Microbial mats: layered communities of microorganisms

Structure and functioning

Mats are stratified: different microbial groups occupy layers where the available light, electron donors and acceptors vary. Surface layers often host photosynthetic microbes that capture sunlight, while underlying layers are dominated by organisms using chemical energy or fermentative processes. Mats are cemented by extracellular polymeric substances, commonly polysaccharides, which microbes secrete to bind cells and sediments into a coherent sheet. Filamentous microbes can form tangled networks that increase tensile strength. Together these features produce microscale niches in which oxygen, reduced sulfur, methane and other compounds form sharp gradients exploited by specialized metabolisms.

History and evolutionary significance

Microbial mats are among the oldest recognizable ecosystems in the geological record; putative mat structures appear in rocks dated to about 3.5 billion years ago and in a variety of fossil deposits. Early mats may have been centered around chemical sources such as hydrothermal vents, using inorganic molecules for energy before photosynthesis became widespread. The later emergence of photosynthetic mat organisms — first anoxygenic phototrophs and then oxygen‑producing phototrophs — transformed surface chemistry by converting carbon dioxide and water into biomass and releasing free oxygen. That shift contributed to atmospheric change and set the stage for the rise of eukaryote cells and multicellular life.

Habitats and modern distribution

Although mats were formerly widespread on shallow seafloors, their prominence declined after animals began extensive burrowing and bioturbation during the Cambrian period. Today microbial mats persist where disturbance and burrowers are limited: on rocky intertidal platforms and shores (rocky seabeds and shores), in hypersaline and brackish lagoons (hyper-saline and brackish lagoons), on the floors of the deep oceans, and in other extreme or isolated settings. They can tolerate a wide span of temperatures and chemical conditions and are capable of exploiting diverse sources of nutrients and energy.

Forms and visible features

Physical manifestations range from flat carpets to pinnacles and columnar structures. Some mats mineralize over time to create laminated accretions known as stromatolites, while other mats form nodular or spherical aggregates. The internal layering can be visible as distinct colored bands—often green, purple, brown or black—reflecting the dominant pigments and redox chemistry at each depth. These visible characteristics can aid field identification and guide sampling for microbiological analysis.

Uses, importance and notable distinctions

Microbial mats remain important for basic science and applied fields. They are model systems for studying microbial ecology, early Earth environments and biogeochemical cycling within ecosystems. Because mats can metabolize a broad range of substrates, there is interest in harnessing them for practical tasks such as wastewater treatment, bioremediation and mitigating industrial pollution. Lists of typical functions include:

• Primary production via various forms of photosynthesis and chemoautotrophy.
• Transformation of carbon, sulfur and nitrogen compounds, including consumption of carbon dioxide and cycling of reduced sulfur species.
• Stabilizing sediments and creating microhabitats that support higher biodiversity.

Microbial mats are distinct from loose biofilms by their thickness, pronounced internal stratification and the presence of multiple interacting metabolic guilds. They provide a living link to Earth’s formative biosphere and a resource for modern biotechnology and environmental management. For further reading and resources, consult focused literature and databases via the following links: microorganisms overview, bacterial diversity, archaeal roles, historical notes, colonization processes, environmental ranges, symbioses, matrix polymers, secretion biology, stromatolite studies, fossil records, ecosystem impacts, vent ecosystems, photosynthesis types, carbon cycling, oxygenation events, eukaryogenesis, coastal mats, saline lagoons, deep sea mats, nutrient sources and pollution remediation.