Phylogenetic analysis To gain a better taxonomic understanding of the Serratia G3 isolate a 16S rDNA-based phylogenetic tree was compiled using the neighbour-joining method of MEGA 4. The 16S rRNA gene sequence from the G3 isolate, we BI 10773 recently published elsewhere [23] was analysed together with those from other members of the genus Serratia, including the S. plymuthica DSM 4540 type strain as a reference and the related strains check details S. proteamaculans DSM 4543, S. ficaria DSM 4569, S. entomophila DSM 12358, S. odorifera DSM 4582, S. marcescens DSM 30121, as well as S. plymuthica RVH1 from a raw vegetable

processing line and an endophytic strain JA05 isolated from ginseng plants. In addition, Escherichia coli ATCC 25922 as an outgroup. These 16S rRNA sequences were obtained from GenBank. The tree topology was tested by bootstrap analysis buy GSK872 of 1000 samplings. Cloning

and sequencing of two pairs of LuxIR homologues from S. plymuthica strain G3 Production of AHL signal molecules in strain G3 was detected using a T-streak assay with C. violaceum CV026 on plates. The following two pairs of primers for the cloning the splIR and spsRI loci were designed to the conserved regions of the corresponding genes in the genus Serratia using the ClustalW multiple sequence alignment program: SplIR-F: 5′-TTTGTAGAATACCGGCAAGCTGTT -3′ and SplIR-R: 5′-CAGATCGTCACGGAGCCTGT-3′; SpsRI-F:5′-GAGAGGGTTCAGTGTCAAAT-3′ and SpsRI-R: 5′-CCATGGAAGATGTAGAAATG-3′. These genes were amplified using G3 genomic DNA as a template by PCR and cloned into pMD-19T (Takara, Dalian, China). The clones expressed the AHL synthases SplI or SpsI in E. coli

DH5α were selected by T-streak with C. violaceum CV026 for further identification of AHL profiles, and confirmed by PCR and sequencing (Sangon Co. Ltd., Shanghai, China). A neighbour-joining tree of LuxI family members was produced using the P-type ATPase MEGA 4. Amino acid sequences of SplI and SpsI from the G3 isolate were aligned and analysed together with LuxI homologs from other eight members of Serratia and EsaI from Pantoea stewartii DC283. TraI of Agrobacterium vitis S4 was tested as outgroup. These amino acid sequences of LuxI homologs were obtained from GenBank. Confidence in neighbour-joining tree was determined by analysing 1000 bootstrap replicates. AHL degradation by heterologous expression of the AiiA acyl-homoserine lactonase A quorum-quenching approach was used to identify AHL-regulated biocontrol-related phenotypes in the endophytic strain G3. E. coli S17-1/pME6863 carrying the AHL-lactonase aiiA from the Bacillus sp. strain A24 under the control of the constitutive lac promotor [21] was used to mobilise aiiA into G3 by conjugation to obtain G3/pME6863-aiiA. G3 containing pME6000 was used as a control.