In 1894 Thaxter described M. bisporalis on pig dung in Burbank, in Eastern Tennessee. It has also been observed at Kittery Point, Maine, on skunk and mice dung, and also at Intervale, New Hampshire on squirrel dung (Thaxter, 1914). Thaxter mentioned that the species was not rare and had escaped notice due to its resemblance to hyphomycetes of the Hyolopus type. More recently, the geographic distribution of M. bisporalis based on Global Biodiversity Information Facility database maps shows this species was isolated in Italy (Figure 2). Another recent study by Sharma et al., 2015 found M. bisporalis in Arunachal Pradesh, India.
In anaerobic growth studies by Hesseltine, M. bisporalis grew 3. 8 cm for aerobic growth total inhibition under anaerobic conditions. Species in the Mortierella are mostly considered saprotrophs, obtaining their energy from dead organic matter. However, there is no accurate reference or information on the trophic status of M. bisporalis.
The genus Mortierella have shown to produce greater amounts of lipid and essential fatty acids (EFAs) compared to other organism such as algae, moss and protozoa (Kotula and Yi, 1993). Mortierella also has high growth rates, and can be grown in basic media and simply manipulated (Kotula and Yi, 1993). Studies have shown that different Mortierella species can vary in their amount of lipid and biosynthesis of EFAs (Dyal and Narine, 2005). A study from Kyoto University, Japan screened Mortierella, Mucorales and Entomophthorales and found that Mortierella isolates produced the greatest amount of C-20 polynsaturated fatty acids (PUFAs) (Kotula and Yi, 1993). Shimizu et al (1988a) also found that Mortierella accumulate Eicosapentaenoic acid (EPA) in the mycelia when grown in conventional media with glucose.These authors also noted that lower temperatures increase the production of lipids and fatty acids in Mortierella (Shimizu et al., 1988a). Kotula and Yi (1993) studied the process of EPA production in eight different strains of Mortierella including M. bisporalis. However, in this study M. bisporalis did not produce EPA at the various temperatures that they tested. However, further studies are required to investigate M. bispolaris for EPA, EFA, and PUFAs productions in various temperature conditions and parameters.
Latin name: Mortierella bisporalis (Thaxt.) Björl; (Bjorling, 1936).
Synonym name: Haplosporangium bisporale (Thaxt.) Björl.
Classification
Kingdom: Fungi
Phylum: Mucoromycota
Subphylum: Mortierellomycotina
Order: Mortierellalus
Family: Mortierellaceae
Genus: Mortierella
Species: M. bisporalis
Roland Thaxter first described the Haplosporangium genus with two species, H. bisporale and H. decipiens. This was first published in Botanical Gazette in October 1914 (Thaxter, 1914). Bjorling renamed these species to Mortierella genus in 1936 K. (Mycobank) in memory of the Societe de Botanique de Belgique (M. Du Mortier) (Coemans, 1863).
Thaxter described the growth of M. bisporalis as clear white, becoming yellowish, as it gets older. It forms cobweb-like layers on the top of the substratum composed of fine filaments (Thaxter, 1914). This species only produces a single sporangiophore or rarely two (Thaxter, 1914). The sporangiosphores of Mortierella usually do not produce columella or rudimentary. Their sporangiophores are simple, or rarely furcate, straight or sometime slightly bent (Thaxter, 1914). They bear the primary sporangium and often two, the secondary sporangia borne on short straight fine branchlets. If two sporangia are present they are opposite of each other. Thaxter described in detail the shape and size of primary and secondary sporangia- “minute spherical, smooth; containing one spherical spore, or less frequently to which are subshperical in shapes becoming somewhat rounded. Bisporous sporangia 11-12 µm, monosporous 8 µm, sporangiospores, average to 48-55 µm, hyphae 1-3 µm, segment to 6.5 µm in diameter”. The sporangiolum is a structure where there is only a single spore and it can function like a conidium. M. bisporalis can have two-spore sporangioles (Figure 3) or monosporous sporangiole (Figure 4). Thaxter noted that the M. bisporalis species is not rare, and probably escaped notice given its resemblance to some very insignificant hyphomycetes (Thaxter, 1914).
In 1943 while culturing squirrel dung at State Rocky Arbo Park, Wisconsin Hesseltine found a small fungus that fit the descriptions Thaxter made in 1914 of M. bisporalis. Upon examination, this culture was confirmed to be M. bisporalis (Hesseltine, 1943). After culturing M. bisporalis Hesseltine mentioned that this species is easily cultured (Hesseltine, 1943). He grew this fungus in a different media including corn, and potato dextrose agar. Additionally, he used Czapeck media where he noticed that spores were rapidly produced and described “the mycelium of this fungus was white and delicate consisting of fertile and sterile portions, the fertile portions produced many sporangiosphores for a long distance but in other places only few sporangiosphores were present”. The sporangiosphores all arise from the main hyphal stand and at right angles to it as (Figure 5). The sporangiosphores are divided into segments. Hesseltine described in detail the size of the sporangiospores 66-36 µm in length, the average 48 µm, width at the base from 4-9 µm, on average 7,5 µm, the tips about 1 µm and often bent backward, usually with one or two branches. The branchlets were short and very small at more, or less right angles to the main sporangiophore. The bisporus sporangia in water mounts showed distinct surrounding membranes, the two spores at first are flattened on one side in the sporangium, however, after releasing from the sporangium they become round, and are oval in shape (Hesseltine, 1943). The sexual “zygospore” has not been observed for M. bisporalis, only asexual states are known (Gwynne-Vaughan and B. Barnes, 1962).
Mortierella is the largest genus in the phylum Mucoromycota with around 100 recognized species (Wagner et al., 2013). However, the phylogeny of this genus is poorly resolved. Some species of Mortierella are better studied than others. Wagner resolved the phylogenetic placement of M. bisporalis by analysis of the large sub-unit (LSU) and internal transcribed spacer (ITS) (Wagner et al., 2013). These analyses showed a topology where M. bisporalisis in clade 6 and well supported by bootstrap values of BS=99% and BS=100% for the LSU and ITS respectively, compared to sequence data of other Mortierella species (Figure 1).
