Comparison of methods for estimating the biomass of three food-borne fungi with different growth patterns

Mycotoxin determination in fungal contaminated Canadian silage toxic to dairy cows and goats

Silage has become a key component of year-long animal feed in Canada and parts of northern Europe. It provides several advantages to farmers over traditional feed components, such as increased digestibility, higher nutrient content and preservation of the forages to meet seasonal feeding demands. Some ensiled materials can contain toxic fungal metabolites resulting from ‘in field’ contamination. In addition, when improperly stored or exposed to air during the feedout stage, silage is highly susceptible to aerobic spoilage by yeasts and filamentous fungi resulting in lower nutrient value and further mycotoxin contamination. In this study, silage samples were collected from 25 Canadian dairy goat and cattle farms where animals experienced feed-related health issues. Twenty-six unique fungal species were isolated from these samples, with the majority being Penicillium. High resolution liquid chromatography tandem mass spectrometry (HRLC-MS/MS) was used to identify a total of 125 known mycotoxins and fungal secondary metabolites from these silage samples, many of which were not produced by the 26 isolated filamentous fungi grown in agar cultures. Various mycotoxins resulting from preharvest contamination were detected, including ergot alkaloids, fumonisins and trichothecenes, some in high concentrations. Toxins produced after harvest included roquefortine C, citrinin and penitrem A. This study reinforces the need for farmers to implement best management practices to minimise fungal contamination and the resulting mycotoxin deposition in their crop and stored feed to maintain animal health.

Strong effect of Penicillium roqueforti populations on volatile and metabolic compounds responsible for aromas, flavor and texture in blue cheeses

Studies of food microorganism domestication can provide important insight into adaptation mechanisms and lead to commercial applications. Penicillium roqueforti is a fungus with four genetically differentiated populations, two of which were independently domesticated for blue cheese-making, with the other two populations thriving in other environments. Most blue cheeses are made with strains from a single P. roqueforti population, whereas Roquefort cheeses are inoculated with strains from a second population. We made blue cheeses in accordance with the production specifications for Roquefort-type cheeses, inoculating each cheese with a single P. roqueforti strain, using a total of three strains from each of the four populations. We investigated differences between the cheeses made with the strains from the four P. roqueforti populations, in terms of the induced flora, the proportion of blue color, water activity and the identity and abundance of aqueous and organic metabolites as proxies for proteolysis and lipolysis as well as volatile compounds responsible for flavor and aroma. We found that the population-of-origin of the P. roqueforti strains used for inoculation had a minor impact on bacterial diversity and no effect on the abundance of the main microorganism. The cheeses produced with P. roqueforti strains from cheese populations had a higher percentage of blue area and a higher abundance of the volatile compounds typical of blue cheeses, such as methyl ketones and secondary alcohols. In particular, the Roquefort strains produced higher amounts of these aromatic compounds, partly due to more efficient proteolysis and lipolysis. The Roquefort strains also led to cheeses with a lower water availability, an important feature for preventing spoilage in blue cheeses, which is subject to controls for the sale of Roquefort cheese. The typical appearance and flavors of blue cheeses thus result from human selection on P. roqueforti, leading to the acquisition of specific features by the two cheese populations. These findings have important implications for our understanding of adaptation and domestication, and for cheese improvement.

Wood-water relationships and their role for wood susceptibility to fungal decay

Wood in service is sequestering carbon, but it is principally prone to deterioration where different fungi metabolize wood, and carbon dioxide is released back to the atmosphere. A key prerequisite for fungal degradation of wood is the presence of moisture. Conversely, keeping wood dry is the most effective way to protect wood from wood degradation and for long-term binding of carbon. Wood is porous and hygroscopic; it can take up water in liquid and gaseous form, and water is released from wood through evaporation following a given water vapour pressure gradient. During the last decades, the perception of wood-water relationships changed significantly and so did the view on moisture-affected properties of wood. Among the latter is its susceptibility to fungal decay. This paper reviews findings related to wood-water relationships and their role for fungal wood decomposition. These are complex interrelationships not yet fully understood, and current knowledge gaps are therefore identified. Studies with chemically and thermally modified wood are included as examples of fungal wood substrates with altered moisture properties. Quantification and localization of capillary and cell wall water - especially in the over-hygroscopic range - is considered crucial for determining minimum moisture thresholds (MMThr) of wood-decay fungi. The limitations of the various methods and experimental set-ups to investigate wood-water relationships and their role for fungal decay are manifold. Hence, combining techniques from wood science, mycology, biotechnology and advanced analytics is expected to provide new insights and eventually a breakthrough in understanding the intricate balance between fungal decay and wood-water relations. KEY POINTS: • Susceptibility to wood-decay fungi is closely linked to their physiological needs. • Content, state and distribution of moisture in wood are keys for fungal activity. • Quantification and localization of capillary and cell wall water in wood is needed. • New methodological approaches are expected to provide new insights.

