POSSIBLE INVOLVEMENT OF RED PIGMENTS IN DEFENSE AGAINST MERCURY IN PSEUDOMONAS K-62

To study the physiological role of the red pigments in soil strain Pse udomonas K-62, we isolated a red pigment-deficient white mutant from t he soil strain by treatment with mitomycin C and compared the phenotyp ic properties of the mutant and parent strain. The red pigments, which were classified as one of carotenoids based on their physicochemical properties, were separated into two groups, designated pigment A and B respectively on NH-Chromatorex HPLC. The crude pigments and pigment B which could react with Hg2+ in the wild-type Pseudomonas K-62 and its mercury-resistant plasmid-deficient strain were enhanced by the addit ion of Hg2+. Th, white mutant thus obtained showed a greater sensitivi ty to Hg2+ than the wild-type reddish strain despite containing the re sistant plasmids. The major component in pigment B was identified by m ass spectrometric analysis as y-1,2,1',2',7',8'-hexahydro-psi,psi-caro ten-4-one, a carotenoid monoketone. These results suggested that red p igments, especially pigment B, may account, at least partially, for de fense against Hg2+ in the bacterial environments.