Schematic of MCP pathways discussed in the text. (A) Pdu MCP; (B) Eut MCP; (C) Cut MCP; (D) Grp MCP. Shell protein names are shown in brown, signature enzymes in green, accessory enzymes (where applicable) in light green, aldehyde dehydrogenase in purple, alcohol dehydrogenase in red, phosphotransacetylase in blue, and acetate kinase in gold.