Time-Dependent Changes in Morphostructural Properties and Relative Abundances of Contributors in Pleurotus ostreatus/Pseudomonas alcaliphila Mixed Biofilms

Pleurotus ostreatus dual biofilms with bacteria are known to be involved in rock phosphate solubilization, endophytic colonization, and even in nitrogen fixation. Despite these relevant implications, no information is currently available on the architecture of P. ostreatus-based dual biofilms. In addition to this, there is a limited amount of information regarding the estimation of the temporal changes in the relative abundances of the partners in such binary systems. To address these issues, a dual biofilm model system with this fungus was prepared by using Pseudomonas alcaliphila 34 as the bacterial partner due to its very fast biofilm-forming ability. The application of the bacterial inoculum to already settled fungal biofilm on a polystyrene surface coated with hydroxyapatite was the most efficient approach to the production of the mixed system the ultrastructure of which was investigated by a multi-microscopy approach. Transmission electron microscopy analysis showed that the adhesion of bacterial cells onto the mycelial cell wall appeared to be mediated by the presence of an abundant layer of extracellular matrix (ECM). Scanning electron microscopy analysis showed that ECM filaments of bacterial origin formed initially a reticular structure that assumed a tabular semblance after 72 h, thus overshadowing the underlying mycelial network. Across the thickness of the mixed biofilms, the presence of an extensive network of channels with large aggregates of viable bacteria located on the edges of their lumina was found by confocal laser scanning microscopy; on the outermost biofilm layer, a significant fraction of dead bacterial cells was evident. Albeit with tangible differences, similar results regarding the estimation of the temporal shifts in the relative abundances of the two partners were obtained by two independent methods, the former relying on qPCR targeting of 16S and 18S rRNA genes and the latter on ester-linked fatty acid methyl esters analysis.

Fungal Fragments and Fungal Aerosol Composition in Sawmills

Assessment of exposure to fungi has commonly been limited to fungal spore measurements that have shown associations between fungi and development or exacerbation of different airway diseases. Because large numbers of submicronic fragments can be aerosolized from fungal cultures under laboratory conditions, it has been suggested that fungal exposure is more complex and higher than that commonly revealed by spore measurements. However, the assessment of fungal fragments in complex environmental matrix remain limited due to methodological challenges. With a recently developed immunolabeling method for field emission scanning electron microscope (FESEM), we could assess the complex composition of fungal aerosols present in personal thoracic samples collected from two Norwegian sawmills. We found that large fungal fragments (length >1 µm) dominated the fungal aerosols indicating that the traditional monitoring approach of spores severely underestimate fungal exposure. The composition of fungal aerosols comprised in average 9% submicronic fragments, 62% large fragments, and 29% spores. The average concentrations of large and submicronic fragments (0.2–1 µm) were 3 × 10⁵ and 0.6 × 10⁵ particles m⁻³, respectively, and correlated weakly with spores (1.4 × 10⁵ particles m⁻³). The levels of fragments were 2.6 times higher than the average spore concentration that was close to the proposed hazardous level of 10⁵ spores per m³. The season influenced significantly the fungal aerosol concentrations but not the composition. Furthermore, the ratio of spores in the heterogeneous fungal aerosol composition was significantly higher in saw departments as compared to sorting of green timber departments where the fungal fragments were most prevalent. Being the dominating particles of fungal aerosols in sawmills, fungal fragments should be included in exposure-response studies to elucidate their importance for health impairments. Likewise, the use of fungal aerosol composition in such studies should be considered.

In vitro selection of ecologically adapted ectomycorrhizal fungi through production of fungal biomass and metabolites for use in reclamation of biotite mine tailings

Mineral weathering plays an important role in poor-nutrient environments such as mine spoils and tailings. Ectomycorrhizal (ECM) fungi are able to enhance mineral weathering through different mechanisms, thereby increasing the availability of minerals and nutrients to plants. Six ECM fungi (Cadophora finlandia, Cenococcum geophilum, Hebeloma crustuliniforme, Lactarius aurantiosordidus, Paxillus involutes, and Tricholoma scalpturatum) were tested here for their tolerance to biotite-quartz-rich mine tailings. Either solid- or liquid-medium methods were used for in vitro selection of ECM fungi for their ability to grow on mine tailings. ECM fungi were selected based on their mycelial radial growth and metabolite production (ergosterol and low-molecular-mass organic acids, LMMOAs). We found a strong correlation between fungal ergosterol content and mycelial radial growth using the solid-medium method. However, the liquid-medium method was more appropriate for ergosterol synthesis and permitted direct measurement of organic acid production. We found that LMMOAs were exuded by ECM fungi, which solubilized mine tailings for their own growth and nutrition. Finally, we concluded that the ECM fungi C. finlandia and T. scalpturatum are the species most tolerant to tailings and could potentially improve the survival rate, growth, and health of white spruce seedlings planted on biotite mine spoils and tailings.

