PARENT SESSION
Posters P5C Biosynthesis and assembly: Pigments. Abstracts (643-659)

Carotenoids and carotenogenesis pathway in the cyanobacterium Anabaena sp. PCC 7120 and Nostoc punctiforme PCC 73102. Mari Mochimaru^*,1, Shinichi Takaichi², ¹ Natural Science Faculty, Setagaya, Tokyo, Japan² Biological Laboratory, Kawasaki, Kanagawa, Japan

ABSTRACT- Anabaena sp. PCC7120 and Nostoc punctiforme PCC73102 are filamentous, heterocystous cyanobacteria, and their entire genome have already been analyzed. In spite of their prominency as experimental material, pigments of these species have not been adequately characterized. Recently, pigments of another cyanobacterium Synechocystis sp. PCC6803 have been identified; myxol 2′-dimethyl-fucoside (not rhamnoside), -carotene, zeaxanthin, and echinenone (Takaichi et al. (2001) Plant Cell Physiol. 42:756-762). In this study, we identified the pigments of Anabaena sp. PCC7120 and Nostoc punctiforme PCC73102. In A. 7120, chlorophyll a was sole chlorophyll. (3R,2′S)-Myxol 2′-fucoside (8%, mol% of total carotenoids) and (3S,2′S) 4-keto-myxol 2′-fucoside (4%) were polar carotenoids. Other carotenoids were -carotene (62%), echinenone (25%), canthaxanthin (1%), and some minor components (less than 1%). In N. 73102, the compositions of the major pigments were almost similar to those in A. 7120; (3R,2′S)-myxol 2′-fucoside (11%), (3S,2′S) 4-keto-myxol 2′-fucoside (13%), -carotene (45%), echinenone (17%) and canthaxanthin (13%). We will present a proposed biosynthetic pathway of the carotenoids in those two cyanobacteria. 7 genes (crtE, B, P, Q, H, R and O) have already been functionally identified in other bacteria, and close homologues of these genes were found in the genome of A. 7120 and N. 73102 by similarity search. In comparison with the enzymes of Synechocystis sp. PCC6803, there seem to be some differences in substrate specificity. The substrates of -carotene ketolase (CrtO) are determined to be -carotene and -cryptoxanthin in S. 6803, but may be -carotene, echinenone, and myxol fucoside in A. 7120 and N. 73102. -carotene hydroxylase (CrtR) in S. 6803 can synthesize -cryptoxanthin, 3′-OH-echinenone, and zeaxanthin, but in A. 7120 and N. 73102 this enzyme has little or very low activity in this pathway. The pathway from lycopene to myxol fucoside remains unknown.

KEY WORDS: Anabaena sp. PCC7120, carotenoid, Nostoc punctiforme PCC73102, crt-gene