Six unique isolates possessed single transposon insertions within the coding region of six different genes (see Table S1 in the supplemental material). nrdD encodes an anaerobic nucleotide reductase required for production of nucleotides during anaerobic growth of L. monocytogenes (21). pdhC encodes the E2 subunit of pyruvate dehydrogenase, which converts pyruvate to acetyl-coenzyme A (acetyl-CoA) while generating NADH (22). menF and menD encode enzymes for the first two dedicated steps in the biosynthesis of MK, a membrane-bound molecule which shuttles electrons between different complexes of the election transport chain (23). Finally, two genes of unknown function were identified in this genetic screen: lmo1602 and yvcJ. lmo1602 appears to be a sigma B-regulated gene associated with stress responses (24, 25), whereas yvcJ is cotranscribed with yvcK (26), a gene previously found to be required for cytosolic survival of L. monocytogenes (8).