Differences in carbon source utilisation by orchid mycorrhizal fungi from common and endangered species of Caladenia (Orchidaceae)

Terrestrial orchids depend on orchid mycorrhizal fungi (OMF) as symbionts for their survival, growth and nutrition. The ability of OMF from endangered orchid species to compete for available resources with OMF from common species may affect the distribution, abundance and therefore conservation status of their orchid hosts. Eight symbiotically effective OMF from endangered and more common Caladenia species were tested for their ability to utilise complex insoluble and simple soluble carbon sources produced during litter degradation by growth with different carbon sources in liquid medium to measure the degree of OMF variation with host conservation status or taxonomy. On simple carbon sources, fungal growth was assessed by biomass. On insoluble substrates, ergosterol content was assessed using ultra-performance liquid chromatography (UPLC). The OMF grew on all natural materials and complex carbon sources, but produced the greatest biomass on xylan and starch and the least on bark and chitin. On simple carbon sources, the greatest OMF biomass was measured on most hexoses and disaccharides and the least on galactose and arabinose. Only some OMF used sucrose, the most common sugar in green plants, with possible implications for symbiosis. OMF from common orchids produced more ergosterol and biomass than those from endangered orchids in the Dilatata and Reticulata groups but not in the Patersonii and Finger orchids. This suggests that differences in carbon source utilisation may contribute to differences in the distribution of some orchids, if these differences are retained on site.

Comparison of methods to evaluate the fungal biomass in heating, ventilation, and air-conditioning (HVAC) dust

Heating, ventilation, and air-conditioning (HVAC) systems contain dust that can be contaminated with fungal spores (molds), which may have harmful effects on the respiratory health of the occupants of a building. HVAC cleaning is often based on visual inspection of the quantity of dust, without taking the mold content into account. The purpose of this study is to propose a method to estimate fungal contamination of dust in HVAC systems. Comparisons of different analytical methods were carried out on dust deposited in a controlled-atmosphere exposure chamber. Sixty samples were analyzed using four methods: culture, direct microscopic spore count (DMSC), β-N-acetylhexosaminidase (NAHA) dosing and qPCR. For each method, the limit of detection, replicability, and repeatability were assessed. The Pearson correlation coefficients between the methods were also evaluated. Depending on the analytical method, mean spore concentrations per 100 cm² of dust ranged from 10,000 to 682,000. Limits of detection varied from 120 to 217,000 spores/100 cm². Replicability and repeatability were between 1 and 15%. Pearson correlation coefficients varied from -0.217 to 0.83. The 18S qPCR showed the best sensitivity and precision, as well as the best correlation with the culture method. PCR targets only molds, and a total count of fungal DNA is obtained. Among the methods, mold DNA amplification by qPCR is the method suggested for estimating the fungal content found in dust of HVAC systems.

Degradation of PAHs in soil by Lasiodiplodia theobromae and enhanced benzo[a]pyrene degradation by the addition of Tween-80

Benzo[a]pyrene (BaP), a five-ring polycyclic aromatic hydrocarbon (PAH), which has carcinogenic potency, is highly recalcitrant and resistant to microbial degradation. A novel fungus, Lasiodiplodia theobromae (L. theobromae), which can degrade BaP as a sole carbon source in liquid, was isolated in our laboratory. To prompt the further application of L. theobromae in remediation of sites polluted by BaP and other PAHs, the present study was targeted toward the removal of BaP and PAHs from soil by L. theobromae. The degradation of BaP by L. theobromae was studied using a soil spiked with 50 mg/kg BaP. L. theobromae could remove 32.1 % of the BaP after 35 days of cultivation. Phenanthrene (PHE) inhibited BaP degradation as a competitive substrate. The tested surfactants enhanced BaP degradation in soil by different extents, and a removal rate of 92.1 % was achieved at a Tween-80 (TW-80) concentration of 5 g/kg. It was revealed that TW-80 could not only enhance BaP bioavailability by increasing its aqueous solubility and decreasing the size of its colloid particles but also increase enzyme secretion from L. theobromae and the population of L. theobromae. Moreover, ergosterol content together with the biomass C indicated the increase in L. theobromae biomass during the BaP biodegradation process in soils. Finally, a soil from a historically PAH-contaminated field at Beijing Coking Plant in China was tested to assess the feasibility of applying L. theobromae in the remediation of polluted sites. The total removal rate of PAHs by L. theobromae was 53.3 %, which is 13.1 % higher than that by Phanerochaete chrysosporium (P. chrysosporium), an effective PAH degrader. The addition of TW-80 to the field soil further enhanced PAH degradation to 73.2 %. Hence, L. theobromae is a promising novel strain to be implemented in the remediation of soil polluted by PAHs.

