Spent media from coenzyme Q-deficient E. coli contain high concentrations of D-lactic acid that serves as an energy source for respiring bacteria but has no direct effect on worm survival. (A) GD1 E. coli has fermentative metabolism at normal oxygen levels. Spent media of indicated cultures or LB medium were assayed for D-lactic acid. Asterisks indicate p-values < 0.05 when compared to D-lactic acid content in OP50 spent media. (B) GD1:pAHG cells carrying a wild-type copy of the ubiG in a plasmid were suspended in either their own spent media or the respiration deficient GD1:pBSK spent media (see flow chart below panel B). One cohort of plates was UV-irradiated to kill the E. coli cells. Wild-type worms were fed these diets starting at the L4 larval stage. Diets were composed of E. coli cells suspended in: GD1:pAHG spent media (black squares, n = 52); GD1:pBSK spent media (grey squares, n = 60); GD1:pBSK spent media + UV (grey dashed line, n = 64); GD1:pAHG spent media + UV (black dashed line, n = 64). UV treatment of E. coli cells suspended in spent media increased nematode mean life span as compared to nematodes fed designated diets without UV treatment (p-value < .0001). For (A and B) data were subjected to one-way ANOVA with Fisher’s test at a significance level of p < 0.05. (C) E. coli cells from overnight GD1:pAHG cultures were pelleted and the spent media kept on ice. The cells were diluted to an A600nm of 0.1 in either LB medium (black), GD1:pAHG spent medium (dark grey), or GD1:pBSK spent media (light grey). Cultures were grown at 37°C, 250 rpm, and the A600nm was determined after 23 h. Asterisk indicates p-value < 0.05 determined with Student’s t-test for comparison of GD1:pAHG with GD1:pBSK.