Prophage induction and acetate availability are associated with distinct <i>Lactiplantibacillus plantarum</i> electrode responses

grown in a chemically defined medium supplemented with quinones, depending on substrate and cultivation regime. In batch culture on glucose, the anode slows growth despite yielding an over four-fold higher ratio of acetate to lactate than the open-circuit control, a fermentation profile associated with higher ATP yield. In batch culture on the more reduced substrate mannitol, the anode facilitates growth by enabling the dissipation of reducing equivalents. However, when acetate is also present as an alternate electron sink, the anode prolongs the lag phase while maintaining a growth rate similar to the open-circuit control, despite the expected ATP cost of acetate-to-ethanol reduction. Under semi-continuous cultivation on mannitol in the absence of acetate, anode polarization reduces growth yield relative to open-circuit conditions. Although the anode promotes more energetically favorable fermentation patterns during batch growth on both glucose and mannitol, these are likely counterbalanced by prophage induction to affect population growth, as confirmed by transcriptomic analysis, extracellular DNA measurement, and transmission electron microscopy. Together, these results indicate that extracellular electron transfer associated with an anode is not necessarily beneficial for fermenters and prompt further inquiry into the context-dependent nature of this style of metabolism. IMPORTANCE: growth and is associated with induction of prophages, increasing the rate of lysis and thereby possibly counteracting the benefits of metabolic flexibility and more energetic fermentation patterns. These results make a new connection between electron balancing and a mobile genetic element and suggest a dynamic, context-dependent role of these mediators as public goods.