Prokaryotic and eukaryotic airborne microorganisms as tracers of microclimatic changes in the underground (Postojna Cave, Slovenia)

Bioaerosols in cave air can serve as natural tracers and, together with physical parameters, give a detailed view of conditions in the cave atmosphere and responses to climatic changes. Airborne microbes in the Postojna Cave system indicated very dynamic atmospheric conditions, especially in the transitory seasonal periods between winter and summer. Physical parameters of cave atmosphere explained the highest variance in structure of microbial community in the winter and in the summer. The airborne microbial community is composed of different microbial groups with generally low abundances. At sites with elevated organic input, occasional high concentrations of bacteria and fungi can be expected of up to 1,000 colony-forming units/m(3) per individual group. The most abundant group of airborne amoebozoans were the mycetozoans. Along with movements of air masses, airborne algae also travel deep underground. In a cave passage with elevated radon concentration (up to 60 kBq/m(3)) airborne biota were less abundant; however, the concentration of DNA in the air was comparable to that in other parts of the cave. Due to seasonal natural air inflow, high concentrations of biological and inanimate particles are introduced underground. Sedimentation of airborne allochthonous material might represent an important and continuous source of organic material for cave fauna.

Comparison of biomass dry weights and radial growth rates of fungal colonies on media solidified with different gelling compounds

Penicillium commune, Aureobasidium pullulans, and Paecilomyces farinosus were grown on two different media solidified with agar, Pluronic F-127, Carrageenan X-4910, or Carrageenan X-4910 overlaid with cellophane. Growth on Carrageenan X-4910 was generally the same as that on agar, as was the visual appearance of the colonies, e.g., the pigmentation. The Carrageenan X-4910 gels had a melting point, depending on the medium, of 41 to 46(deg)C, and the dry weights of the colonies were readily determined at 60(deg)C. To determine the dry weights of the colonies grown on agar plates, the gels were boiled for 10 min to melt the agar. Comparison of these two procedures showed that the boiling procedure resulted in a 22% reduction of the biomass dry weight. Cellophane membranes did not affect the radial growth rate profoundly. The biomass density was almost halved for P. commune and P. farinosus grown with membranes, whereas the presence of the membrane did not affect the biomass density of A. pullulans. The biomass densities of the colonies grown on Pluronic F-127 were significantly reduced, while in most cases, the radial growth rates of colonies grown on Pluronic F-127 were significantly higher than those obtained on agar or Carrageenan X-4910. Furthermore, the morphology of the leading hyphae was altered, and the hyphal growth unit length was more than twice that obtained on agar and Carrageenan X-4910. Carrageenan X-4910 is a valuable gelling compound for the study of the growth of fungi, as the biomass dry weight is readily determined and growth is similar to that obtained on agar gels.

Total and free ergosterol in mycelia of saltmarsh ascomycetes with access to whole leaves or aqueous extracts of leaves

Three species of saltmarsh ascomycetes were grown in the presence of all of the constituents of their natural substrate (leaves of cordgrass) or were presented only with aqueous extracts of the leaves. These two growth-condition treatments had no significant effect on total ergosterol content of the fungal mycelia, contrary to an earlier hypothesis that availability of plant lipids would lower fungal ergosterol contents. Mycelial content of free ergosterol was about twice as variable as that for total (free plus esterified) ergosterol. Total ergosterol (data pooled for all species) was strongly correlated to organic mycelial mass (r = 0.43, P < 0.00001, and slope = 4.59 mug of ergosterol mg of organic mass).

Grading of fermented and dried cocoa beans using fungal contamination, ergosterol index and ochratoxin a production

Sixty four samples of cocoa beans replicated in quadruplicates were collected from five warehouses from southwest Nigeria and examined for fungal loads, ergosterol and ochratoxin A The levels of all the variables obtained were further used as indices for cocoa grading into food quality, FoQ (erg < 5 mg/kg; OTA < 1 µg/kg), feed quality, FeQ (erg = 5~10 mg/kg; OTA in the range of 1.1~3.11 µg/kg), Screen for mycotoxin, SFM (erg = 10~20 mg/kg; OTA from 3.12 µg/kg and above) with fuel quality, FuQ having erg > 20 mg/kg and OTA > 6.12 µg/kg. Using these ergosterol indices, 18.75% of the cocoa beans examined was classified with the FoQ, 18.75% with the FuQ while 31.25% was classified with both the FeQ and the SFM, respectively. In conclusion, ergosterol can be used as a rapid index to grade fermented, dried cocoa beans meant for export.

