate, or citrate slightly stimulated HCO3− fixation, 5 to 10 mM malate inhibited HCO3− fixation by 90%. Pure Thiothrix cultures isolated from Chekika fixed HCO3− at rates as high as 29.9 ± 2.8 nmol of HCO3− per min per mg of dry weight in the presence of growth medium. Malate did not have a suppressive effect but rather slightly stimulated in vivo HCO3− fixation. Images

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