Natural occurrence of Alternaria toxins in pomegranate fruit and the influence of some technological processing on their levels in juice

Alternaria species produce several mycotoxins that are of particular health concern. The natural occurrence of three Alternaria toxins; alternariol (AOH), alternariol methyl ether (AME), and tenuazonic acid (TA) in pomegranate fruit was considered. A. alternata and A. tenuissima were identified by analysis of partial sequence of ITS-region. All studied strains produced high quantities of AOH in vitro on rice. A. tenuissima produces high quantities of AME and TA compared with A. alternata. In rotten tissues AME was the highest determined toxin with frequency percentage of 95.6%, followed by AOH and TA. All toxins were detected in the healthy tissues surrounding the infected tissues but at low levels. No visible changes were noted in Alternaria toxins after pasteurization of pomegranate juice, but they appeared after clarification. In conclusion, pasteurization and/or clarification are not sufficient to reduce Alternaria toxins in juice. The removal of the rotten parts does not ensure excluding Alternaria toxins

Species diversity of Trichoderma in Poland

In the present study, we reinvestigate the diversity of Trichoderma in Poland utilizing a combination of morphological and molecular/phylogenetic methods. A total of 170 isolates were collected from six different substrata at 49 sites in Poland. These were divided among 14 taxa as follows: 110 of 170 Trichoderma isolates were identified to the species level by the analysis of their ITS1, ITS2 rDNA sequences as: T. harzianum (43 isolates), T. aggressivum (35), T. citrinoviride (11), T. hamatum (9), T. virens (6), T. longibrachiatum (4), T. polysporum (1), and T. tomentosum (1); 60 isolates belonging to the Viride clade were identified based on a fragment of the translation-elongation factor 1-alpha (tef1) gene as: T. atroviride (20 isolates), T. gamsii (2), T. koningii (17), T. viridescens (13), T. viride (7), and T. koningiopsis (1). Identifications were made using the BLAST interface in TrichOKEY and TrichoBLAST (http://www.isth.info). The most diverse substrata were soil (nine species per 22 isolates) and decaying wood (nine species per 75 isolates). The most abundant species (25%) isolated from all substrata was T. harzianum

Assimilation of alternative sulfur sources in fungi

Fungi are well known for their metabolic versatility, whether it is the degradation of complex organic substrates or the biosynthesis of intricate secondary metabolites. The vast majority of studies concerning fungal metabolic pathways for sulfur assimilation have focused on conventional sources of sulfur such as inorganic sulfur ions and sulfur-containing biomolecules. Less is known about the metabolic pathways involved in the assimilation of so-called “alternative” sulfur sources such as sulfides, sulfoxides, sulfones, sulfonates, sulfate esters and sulfamates. This review summarizes our current knowledge regarding the structural diversity of sulfur compounds assimilated by fungi as well as the biochemistry and genetics of metabolic pathways involved in this process. Shared sequence homology between bacterial and fungal sulfur assimilation genes have lead to the identification of several candidate genes in fungi while other enzyme activities and pathways so far appear to be specific to the fungal kingdom. Increased knowledge of how fungi catabolize this group of compounds will ultimately contribute to a more complete understanding of sulfur cycling in nature as well as the environmental fate of sulfur-containing xenobiotics

Mycotoxigenic fungi contaminating wheat; toxicity of different Alternaria compacta strains

We studied mycotoxigenic fungi contaminating stored wheat grain, measured the toxins they secreted, and assessed their harmfulness. We focused on one common genus Alternaria, and chose 19 isolates representing A. compacta to study how different strains differed in their mycotoxin secretion and toxicity. Toxicity was assessed in a bioassay with a model bacteria Bacillus subtilis. All 19 A. compacta strains secreted toxins. Both the mycotoxin pattern and the fungal toxicity differed between the A. compacta stains. It seemed that some other toxins than alternariols or altenue acted as the main virulence factors of A. compacta against B. subtilis. We suggest that the most commonly studied mycotoxins do not necessarily indicate the toxicity of the fungi. The high variation in the amounts and toxins that different Alternaria species and strains secrete pose a challenge to the food supply chain. Keywords: Alternaria, Mycotoxins, Wheat grains, B. subtili

