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

Abstract

6-Methoxy-benzoxazolin-2(3H)-one (MBOA) is a degradation product derived from 2,4-Dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one (DIMBOA), one of the bioactive compounds found e.g., in maize. Here we present hitherto unknown 6-methoxy-4-nitro-benzoxazolin-2(3H)-one (NMBOA) produced in Czapek medium by Pantoea ananatis (Enterobacteriaceae). P. ananatis is a member of a microbial consortium dominated by the zygomycete Actinomucor elegans, which was isolated from roots of Abutilon theophrasti. NMBOA was identified by NMR spectra and HR-ESI-MS analyses, revealing an unusual position of the nitro group at C-4. Nitration of MBOA initiates the degradation of the compound that is almost completed within three days by the entire consortium and isolated P. ananatis. The yeast Papiliotrema baii, another member of the consortium, is unable to degrade NMBOA but stored it at the surface of its polysacchararide capsule. NMBOA has negative effects on microbial growth in liquid medium whereas seedlings of Brassica oleracea var. gongylodes L. (kohlrabi) or Lepidium sativum (cress) are not impaired up to 500 μM. Degradation via nitration may be important to understand the behavior of microbial species and effects of microbiomes when exposed to MBOA.