Modification of the esterifying farnesyl chain in light-harvesting bacteriochlorophylls in green sulfur photosynthetic bacteria by supplementation of 9-decyn-1-ol, 9-decen-1-ol, and decan-1-ol

• Green sulfur bacteria were cultivated with 9-decyn-1-ol, 9-decen-1-ol and decan-1-ol.
• Cba. tepidum produced unnatural BChls c esterified with the exogenous alcohols.
• Terminal unsaturated moieties in the alcohols barely affected BChl c biosynthesis.
• Cba. limnaeum produced no BChl e esterified with the exogenous alcohols.

Green sulfur photosynthetic bacteria Chlorobaculum (Cba.) tepidum and Cba. limnaeum were cultivated with the supplementation of 9-decyn-1-ol, 9-decen-1-ol, and decan-1-ol by two methods to biosynthesize unnatural chlorosomal bacteriochlorophyll (BChl) pigments possessing an (un)saturated bond at the terminus of the esterifying chain. The supplementation of the acetone solutions of the exogenous alcohols every 24 h to Cba. tepidum (denoted as Method A) successfully produced unnatural BChls c esterified with the alcohols in vivo. The ratios of unnatural BChls c esterified with 9-decyn-1-ol, 9-decen-1-ol, and decan-1-ol over the total BChls c in Cba. tepidum were not so different from each other, indicating that terminal unsaturated moieties in the exogenous alcohols barely affected the last reaction in the BChl c biosynthesis catalyzed by the BChl c synthase. Cba. tepidum grown in a liquid culture that initially contained 9-decyn-1-ol and 9-decen-1-ol (denoted as Method B) also accumulated BChls c esterified with these alcohols; the relative ratios of the unnatural BChls c were analogous to those obtained by Method A at the corresponding final concentrations. In contrast, Cba. limnaeum did not synthesize BChl e esterified with the three exogenous alcohols. The incorporation of unsaturated bonds into the esterifying moieties of BChl c by a biosynthetic reaction will be useful as structural probes for the investigation of pigment interactions and the biogenesis of chlorosomes as well as the scaffolds for bioorthogonal modifications.

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