Figure 1.

C. elegans is attracted to lactic acid bacteria grown on media containing citrate. (a) Strategy of study. L. paracasei (LAB) or E. coli strain OP50 is grown on several types of media (media +bacteria) including a rich MRS media (rich), a minimal media (min), minimal media containing glucose (min+glu), minimal media containing citrate (min+citr), minimal media containing both glucose and citrate (min+glu+citr) and nematode growth media (NGM). Media without bacteria (media−bacteria) is used as a control. A 7.5-mm agar plug is taken from each plate and used either for colorimeteric analysis to measure diacetyl production, or attraction behavior assay. In the attraction behavior assay, the +bacteria agar plug is placed on the lid of a 9-cm plate, and the –bacteria agar plug is placed on the opposite side, and C. elegans are allowed to move freely on an agar assay plate (see Materials and Methods). (b) Diacetyl production of L. paracasei grown for 2 days on different types of media. Diacetyl concentration is measured by colorimetric analysis in four separate experiments (Diacetyl standard curves are provided in Supplementary Figure S2). Error bars indicate s.e. (c) C. elegans attraction behavior to diacetyl (1:1000 dilution), E. coli strain OP50 or L. paracasei (LAB) grown for 2 days on rich or citrate media. Error bars indicate s.e. (d) Bacterial colony count (top), diacetyl production (middle) and C. elegans attraction behavior (bottom) to LAB grown on citrate media over 72 h. Colony count is measured as colony forming units (cfu). Diacetyl levels are measured as sample absorbance at 525 nm. Error bars indicate s.e. Significance was calculated by Student's t-test and P-values are indicated.