ABSTRACT
Stromatolites are complex microbial mats that form lithified layers and ancient forms are the oldest evidence of life on earth, dating back over 3.4 billion years. Their emergence aligns with the oxygenation of the Earth’s atmosphere and insight into these ancient structures would shed light on the earliest days of Earth. Modern stromatolites are relatively rare but may provide clues about the function and evolution of their ancient counterparts. Previous studies have assessed microbial diversity and overall functional potential but not at a genome-resolved level. In this study, we focus on peritidal stromatolites occurring at Cape Recife and Schoenmakerskop on the southeastern South African coastline. We identify functional gene sets in bacterial species conserved across two geographically distinct stromatolite formations and show that these bacteria may promote carbonate precipitation through the reduction of sulfur and nitrogenous compounds and produce calcium ions that are predicted to play an important role in promoting lithified mats. We propose that abundance of extracellular alkaline phosphatases, in combination with the absence of transport regulatory enzymes, may lead to the precipitation of phosphatic deposits within these stromatolites. We conclude that the cumulative effect of several conserved bacterial species drives accretion in these two stromatolite formations.
Footnotes
Competing interests: The authors declare no competing financial interests
