Figure 1

Four representative scenarios for the early evolution of the photosynthetic process among photosynthetic bacteria. (a) The branching order of photosynthetic organisms based on 16S rRNA [4,18,19]. (b) The branching order for photosynthetic organisms proposed by Gupta and coworkers [20] using heat shock proteins; (c) the branching order that we [29] derived from analysis of (bacterio)chlorophyll biosynthesis genes (yellow arrows represent the direction of lateral gene transfer for the type II reaction center; green arrows represent the direction of lateral gene transfer for the type I reaction center); and (d) the branching order evolutionary pathway derived from analysis of photosynthesis genes by Galperin and coworkers [2] (black arrows represent the direction of lateral gene transfer for some photosynthesis genes).