An extremophile is an organism that is able to live in extreme environments,i.e.,environments with conditions approaching or stretching the limits of what known life can adapt to,such as extreme temperature,radiation,salinity,or pH level.
A microorganism,or microbe,is an organism of microscopic size,which may exist in its single-celled form or as a colony of cells.
Stromatolites or stromatoliths are layered sedimentary formations (microbialite) that are created mainly by photosynthetic microorganisms such as cyanobacteria,sulfate-reducing bacteria,and Pseudomonadota. These microorganisms produce adhesive compounds that cement sand and other rocky materials to form mineral "microbial mats". In turn,these mats build up layer by layer,growing gradually over time.
An endolith or endolithic is an organism that is able to acquire the necessary resources for growth in the inner part of a rock,mineral,coral,animal shells,or in the pores between mineral grains of a rock. Many are extremophiles,living in places long considered inhospitable to life. The distribution,biomass,and diversity of endolith microorganisms are determined by the physical and chemical properties of the rock substrate,including the mineral composition,permeability,the presence of organic compounds,the structure and distribution of pores,water retention capacity,and the pH. Normally,the endoliths colonize the areas within lithic substrates to withstand intense solar radiation,temperature fluctuations,wind,and desiccation. They are of particular interest to astrobiologists,who theorize that endolithic environments on Mars and other planets constitute potential refugia for extraterrestrial microbial communities.
Geomicrobiology is the scientific field at the intersection of geology and microbiology and is a major subfield of geobiology. It concerns the role of microbes on geological and geochemical processes and effects of minerals and metals to microbial growth,activity and survival. Such interactions occur in the geosphere,the atmosphere and the hydrosphere. Geomicrobiology studies microorganisms that are driving the Earth's biogeochemical cycles,mediating mineral precipitation and dissolution,and sorbing and concentrating metals. The applications include for example bioremediation,mining,climate change mitigation and public drinking water supplies.
Microbial ecology is the ecology of microorganisms:their relationship with one another and with their environment. It concerns the three major domains of life—Eukaryota,Archaea,and Bacteria—as well as viruses.
Geobiology is a field of scientific research that explores the interactions between the physical Earth and the biosphere. It is a relatively young field,and its borders are fluid. There is considerable overlap with the fields of ecology,evolutionary biology,microbiology,paleontology,and particularly soil science and biogeochemistry. Geobiology applies the principles and methods of biology,geology,and soil science to the study of the ancient history of the co-evolution of life and Earth as well as the role of life in the modern world. Geobiologic studies tend to be focused on microorganisms,and on the role that life plays in altering the chemical and physical environment of the pedosphere,which exists at the intersection of the lithosphere,atmosphere,hydrosphere and/or cryosphere. It differs from biogeochemistry in that the focus is on processes and organisms over space and time rather than on global chemical cycles.
Microbially induced sedimentary structures (MISS) are primary sedimentary structures formed by the interaction of microbes with sediment and physical agents of erosion,deposition,and transportation. The structures commonly form when microbial mats are preserved in the sedimentary geological record. There are 17 main types of macroscopic and microscopic MISS. Of those,wrinkle structures and microbial mat chips are the most abundant in the fossil record. Other MISS include sinoidal structures,polygonal oscillation cracks,multidirected ripple marks,erosional remnants and pockets,or gas domes.
A microbial consortium or microbial community,is two or more bacterial or microbial groups living symbiotically. Consortiums can be endosymbiotic or ectosymbiotic,or occasionally may be both. The protist Mixotricha paradoxa,itself an endosymbiont of the Mastotermes darwiniensis termite,is always found as a consortium of at least one endosymbiotic coccus,multiple ectosymbiotic species of flagellate or ciliate bacteria,and at least one species of helical Treponema bacteria that forms the basis of Mixotricha protists' locomotion.
A microbiome is the community of microorganisms that can usually be found living together in any given habitat. It was defined more precisely in 1988 by Whipps et al. as "a characteristic microbial community occupying a reasonably well-defined habitat which has distinct physio-chemical properties. The term thus not only refers to the microorganisms involved but also encompasses their theatre of activity". In 2020,an international panel of experts published the outcome of their discussions on the definition of the microbiome. They proposed a definition of the microbiome based on a revival of the "compact,clear,and comprehensive description of the term" as originally provided by Whipps et al.,but supplemented with two explanatory paragraphs. The first explanatory paragraph pronounces the dynamic character of the microbiome,and the second explanatory paragraph clearly separates the term microbiota from the term microbiome.
The mycobiome,mycobiota,or fungal microbiome,is the fungal community in and on an organism.