Importance of mold allergy in asthma

Fungal exposure is hypothesized (controversially) to contribute to asthma development and to trigger symptoms in patients with asthma. The ubiquity of environmental fungal exposure makes a careful review of evidence essential. Evidence that exposure to high concentrations of fungal spores, antigens, or metabolites is associated with asthma development is limited. However, because mechanisms of asthma genesis are poorly understood, so too are the mechanisms of this potential association. This association is not proof of causality. Stronger evidence supports the hypothesis that fungal exposure triggers symptoms in asthmatic individuals. Proposed mechanisms have been tested and correlations between exposure and symptoms demonstrated. Though some correlations remain speculative, controlled studies could test such hypotheses. Because asthma is common and fungal exposure is ubiquitous, it is surprising that asthmatics don't have more symptoms when exposed to fungi. Fortunately, symptoms are dose dependent, creating an opportunity to develop clinically effective interventions. Given the right guidance, even patients with severe asthma can create healthy indoor environments.

Fungal colonization of sago starch in Papua New Guinea

Sago starch is an important source of dietary carbohydrates in lowland Papua New Guinea. Over the past 30 years there have been sporadic reports of severe illness following consumption of sago starch. A common assumption is that fungal metabolites might be associated with the illness, leading to the need for a more thorough investigation of the mycoflora of sago starch. Sago starch was collected from areas of high sago consumption in Papua New Guinea for fungal analysis (69 samples). Storage methods and duration were recorded at the time of collection and pH on arrival at the laboratory. Yeasts were isolated from all samples except two, ranging from 1.2 x 10(3) to 8.3 x 10(7) cfu/g. Moulds were isolated from 65 of the 69 samples, ranging from 1.0 x 10(2) to 3.0 x 10(6) cfu/g. Of 44 samples tested for ergosterol content, 42 samples showed the presence of fungal biomass. Statistical analyses indicated that sago starch stored for greater than five weeks yielded significantly higher ergosterol content and higher numbers of moulds than sago stored for less than five weeks. The method of storage was also shown to influence mould numbers with storage in natural woven fibre containers returning significantly greater numbers than present in other storage methods tested. Potentially mycotoxigenic genera of moulds including Aspergillus and Penicillium were commonly isolated from sago starch, and as such storage factors that influence the growth of these and other filamentous fungi might contribute to the safety of traditional sago starch in PNG.

Image analysis for monitoring the barley tempeh fermentation process

AIMS

To develop a fast, accurate, objective and nondestructive method for monitoring barley tempeh fermentation.

METHODS AND RESULTS

Barley tempeh is a food made from pearled barley grains fermented with Rhizopus oligosporus. Rhizopus oligosporus growth is important for tempeh quality, but quantifying its growth is difficult and laborious. A system was developed for analysing digital images of fermentation stages using two image processing methods. The first employed statistical measures sensitive to image colour and surface structure, and these statistical measures were highly correlated (r=0.92, n=75, P<0.001) with ergosterol content of tempeh fermented with R. oligosporus and lactic acid bacteria (LAB). In the second method, an image-processing algorithm optimized to changes in images of final tempeh products was developed to measure number of visible barley grains. A threshold of 5 visible grains per Petri dish indicated complete tempeh fermentation. When images of tempeh cakes fermented with different inoculation levels of R. oligosporus were analysed the results from the two image processing methods were in good agreement.

CONCLUSION

Image processing proved suitable for monitoring barley tempeh fermentation. The method avoids sampling, is nonintrusive, and only requires a digital camera with good resolution and image analysis software.

SIGNIFICANCE AND IMPACT OF THE STUDY

The system provides a rapid visualization of tempeh product maturation and qualities during fermentation. Automated online monitoring of tempeh fermentation by coupling automated image acquisition with image processing software could be further developed for process control.

Rhizopus oligosporus and yeast co-cultivation during barley tempeh fermentation—Nutritional impact and real-time PCR quantification of fungal growth dynamics

Barley tempeh was produced by fermenting barley kernels with Rhizopus oligosporus. The potential of the yeasts Saccharomyces cerevisiae (three strains), S. boulardii (one strain), Pichia anomala (one strain) and Kluyveromyces lactis (one strain) to grow together with R. oligosporus during barley tempeh fermentation was evaluated. All yeast strains grew during the fermentation and even during cold storage of tempeh (P<0.01). The growth of yeasts slightly increased the ergosterol contents, but did not influence amino acid contents and compositions, and did not reduce phytate contents. Slight increases of vitamins B(6) and niacinamide, and slight decreases of B(1) and biotin were observed. Quantification of fungal growth is difficult during mixed species fermentations because ergosterol is found in all fungal species, and colony-forming-unit (cfu) estimations are not reliable for R. oligosporus and other sporulating fungi. Therefore, we developed a quantitative real-time PCR method for individually quantifying S. cerevisiae and R. oligosporus growth in barley tempeh. The PCR results were highly correlated with the ergosterol content of R. oligosporus and with the number of cfu of S. cerevisiae. Thus, real-time PCR is a rapid and selective method to quantify yeasts and R. oligosporus during mixed species fermentation of inhomogenous substrate such as barley tempeh.

