Molecular Characters of Zygomycetous Fungi

Abstract

The traditional Zygomycota has recently been considered polyphyletic as evidenced by a lot of molecular phylogenetic analyses. As a result, it has been distributed into a new phylum and four pending subphyla. Before the taxonomic status for these four subphyla could be determined, the term “zygomycetous fungi” is used for those members traditionally included in the classical phylum Zygomycota. Most current molecular characters of zygomycetous fungi have revealed that there is an obvious conflict between the traditional morphology-based classification scheme and recent DNA-based phylogenies. Except for the notable adjustments at the phylum and subphylum level, major changes at the order level can be observed for Amoebidiales, Basidiobolales, Eccrinales, Entomophthorales, Geosiphonales and Mortierellales. With respect to families, studies on the order Mucorales have suggested an unnatural feature for its traditional family-level classification scheme. Some genera such as Absidia, Cunninghamella and Rhizopus have also been intensively investigated by molecular methods. Genes encoding glucoamylases, polygalacturonases, fumaric acids and polyunsaturated fatty acids, have been intensively studied for industrial purposes. Another important area is the study of the clinical relevance of zygomycetous fungi as pathogens. The poor sensitivity of histological practices, the difficult pure cultivation, and the inaccurate susceptibility and serological tests, have led to the development of highly sensitive and specific molecular techniques, such as microsatellite, oligonucleotide probes, microarrays of gene markers and their expression, fluorescent capillary electrophoresis, real-time PCR (polymerase chain reaction), PCR-RFLP (PCR-restriction fragment length polymorphism), RAPD (randomly amplified polymorphic DNA), PFGE (Pulsed Field Gel Electrophoresis), and direct sequencing of PCR products, but these methods are not widely available and are reserved primarily for research purposes. New techniques in the molecular identification of zygomycetous fungi need to be further developed and validated. So far, there are only five genome projects relevant to zygomycetous fungi, including Mortierella verticillata, Mucor circinelloides, Phycomyces blakesleeanus, Rhizopus arrhizus, and Smittium culisetae. More genome projects about industrially, agriculturally, medically and environmentally important zygomycetous fungi are hopeful to provide a better understanding of their natural status in the whole organismic system in the world and their potential to benefit the human being.