Aerobic denitrification in various heterotrophic nitrifiers.

Various heterotrophic nitrifiers have been tested and found to also be aerobic denitrifiers. The simultaneous use of two electron acceptors (oxygen and nitrate) permits these organisms to grow more rapidly than on either single electron acceptor, but generally results in a lower yield than is obtained on oxygen, alone. One strain, formerly known as "Pseudomonas denitrificans", was grown in the chemostat and shown to achieve nitrification rates of up to 44 nmol NH3 min-1 mg protein-1 and denitrification rates up to 69 nmol NO3(-1) min-1 mg protein-1.

Isoleucine synthesis by Clostridium sporogenes from propionate or alpha-methylbutyrate.

Preliminary studies demonstrated that Clostridium sporogenes synthesized isoleucine by a pathway not involving threonine or threonine dehydratase. Radiotracer experiments with cells grown in a defined carbohydrate-free medium showed that radioactivity from [U-14C]serine, [3-14C]pyruvate, [14C]NaHCO3 and [1-], [2-] and [3-14C]propionate was incorporated into isoleucine. Conversely, there was no detectable incorporation of 14C into isoleucine during growth with [U-14C]glutamate, [U-14C]threonine, [U-14C]valine, [U-14C]leucine or [U-14C]methionine.