Decanal

Twenty types of compounds, derived from tea plants and plant-derived semiochemicals attracted to other thrips, were used in our trials [4 (link),24 (link),25 (link),26 (link)]. In particular, 4-acetylpyridine, p-anisaldehyde, decanal, eugenol, farnesene (mixture of isomers, α-farnesene, and (E)-β-farnesene), geraniol, (Z)-3-hexenol, (Z)-3-hexenyl butyrate, limonene, methyl anthranilate, methyl benzoate, 3-methyl butanal, methyl isonicotinate, methyl salicylate, β-myrcene, nonanal, (E)-β-ocimene, (−)-α-pinene, (+)-α-pinene, and γ-terpinene were all purchased from Sigma-Aldrich (St. Louis, MO, United States) (Table S1). Hexane (HPLC grade, CNW Technologies GmbH (Düsseldorf, Germany)) was chosen as solvent, and the abovementioned synthetic volatiles were diluted to a specific concentration.

Laboratory grade dodecane (D–H, D = C₁₂H₂₅) was purchased from Fisher Chemical and used as is. Analytical standard grade chemicals used for GC-TOFMS identification of octanol, octanal, decanal, dodecanol, and dodecene were purchased from Sigma Aldrich and used as is. All other compounds were synthesized in-house and had a purity >97% as measured with ¹³C- and ¹H-NMR spectroscopy.

Erythromycin was purchased from Tokyo Chemical Industry (Tokyo, Japan). NF-κB inhibitor, 5HPP-33, was purchased from Merck KGaA (Darmstadt, Germany). Acrolein, crotonaldehyde, dansyl hydrazine (DH), glyoxal, 2,4-decadienal (DDE), heptadecanal, hexadecanal, 2,4-nonadienal (NDE), octadecanal, 2-octenal, pentadecanal, tetradecanal and 2-undecenal were also purchased from Tokyo Chemical Industry (Tokyo, Japan). Acetaldehyde, p-Toluenesulfonic acid (p-TsOH) and the reactive carbonyl species (RCs), including propanal, pentanal, butanal, 2-hexenal, hexanal, 2-heptenal, heptanal, octanal, 2-nonenal, nonanal, decanal, undecanal, dodecanal and tridecanal, were obtained from Sigma-Aldrich (St. Louis, MO). 4-Hydroxy-2-hexenal (HHE), 4-hydroxy-2-nonenal (HNE) and 4-oxo-2-nonenal (ONE) were purchased from Cayman Chemical Company (Ann Arbor, MI). p-Benzyloxybenzaldehyde (p-BOBA) was purchased from Wako Pure Chemical Industries (Osaka, Japan). 8-Heptadecenal (8-HpDE), 8,11-heptadecadienal (8,11-HpDDE) and 8,11,14-heptadecatrienal (8,11,14-HpDTE) were synthesized using a previously described method.^{(10 (link),11 (link))} Secosterol-A and B were synthesized according to a procedure reported by Wentworth et al.^{(12 (link))} Stock solutions of the RCs and an internal standard (IS) (p-BOBA, 10 µM) were prepared separately in acetonitrile and stored at −20°C prior to use.

The bioassay was performed as previously described^{41 (link)}. Briefly, B. cenocepacia H111–rpfF_Bc (pan-L15) was grown in Luria Bertani (LB) medium with chloramphenicol (80 µg/mL) and kanamycin (100 µg/mL) at 30 °C. A fresh overnight culture at an OD 600 of 1.8–2.0 was diluted 1:1 with LB medium from which, 200 μL was added to 96-well plates (transparent, Brandt)^{41 (link)}. Before addition of the biosensor culture, synthetic standard compounds or extracts from acidophile bacterial cultures were added to the plate in triplicate. Synthetic BDSF, DSF, and various AHL standards dissolved in DMSO were added to individual wells in the 96-well plate (DMSO was used for the control). Extracts from Leptospirillum spp. pyrite cultures (300 µL) were re-dissolved in ethanol and added to individual wells in the plate. The solvent was evaporated at room temperature in a laminar flow chamber before addition of the biosensor culture. The plates were incubated for 20 h at 30 °C. Afterwards, 2 μL decanal (Sigma) was added to each well to detect luciferase activity of the biosensor using a luminometer. Luminescence levels in arbitrary units (AU) were recorded using a plate reader (FLUOstar Omega™, BMG Labtech®).

2-Butanone (≥99%), 2-furaldehyde (≥99%), 2-methylbutanal (90%), 4-heptanone (97%), carvone (≥98.5%), decanal (95%), decane (≥99%), formaldehyde (37% aqueous solution), hexanal (97%), methylglyoxal (40% aqueous solution), O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine hydrochloride (PFBHA) (≥ 99%), octanal (≥99%) and p-cresol (4-methylphenol) (≥98%) were purchased from Sigma-Aldrich (Madrid, Spain). Sodium chloride was supplied by VWR (Leuven, Belgium).

Colonies of the bacterial strains MG1655 (K-12), JON53-clyA⁺::luxAB (COE2), COE3, COE4 and COE6, from plates incubated overnight were inoculated into LB broth medium. The bacteria were cultured aerobically at 37°C. The optical density (OD_600nm) was measured during growth at different time points. In parallel, the transcriptional activity was measured in a Sirius luminometer using decanal as a substrate. One hundred μl of a 0.1% v/v suspension of decanal (Sigma) in water was added to 100 μl of bacterial culture as programmed by the Sirius instrument and light emission was measured. Triplicates were measured for each sample and specific activity (lux activity units/OD_600nm) was calculated and plotted.