The Value of Long-Chain Fatty Acid Composition in the Identification of Species Representing the Basidiomycetous Genus Rhodosporidium Banno

Unique odd-chain polyenoic phospholipid fatty acids present in chytrid fungi

Chytrid fungi are ubiquitous components of aquatic and terrestrial ecosystems yet they remain understudied. To investigate the use of phospholipid fatty acids as phenotypic characteristics in taxonomic studies and biomarkers for ecological studies, 18 chytrid fungi isolated from soil to freshwater samples were grown in defined media and their phospholipid fatty acid profile determined. Gas chromatographic/mass spectral analysis indicated the presence of fatty acids typically associated with fungi, such as 16:1(n-7), 16:0, 18:2(n-6), 18:3(n-3) 18:1(n-9), and 18:0, as well as, a number of odd-chain length fatty acids, including two polyunsaturated C-17 fatty acids. Conversion to their 3-pyridylcarbinol ester facilitated GC-MS determination of double-bond positions and these fatty acid were identified as 6,9-17:2 [17:2(n-8)] and 6,9,12-17:3 [17:3(n-5)]. To the best of our knowledge, this is the first report of polyunsaturated C-17 fatty acids isolated from the phospholipids of chytrid fungi. Cluster analysis of PLFA profiles showed sufficient correlation with chytrid phylogeny to warrant inclusion of lipid analysis in species descriptions and the presence of several phospholipid fatty acids of restricted phylogenetic distributions suggests their usefulness as biomarkers for ecological studies.

A high-throughput microcultivation protocol for FTIR spectroscopic characterization and identification of fungi

Characterization and identification of fungi in food industry is an important issue both for routine analysis and trouble-shooting incidences. Present microbial techniques for fungal characterization suffer from a low throughput and are time consuming. In this study we present a protocol for high-throughput microcultivation and spectral characterization of fungi by Fourier transform infrared spectroscopy. For the study 11 species of in total five different fungal genera (Alternaria, Aspergillus, Mucor, Paecilomyces, and Phoma) were analyzed by FTIR spectroscopy. All the strains were isolated from trouble-shooting incidents in the production of low and high acid beverages. The cultivation was performed in malt extract broth (liquid medium) in a Bioscreen C system, allowing high-throughput cultivation of 200 samples at the same time. Mycelium was subsequently investigated by high-throughput Fourier transform infrared spectroscopy. Four spectral regions, fatty acids + lipid (3200-2800 cm(-1), 1300-1000 cm(-1)), protein-lipid (1800-1200 cm(-1)), carbohydrates (1200-700 cm(-1)) and "finger print" (900-700 cm(-1)) were evaluated for reproducibility and discrimination ability. The results show that all spectral regions evaluated can be used as spectroscopic biomarkers for differentiation of fungi by FTIR. The influence of different growth times on the ability of species discrimination by FTIR spectroscopy was investigated, and an optimal separation of all five genera was observed after five days of growth. This work presents a novel concept for high-throughput cultivation of fungi for FTIR spectroscopy that enables characterization or identification of hundreds of strains per day.

Typing of Histoplasma capsulatum strains by fatty acid profile analysis

The performance of fatty acid profiling for strain differentiation of Histoplasma capsulatum was assessed. Total fatty acids were isolated from the yeast-phase cells of seven stock and two previously unreported clinical strains of H. capsulatum var. capsulatum, as well as from one unreported clinical strain and one stock strain of H. capsulatum var. duboisii, and one strain of each of three other dimorphic zoopathogenic fungal species, Blastomyces dermatitidis, Paracoccidioides brasiliensis and Sporothrix schenckii. Different colony morphology and pigmentation types of the H. capsulatum strains were also included. The most frequently occurring fatty acids were oleic, palmitic, stearic and linoleic acids. There were variations in the relative percentage fatty acid contents of H. capsulatum strains that could be used for strain identification and discrimination. Differentiation between H. capsulatum strains was achieved by the comparison of detected fatty acids accompanied by principal component analysis using calculated Varimax-rotated principal component loadings. Statistical analysis yielded three major principal components that explained over 94 % of total variance in the data. All the strains of H. capsulatum var. capsulatum RFLP classes II and III were grouped into two distinct clusters: the heterogenic RFLP class I formed a large, but also well-defined group, whereas the outgroup strains of H. capsulatum var. duboisii, B. dermatitidis, P. brasiliensis and S. schenckii were shifted away. These data suggest that fatty acid profiling can be used in H. capsulatum strain classification and epidemiological studies that require strain differentiation at the intraspecies level.

Characterization and differentiation of filamentous fungi based on Fatty Acid composition

Cellular fatty acid composition of 100 different filamentous fungi, including oomycetes, zygomycetes, ascomycetes, basidiomycetes, and sterile mycelia, was analyzed to determine if they can be differentiated from one another on this basis and how minor variations in culture temperature and age affect this characteristic. Many fungi were found to possess the same fatty acids but produced different relative concentrations of each. Some fungi differed in both the fatty acids produced and in the relative concentrations of others. Multivariate discriminant analysis demonstrated that all of the species included in this study had significantly different (P < 0.001) fatty acid profiles. Each of the three phyla from which representative species were analyzed and the sterile forms had distinctive fatty acid profiles. Significant differences in fatty acid composition were also found at the intraspecific level. Both culture temperature and age affected fatty acid composition in the fungi examined, but when these factors were held constant, variance in fatty acid composition was not a problem and fungal fatty acid profiles could be differentiated statistically.

Application of fatty acid profiles in the identification of yeasts

In order to develop a rapid yeast identification technique using fatty acid profiles, an extensive survey has been conducted in our laboratory on the long-chain fatty acid composition (CLFAC) of yeasts representing the endomycetous and basidiomycetous yeast domain. It was accomplished by cultivating the yeast strains under standardized conditions in a synthetic liquid medium. When stationary phase was reached the cells of each culture were freeze-dried and the CLFAC was examined by gas chromatography. It was found that the fatty acid profile obtained for each strain was reproducible. However, as work progressed, it became clear that variation exists within species and that the relative percentages of some strains from different species may overlap. Identification of species could therefore not be achieved in all attempts, even when the resolution of the fatty acid analyses was enhanced by using capillary columns, useful for the detection of minor fatty acids. When used in isolation, CLFAC analyses is therefore not a generally applicable identification technique for yeast species. However, the technique was found to be a valuable chemotaxanomical tool to distinguish between strains of certain species, species of certain genera and species from particular environments. The technique currently finds application in the South African food and beverage industry as a quick, cheap and easy way to distinguish between strains of Saccharomyces cerevisiae. It is also used by an industry which produces bioprotein from Geotrichum candidum, to determine fungal contaminants in a quality control process.