Serratia odorifera, an antagonistic rhizobacterium, emits a diverse and complex bouquet of volatiles. Three different in vitro experimental culture systems indicated that these volatiles promote the growth of Arabidopsis thaliana. CO(2) trapping and significant rise of CO(2) levels (390-3000 ppm CO(2) within 24 h) due to bacterial growth in sealed Petri dishes verified the enhanced effects of rhizobacterial CO(2) on A. thaliana's growth. In contrast, open cocultivations abrogated growth promotion, and inhibitory effects come to the fore at ambient CO(2) concentrations.