Astro microbiology,or exo microbiology,is the study of microorganisms in outer space. It stems from an interdisciplinary approach,which incorporates both microbiology and astrobiology. Astrobiology's efforts are aimed at understanding the origins of life and the search for life other than on Earth. Because microorganisms are the most widespread form of life on Earth,and are capable of colonising almost any environment,scientists usually focus on microbial life in the field of astrobiology. Moreover,small and simple cells usually evolve first on a planet rather than larger,multicellular organisms,and have an increased likelihood of being transported from one planet to another via the panspermia theory.
Hologenomics is the omics study of hologenomes. A hologenome is the whole set of genomes of a holobiont,an organism together with all co-habitating microbes,other life forms,and viruses. While the term hologenome originated from the hologenome theory of evolution,which postulates that natural selection occurs on the holobiont level,hologenomics uses an integrative framework to investigate interactions between the host and its associated species. Examples include gut microbe or viral genomes linked to human or animal genomes for host-microbe interaction research. Hologenomics approaches have also been used to explain genetic diversity in the microbial communities of marine sponges.
The earliest known life forms on Earth may be as old as 4.1 billion years old according to biologically fractionated graphite inside a single zircon grain in the Jack Hills range of Australia. The earliest evidence of life found in a stratigraphic unit,not just a single mineral grain,is the 3.7 Ga metasedimentary rocks containing graphite from the Isua Supracrustal Belt in Greenland. The earliest direct known life on land may be stromatolites which have been found in 3.480-billion-year-old geyserite uncovered in the Dresser Formation of the Pilbara Craton of Western Australia. Various microfossils of microorganisms have been found in 3.4 Ga rocks,including 3.465-billion-year-old Apex chert rocks from the same Australian craton region,and in 3.42 Ga hydrothermal vent precipitates from Barberton,South Africa. Much later in the geologic record,likely starting in 1.73 Ga,preserved molecular compounds of biologic origin are indicative of aerobic life. Therefore,the earliest time for the origin of life on Earth is at least 3.5 billion years ago,possibly as early as 4.1 billion years ago —not long after the oceans formed 4.5 billion years ago and after the formation of the Earth 4.54 billion years ago.
Microbialite is a benthic sedimentary deposit made of carbonate mud that is formed with the mediation of microbes. The constituent carbonate mud is a type of automicrite;therefore,it precipitates in situ instead of being transported and deposited. Being formed in situ,a microbialite can be seen as a type of boundstone where reef builders are microbes,and precipitation of carbonate is biotically induced instead of forming tests,shells or skeletons.
Tanja Bosak is a Croatian-American experimental geobiologist who is currently an associate professor in the Earth,Atmosphere,and Planetary Science department at the Massachusetts Institute of Technology. Her awards include the Subaru Outstanding Woman in Science Award from the Geological Society of America (2007),the James B. Macelwane Medal from the American Geophysical Union (2011),and was elected an AGU fellow (2011). Bosak is recognized for her work understanding stromatolite genesis,in addition to her work in broader geobiology and geochemistry.
All animals on Earth form associations with microorganisms,including protists,bacteria,archaea,fungi,and viruses. In the ocean,animal–microbial relationships were historically explored in single host–symbiont systems. However,new explorations into the diversity of marine microorganisms associating with diverse marine animal hosts is moving the field into studies that address interactions between the animal host and a more multi-member microbiome. The potential for microbiomes to influence the health,physiology,behavior,and ecology of marine animals could alter current understandings of how marine animals adapt to change,and especially the growing climate-related and anthropogenic-induced changes already impacting the ocean environment.
Marine prokaryotes are marine bacteria and marine archaea. They are defined by their habitat as prokaryotes that live in marine environments,that is,in the saltwater of seas or oceans or the brackish water of coastal estuaries. All cellular life forms can be divided into prokaryotes and eukaryotes. Eukaryotes are organisms whose cells have a nucleus enclosed within membranes,whereas prokaryotes are the organisms that do not have a nucleus enclosed within a membrane. The three-domain system of classifying life adds another division:the prokaryotes are divided into two domains of life,the microscopic bacteria and the microscopic archaea,while everything else,the eukaryotes,become the third domain.
The holobiont concept is a renewed paradigm in biology that can help to describe and understand complex systems,like the host-microbe interactions that play crucial roles in marine ecosystems. However,there is still little understanding of the mechanisms that govern these relationships,the evolutionary processes that shape them and their ecological consequences. The holobiont concept posits that a host and its associated microbiota with which it interacts,form a holobiont,and have to be studied together as a coherent biological and functional unit to understand its biology,ecology,and evolution.
