CARBOHYDRATE AND AMINO-ACID FERMENTATION IN THE FREE-LIVING PRIMITIVEPROTOZOAN HEXAMITA SP

Hexamita sp. is an amitochondriate free-living diplomonad which inhabi ts O-2-limited environments, such as the deep waters and sediments of lakes and marine basins,C-13 nuclear magnetic resonance spectroscopy r eveals ethanol, lactate, acetate, and alanine as products of glucose f ermentation under microaerobic conditions (23 to 34 mu M O-2). Propion ic acid and butyric acid were also detected and are believed to be the result of fermentation of alternative substrates. Production of organ ic acids was greatest under microaerobic conditions (15 mu M O-2) and decreased under anaerobic (<0.25 mu M O-2) and aerobic (200 to 250 mu M O-2) conditions, Microaerobic incubation resulted in the production of high levels of oxidized end products (70% acetate) compared to that produced under anoxic conditions (20% acetate), In addition, data sug gest that Hexamita cells contain the arginine dihydrolase pathway, gen erating energy from the catabolism of arginine to citrulline, ornithin e, NH4+, and CO2. The rate of arginine catabolism was higher under ano xic conditions than under microaerobic conditions, Hexamita cells were able to grow in the absence of a carbohydrate source, albeit with a l ower growth rate and yield.