ISOLATION AND PARTIAL CHARACTERIZATION OF CAROTENOID UNDERPRODUCING AND OVERPRODUCING MUTANTS FROM AN EXTREMELY THERMOPHILIC THERMUS-THERMOPHILUS HB27

Twenty-two carotenoid underproducing and thirteen overproducing mutant s were obtained from Thermus thermophilus HB27. The strain HB27 was fo und to produce at least seven colored carotenoids, believed to be iden tical to those produced by Thermus aquaticus YT1. Based on the results of the genetic analyses performed on twelve carotenoid underproducing mutants, they were classified into three groups; groups 1, 2 and 3. N o colored carotenoid was extracted from the cells of mutants belonging to groups 2 and 3, although the accumulation of phytoene, a colorless carotenoid, was observed in group 2 strains. Group 1 was subdivided i nto groups 1-a and 1-b, where 1-a strains produced neither colored car otenoids nor phytoene and 1-b strains produced two polar colored carot enoids. All of the overproducing mutants produced about twelve times a s much seven colored carotenoid mixtures as the parental strain. The m utation loci among all the overproducing mutants were very close to on e another, possibly in the same gene. Carotenoid overproducing mutants showed an extensive resistancy to UV-irradiation and showed poorer gr owth at higher temperatures. Carotenoid underproducing mutants were sl ightly more UV-sensitive but they grew almost normally at higher tempe ratures. These results suggest that carotenoids are secondary metaboli tes which are not essential for growth of T. thermophilus.