Use of a MS-electronic nose for prediction of early fungal spoilage of bakery products

A MS-based electronic nose was used to detect fungal spoilage (measured as ergosterol concentration) in samples of bakery products. Bakery products were inoculated with different Eurotium, Aspergillus and Penicillium species, incubated in sealed vials and their headspace sampled after 2, 4 and 7 days. Once the headspace was sampled, ergosterol content was determined in each sample. Different electronic nose signals were recorded depending on incubation time. Both the e-nose signals and ergosterol levels were used to build models for prediction of ergosterol content using e-nose measurements. Accuracy on prediction of those models was between 87 and 96%, except for samples inoculated with Penicillium corylophilum where the best predictions only reached 46%.

Determination of ergosterol as an indicator of fungal biomass in various samples using non-discriminating flash pyrolysis

Ergosterol is the major sterol constituent of most fungi. Since it is present in negligible amounts in higher plants, it can be used as a chemical marker for the presence of fungal contamination. A number of different ergosterol assays have been developed for the quantification of fungi in various samples. The paper presents the development of a new method for ergosterol detection based on the combination of non-discriminating flash pyrolysis with gas chromatography/mass spectrometry (Py-GC/MS). The design of the non-discriminating Py-GC/MS systems assures efficient transfer of high-molecular-weight pyrolysis products to the GC column for separation, followed by analyte detection by MS. The method was tested on different types of samples, including baker's yeast (Saccharomyces cerevisiae), moldy bread, indoor dust, and a leaf infected with powdery mildew. Ergosterol was detected in all these samples at levels ranging from approximately 4 mg/g for the baker's yeast to approximately 6 microg/g for household dust. The main benefits of non-discriminating pyrolysis over other techniques include elimination of the need for sample preparation, small sample size required and short analysis time.

Determination of ergosterol in Fusarium-infected wheat by liquid chromatography-atmospheric pressure photoionization mass spectrometry

A rapid liquid chromatography-atmospheric pressure photoionization mass spectrometry (LC-APPI-MS) method was developed for the determination of ergosterol in wheat grains. The effects of the dopants acetone, toluene and anisole on the ionization efficiency were studied. To identify the predominant ions, APPI-MS-MS studies were performed. Different LC and MS parameters were optimized to obtain maximum sensitivity. The effects of the mobile phase composition and of the flow rate were investigated. Additionally, the effects of the nebulizer gas pressure, the drying gas flow, the vaporizer temperature, the fragmentor voltage and the capillary voltage on the ionization efficiency were evaluated. The calibration curve exhibited good linearity and reproducibility. The detection limit (S/N=3) was 0.15 ng on column, which allows the determination of ergosterol in wheat at a concentration as low as 0.12 microg/g. Twenty wheat varieties artificially infected with Fusarium graminearum were investigated by this method.

Inhalational mold toxicity: fact or fiction? A clinical review of 50 cases

BACKGROUND

Three well-accepted mechanisms of mold-induced disease exist: allergy, infection, and oral toxicosis. Epidemiologic studies suggest a fourth category described as a transient aeroirritation effect. Toxic mold syndrome or inhalational toxicity continues to cause public concern despite a lack of scientific evidence that supports its existence.

OBJECTIVES

To conduct a retrospective review of 50 cases of purported mold-induced toxic effects and identify unrecognized conditions that could explain presenting symptoms; to characterize a subgroup with a symptom complex suggestive of an aeroirritation-mediated mechanism and compare this group to other diagnostic categories, such as sick building syndrome and idiopathic chemical intolerance; and to discuss the evolution of toxic mold syndrome from a clinical perspective.

METHODS

Eighty-two consecutive medical evaluations were analyzed of which 50 met inclusion criteria. These cases were critically reviewed and underwent data extraction of 23 variables, including demographic data, patient symptoms, laboratory, imaging, and pulmonary function test results, and an evaluation of medical diagnoses supported by medical record review, examination, and/or test results.

