Methods to preserve potentially toxigenic fungi

Abstract

Microorganisms are a source of many high-value compounds which are useful to every living being, such as humans, plants and animals. Since the process of isolating and improving a microorganism can be lengthy and expensive, preserving the obtained characteristic is of paramount importance, so the process does not need to be repeated. Fungi are eukaryotic, achlorophyllous, heterotrophic organisms, usually filamentous, absorb their food, can be either macro or microscopic, propagate themselves by means of spores and store glycogen as a source of storage. Fungi, while infesting food, may produce toxic substances such as mycotoxins. The great genetic diversity of the Kingdom Fungi renders the preservation of fungal cultures for many years relevant. Several international reference mycological culture collections are maintained in many countries. The methodologies that are most fit for preserving microorganisms for extended periods are based on lowering the metabolism until it reaches a stage of artificial dormancy. The goal of this study was to analyze three methods for potentially toxigenic fungal conservation (Castellani’s, continuous subculture and lyophilization) and to identify the best among them.

Evaluation of two storage methods for fungal isolates of Fusarium sp. and Cochliobolus sativus

“…Thus, this assessment method depends on visual evaluation for the viability, purity and morphological stability. The evaluation method employed in the current research has been applied in several studies for human and phytopathogenic agents and yielded satisfactory results for extended storage period: 147 species belonging to 66 genera of filamentous fungi, yeasts, and aerobic actinomycetes (McGinnis et al, 1974), 160 medical species represented 594 isolates (de Capriles et al, 1989), 1474 clinical and environmental isolates of molds, yeasts, aerobic actinomycetes, and algae belonging to 164 genera (382 taxa) (Pasarell and McGinnis, 1992), 18 strawberry pathogenic fungi of genera Colletotrichum and Phomopsis (Legard and Chandler, 2000), 43 medical species of genera Aspergillus, Cladosporium, Fusarium, Mucor, Penicillium and Rhizopus (Diogo et al, 2005), 179 isolates of 45 species of pathogenic filamentous fungi (Borman et al, 2006), and 12 potentially toxigenic species of the genera Aspergillus and Penicillium (Guimaraes et al, 2014). (Table 1) showed that the viability of 70 isolates of five species was 100% for the two storage methods for a period of one year.…”

“…The culture remains in an inactive state as water suppresses the growth of the fungi and the culture gets revived when transferred to fresh medium besides avoiding morphological changes in most fungi (Nakasone et al, 2004). High recovery rates were reported for human and phytopathogenic cultures stored in sterile water (McGinnis et al, 1974;de Capriles et al, 1989;Hornby and Bateman, 1998;Diogo et al, 2005;Elliott, 2005;Borman et al, 2006;Garcıa-Garcıa et al, 2014;Guimaraes et al, 2014).…”

“…The long-term preservation of plant pathogens in stable conditions without any morphological and physiological alternations is important for teaching, mycological and agricultural researches, and biotechnological purposes (Abd-Elsalam et al, 2010). Ideally, stored isolate should remain viable for extended period by lowering the metabolism until it reaches a stage of artificial dormancy (Guimaraes et al, 2014). This procedure prevents the accumulation of mutations causing morphological and biochemical alterations (Nakasone et al, 2004).…”

“…No preservation method can be universally applied to all fungi and intraspecific variability makes it impossible to apply standard protocols, even at the species level (Ryan et al, 2000). The choice of a preservation technique for specific plant pathogens depends, among other factors, on the characteristics of the method, maintenance costs, importance of the collection and equipment availability (Guimaraes et al, 2014).…”

Polyphasic, Including MALDI-TOF MS, Evaluation of Freeze-Drying Long-Term Preservation on Aspergillus (Section Nigri) Strains

“…Although several studies have evaluated the use of different methods of preservation on Aspergillus strains viability [19,31,32,33,34,35], to our knowledge, none have assessed possible effects on a wide range of phenotypical characteristics after preservation in this genus. The biotechnological relevant species— Aspergillus niger —was also included in this selection as a model organism since it has been used as a cell factory for the production of a wide range of metabolites, such as organic acids, antibiotics, extracellular enzymes, as well as native and recombinant proteins.…”