Cellularlife on earth can be divided in three different domains – the eukaryotic, prokaryoticand archaea. Within these, further sub distinctions can be made, resulting in abranched and complex annotation of life. Fungi belong to the eukaryotic domain, inwhich they constitute their own kingdom, besides the plant and animal kingdoms.As other eukaryotic cells, fungi cells accommodate organelles and a truenucleus, all contained within a membrane, while they differ by having a cellwall consisting of chitin, as well as lacking chlorophyll. The general schemeof a fungi is relatively simple.
Composing of a main body, a mycelium, made upby a branched network of tubes, hyphae. Through hyphae, nutrients are absorbed,in which organic carbon, from either living or dead biological organisms,function as the main energy source. Reproduction of fungi can occur in two separate,yet connected, ways. Either reproduction takes place asexually, mainly through themeans of the release of small identical copies of parent fungi as spores, orreproduction occurs sexually. Sexual reproduction varies between differentphylums and therefore a generic description does not make sense. Instead adetailed description is integrated within the description of each phylum.
The fungikingdom can be subdivided in 5 different phyla, these are named Chytridiomycota, Zygomycota, Ascomycota, Basidiomycota and Deuteromycota. Phylum Chytridiomycotacontainsall fungi, which at some point in their life cycles exists as flagellatedswimming cells and these fungi are therefore, primarily, found in aquaticenvironments. These fungi reproduce asexually when a zoospore, who areuniflagellate asexual spores, lands on a substrate, after which a cell wallforms around it, thus, creating a fungi body.
Long threads, rhizoids, attach tothe substrate and through these nutrient is absorbed. After a period offeeding, the fungi body is converted into a sporangium, a structure whichcontains and subsequently releases zoospores. Sexual reproduction occurs byfusing zoospores, thus creating a diploid zygote, which then hardens andcreates a meiosporangium. Later fusing of nuclei create meiospores, which can thenswim away and form a new fungi body.
Fungi of this phyla are mostly harmless,saprotrophic fungi, although a few pathogens such as Batrachochytrium dendrobatidis, which causes chytridiomycosis in amphibious animalshave been found. Phylum Zygomycota clusters more than 1100 different species, mostlysaprotrophic soil fungi, who exploits nutrients by decomposing waste products,such as rotten fruit. Their name, refers to their reproductive sexualmechanism, as it forms a structure called zygosporangium, arising from theconjugation between two compatible hyphae, with each hyphae stemming from a separateorganism. After conjugation, a cell wallis formed behind the fusing hyphae, which at this point are called gametangia.Next to this, the wall separating the two hyphae is broken down, leading tofusion of both hyphae’s cell components into one organism, except their nuclei,which are still separate entities. Following this, their nuclei fuse and thewalls around the zygosporangium grows even harder and thicker than before – thisconverts the sporangium to a zygospore.
After a long resting period, meiosis occurs,and the fused nuclei are divided into two separate recombinant nuclei. These are then later integrated and releasedas meiospores. Most Zygomycota are harmless to humans, although a few arepathological causing a disease called mucormycose,which arises when spores are inhaled from dusty environments.
Fungi in the thirdphyla, phylum Ascomycota, are themost abundant phylum as more than 65.000 species belong here. Their trademarkis their structural component, the ascus, which is a sac-like unit, harboringeight ascospores, in which sexual and asexual reproduction occurs. The formationof this component arises when a spore lands on a suitable substrate, afterwhich a haploid mycelium is formed. From this, asexual structures can beproduced, or sexual structures, gametangia, can be formed. The female sexualstructure is called ascogonium, while the male sexual structure is anantheridium. Fusing of sexual structuresleads to formation of one organism with two separate nuclei, this is called anascogonius hypha. Fusing of nuclei, takes place at the tip of this hyphae,creating a diploid ascus, who undergoes meiosis and thus produces 4 recombinanthaploid nuclei.
Followed by a round of mitosis eight ascospores are formed,which can then be released and the cycle repeats. Due to the sheer amount ofspecies, phylum Ascomycota, exert both a positive and negative effect on thehuman condition. Beneficial species such as Penicilliumnotatum and Saccharomyces cerevisiaecontribute to our health and or ability to produce beverages, while maligneffects are seen by species of the Aspergillus genus who can cause a respiratorydisease, decay food, synthetize carcinogenic toxins in nuts etc. TheAspergillus genus will be investigated extensively later in this paper. Thefourth phyla, Basidiomycata, are nextto Ascomycota the most abundant phyla with more than 30.000 separate speciesand because of this abundance, their diversity is large and plentiful.
Thisphylum encompasses the largest and most complex fungi, in which most species sharea common structural component coined basidium. The basidium is a club shaped structure, in which meiosis takes placeand where basidiospores are synthesized, often located on fruiting bodies suchas mushrooms. Basidiomycotareproduce asexually by producing spores or by a mechanism called budding, inwhich an extension of a cell is separated into its own cell. Sexualreproduction happens when haploid hyphae meet and fuse, often followed by thetransfer of a nuclei from each parent hyphae to the other, which reproducesmitotic, thus, creating a dikaryotic mycelium. From dikaryotic mycelium a fruiting bodyarises, by hyphae, who communicate and create different components. Some createthe stalk, other the gills of the fruiting body. The tips of the hyphae whichconstitutes the gills is the basidium and when these swell, nuclei are fusedand a bit after 4 basidiospores are formed, which will then be ready to bereleased. Basidiomycota play an important role in ecosystems, as they achievenutrient by breaking down decomposing organic material, unfortunately they alsobreak down wood, which have negative economical consequences.
The last phyla, phylum Glomerucyto, is a new addition tothe additional four phylae. These fungi live in close association with theroots of trees. Their relationship is symbiotic in which the roots contributewith carbohydrates and carbon, while the fungi stacks essential vitamins andminerals which the plant can utilize. Glomeromycota do not reproduce sexuallyand cannot sustain life without support from plant roots. Theremaining fungi that do not fit in any of these phyla, belong to a sixthinformal phylum called phylum Deuteromycata.
These fungi all reproduce solelyasexually are as individuals closer to other phyla but not close enough to beconsidered a valid part of these.