Characterization and harnessing of sterile fungi: Philippine scenario, prospects and challenges

Fungi make up large, diverse and widespread group of organisms, which include the microscopic molds and yeasts. Fungi interact with a broad array of other organisms as decomposers, mutualists or parasites, owing to their heterotrophic and absorptive nutrition. Some produce enzymes and secondary metabolites such as antibiotic, which are of industrial importance. Global estimates suggest that 1.5 million fungal species may exist but only 4 to 5% have been described. Fungal identification and classification relies heavily on morphology of spores and other reproductive structures. However, not all Fungi sporulate, i.e., are sterile fungi may be anamorphs with specific nutritional and environmental requirements for the production of spores that are not provided under cultivation conditions. Other may be truly sterile forms that reproduce by hyphal fragmentation. Induction of sporulation in the former types entails considerable experimentation with various media and environmental conditions that may take several weeks or months, which is impractical for large scale surveys. Sterile fungi may be found almost everywhere, including soil, plants and plant debris, household, humans, etc. A survey of literature and communications with researchers and scientists revealed that fungal researches thus far conducted in the country relied heavily on phenotypic method that characterized the reproductive structures. Isolates that fail to produce sexual/asexual spores are often disregarded. Two independent studies that employed molecular techniques to identify and classify sterile fungi were spearheaded by the author with graduate students and collaborators in the University. Sterile fungal isolates from the Mycology Research Laboratory, UPLB and from Mt. Makiling were identified to, at least, the genus level by implication using polymerase chain reaction (PCR) and subsequent analysis of the sequences of the full-length ITS (internal transcribed spacer) 1-5.8S-ITS2 regions of the rRNA gene. Because the ITS regions are non-coding and non-functional, they are subject to fewer constrains that allow accumulation of mutations at a faster rate, resulting in greater sequence variation between closely related species. The ITS region has recently been proposed as the official primary barcoding marker for Fungi. However, identification of potentially new genus and species of sterile fungi as very challenging for taxonomists who are limited to the analysis of DNA sequences. As of 2012, only ~172,000 full-length fungal ITS sequences are in GenBank, of which 56% represent ~15,500 species and 2,500 genera. Other challenges in studying the sterile fungi include preservation of isolates and screening for important traits. Some isolates became contaminated during periodic serial sub-culturing while others failed to revive from storage. Screening a large collection of isolates for useful properties such as production of enzymes and metabolites with potential economic significance is hampered by the high costs of commercially available substrates and analytical services, if at all available. However, modernization of research facilities, increase in funding support, and increasing pool of experts on molecular approach will lead to wide-ranging discovery of the phylogenetic distribution of sterile fungi, growth in global ITS database, and exploration of the potential of this form group of fungi.