Identification of the bchP gene, encoding geranylgeranyl reductase in Chlorobaculum tepidum

Abstract

The Chlorobaculum tepidum genome contains two paralogous genes, CT2256 and CT1232, whose products are members of the FixC dehydrogenase superfamily and have sequence similarity to geranylgeranyl reductases. Each gene was insertionally inactivated, and the resulting mutants were characterized. CT2256 encodes geranylgeranyl reductase (BchP); CT1232 is not involved in bacteriochlorophyll or chlorophyll biosynthesis.

FIG. 1.

Esterifying alcohols of GSB (B)Chls. (A) phytol; (B) Δ2,6-phytadienol; (C) farnesol; and (D) geranylgeraniol.

FIG. 2.

HPLC elution profile of pigment extracts from the C. tepidum wild type and the CT2256 and CT1232 mutant strains. (A) HPLC elution profile recorded at 667 nm for pigment extracts from the wild type (solid line), the CT2256 mutant (dashed line), and the CT1232 mutant (dotted line). Peaks 1 through 6 have absorption spectra identical to those of BChl c but are esterified with alcohols other than farnesol, including phytol. (B) HPLC elution profile of pigment extracts recorded at 770 nm, the absorbance maximum of BChl a in HPLC solvents, for the wild type (solid line), the CT2256 mutant (dashed line), and the CT1232 mutant (dotted line).

FIG. 3.

HPLC elution profile of pigment extracts recorded at 770 nm for the C. tepidum wild type (A), the CT2256 mutant of C. tepidum (B), and the R. sphaeroides strains T6G5 (C) and T6G4 (D). The identified peaks are BChl a_P (1), BChl a esterified with tetrahydro-GG (Δ2,6-phytadienol) (2), BChl a esterified with dihydro-GG (3), and BChl a_GG (4).