The genus Rhizomucor is in the family Mucoraceae in the order Mucorales. The genus is distinguished from related genera Mucor and Rhizopus by their ability to grow at temperatures of 40 C or above (thermophilic growth). The genus consists of three members: R. miehei, R. pusillus, and R. variabilis.
Other species have been described but phylogenetic placement in the genus is still uncertain (Lukács, Papp, Nyilasi, Nagy, & Vágvölgyi, 2004). Molecular phylogenies indicate that R. miehei and R. pusillus are closely related (Voigt, Cigelnik, & O’donnell, 1999).
Like Mucor species, R. miehei have nonapophysate sporangia (sporophore straight or constricted where it joins the sporangium) and irregularly branched sporangiophores (Schipper, 1978). Rhizomucor species were originally placed in the genus Mucor and are morphologically similar but are distinguished by their ability to grow at higher temperatures (Hoog, 2000) and produce rhizoids and stolons (Papp, Nyilasi, Tako, Nagy, & Vagvolgyi, 2011).
Within the genus, R. miehei can be distinguished from other species by maximum temperature growth. R. miehei has a higher maximum temperature than related species R. pusillus and R. variabilis. R. miehei also produce smaller sporangia and lack chlamydospores (Papp et al., 2011). The species can also be distinguished by their sensitivities to Lovastatin (Lukács et al., 2004) and mating system (Papp et al., 2011). The mating system of R. miehei is always homothallic, whereas R. pusillus are generally heterothallic with rare instances of homothallic isolates.
Rhizomucor miehei is a saprophytic, filamentous fungus with a worldwide distribution. R. miehei is ubiquitous in nature and can be isolated from soil and decaying organic matter, e.g. garden composting, poultry droppings, compost, and municipal waste (Gomes, Lewis, & Kontoyiannis, 2011).
Though unusual, R. miehei is also an opportunistic human pathogen that can cause zygomycosis, an often fatal disease of immunocompromised individuals.
R. miehei can grow at temperatures of 50 C or above and due to this thermophilic nature R. miehei is important in the production of thermostable enzymes in industry.
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The genome of R. miehei (CAU432 strain) was sequenced in 2013 to explore its full potential in the industrial use of thermostable enzymes (Zhou et al., 2014). Zhou et al found that the genome is 27.6 Mb, with 10,345 coding genes (47.1% of the genome). Genome analysis revealed an abundance of genes encoding proteases (155) and lipolytic enzymes, many of which have yet to be exploited in industrial processes.
Current biotechnology research focuses on increasing enzymatic activity and reducing the production costs of exploiting R. miehei’s enxymatic repertoire (Huang et al., 2014).
Taxonomy of Rhizomucor species is still shifting, as there is evidence that the mesophilic R. variabilis may belong to the genus Mucor (Papp et al., 2011). Genome sequencing has revealed that R. miehei may be more closely related to Phycomyces blakesleeanus and Mucor circinelloides even though current phylogenetic placement is in the family Mucoraceae with the genera Mucor and Rhizopus (Zhou et al., 2014).
Though rare, R. miehei is one of the causal agents of zygomycosis and improved molecular identification and diagnostic tools are goals for the medical mycologists (Papp et al., 2011).
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Since R. miehei is thermophilic (able to grow at 50 C or above), it has been exploited in the production of thermostable enzymes that can be used in industrial high temperature bioprocesses, mainly proteases and lipases.
Rhizomucor miehei lipase (RML) is a highly versatile biocatalyst used in laboratory, commercial, and industrial applications (Huang et al., 2014). Other extracellular enzymes from R. miehei have been characterized but have not been used commercially including fibrinolytic enzyme, β-glucanase and xylanase (Zhou et al., 2014).
The aspartic protease produced by R. miehei has been widely used as a calf chymosin substitute in industrial cheese making (Zhou et al., 2014). Since R. miehei is a microbial source of rennet in the cheese making process it is suitable for vegetarians.
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Unlike other genera in the Mucorales, R. miehei accounts for only 1-5% of cases of zygomycosis (Gomes et al., 2011). Zygomycosis is a disease characterized by cutaneous infection, rhinofacial disease, and bone infection (Papp et al., 2011). Transmission generally occurs through the inhalation of spores and dissemination arise from pulmonary infections. Members of Rhizomucor in infected tissue are visible as hyaline (clear) and aseptate hyphae. Treatment involves amphotericin B and surgical intervention (Papp et al., 2011).
Rhizomucor miehei (also: Mucor miehei [1]) is a species of fungus. It is commercially used to produce enzymes which can be used to produce a microbial rennet to curd milk and produce cheese.[2]
Under experimental conditions, this species grows particularly well at temperatures between 24 and 55°C, and their growth becomes negligible below 21°C or above 57°C.[3]
It is also used to produce lipases for interesterification of fats.[4]
Rhizomucor miehei (also: Mucor miehei ) is a species of fungus. It is commercially used to produce enzymes which can be used to produce a microbial rennet to curd milk and produce cheese.
Under experimental conditions, this species grows particularly well at temperatures between 24 and 55°C, and their growth becomes negligible below 21°C or above 57°C.
It is also used to produce lipases for interesterification of fats.
