Event Title

High Incidence of Lux Merodiploids Indicates Frequent Horizontal Gene Transfer in Vibrios

Mentor 1

Chuck Wimpee

Location

Union Wisconsin Room

Start Date

29-4-2016 1:30 PM

End Date

29-4-2016 3:30 PM

Description

This laboratory has been carrying out a long-term study of bacterial bioluminescence as a model system for bacterial molecular evolution and interspecific gene mobility. In a diversity study of bioluminescent bacteria from Puerto Rico, we encountered a surprising number of Vibrio isolates possessing two copies of luxA. These merodiploids were initially detected by restriction endonuclease fingerprinting of luxA PCR products, in which the restriction fragments generated from certain strains added up to twice the size of the luxA amplicon. In addition, sequencing of amplified luxA from these strains revealed numerous mixed sites. Fingerprinting of multiple single colonies from each of these strains demonstrates that the two copies are not a result of contaminating single-copy lux strains. These merodiploids are not identical. Among 96 isolates from 2 ml of seawater, the diversity of luxA restriction patterns indicates that there are five different strain types carrying two copies. Merodiploids might arise by either gene duplication or by horizontal gene transfer (HGT). To distinguish between these two possibilities, PCR-amplified luxA genes from each merodiploid type were cloned, and multiple separate clones were fingerprinted and sequenced. Phylogenetic analysis of the cloned luxA sequences indicates that the merodiploids did not arise by gene duplication, but rather by import of luxA from other strains (HGT). Furthermore, we have identified the closest relatives for the individual luxA genes of the merodiploids, and find them among the single-copy lux strains we have isolated in the same water sample. These merodiploids thus represent intermediates in the process of HGT. The diversity of merodiploids that we find in only 2 ml of seawater supports the hypothesis that horizontal transfer of lux genes is a frequent and ongoing process in Vibrios. It is therefore likely that many other Vibrio genes that are less easily detected undergo frequent horizontal transfer, as well.

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Apr 29th, 1:30 PM Apr 29th, 3:30 PM

High Incidence of Lux Merodiploids Indicates Frequent Horizontal Gene Transfer in Vibrios

Union Wisconsin Room

This laboratory has been carrying out a long-term study of bacterial bioluminescence as a model system for bacterial molecular evolution and interspecific gene mobility. In a diversity study of bioluminescent bacteria from Puerto Rico, we encountered a surprising number of Vibrio isolates possessing two copies of luxA. These merodiploids were initially detected by restriction endonuclease fingerprinting of luxA PCR products, in which the restriction fragments generated from certain strains added up to twice the size of the luxA amplicon. In addition, sequencing of amplified luxA from these strains revealed numerous mixed sites. Fingerprinting of multiple single colonies from each of these strains demonstrates that the two copies are not a result of contaminating single-copy lux strains. These merodiploids are not identical. Among 96 isolates from 2 ml of seawater, the diversity of luxA restriction patterns indicates that there are five different strain types carrying two copies. Merodiploids might arise by either gene duplication or by horizontal gene transfer (HGT). To distinguish between these two possibilities, PCR-amplified luxA genes from each merodiploid type were cloned, and multiple separate clones were fingerprinted and sequenced. Phylogenetic analysis of the cloned luxA sequences indicates that the merodiploids did not arise by gene duplication, but rather by import of luxA from other strains (HGT). Furthermore, we have identified the closest relatives for the individual luxA genes of the merodiploids, and find them among the single-copy lux strains we have isolated in the same water sample. These merodiploids thus represent intermediates in the process of HGT. The diversity of merodiploids that we find in only 2 ml of seawater supports the hypothesis that horizontal transfer of lux genes is a frequent and ongoing process in Vibrios. It is therefore likely that many other Vibrio genes that are less easily detected undergo frequent horizontal transfer, as well.