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The complete sequences and ecological roles of two IncP-1 beta plasmids, pHB44 and pBS64, isolated from the mycosphere of Laccaria proxima

Zhang, M., Brons, J. K. & van Elsas, J. D., 21-Jun-2016, In : Frontiers in Microbiology. 7, 11 p., 909.

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Two novel plasmids, coined pHB44 and pBS64, were recently found in Variovorax paradoxus strains HB44 and BS64 isolated from the mycosphere of Laccaria proxima, on two different sampling occasions. We here describe the full sequences of pHB44 and pBS64 and establish their evolutionary placement and ecological function. Both plasmids, unique for mycospheric V paradoxus, were around 58 kb in size. They possessed, in a very similar fashion, three main plasmid backbone regions, which were predicted to be involved in plasmid replication, central control of maintenance, and conjugational transfer. Phylogenetic inference on the basis of seven selected and concatenated plasmid backbone genes provided solid evidence for the placement of the two plasmids in the IncP-10 group, with the recently isolated IncP-10 plasmid pMBUI8 as the closest relative. A comparative analysis of the sequences present in each of the recombinational hot spots (RHS) I to III across plasmids pHB44, pBS64, and pMBUI8 revealed the insertions found in plasmids pHB44 and pBS64 to be different from those of pMBUI8. Whereas, in the former two plasmids, RHS I and III were devoid of any major inserts, their RHS II regions contained inserts of 15,043 (pHB44) and 16,406 kb (pBS64), against about 9,3 kb for pMBUI8. Interestingly, these regions were highly similar across plasmids pHB44 and pBS64, and differed from that of pMBUI8. Closer inspection revealed the insert in the former plasmids to contain, next to transposases, an "mmf" gene cassette previously reported to encode metal-responsiveness" in the PromA plasmid pM0L98. Whereas the plasmid pHB44 RHS II contained the canonical mmf sequence, that in pBS64 contained, in addition, a "two-gene duplicated region" flanking the mmfC2 gene. In vitro experiments on the growth and survival of strains with or without plasmid pHB44 suggested this plasmid was involved in the binding and import of Fe3+ as well as V3+ ions into the host cells, thus yielding a growth advantage under "metal ion-limiting" conditions. In addition, pHB44 was found to confer a bacitracin resistance phenotype to its host strain HB44. The metal import and bacitracin resistance traits were tentatively attributed to specific genes present in the RHS II inserts.

Original languageEnglish
Article number909
Number of pages11
JournalFrontiers in Microbiology
Volume7
Publication statusPublished - 21-Jun-2016

    Keywords

  • IncP-1 beta plasmids, horizontal gene transfer, plasmid evolution, mycosphere, Variovorax paradoxus, HOST-RANGE PLASMIDS, HORIZONTAL GENE-TRANSFER, ACCESSORY GENES, PROVIDES EVIDENCE, RECOMBINATION, EVOLUTIONARY, RESISTANCE, BACKBONE, SELECTION, INSERTION

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