The heliobacteria, a family of anoxygenic phototrophs, possess the simplest known photosynthetic apparatus. Although they are photoheterotrophs in the light, the heliobacteria can also grow chemotrophically via pyruvate metabolism in the dark. In the heliobacteria, the cytochrome bc complex is responsible for oxidizing menaquinol and reducing cytochrome c₅₅₃ in the electron flow cycle used for phototrophy. However, there is no known electron acceptor for the mobile cytochrome c₅₅₃ other than the photochemical reaction center. We have, therefore, hypothesized that the cytochrome bc complex is necessary for phototrophy, but unnecessary for chemotrophic growth in the dark. We used a two-step method for CRISPR-based genome editing in Heliobacterium modesticaldum to delete the genes encoding the four major subunits of the cytochrome bc complex. Genotypic analysis verified the deletion of the petCBDA gene cluster encoding the catalytic components of the complex. Spectroscopic studies revealed that re-reduction of cytochrome c₅₅₃ after flash-induced photo-oxidation was over 100 times slower in the ∆petCBDA mutant compared to the wild-type. Steady-state levels of oxidized P₈₀₀ (the primary donor of the photochemical reaction center) were much higher in the ∆petCBDA mutant at every light level, consistent with a limitation in electron flow to the reaction center. The ∆petCBDA mutant was unable to grow phototrophically on acetate plus CO₂ but could grow chemotrophically on pyruvate as a carbon source similar to the wild-type strain in the dark. The mutants could be complemented by reintroduction of the petCBDA gene cluster on a plasmid expressed from the clostridial eno promoter.

日光细菌属无氧光合生物家族，拥有已知的最简单的光合作用装置。尽管它们是光照下的光能异养菌，但日光菌也可以通过丙酮酸在黑暗中代谢进行化学营养生长。在日光细菌中，细胞色素bc复合物负责在用于光养的电子流循环中氧化甲基萘醌并还原细胞色素c ₅₅₃。然而，除了光化学反应中心之外，没有已知的可移动细胞色素c _{553 的}电子受体。因此，我们假设细胞色素bc复合物是光养所必需的，但对于黑暗中的化学营养生长则是不必要的。我们在Heliobacterium modeticaldum 中使用基于 CRISPR 的基因组编辑的两步法删除编码细胞色素bc复合体的四个主要亚基的基因。基因型分析证实了编码复合物催化成分的petCBDA基因簇的缺失。光谱研究表明，与野生型相比，ΔpetCBDA突变体在闪光诱导的光氧化后细胞色素c _{553 的}再还原速度要慢 100 倍以上。氧化 P _{800 的}稳态水平（光化学反应中心的主要供体）在ΔpetCBDA突变体中在每个光照水平上都高得多，这与电子流向反应中心的限制一致。所述ΔpetCBDA突变体不能在乙酸加CO光养增长₂，但可以对丙酮酸类似于在黑暗中野生型菌株的碳源chemotrophically生长。突变体可以通过在由梭菌eno启动子表达的质粒上重新引入petCBDA基因簇来补充。