6-Hydroxy-5-nitrobenzo[d]oxazol-2(3H)-one—A degradable derivative of natural 6-Hydroxybenzoxazolin-2(3H)-one produced byPantoea ananatis

Abstract

Pantoea ananatis is a bacterium associated with other microorganisms on Abutilon theophrasti Medik. roots. It converts 6-hydroxybenzoxazolin-2(3H)-one (BOA-6-OH), a hydroxylated derivative of the allelochemical benzoxazolin-2(3H)-one, into 6-hydroxy-5-nitrobenzo[d]oxazol-2(3H)-one. The compound was identified by NMR and mass spectrometric methods. In vitro synthesis succeeded with Pantoea protein, with isolated proteins from the Abutilon root surface or with horseradish peroxidase in the presence of nitrite and H2O2. Nitro-BOA-6-OH is completely degraded further by Pantoea ananatis and Abutilon root surface proteins. Under laboratory conditions, 6-hydroxy-5-nitrobenzo[d]oxazol-2(3H)-one inhibits Lepidium sativum seedling growth whereas Abutilon theophrasti is much less affected. Although biodegradable, an agricultural use of 6-hydroxy-5-nitrobenzo[d]oxazol-2(3H)-one is undesirable because of the high toxicity of nitro aromatic compounds to mammals.

Conversions of Benzoxazinoids and Downstream Metabolites by Soil Microorganisms

“…Therefore, the nitration of MBOA is a rate limiting step. The reduction of nitrate presents a key step for NBOA-6-OH formation, whereas the subsequent nitration of BOA-6-OH occurs spontaneously but is dramatically accelerated by peroxidase (Schulz et al, 2017b). Hydroxylation of BOA by plants is a prerequisite for nitration by bacteria.…”

“…The compound can be attached to cellular surfaces, as found with the yeast Papiliotrema baii. NBOA-6-OH and NMBOA are degraded by P. ananatis and the A. elegans consortium (Schulz et al, 2017b(Schulz et al, , 2018. Hydroxylation of BOA prevents its degradation to AP and subsequent formation of APO or AAPO (19).…”

“…Compounds used for incubations or as references were either purchased (AP, AAP, BOA, MBOA, BOA-6-OH from Sigma-Merck, Munich, Germany) or synthesized (NBOA-6-OH, APO, according to the methods described in Schulz et al, 2017b). GDIBOA, DIBOA, DIMBOA glucoside carbamate, oHPMA and HBOA were either isolated from plants or synthesized (Sicker et al, 1989;Hartenstein et al, 1993;Friebe et al, 1998;Wieland et al, 1998).…”

Pantoea ananatis Converts MBOA to 6-Methoxy-4-nitro-benzoxazolin-2(3H)-one (NMBOA) for Cooperative Degradation with its Native Root Colonizing Microbial Consortium

“…The dissolved residue was purified by TLC as described [10]. A yellow band (R f = 0.82) containing the compound was extracted with methanol/chloroform, centrifuged at 20.000g und evaporated to dryness.…”

“…Natural Product Communications Vol. 13(10) 2018 1277 and by gas chromatography electron ionization mass spectrometry (GC-EI-MS).Incubation of the consortium and of the Pantoea ananatis isolate with 1mg DIMBOA pre-dissolved in 0.5 mL methanol/15 mL medium led to the same compound. Larger amounts were obtained by an in vitro assay at room temperature composed of 16 mg MBOA in 60 mL 100 mM phosphate buffer pH 6.8, 10 mM NaNO 2 , 1mM H 2 O 2 and 1U horseradish peroxidase (HRP, Sigma): the assay was stopped after one hour by extraction with EtOAc.…”