Confocal laser scanning micrographs of rhizoxin-producing bacterial endosymbionts (Burkholderia rhizoxinica, labeled with GFP) in the mycelium of Rhizopus microsporus (main image) and in spores (inset). Bars: 10 μm (main image), 5 μm (inset).
The presence of endobacteria in the rhizonin-positive Rhizopus strain was unequivocally proven by transmission electron microscopy and the amplification of bacterial 16S rRNA gene sequences. The rod-shaped bacterial symbionts within the mycelium could be isolated and grown in pure culture. It turned out that the rhizonin producer is a close relative of B. rhizoxinica and is also capable of producing rhizoxin. Despite high similarity on the 16S rRNA sequence level, genome–genome hybridization experiments suggest defining a new species named Burkholderia endofungorum