Australia: The Land Where Time Began
Fungal Biology Involvement Early in the Emergence of Life
According to Moore the most common proposals for the environment in which the prebiological chemical evolution could have occurred that led to the appearance of first life on Earth could possibly have occurred is the early oceans. Moore proposes that for an extensive period of time, in the billions of years, there were vast numbers of aerosol droplets all over proto-Earth. In these aerosols vast numbers of different chemical reactions took place over billions of years, the result being the molecules and reaction trains formed that might have contributed to the origin of life.
Moore suggests this leads naturally to speculation about evolution of many varieties of protocells that are almost living. Some of these had no genetic apparatus, some containing autocatalytic chemical cycles, “the RNA world and protein-world precursors of livings things” and those exploiting the advantages of having lipid envelopes surrounding them. All of these existed at the same time, though in different aerosol droplets.
When the aerosols were brought to Earth in rain or spindrift they would form slime on the solidified lava that formed the surface of the Earth at that early period in Earth history. Any slime that reaches a spot that was protected from solar radiation by tephra or a bubble cave in the lava would form something that could be described as a prebiological biofilm. Within this biofilm all pathways were effective (if they could happen, they did happen) and they could work together where they coexisted and were coextensive, to form chemical systems that with passing time were ever more integrated and interconnected.
According to this proposed mechanism, from systems of autocatalytic chemical cycles which later acquired the ability to control metabolism enzymatically.
The characteristics that were expressed by the earliest living, or possibly even non-living, things, were those which at the present would be characterised as being heterotrophic. Nutrients that were readily available were used by the first chemical machines. As these became increasingly difficult to acquire, because they were gradually being used up, those chemical machines that had the ability to release chemical catalysts into their environment could degrade the tars and other polymers that had been accumulating over hundreds of hundreds of millions of years of abiotic chemical reactions.
Much of current biology depends of symbiosis, therefore ‘symbiotic associations’ must have also been important in prebiology.
Moore suggests that this will lead logically to the idea that different types of protocells, each of which was good at 1 particular process, must have coexisted. Some of these might have had a selective value in collaborating, or in absorbing and using other protocells symbiotically, or in exuding factors (primitive enzymes and/or toxins) that opened other protocells and make use of their constituents.
The first living things arose on the Earth as soon as they were allowed to by the conditions, and after a relatively short time, the Earth was dominated by primitive bacteria, the majority of which were still in biofilms.
The higher organisms, the eukaryotes, resulted from further levels of collaboration within those biofilms; initially eukaryotes were single-celled organisms possessing a mixture of characteristics from which the animal, fungal and plant lineages of the present evolved.
Moore suggests the unique feature of his argument is that it is based on the central role of the fungal grade of organisation in the evolution of higher organisms. Moore says he is not aware of any previous suggestion of the fungal grade of organisms being central to the origin and evolution of life. He believes this is because of the authors of previous suggestions on the subject having been essentially ignorant of the distinctive features of the fungal cell biology that distinguished fungi from plants and animals.
Fungi are very different from plants and animals, yet fungi were long believed to be plants, though peculiar and non-photosynthetic plants. Moore suggests that generally speaking fungi, thought of as mushrooms and toadstools, were probably believed to be plants because their fruiting bodies, the mushrooms and toadstools, are seen near the ground among green plants in nature accounts for their association with plants. Initially, fungi were firmly classified as plants and their evolutionary history was believed to have derived from algae by the loss of their photosynthetic properties. It became increasingly clear early in the 20th century that there are a large number of fungi. As well as the mushrooms and toadstools, which are also incredibly diverse and numerous, there are also large numbers of filamentous moulds: microscopic and soil fungi which have colonies, called mycelia, where the main body of the fungus is comprised of thin, cottony, thread-like filaments, the hyphae. There are also a large number of yeasts: which are single celled organisms specialised for growth in liquids, in particular small bodies of liquids such as the sugary fluid in the nectaries of flowers, raindrops and dew drops from fruits and flowers, as well as the circulating fluid streams in plants and animals, as occurs in parasitic or pathogenic species. Yeasts, though their specialisation to a particular habitat has led to a form and structure that has been reduced compared to other fungi, so their relationship to the overwhelming majority of other fungi, characteristically filamentous (or hyphal), which Moore says is similar in many respects to the relationship of flightless birds to the majority of other birds.
According to Moore most authors of books on the origin of life are physicists, cosmologists, astronomers and molecular biologists.
Moore believes that the lack of a proper appreciation of the fungal biology is a severe limitation to gaining an understanding of the origin and evolution of life. Moore suggests that the first eukaryotes had nutritional; and cell-biological attributes very similar to those of fungi, as well as features that emerged later in plants and animals. The plants were the first to emerge from this primitive stem, which was almost protofungal. This left organisms known as opisthokonts, which had a single posterior flagellum, that were ancestors of both animals and fungi. Animals then diverged from these after which the ancestral sister group of animals, the opisthokonts, evolved into fungi. According to Moore the animals were the last of the crown group of eukaryotes to diverge and therefore the animals are least informative concerning the point of origin of eukaryotes; and plants are channelled narrowly into a specific way of life and therefore are less informative than the fungi about the origin point. Conservatism and continuity are a characteristic of known fungal evolution, rather than change and extinctions (Pirozynski, 1976); an observation that compared fossil fungal spores that were very ancient to those of modern fungi, which implies that the fungal body plan will be informative about the point of origin.
