Preliminary studies on the use of biochemical and physiological tests for the characterization of Fusarium isolates

Advances in Fungal Phylogenomics and Their Impact on Fungal Systematics

In the past decade, advances in next-generation sequencing technologies and bioinformatic pipelines for phylogenomic analysis have led to remarkable progress in fungal systematics and taxonomy. A number of long-standing questions have been addressed using comparative analysis of genome sequence data, resulting in robust multigene phylogenies. These have added to, and often surpassed traditional morphology or single-gene phylogenetic methods. In this chapter, we provide a brief history of fungal systematics and highlight some examples to demonstrate the impact of phylogenomics on this field. We conclude by discussing some of the challenges and promises in fungal biology posed by the ongoing genomics revolution.

Phenotypic degeneration occurs during sector formation in Metarhizium anisopliae

AIMS

The formation of sectors was observed during subculturing of an isolate of the entomopathogenic fungus Metarhizium anisopliae, a fungus used for biological control of insect pests. The aim of the investigation was to establish whether sector formation was accompanied by changes in physiological characters.

METHODS AND RESULTS

Four degenerative morphological states, with reduced sporulation capacity, were characterized. Subcultures were taken from each sector and four new culture lines established. The new lines were further subcultured every 21 d. A physiological assessment of each line was undertaken after 42 d using TLC of secondary metabolites and fluorogenic enzyme tests. Full sporulation capacity was not regained on subculture, although some cultures recovered partially. Changes in secondary metabolite profiles and the loss in detection of activity of specific enzymes were observed.

CONCLUSIONS

Sector formation was frequently accompanied by changes in the ability to produce secondary metabolites and enzymes.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results illustrate the importance of maintaining the stability of important cultures during routine subculture. The consequences could have significant implications if degenerate cultures are used as inocula for liquid fermentation cultures or industrial scale production.

Developments in fungal taxonomy

Fungal infections, especially those caused by opportunistic species, have become substantially more common in recent decades. Numerous species cause human infections, and several new human pathogens are discovered yearly. This situation has created an increasing interest in fungal taxonomy and has led to the development of new methods and approaches to fungal biosystematics which have promoted important practical advances in identification procedures. However, the significance of some data provided by the new approaches is still unclear, and results drawn from such studies may even increase nomenclatural confusion. Analyses of rRNA and rDNA sequences constitute an important complement of the morphological criteria needed to allow clinical fungi to be more easily identified and placed on a single phylogenetic tree. Most of the pathogenic fungi so far described belong to the kingdom Fungi; two belong to the kingdom Chromista. Within the Fungi, they are distributed in three phyla and in 15 orders (Pneumocystidales, Saccharomycetales, Dothideales, Sordariales, Onygenales, Eurotiales, Hypocreales, Ophiostomatales, Microascales, Tremellales, Poriales, Stereales, Agaricales, Schizophyllales, and Ustilaginales).

Opportunistic fusarial infections in humans

Fusarium species are common hyaline soil saprophytes and plant pathogens which have frequently been reported as etiologic agents of opportunistic infections in humans. These infections have usually been limited to superficial mycoses, but recently the number of infections of deep tissues and disseminated infections has greatly increased, especially in patients with an underlying immunosuppressive condition. The characteristic signs of these infections are disseminated skin nodules, fungemia and multiorgan involvement. Frequently, myalgia is also present. Skin involvement occurred in over 80% of cases of disseminated infections. These lesions are significant because they are readily accessible for biopsy and culture, thus permitting an early diagnosis. The therapy and outcome are dependent on the degree of invasion of the organisms and the status of the host. Identification of the pathogen to genus level is not difficult, but identification to species level requires a greater degree of expertise. Up to now, 15 species of Fusarium have been reported to cause infections in humans and animals. Few patients with disseminated fusarial infections have survived, even after receiving an adequate dosage of amphotericin B, the only antifungal agent that has some effect against these fungi. In vitro susceptibility to amphotericin B is a poor predictor of the clinical outcome of invasive fungal infections. Recovery of the phagocytic mechanisms in the form of rising neutrophil counts appears to be mandatory for clinical resolution. The resolution of neutropenia may be aided by the use of exogenous growth factors. Outside the USA, the majority of cases of disseminated fusarial infection have been reported from Mediterranean or tropical countries.

Based on biochemical and physiological behavior, where is Aspergillus egyptiacus better placed?

Physiological and biochemical properties were tested in 45 isolates of Aspergillus egyptiacus (16 isolates), Emericella nidulans (16) and Aspergillus versicolor (13). The three fungal species exhibited common and similar features. The big similarity between A. egyptiacus and E. nidulans was greater than between A. egyptiacus and A. versicolor. It included the inability to produce base either from sodium citrate or lactic acid media, growth at 45 degrees C (thermophilicity), and production of very similar pigmentations on Aspergillus flavus and parasiticus agar. A. egyptiacus is therefore better placed in the Aspergillus nidulans-Emericella assemblage.

Use of a colorimetric system to detect enzymes expressed by germinating conidia of entomopathogenic fungi

An apiZYM system, with 19 substrates, was used to detect enzymes expressed by germinating conidia of Nomuraea rileyi (5 isolates), Nomuraea atypicola, Nomuraea anemonoides, Beauveria bassiana and Metarhizium anisopliae. Similar enzyme profiles were obtained for two of the N. rileyi isolates (Mississippi, Ecuador) regardless of whether culture medium (Sabouraud-maltose-yeast) or cuticle (from larvae of Trichoplusia ni, Heliothis zea or Heliothis virescens) were used as substrates. Centroid-clustering analysis revealed three distinct enzyme profiles.

Enzymatic activity profiling as a potential biotyping method for Ajellomyces dermatitidis

Enzyme profiling was investigated as a means of recognizing biotypes and individual strains of Ajellomyces dermatitidis (anamorph, Blastomyces dermatitidis). Eighteen North American and 2 African representatives were tested with the Yeast-IDENT enzymatic activity profiling system (Analytab Products, Plainview, N.Y.). Significant variation was found between isolates, particularly in beta-galactosaminidase activity.