Fig. 1. GABA induction of spore formation and production of SDF-2. (A) KP cells developing as monolayers were treated with various concentrations of GABA and the proportion of spores determined after 1 hour (circles). They were also incubated with antibodies to AcbA for 30 seconds before adding various concentrations of GABA (squares). Each experiment was repeated three to five times; the error bars represent one s.d. (B) 10 nM GABA was added to KP cells (squares) and dhkA^–/K cells (circles) developing as monolayers. Aliquots of the surrounding buffer were collected at the times indicated and stored frozen. SDF-2 activity was determined in serial dilutions of the samples using the KP cell bio-assay as previously described (Anjard et al., 1998). The amount of SDF-2 is given as units per 10³ cells. The lower limit in this assay is five units per 10³ cells.