Mortierella

Mortierella species are soil fungi belonging to the order Mortierellales within the subphylum Mortierellomycotina (phylum: Mucoromycota). The widespread genus contains about 85 species. Species of Mortierella live as saprotrophs in soil, on decaying leaves and other organic material. Other species live on fecal pellets or on exoskeletons of arthropods Penicillium, Trichoderma, Mucor and Mortierella species belong to an ecology group which are the first organisms growing on roots. Salt described that the frequency of Mortierella species growing on the surface of roots from spruce is higher in comparison to other species (e.g. Fusarium, Pythium etc.). (Distribution map on EOL) Mortierella fungi are typically coenocytic, but compared with the genus Mucor (Mucoromycotina, Mucorales), they have a stronger tendency towards septum formation. Compared with Mucor-like fungi, the mitosporangia are typically smaller, contain fewer spores and lack a columella (Fig. 1). Many Mortierella-like fungi are asexual. However, if zygospores are found, they strongly resemble Mucor-zygospores. Sometimes sexual structures are embedded in loosely arranged hyphal networks. Mortierella can grow on yeast extract, fish meal, or other media; rich in nutrients. Most laboratories grow these fungi on potato dextrose agar or corn meal agar. The genus can also grow on PARP media, which is used as a common selective medium for Pythium. Because of its similar appearance to Pythium in culture, separation of the two can be difficult until sporulation occurs. Cultivation and growth of Mortierella fungi are affected by the carbon source, addition of minerals and nitrogen source. Monosaccharides are most frequently used for the growth. Yeast extract and soybean meal are widely used as nitrogen source. Especially the balance between carbon and nitrogen in the medium influences the fungal culture. Many Mortierella spp. are chitinolytic. Experiments show that they degrade chitin nearly as efficiently as chitinolytic actinomycetes. From some Mortierella species it is also known that they are able to degrade hemicelluloses to sugar by using the enzyme xylanase. This fungus can degrade the hemicellulose from plants to get sugars for their growth. Some Mortierella species show sexual developmental programs in addition to mitotic reproduction. Mortierella forms zygospores that are the developmental consequence of plasmogamy between gametangia belonging to complementary mating types. The zygospores of Mortierella spp. may be naked (Fig 2 A) or surrounded by sterile hyphae (Fig 2 B) that form a nest-like structure, which may be interpreted as evolutionary early fruiting bodies. Some Mortierella species are homothallic (M. epigama, M. parvispora, M. nigrescens,M. rostafinskii, M. polycephala, M.renispora), but most are heterothallic (M. elongata, M. marburgensis, M. umbelata, M. capitata, M. indohi). The species Mortierella alpina was found to be homothallic and to form zygospores with a hyphal coat. Most Mortierella species have been found to be heterothallic and to produce naked zygospores with unequal suspensors. Very often sexual structures differ in size between mating types. The smaller suspensor, progametangium or gametangium does not enlarge during sexual development and may disappear soon after plasmogamy. The early development of such heterogametangic zygospores is illustrated in the heterothallic species, M. umbellata. In this species, hyphal coiling occurs at the contact site of sexually compatible mycelia. This is followed by development of progametangia which grow in parallel and close to each other. At the end of this development, one partner, the macroprogametangium will be larger than the other, the microprogametangium.