FIG 4.

Proposed model of electron flow from lactate by confurcation to APS for sulfite production in D. alaskensis G20 in exponential phase of growth. (A) Wild-type cultures with lactate-sulfate medium where small amounts of reductant appear in hydrogen (8%) and formate (not detected) (Table 2). Menaquinol is produced by either route a or b or both route a and b (indicated in blue) in the model. (B) Wild-type cultures with pyruvate-sulfate medium where small amounts of reductant are produced as hydrogen (9%) and formate (9%). Menaquinol is produced by electrons delivered to the Qrc complex by the TpIc₃ by route a. (C) CycA mutant cells with pyruvate sulfate medium unable to generate menaquinol by either route a or b and, therefore, not able to use reduced ferredoxin for reduction of APS. Reductant appears in hydrogen (88%) and formate (12%). In this model, the abbreviation of TMC is used as a generic term for an unidentified transmembrane complex. FDH, formate dehydrogenase; Hase, hydrogenase; MQ, menaquinone; Fd, ferredoxin; PPi, inorganic pyrophosphate.