FIGURE 3.

Regulation of the sodorifen emission in Serratia spp. by the carbon source. S. plymuthica 4Rx13 was cultivated in minimal medium supplemented with either 55 mM succinate, glucose, or a mixture of both (each 55 mM). (A) Relative sodorifen emission of S.p. 4Rx13. The volatiles were collected every 24 h by solid phase micro extraction (SPME) and analyzed using GC/MS. The peak area of sodorifen after 24 h cultivation in complex medium was used as reference (100%). ^∗p ≤ 0.01. (B) Concentration dependent inhibition of the sodorifen emission in S.p. 4Rx13. ^∗p ≤ 0.01; ^#p < 0.005; ^∗∗p < 0.05. (C) Growth of S.p. 4Rx13 in MM + 55 mM glucose and MM + 55 mM succinate. (D) Positive effects of succinate on the sodorifen emission in different sodorifen producing strains (S.p. 4Rx13, S.p. HRO- C48, S.p. 3Re4-18, S.p. S13). NB = complex medium (nutrient broth); succ = minimal medium + 55 mM succinate. For (B,D) sodorifen emission was assessed using the closed VOC collection system (modified after Kai et al., 2010) and analyzed by GC/MS. Quantification was performed with an internal standard (nonylacetate, 5 ng) and nutrient broth (NB) used as a reference. ^∗p ≤ 0.05. (E) Expression level of the terpene cyclase gene of the sodorifen biosynthesis cluster in S.p. 4Rx13 after 24 h cultivation in MM + 55 mM succinate. Each lane contained 5 μg of total RNA. A DIG – dUTP – labeled probe was used for detection of terpene cyclase mRNA (upper panel). A second hybridization with a 16S rRNA probe was used as a positive control (lower panel). Hybridization of probes to the corresponding mRNAs was detected by fluorescence measurements for 1 min. Experiments were performed in triplicates and error bars represent standard deviation.