There is not much literature that relates to the ecology aspects of Umbelopsis isabellina. This fungus is a saprotrophic that lives in soil, decaying wood, decaying leaves and in other organic material. They are heterotroph, and their nutrition is obtained from non-living organic material by secreting enzymes into it and then absorbing its nutrients. They interact with the environment at a microscopic level (Crowther, Boddy, & Hefin Jones, 2012). This fungus was first isolated in Netherlands, but it has been found in the United Kingdom, Malaysia, Australia, Ukraine, Japan, and Taiwan, and the United States. Thus it has a worldwide distribution(Chien; & Liou, 2010).
Umbelopsis isabellina, formerly called Mortierela isabellina, Micromucor isabellinus, Mortierella fusca, Mortierella pusilla, and Mortierella atrogrisea is a fungus that belongs to the order Umbelopsidales (Spatafora et al., 2016). Umbelopsis isabellina was first described by the scientist Oudemans, C.A.J.A., in April of 1902, and published in the Archives Neerlandaises des Sciences Exacted et Naturelle (“Umbelopsis isabellina,” n.d.). It is commonly named filamentous fungus and grows as coenocytic polynucleated (Chien; & Liou, 2010).
After many years of debate caused by observations in the morphological structure of the fungus, Gams renamed it in 2003. According to Ruiter, Lugt, & Rombouts (1993)Umbelopsis isabellina did not fit within Mortierella. They observed that U. isabellina showed antigenic similarity with mucoralean species, and so it was likely that it did not relate to the Mortierellaceae group. This was attested ten years later when researchers said: “The M. isabellina group or subgenus Micromucor, though generally classified in Mortierella, with M. isabellina and M. ramanniana as the best known species, deviates from the remaining taxa of the genus” (Meyer & Gams, 2003). In their study they investigated the U. isabellina group by RFLP and ITS1 sequence analysis and it clearly separates this group from Mortierella clearly saying that Umbelopsis isabellina is unrelated to Mortierella, and it is distant related to the group of the Mucoraceae. The confirmation came with the genome sequence published in 2014. Researchers performed the whole-genome sequencing for Umbelopsis isabellina using the strain U.isabellinaNBRC 7884 acquired from the Japanese Biological Center.The assembled genome was 22,588,838bp with 84 scaffolds, and genome content was 41.79%. They predicted a total of 9.081 protein-coding genes, and about 76,1% of this protein-genes were homologous to the Umbelopsis ramanniana. They acknowledged: “Umbelopsis isabellina is a Mucoromycotina belonging to the order Mucorales, which includes the genera Rhizopus, Mucor, Cunninghamella, etc. Interestingly, U. isabellina was formerly classified in the order Mortierellales, but a molecular phylogenic analysis has shown that Umbelopsis species belong in the Mucorales order” (Takeda, Tamano, & Yamane, 2014)(Figure 1).
Umbelopsis isabellina is known for being an oleaginous fungus. It accumulates lipids to more than 40% of their biomass (Takeda, Tamano, & Yamane, 2014). It is important for being an effective producer of γ-Linolenic acid, an unsaturated fatty acid (Fakas, Makri, Mavromati, Tselepi, & Aggelis, 2009). Since researchers started to show that γ-Linolenic acid could be a great agent used in the treatment of endocrine-sensitive breast cancer, the industry has Umbelopsis isabellina as a potential target for industrial development: “Gamma linolenic acid (GLA) has been proposed as a valuable new cancer therapy having selective anti-tumor properties with negligible systemic toxicity” (Kenny et al., 2000). They are not only cytotoxic to tumor cells; they appear to be the ideal cancer treatment for offering none or minor side effects, and no damage to the normal cells. During the trial none of the patients died, and they had an improvement in their quality of life, including a reduction of painkillers and no weight loss. (Fallis, 2013).
In their pilot clinic trials researchers show that GLA potentiate the action of radiotherapy and of the cytotoxic drugs, leading to achievement of positive responses in the inhibition of tumor spreading and even improving survival. Also, that GLAs have an additional influence on tamoxifen, a drug largely used in the treatment of breast cancer, that is known for suppressing the clinical breast cancer through the estrogen receptor (ER) pathway (Kenny et al., 2000).
