Archaean metabolic evolution of microbial mate

Microbial mats of coexisting bacteria and archaea date back to the early Ar chaean: many of the major steps in early evolution probably took place with in them. The earliest mats may have formed as biofilms of cooperative chemo lithotrophs in hyperthermophile setting-a, with microbial exploitation of d iversifying niches. Anoxygenic photosynthesis using bacteriochlorophyll cou ld have allowed mats, including green gliding bacteria, to colonize anaerob ic shallow-water mesothermophile habitats. Exploitation of the Calvin-Benso n cycle by purple bacteria allowed diversification of microbial mats, with some organisms in more aerobic habitats, while green sulphur bacteria speci alized in anaerobic niches. Cyanobacterial evolution led to more complex ma ts and plankton, allowing widespread colonization of the globe and the crea tion of further aerobic habitat. Microbial mat structure may reflect this e volutionary development in broad terms, with anaerobic lower levels occupie d by archaeal and bacterial respirers, fermenters and green bacteria, while the higher levels contain aerobic purple bacteria and are dominated by cya nobacteria. A possible origin of eukaryotes is from a fusion of symbiotic p artners living across a redox boundary in a mat. The geological record of A rchaean mats may be present as isotopic fingerprints: with the presence of cyanobacteria, mats may have had a nearly modern structure as early as 3.5 Ga ago (1 Ga = 10(9) years).