Isolation and characterization of selenate resistant mutants of Acremoniumchrysogenum

Mutants unable to convert exogenous sulfate to sulfite were isolated using the toxic analogue selenate. Three of twenty-eight isolated mutants were ch romate sensitive. They showed a possible lesion in the gene that codes the ATP sulfurylase. The others were chromate resistant, and probably had a les ion in one or both of the genes that code the sulfate permease. Methionine increased the resistance levels to selenate. In addition, the frequency of spontaneous mutants obtained in a medium containing methionine was higher ( between 2.4 x 10(-6) and 18.0 x 10(-6)) than that obtained using a medium w ithout any intentional source ofsulfur (between 0.7 x 10(-6) and 5.0 x 10(- 6)). The original strain, as well as the mutants, were able to grow in a su lfur-free liquid medium even after 4 consecutive inoculation procedures. Th ese results indicated the existence of sulfur traces in the medium and/or a n efficient intracellular storage system. There was no significant differen ce between cephalosporin C production in mutants and the original strain.