Functional verification of bacteriochlorophyll biosynthetic genes distributed in pink-pigmented facultative...

Pink-pigmented facultative methylotrophs (PPFMs), represented by the genera Methylobacterium and Methylorubrum, are ubiquitous bacteria commonly found in nutrient-poor environments such as plant leaf surfaces. Comparative genomics has revealed that many PPFMs possess genes for bacteriochlorophyll (BChl) biosynthesis; however, whether these genes support functional phototrophy has remained largely unknown. Here, we systematically investigated BChl production and its physiological function in PPFMs. Among 43 Methylobacterium/Methylorubrum type strains examined, 36 produced BChl, demonstrating that BChl production is widespread despite substantial diversity in the culture conditions required for its induction. In Methylorubrum extorquens AM1, BChl production required light and specific carbon substrates, and light stimulated the expression of BChl biosynthetic genes. In contrast, Methylobacterium phyllosphaerae CBMB27 produced BChl under standard growth conditions, with a modest transcriptional response to light. Comparison of intracellular ATP levels between the wild-type and the ΔbchZ strains demonstrated BChl-dependent ATP production in Methylobacteriumphyllosphaerae CBMB27, but not in Methylorubrumextorquens AM1. Under carbon-limited conditions, this BChl-dependent ATP production conferred a measurable growth advantage. These findings demonstrate that BChl-mediated phototrophy is physiologically functional in at least a subset of PPFMs, and suggest that the regulation and ecological roles of BChl production have diversified among species.