Neisseria gonorrhoeae and humans perform an evolutionary LINE dance

Abstract

Horizontal gene transfer is an important mechanism for generating genetic diversity. As the number of sequenced genomes continues to increase, so do the examples of horizontal genetic exchange between both related and divergent organisms. Here we discuss the recent finding that certain strains of the human pathogen Neisseria gonorrhoeae have incorporated a small fragment of human DNA sequence into their genomes. The horizontally acquired sequence exhibits 98-100% nucleotide identity to a 685 bp portion of the highly repetitive retrotransposable element L1 and its presence in the gonococcal genome has been confirmed by multiple molecular techniques. The possibility of similar L1 horizontal gene transfer events having occurred in other bacteria based on genomic sequence evidence is explored. Potential mechanisms of how N. gonorrhoeae was able to acquire and maintain this human sequence are also discussed in addition to the evolutionary implications of such an event.

Figure 1

Schematic of the N. gonorrhoeae nL1 HGT event. (A) Gene organization of a full-length L1 retrotransposable element (Genbank, U09116.1). The sequence corresponding the nL1 fragment found in N. gonorrhoeae is indicated by the black line below the L1 element. The horizontal lines above the L1 element indicate approximate locations of sequences that were identified by BLAST analysis as having a high degree of similarity to other bacterial genome or protein sequences, as described in the text. The NCBI DNA and protein accession numbers given above the lines indicate the specific bacterial sequences that exhibit identity to L1. (B) The nL1 fragment (orange) containing portions of L1 ORF1 and the 5′ UTR is shown in relation to neighboring gonococcal genes (gray arrows).