Identifying and characterizing antibiotic producers found in and on the haustorium of Epifagus virginiana.

Abstract

Epifagus virginiana, a holoparsite of Fagus grandifolia, utilizes haustoria to parasitize its host. Little is known about the microbiome of this plant's parasitic organ. To shed light on these unexplored ecological interactions we collected eight individual E. virginiana specimens from Kanawha State Forest (Charleston, West Virginia) and used culture-based methods and microscopy to assess total counts and morphotypes, revealing a diverse microbial community on the haustorium surface, including 3 bacterial phyla and fungi. The internal haustorium environment was lower in counts and diversity, indicating the haustorium's internal microbiome is likely a subset of the soil microbiome. We explored the capabilities of these microorganisms to produce bioactive compounds. Fifty-eight morphospecies were investigated for cellulose degradation and antibiotic production. Forty-six isolates were challenged in a cross-streak assay against a Micrococcus roseus (Gram-positive) and Escherichia coli K12(Gram-negative) and 35% showed antagonism for at least one type. Seven surface isolates showed a range of antagonism against M. roseus from 0.85 cm ±0.21 cm to 2.25 cm ±0.07 cm, and 2 against E. coli from 0.75 cm ±0.35 cm to 100%. Two of the internal isolates showed a range of antagonism against M. roseus and E. coli from 1.25 cm ±0.07 cm to 2.35 cm ±0.07 cm and 0.4 cm ±0.00 cm to 2.05 cm ±0.21 cm, respectively. Currently, we are testing these isolates against ESKAPE pathogens and using 16S rRNA sequencing and Biolog ® to further characterize them and their potential as a source of novel antibiotics or bioactive compounds.