A Burkholderia strain living inside the arbuscular mycorrhizal fungus Gigaspora margarita possesses the vacB gene, which is involved in host cell colonization by bacteria

The arbuscular mycorrhizal (AM) fungus Gigaspora margarita harbors a reside nt population of endosymbiontic Burkholderia in its cytoplasm. Nothing is k nown about the acquisition of such bacteria and about the molecular bases w hich allow colonization of the fungus. We wondered whether the intracellula r Burkholderia strain possesses genetic determinants involved in colonizati on of a eukaryotic cell. Using degenerated oligonucleotide primers for vacB , a gene involved in host cell colonization by pathogenic bacteria, an 842 by DNA fragment was cloned, sequenced, and identified as a part of the vacB gene in Burkholderia sp. The insert was used as a probe to screen a fungal library that, because of the presence of intracellular Burkholderia cells, was also representative of the bacterial genome. The complete nucleotide s equence of vacB and flanking genes was determined. The bacterial origin of this genomic region was established by PCR, using specific vacB primers on DNA from Gigasporaceae that did or did not contain cytoplasmic Burkholderia , as well as on DNA from other bacteria, including free-living Burkholderia . We hypothesize that the vacB gene is part of a new genetic region acquire d by a rhizospheric Burkholderia strain, which became able to establish a s ymbiotic interaction with the AM fungus G. margarita.