Mutants of Volvox carteri affecting nitrogen assimilation

Three genes of Volvox carteri f. nagariensis have been identified which affect nitrogen assimilation. Mutants in two unlinked genes, nitA and nitC, were isolated as chlorate resistant and they exhibit no measureable nitrate reductase activity. The mutant in the nitB gene which is linked to nitA has slightly reduced levels of nitrate reductase activity and grows poorly on the nitrate concentration in standard medium but grows normally if the level of nitrate is increased. All of the mutants utilize ammonia, urea or nitrite for growth.