RESULTS

Upper respiratory tract, lower respiratory tract, systemic, and neurocognitive symptoms were reported in 80%, 94%, 74%, and 84% of patients, respectively. Thirty patients had evidence of non-mold-related conditions that explained their presenting complaints. Two patients had evidence of allergy to mold allergens, whereas 1 patient exhibited mold-induced psychosis best described as toxic agoraphobia. Seventeen patients displayed a symptom complex that could be postulated to be caused by a transient mold-induced aeroirritation.

CONCLUSION

The clinical presentation of patients with perceived mold-induced toxic effects is characterized by a disparate constellation of symptoms. Close scrutiny revealed a number of preexisting diagnoses that could plausibly explain presenting symptoms. The pathogenesis of aeroirritation implies completely transient symptoms linked to exposures at the incriminated site. Toxic mold syndrome represents the furtive evolution of aeroirritation from a transient to permanent symptom complex in patients with a psychogenic predisposition. In this respect, the core symptoms of toxic mold syndrome and their gradual transition to chronic symptoms related to nonspecific environmental fragrances and irritants appear to mimic what has been observed with other pseudodiagnostic categories, such as sick building syndrome and idiopathic chemical intolerance.

Growth of lactic acid bacteria and Rhizopus oligosporus during barley tempeh fermentation

The zygomycete Rhizopus oligosporus is traditionally used to ferment soybean tempeh, but it is also possible to ferment other legumes and cereals to tempeh. The traditional soybean tempeh harbours a multitude of microorganisms with potentially beneficial or detrimental effects on quality. Lactic acid bacteria (LAB) have positive effects on the safety of soybean tempeh, but the effects of LAB on R. oligosporus growth have not been investigated. We have developed a cereal grain tempeh by fermenting pearled barley with R. oligosporus ATCC 64063. Four LAB species, Lactobacillus plantarum, Lactobacillus fermentum, Lactobacillus reuteri and Lactococcus lactis were assessed for their growth abilities and their effects on R. oligosporus growth during barley tempeh fermentation. Growth of LAB was assayed as colony forming units (cfu), while growth of R. oligosporus was measured as ergosterol content and hyphal length. The two fungal measurements highly correlated (r=0.83, P<0.001, n=90). The ergosterol content of fungal mycelia ranged from 11.7 to 30.1 mg/g fungal dry matter. L. plantarum multiplied from 4.8 to 7.4 log cfu/g dry tempeh and L. fermentum increased from 4.4 to 6.8 log cfu/g during 24 h incubation at 35 degrees C. L. reuteri and L. lactis had significantly slower growth, with increases from 4.8 to 5.6 log cfu/g and 5.0 to 5.4 log cfu/g, respectively. The growth of R. oligosporus and the final pH (4.9) in barley tempeh were not significantly influenced by any of the LAB investigated.

Comparison of methods for the assessment of growth of food spoilage moulds in solid substrates

The objective of the study was to evaluate the general suitability of ergosterol content, CFU, and colony diameters determinations for a range of fungi representing food spoilage moulds for the assessment of their growth on solid substrates, in particular intermediate moisture foods. Sixteen food-borne mould species were inoculated onto DG18 agar overlaid with cellophane, allowing determination of a direct measurement of biomass density weighing. The samples were also evaluated with regard to visible and microscopic colony diameters, total ergosterol content, Thoma counts, viable CFU counts, and so on. The same parameters were assayed in the spore suspensions obtained from those cultures. Data were evaluated by multivariate data analysis using projection methods such as principal component analysis (PCA), showing some groupings among the measured variables, mainly linked to the sporulating/nonsporulating nature of the different species tested. Ratios among the different variables were obtained, compared among the species, and evaluated along time (2-10 days). It was concluded that, as a general rule for all the species, ergosterol content and colony diameters were better correlated to fungal biomass dry weight than CFU counts were. Conversion factors were 0.3-3 microg ergosterol mg(-1) biomass dry weight and 76-227 mg biomass dry weight cm(-2), depending on the species.

Correlation betweenin vitrogrowth rate andin vivovirulence inAspergillus fumigatus

We describe a kinetic microbroth method of measuring the growth rate of Aspergillus fumigatus spectrophotometrically. Using this method, growth rates were determined for nine A. fumigatus isolates for which an LD90 value in immunosuppressed CD-1 mice had previously been obtained. Comparison of the growth rates and LD90 values of these isolates suggests that a correlation exists between the two parameters.

Ergosterol as an indicator of mould growth on building materials

Ergosterol was used as a specific indicator of fungal biomass to determine and assess mould growth on damp building material. The samples were saponified, cleaned up on a silica gel column and the sterols silylated and analysed by gas chromatography and mass spectrometry in MS/MS mode. Ninety-one samples of building materials from damp rooms were analysed including plaster, plaster/paint, paint, wood-chip wallpaper and paper wall covering. The concentrations of ergosterol ranged from 0.1 to 130 microg/g dry mass and depended on carbon content of the material. The highest concentrations were determined for wallpaper, the lowest for plaster and intermediate ones for paint. Based on ergosterol content and inspection of the room during sampling a rough classification of mould infestation is presented. The applicability of the ergosterol method was further tested in two case studies on the spatial distribution of fungi on damp walls and irregular distributions were found. With few exceptions the concentration of ergosterol in building materials was found to be a suitable indicator to estimate fungal biomass.

