Electrotransformation of the human pathogenic fungus Scedosporium prolificans mediated by repetitive rDNA sequences

Pseudomonas aeruginosa inhibits the growth of Scedosporium aurantiacum, an opportunistic fungal pathogen isolated from the lungs of cystic fibrosis patients

The filamentous fungus Scedosporium aurantiacum and the bacterium Pseudomonas aeruginosa are opportunistic pathogens isolated from lungs of the cystic fibrosis (CF) patients. P. aeruginosa has been known to suppress the growth of a number of CF related fungi such as Aspergillus fumigatus, Candida albicans, and Cryptococcus neoformans. However, the interactions between P. aeruginosa and S. aurantiacum have not been investigated in depth. Hence we assessed the effect of P. aeruginosa reference strain PAO1 and two clinical isolates PASS1 and PASS2 on the growth of two clinical S. aurantiacum isolates WM 06.482 and WM 08.202 using solid plate assays and liquid cultures, in a synthetic medium mimicking the nutrient condition in the CF sputum. Solid plate assays showed a clear inhibition of growth of both S. aurantiacum strains when cultured with P. aeruginosa strains PASS1 and PAO1. The inhibitory effect was confirmed by confocal microscopy. In addition to using chemical fluorescent stains, strains tagged with yfp (P. aeruginosa PASS1) and mCherry (S. aurantiacum WM 06.482) were created to facilitate detailed microscopic observations on strain interaction. To our knowledge, this is the first study describing successful genetic transformation of S. aurantiacum. Inhibition of growth was observed only in co-cultures of P. aeruginosa and S. aurantiacum; the cell fractions obtained from independent bacterial monocultures failed to initiate a response against the fungus. In the liquid co-cultures, biofilm forming P. aeruginosa strains PASS1 and PAO1 displayed higher inhibition of fungal growth when compared to PASS2. No change was observed in the inhibition pattern when direct cell contact between the bacterial and fungal strains was prevented using a separation membrane suggesting the involvement of extracellular metabolites in the fungal inhibition. However, one of the most commonly described bacterial virulence factors, pyocyanin, had no effect against either of the S. aurantiacum strains. This study shows that P. aeruginosa has a substantial inhibitory effect on the growth of the recently described CF fungal pathogen S. aurantiacum. The findings also highlighted that P. aeruginosa biofilm formation is important but not crucial for inhibiting the growth of S. aurantiacum in a lung- mimicking environment.

Molecular characterization and evaluation of mycorrhizal capacity of Suillus isolates from central Spain for the selection of fungal inoculants

Suillus fungal specimens of pine forests from a Mediterranean area of central Spain (Madrid region) were studied based on molecular and physiological analysis of sporocarps to obtain fungal native inocula to produce mycorrhizal Pinus halepensis Miller in nursery. Variation within the internal transcribed spacer (ITS) region of the ribosomal RNA genes of Suillus was examined by restriction fragment length polymorphism (RFLP) and direct sequencing of polymerase chain reaction products. Ribosomal DNA (rDNA) spacers were amplified from pure cultures obtained from fruit bodies of a range of Suillus species: Suillus bellinii (Inzenga) Watling, Suillus bovinus (Pers.) Kuntze, Suillus collinitus (Fr.) Kuntze, Suillus granulatus (L.) Snell, Suillus mediterraneensis (Jacquet. & Blum) Redeuil, Suillus luteus L. (Gray), and Suillus variegatus (Sw.) Kuntze. Interspecific variation in the length and number of restriction sites of the amplified ITS region was observed. This variation was confirmed by sequencing, which allowed us to identify some isolates. This is the first time that the ITS sequence of S. mediterraneensis is completely described. No intraspecific rDNA variation was observed within isolates of S. collinitus, S. mediterraneensis, and S. luteus. The phylogenetic analysis established the close relationship among these Mediterranean fungal species. As a further step to characterize the different isolates and to understand the relation between genetic and functional diversity, some physiological variables were evaluated. Intraspecific variation in axenic fungal growth and in mycorrhizal capacities was detected, especially within S. collinitus isolates. The fungal isolates stimulated the growth of P. halepensis in different rates. These studies indicated that ITS analysis, in conjunction with mycorrhizal tests, provides suitable combined tools for the analysis of Suillus spp. in a small geographic area for selecting isolates with final afforestation purposes.

Approaches to functional genomics in filamentous fungi

The study of gene function in filamentous fungi is a field of research that has made great advances in very recent years. A number of transformation and gene manipulation strategies have been developed and applied to a diverse and rapidly expanding list of economically important filamentous fungi and oomycetes. With the significant number of fungal genomes now sequenced or being sequenced, functional genomics promises to uncover a great deal of new information in coming years. This review discusses recent advances that have been made in examining gene function in filamentous fungi and describes the advantages and limitations of the different approaches.

Establishment of an overall transformation system for an oil-producing filamentous fungus, Mortierella alpina 1S-4

Oil-producing fungus Mortierella alpina 1S-4 is an industrial strain. To determine its physiological properties and to clarify the biosynthetic pathways for polyunsaturated fatty acids, a transformation system for this fungus was established using a derivative of it, i.e., a ura5- mutant lacking orotate phosphoribosyl transferase (OPRTase, EC.2.4.2.10) activity. Transformation with a vector containing the homologous ura5 gene as a marker was successfully performed using microprojectile bombardment, other methods frequently used for transformation, such as the protoplasting, lithium acetate, or electroporation methods, not giving satisfactory results. As a result, two types of transformants were obtained: a few stable transformants overexpressing the ura5 gene, and many unstable transformants showing OPRTase activity comparable to that of the wild-type strain. The results of quantitative PCR indicated that the stable transformants could retain the ura5 genes originating from the transformation vector regardless of the culture conditions. On the other hand, unstable transformants easily lost the marker gene under uracil-containing conditions, as expected. In this paper, we report that an overall transformation system for this fungus was successfully established, and propose how to select useful transformants as experimental and industrial strains.

Biolistic transformation of arbuscular mycorrhizal fungi. Progress and perspectives

Gene transfer systems have proved effective for the transformation of a range of organisms for both fundamental and applied studies. Biolistic transformation is a powerful method for the gene transfer into various organisms and tissues that have proved recalcitrant to more conventional means. For fungi, the biolistic approach is particularly effective where protoplasts are difficult to obtain and/or the organisms are difficult to culture. This is particularly applicable to arbuscular mycorrhizal (AM) fungi, being as they are obligate symbionts that can only be propagated in association with intact plants or root explants. Furthermore, these fungi are aseptate and protoplasts cannot be released. Recent advancements in gene transformation systems have enabled the use of biolistic technology to introduce foreign DNA linked to molecular markers into these fungi. In this review we discuss the development of transformation strategies for AM fungi by biolistics and highlight the areas of this technology which require further development for the stable transformation of these elusive organisms.