Infection of stem bases and grains of winter wheat by Fusarium culmorum and F. graminearum and effects of tillage method and maize-stalk residues

The effects of tillage (ploughing vs minimum tillage) and application of chopped maize stalks on winter wheat cv. Here-ward by Fusarium culmorum and F. graminearum were investigated in two 2-year experiments in eastern England. Supplementary inoculum of each fungus (five isolates) was applied to the ground to the first wheat crop in each experiment. Infection of shoot bases (spring), stem bases (summer) and harvested grain were determined by isolating the fungi on agar media and by quantitative PCR. Stem bases were infected more frequently by F. culmorum (up to 35% where inoculum was applied) than F. grammearum (up to 22% where inoculum applied; otherwise scarce). Despite mist-irrigation to encourage ear infection, the incidence of pathogens in grain was usually low, always less than 4% for F. culmorum, but up to 30% for F grammearum where inoculum was applied to the ground. Lack of rainfall probably limited the dispersal of conidia from the ground to the ears. Ascospores, produced by F. graminearum (Gibberella zeae) but not F. culmorum, are less dependent on rainfall for dispersal. Infection of grains by F. grammearum was usually correlated significantly with stem infection and sometimes, negatively, with grain yield. Both conidia and ascospores were produced on the previous crop's debris, apparently in small amounts, throughout much of the year. Little horizontal (plot to plot) dispersal was evident. Non-inversion cultivation and maize-stalk amendments tended to decrease stem-base disease, presumably through the effects of microbial antagonism or competition. However, the incidence of F. grammearum was increased in stem bases where maize stalks were present and in grain by both the presence of maize stalks and minimum tillage. The results support experimental data and UK survey data that non-inversion tillage increases the risk of ear infection, especially by F. grammearum, and hence of mycotoxin contamination of grain. Maize presents an additional risk where weather conditions do not limit the proliferation of the pathogens. This is consistent with evidence from surveys that the region in which the wheat crop is grown is the main risk factor for ear infection and mycotoxin accumulation in grain

Molecular characterization of ochratoxigenic fungi associated with poultry feedstuffs in Saudi Arabia

Fungal and mycotoxins contamination of food and poultry feeds can occur at each step along the chain from grain production, storage, and processing. A total of 200 samples comprising of mixed poultry feedstuffs (n = 100) and their ingredients (n = 100) were collected from Riyadh, Alhassa, Qassium, and Jeddah cities in Saudi Arabia. These samples were screened for contamination by fungi. Penicillium chrysogenum was the predominant species taking into its account and frequency, respectively, in both mixed poultry feedstuff and barley samples (4,561.9 and 687 fungal colony-forming units (CFU)/g) and (66% and 17%). Moisture content was an important indicator for the count of fungi and ochratoxin A. Ochratoxin analysis of plate cultures was performed by a HPLC technique. Sample of mixed poultry feedstuff which was collected from Jeddah displayed the highest level of ochratoxin (14.8 µg/kg) and moisture content (11.5%). Corn grains samples were highly contaminated by ochratoxin A (450 and 423 µg/kg) and recorded the highest moisture contents (14.1 and 14.5%). Ochratoxin A production in fungal species isolated from mixed poultry feedstuff samples were high with P. verrucosum (5.5 μg/kg) and A. niger (1.1 μg/kg). In sorghum and corn grains, the highest ochratoxins producing species were P. viridicatum (5.9 μg/kg) and A. niger (1.3 μg/kg), respectively. Sixty-three isolates of A. niger were ochratoxigenic, and all of them showed the presence of pks genes using PKS15C-MeT and PKS15KS primer pairs. The detection technique of A. niger in poultry feedstuff samples described in the present study was successfully used as a rapid and specific protocol for early detection of A. niger without cultivation on specific media