According to (Meeuwse, Akbari, Tramper, & Rinzema, 2012), U. isabellina is also being investigated as a promise for production of biodiesel because it has proved to be the most promising strain for solid-state among a large group of oleaginous fungi. They have the potential of converting biomass residues into biodiesel precursors, and use biomass residues as C-source. They modeled growth and lipid production on a solid substrate and their conclusions are that the fungus is only able to accumulate lipids when required amount of carbon for its maintenance and growth is fully satisfied. Otherwise, the lipids production is low. They also concluded that the lipid production rate was much lower in submerged cultures.
Researchers studied Umbelopsis isabellina’s ability to degrade atrazine, an important agricultural chemical used in corn, sugar cane, turf and broadleaf weeds. Atrazine is the most commonly found pesticide in food and drinking water, and its persistency in the groundwater and surface water has been discussed for years because of its maleficence to populations of fish, amphibians, phytoplankton and humans as well. This herbicide can be degraded by the substances produced by plants, which have a great phytoremediation potential. Isolates of Sweet flag (Acorus calamus L.) roots were exposed to Atrazine, then tested in vitro, in different concentrations, and results show that Umbelopsis isabellina is able to degrade synthetic dyes and could be a helpful method of enhancing environment remediation (Marecik et al., 2008).
Another important study reports that Umbelopsis isabellina is being investigated for the ability to biodegrade and decrease the toxicity of this important pollutants, such as Nonylphenol(NP), 4-tert-octylphenol (4-t-OP) and 4 cumylphenol (4-CP). They are Xenobiotics that persist in the environment, and act as endocrine disruptors. Literature says that after only 12 hours of incubation “more than 90% of Nonylphenol(NP), and 4-tert-octylphenol (4-t-OP) was removed after 12 hours of incubation compared with the abiotic controls. The same percentage of 4 cumylphenol (4-CP) elimination was observed as early as after 6h in U. isabellina cultures” (Janicki, Krupiński, & Długoński, 2016). They conclude their research emphasizing that Umbelopsis isabellina is a new promising biological tool in the degradation of contaminants with endocrine activity, and decrease of toxicity of this contaminants.
Umbelopsis isabellina can be grown on potato dextrose agar and research shows that the highest production of γ-Linolenic acid is at the beginning of the growth, in young, growing mycelia, and that is when the phospholipids are more actively involved in these reactions (Fakas et al., 2009). The authors also explained that it is hard, and it requires deep knowledge of the process to regulate the metabolism pathways of GLA to be able to successfully achieve production of it, but that it can be done with the design of a detailed bioprocess for GLA production. For this, it is needed a process that when designed attains the compromise between lipid content in biomass and GLA content in lipid.
Better understanding the lipid production, Meeuwse 2011, developed a method to grow Umbelopsis isabellina in submerged batch fermentation. A mathematical model was created and used to help improving the production of poly-unsaturated fatty acids (PUFA), such as γ-Linolenic acid and arachidonic acid. The experiment was divided in three important subsequent phases: the first when there is a fast increasing growth when carbon and nitrogen are abundant, the second when there is carbon and lipid growth even though nitrogen source is exhausted, and the third when there is a drastic change of accumulated lipids when carbon source is deprived. They found that: “in batch cultures, the initial specific lipid production rate was almost four times higher than in chemostat cultures but it decreased exponentially in time, while the maximum specific lipid production rate in chemostat cultures was independent of residence time” (Meeuwse et al., 2012).
The species U. isabellina is generally characterized by white velvety colonies (Figure 2) that grow slowly and produce sparsely septate hyphae, erect sporangiophores with small collumellae shape in their tips (Figure 3), round sporangiospores, and abundant quantity of chamydospores filled with lipid material (Figure 4). Members of the genus Umbelopsis don’t form sexual structures, and they are known for not growing in high temperatures although they are heat-resistant (Meyer & Gams, 2003)
Umbelopsis does not produce a garlic-like odor characteristic of Mortierella group, and there is no evidence of zygospores ever being found in any species of Umbelopsis (Ruiter, Lugt, & Rombouts, 1993).
Umbelopsis are distinguished from Mortierella also by the morphological differences in sporangiosphores branching and because it forms columella of the sporangium. Some Umbelopsis species are highly variable morphologically, with the example of Umbelopsis isabellina that presents short and long sporangiophores, making difficult the idea of separating Micromucor from Umbelopsis. (Benny, 2010).
