RT Journal
A1 Kunin, Victor
A1 Goldovsky, Leon
A1 Darzentas, Nikos
A1 Ouzounis, Christos A.
T1 The net of life: Reconstructing the microbial phylogenetic network
JF Genome Research 
JO Genome Research 
YR 2005 
FD July 01 
VO 15 
IS 7 
SP 954 
OP 959 
DO 10.1101/gr.3666505 
UL http://genome.cshlp.org/content/15/7/954.abstract 
AB It has previously been suggested that the phylogeny of microbial species might be better described as a network containing vertical and horizontal gene transfer (HGT) events. Yet, all phylogenetic reconstructions so far have presented microbial trees rather than networks. Here, we present a first attempt to reconstruct such an evolutionary network, which we term the “net of life.” We use available tree reconstruction methods to infer vertical inheritance, and use an ancestral state inference algorithm to map HGT events on the tree. We also describe a weighting scheme used to estimate the number of genes exchanged between pairs of organisms. We demonstrate that vertical inheritance constitutes the bulk of gene transfer on the tree of life. We term the bulk of horizontal gene flow between tree nodes as “vines,” and demonstrate that multiple but mostly tiny vines interconnect the tree. Our results strongly suggest that the HGT network is a scale-free graph, a finding with important implications for genome evolution. We propose that genes might propagate extremely rapidly across microbial species through the HGT network, using certain organisms as hubs.