Revisão narrativa sobre a importância de esteiras microbianas na formação de estromatólitos e demais estruturas organosedimentares

Abstract

Microbial mats are complex benthic ecosystems that interact with sediments and form a range of biostratification structures called MISS (“Microbially Induced Sedimentary Structure”), which significantly influence the composition of sedimentary systems, commonly associated with aquatic environments. Microrganisms that form biofilms play an important role in formation of MISS by synthesizing EPS (“Extracellular Polymeric Substances”), trapping and binding suspended sediment grains in the water column and the bioprecipitation of minerals in the EPS structure and cell surfaces. The cells promote sediment biostabilization, which reduces the likelihood of rupture and erosion. The diversity of metabolisms and species found in the microbial mats influence the morphological patterns, as well as the mats' potential to consolidate and subsequently lithify, which gives rise to microbialites. Stromatolites are the best known structures resulting from the metabolism of microbial ecosystems and have a characteristic internal lamination structure, which is a reflection of the overlapping of numerous biofilms of different functional groups, in which there is precipitation of different minerals that end up generating different layers of colors that discriminate the lamination. The specific metabolism and behavior of the MISS-forming bacteria made it possible to preserve part of the planet's past that has little information, compared to geological periods in which there were more diverse and more complex forms of life in terms of body structure. The mineral precipitation of microbial mats enabled the formation of the extensive fossil record of microbialites that fill in paleontological gaps associated with the Precambrian, due to the lack of body fossils. Bioprecipitation, as well as the metabolic diversity and adaptation to extreme physicochemical conditions that microrganisms in these ecosystems usually present, are also of interest in the field of astrobiology, especially regarding the possibility that the soil of Mars harbors life similar to bacteria mat-forming on Earth, or have harbored in the remote past.