According to Cavalier-Smith (2010a, p.127) it cannot be a coincidence that the largest expansion of the diversity of protists in the history of the Earth followed after global glaciations. The earlier origin of eukaryotes had acquired a high level of pent-up potential that set the scene for the innovation and the rapid radiation that resulted from the arrival of major new body plans following deglaciation.
Moore says that Cavalier-Smith included physiological features under the same phrase: the novel body plans such as water splitting (oxygenic) photosynthesis which was achieved by cyanobacteria and their immediate ancestors, phagotrophy by eukaryotes (Cavalier-Smith, 2006, fig. 8 legend.
Moore suggests the fungal body plan has been at the essential centre of life from the very start. According to Whittaker there are 3 principal modes of nutrition, photosynthetic, absorptive and ingestive. The 3 modes to a large extent correspond to the major functional groupings found in natural communities, producers (plants), reducers (saprobes – bacteria and fungi) and consumers (animals). It appears the importance of the reducers in the cycling of materials in ecosystems exceeds that of consumers. Ingestive nutrition evolved secondary to absorptive nutrition found in most monerans and many unicellular eukaryotes. It is considered probable that protists with food vacuoles and metazoans with digestive tracts have evolved from absorptive flagellates, internalising the process of food absorption with the added process of ingestion. It can also be considered that eukaryotic plants have also internalised the absorption of food through a membrane that surrounds chloroplast as symbiont and organelle. A different logic on which the evolution of structure in higher organisms was based is implied by the 3 nutritional modes (Whittaker, 1969, p. 152).
Even in a discussion of prebiotic chemistry it is common to consider that some type of compartment would absorb material external to compartment to be converted to more of the substance of its internal contents (an ‘absorptive protonutrition’).
In a living body which arises by incorporation of polymeric organic compounds into multimolecular systems the absolutely indispensable form of metabolism is the taking in of organic substances that are dissolved in the surrounding aqueous medium which are then transformed into parts of the body (Oparin, 1957a, Ch. IX, p. 400).
According to Moore in most arguments there is a need for a prebiotic component, such as Oparin’s coacervate, that first takes up simple compounds from the medium and as these are exhausted to release catalytic materials, reactive ions or metabolites/peptides/ribozymes, into the medium in order to break down larger molecules into simple compounds that can continue to be absorbed by the compartment.
A step on the way to life, this is a prebiotic stage depending on an evolutionary logic, that is the principal mode of nutrition, saprotrophism, among modern bacteria and fungi; and the point is that it is the shared evolutionary logic. The eukaryotic grade of organisation is a fungal grade of organisation, though the strands of evolutionary logic apply as much to the primeval (prebiotic) period as to periods later in the cellular evolution of both prokaryotes and eukaryotes. Moore says that in spite of the recent antipathy to the word ‘prokaryote’ a profound evolutionary truth is reflected in the prokaryotic-eukaryotic dichotomy (see Cavalier-Smith, 2010a, 113).
At the present fungi form a very large and diverse group of organisms, that had all been classified as plants until the middle of the 20th century. It was at this time that it began to be realised that fungi might be a group of higher organisms that differed from both plants and animals. The idea arose that fungi might form a distinct kingdom of eukaryotes, which are organisms that have cells containing complex structures that are surrounded by membranes, which contrasts with the prokaryotes that were mainly bacterial, that generally lack membranous structures within their cells. The Kingdom Fungi is very diverse, including a range from single-celled organisms, such as yeasts, to others covering hundreds of acres of land. Some fungi are among the largest organisms on Earth (Arnaud-Haond et al., 2012). In the Blue Mountains of northeast Oregon, USA, an individual mycelium has been found of the tree pathogen Armillaria ostoyae in the mixed conifer forests that covers an area of 965 ha (2,384 acres, which is 7 times the size of Hyde Park in London, or 3 times the area of Central Park in New York). This organism has been estimated to be between 1,900 and 8,650 years old (Ferguson et al., 2003).
100,000 species of fungi have been found so far, and it is believed there may be more than 1.5 million that are yet to be discovered. Fungi can live on a wide range of habitats extending from the poles to the tropical forests, and in fresh and salt water. Most fungi live in the soil, the fungi most people recognise are the mushrooms and toadstools, the fruiting bodies of subsoil fungi that are comprised on mycelium that is much larger and more extensive. There is no technical difference between toadstool fungi and mushroom fungi, the common names being essentially synonyms. The Kingdom Fungi is extremely diverse; there are 15,000 known species of fungi in the UK, and of these 4,500 are mushrooms, 200 of these being edible and 50 being poison to some degree. There are only 48 known species of mammal in the UK, 210 species of birds, and 1500 species of higher plant. The number of species of fungi in Britain rivals the number of known British insect species, 22,500, though this comparison is suggested by Moore to possibly misleadingly underestimate the diversity of fungi. According to Moore virtually every individual insect carries a load of parasitic fungi, of which many are species-specific. The result is that in Britain, as well as the remainder of the world, there may be many undiscovered or unnamed entomogenous (‘growing on or in the bodies of insects’) species of fungi.
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