Project description:The Burkholderia cepacia complex (Bcc) comprises strains with a virulence potential toward immunocompromised patients as well as plant growth-promoting rhizobacteria (PGPR). Owing to the link between quorum sensing (QS) and virulence, most studies among Bcc species have been directed toward QS of pathogenic bacteria. We have investigated the QS of B. ambifaria, a PGPR only infrequently recovered from patients. The cepI gene, responsible for the synthesis of the main signaling molecule N-octanoylhomoserine lactone (C8 -HSL), was inactivated. Phenotypes of the B. ambifaria cepI mutant we observed, such as increased production of siderophores and decreased proteolytic and antifungal activities, are in agreement with those of other Bcc cepI mutants. The cepI mutant was then used as background strain for a whole-genome transposon-insertion mutagenesis strategy, allowing the identification of 20 QS-controlled genes, corresponding to 17 loci. The main functions identified are linked to antifungal and antimicrobial properties, as we have identified QS-controlled genes implicated in the production of pyrrolnitrin, burkholdines (occidiofungin-like molecules), and enacyloxins. This study provides insights in the QS-regulated functions of a PGPR, which could lead to beneficial potential biotechnological applications.
Project description:An antifungal aroma substance, 2-phenylethanol (PEA), was isolated from antagonistic yeast strain Kloeckera apiculata extract. Microarry were used to analyse its role citrus. We used microarrays to detail the global programme of gene expression underlying Citrus were treated with 1.0x108 cells/ml K. apiculata (KA), PEA (0.15%), the extract (1000xdilute) and control (CK) for 24 h,
Project description:The biocontrol agent Pythium oligandrum, which is a member of phylum Oomycota, can control diseases caused by a taxonomically wide range of plant pathogens, including fungi, bacteria, and oomycetes. However, whether P. oligandrum could control diseases caused by plant root-knot nematodes (RKNs) was unknown. We investigated a recently isolated P. oligandrum strain GAQ1, and the P. oligandrum CBS530.74 strain, for the control of RKN Meloidogyne incognita infection of tomato (Solanum lycopersicum L.). Initially, P. oligandrum culture filtrates were found to be lethal to M. incognita second-stage juveniles (J2s) with up to 84% mortality at 24 h after treatment compared to 14% in the control group. Consistent with the lethality to M. incognita J2s, tomato roots treated with P. oligandrum culture filtrates reduced the attraction of nematodes, and the number of nematodes penetrating the roots was reduced by up to 78%. In a greenhouse pot trial, P. oligandrum GAQ1 inoculation of tomato plants significantly reduced the gall number by 58% in plants infected with M. incognita. Notably, P. oligandrum GAQ1 mycelial treatment significantly increased tomato plant height (by 36%), weight (by 27%), and root weight (by 48%). Transcriptome analysis of tomato seedling roots inoculated with the P. oligandrum GAQ1 strain identified ~2,500 differentially expressed genes. The enriched GO terms and annotations in the up-regulated genes suggested modulation of plant hormone-signaling and defense-related pathways in response to P. oligandrum. In conclusion, our results support that P. oligandrum GAQ1 can serve as a potential biocontrol agent for M. incognita control in tomato. Multiple mechanisms appear to contribute to the biocontrol effect involving direct inhibition of M. incognita, potential priming of tomato plant defenses, and plant growth promotion.
Project description:Gene expression was examined during four growth conditions which modulated antimicrobial secretion in B. ambifaria AMMD. A minimal salts medium (BSM; Hareland et al. 1975. J Bacteriol 121:272-85) with 0.05% yeast extract was used for all comparisons with the carbon source (4 g/L) and growth condition varied as follows: (i) liquid culture with glucose; (ii) liquid culture with glycerol; (iii) growth on agar with glucose, and (iv) growth on agar with glycerol. For the liquid cultures, 25 ml of growth medium was placed a 250 ml conical flask and inoculated with 0.5 ml of a starter culture of strain AMMD which had been optically adjusted to O.D. 1 at 600 nm and corresponded to a viable count of 10 million colony forming units per ml. After growth with shaking (150 rpm) for 30 h at 30 degrees Celcius, the O.D. 600 nm of the cultures was measured to enable an estimation of cell density to be made, they were then snap-chilled and harvested as previously described (Drevinek et al. 2008. BMC Infect Dis 8:121), and frozen at -80 degrees Celcius. Growth on agar was performed by laying a sterile 47 mm nitrocellulose filter (0.22 ?m) onto a plate of the BSM agar and the same starter culture of AMMD as used for the liquid growth spread over a 2 cm diameter circular area using a sterile cotton swab. The agar cultures were incubated for 30 h at 30 degrees Celcius, the filters removed to sterile 50 ml conical tubes and the bacteria washed off by gentle pipeting using 2 ml ice cold BSM (without any carbon source or yeast extract). This resuspension of surface grown bacteria was processed prior to RNA extraction in an exactly the same way as the liquid cultures