Metabolic bacterial genes and the construction of high-level composite lineages of life

Abstract

Understanding how major organismal lineages originated is fundamental for understanding processes by which life evolved. Major evolutionary transitions, like eukaryogenesis, merging genetic material from distantly related organisms, are rare events, hence difficult ones to explain causally. If most archaeal lineages emerged after massive acquisitions of bacterial genes, a rule however arises: metabolic bacterial genes contributed to all major evolutionary transitions.

Keywords: eukaryogenesis; evolutionary transition; lateral gene transfer; prokaryotic evolution; tree of life; web of life.

Figure 1

Introgression of metabolic bacterial genes: a recurrent evolutionary theme at the origin of novel composite lineages. First reports of bacterial genes contributions to the evolution of lineages were documented in eukaryotes (orange arrows), with the discoveries of eukaryogenesis, the primary chloroplastic endosymbiosis at the origins of Archaeaplastida, or of more recent endosymbioses endowing several eukaryotic lineages with additional metabolic capabilities, exemplified here by the tripartite nested mealybug symbiosis. Nelson-Sathi et al. profoundly expanded this view, as they propose that numerous major archaeal lineages (pink arrows) also originated from the massive acquisition of bacterial genes.