Photosynthesis first emerged in prokaryotes over three billion years ago and represents one of the most fundamental biological processes on Earth. So far, species capable of performing (bacterio)chlorophyll-based phototrophy have been reported in seven bacterial phyla, i.e., Cyanobacteria, Proteobacteria, Chlorobi, Chloroflexi, Firmicutes, Acidobacteria, and Gemmatimonadetes. Here we review the discovery, physiology, genomic characteristics, environmental distribution, and possible evolutionary origin of the bacterium Gemmatimonas phototrophica strain AP64, so far the only phototrophic member of the phylum Gemmatimonadetes. This organism was isolated from a freshwater lake in the Gobi Desert, North China in 2011. It contains fully functional type-2 photosynthetic reaction centers, but they seem to only serve as an auxiliary energy source. Its photosynthesis genes are located in a 42.3 kb long photosynthesis gene cluster which appear to originate from an ancient horizontal gene transfer from a purple phototrophic bacterium. A survey of biomarker genes of phototrophic Gemmatimonadetes bacteria (PGB) in public environmental genomics databases suggests that PGB are widely distributed in diverse environments, including air, river waters/sediment, estuarine waters, lake waters, biofilms, plant surfaces, intertidal sediments, soils, springs, and wastewater treatment plants, but none from marine waters or sediment. PGB make up roughly 0.4-11.9 % of whole phototrophic microbial communities in these habitats. The discovery of PGB presents a strong evidence that genes for anoxygenic phototrophy can be transferred between distant bacterial phyla, providing new insights into the evolution of bacterial photosynthesis.