Quantifying mold biomass on gypsum board: comparison of ergosterol and beta-N-acetylhexosaminidase as mold biomass parameters

Two mold species, Stachybotrys chartarum and Aspergillus versicolor, were inoculated onto agar overlaid with cellophane, allowing determination of a direct measurement of biomass density by weighing. Biomass density, ergosterol content, and beta-N-acetylhexosaminidase (3.2.1.52) activity were monitored from inoculation to stationary phase. Regression analysis showed a good linear correlation to biomass density for both ergosterol content and beta-N-acetylhexosaminidase activity. The same two mold species were inoculated onto wallpapered gypsum board, from which a direct biomass measurement was not possible. Growth was measured as an increase in ergosterol content and beta-N-acetylhexosaminidase activity. A good linear correlation was seen between ergosterol content and beta-N-acetylhexosaminidase activity. From the experiments performed on agar medium, conversion factors (CFs) for estimating biomass density from ergosterol content and beta-N-acetylhexosaminidase activity were determined. The CFs were used to estimate the biomass density of the molds grown on gypsum board. The biomass densities estimated from ergosterol content and beta-N-acetylhexosaminidase activity data gave similar results, showing significantly slower growth and lower stationary-phase biomass density on gypsum board than on agar.

Use of an electronic tongue to analyze mold growth in liquid media

The feasibility of employing an electronic tongue to measure the growth of mold in a liquid medium was studied. We used the electronic tongue developed at Linköping University, which is based on pulsed voltammetry and consists of an array of different metal electrodes. Instead of focusing on a single parameter, this device provides information about the condition or quality of a sample or process. Accordingly, the data obtained are complex, and multivariate methods such as principal component analysis (PCA) or projection to latent structures (PLS) are required to extract relevant information. A gas chromatographic technique was developed to measure ergosterol content in mold biomass and was subsequently used as a reference method to investigate the ability of the electronic tongue to measure the growth of mold in liquid media. The result shows that the electronic tongue can monitor mold growth in liquids. In PLS analysis, the electronic tongue signals correlate well with the amount of ergosterol in the mold biomass as well as the microbially induced changes in the pH of the medium.

Possible role of plant phenolics in the production of trichothecenes by Fusarium graminearum strains on different fractions of maize kernels

Four trichothecene-producing strains of Fusarium graminearum were grown on three maize grain fractions, whole grain, degermed grain, and the germ, to determine the effect of natural substrates on mycotoxin production. Monitoring the ergosterol content after 25 days of incubation indicated that fungal growth on all grain fractions was comparable. Trichothecene (TCT) production was highest on degermed grain, less on whole grain, and very low or nondetectable on the germ; similar results were found with four different strains. It was concluded that inhibitor(s) of TCT biosynthesis were present in maize germ. The presence of phenolic compounds was investigated in the different fractions. The hydroxamate 4-acetylbenzoxazolin-2-one (4-ABOA), a known inhibitor of mycotoxin production, was found in the degermed and whole grain fractions but not in the germ. Therefore, the TCT inhibition observed on the maize germ fraction used in our study is clearly not linked to 4-ABOA. Other soluble phenolic compounds were found at a much higher concentration in the germ than in the two other fractions. The inhibition property of the soluble ester-bound extracts was tested in liquid culture. A possible role for these compounds is discussed.

An antifungal compound produced by Bacillus subtilis YM 10-20 inhibits germination of Penicillium roqueforti conidiospores

AIMS

To identify and characterize an antifungal compound produced by Bacillus subtilis YM 10-20 which prevents spore germination of Penicillium roqueforti.

METHODS AND RESULTS

The antifungal compound was isolated by acid precipitation with HCl. This compound inhibited fungal germination and growth. Identification by HPLC and mass spectrometry analysis showed high similarity to iturin A. Permeabilization and morphological changes in P. roqueforti conidia in the presence of the inhibitor were revealed by fluorescence staining and SEM, respectively. CONCLUSOINS: The iturin-like compound produced by B. subtilis YM 10-20 permeabilizes fungal spores and blocks germination.

SIGNIFICANCE AND IMPACT OF THE STUDY

Fluorescence staining in combination with flow cytometry and scanning electron microscopy are efficient tools for assessing the action of antifungal compounds against spores. Iturin-like compounds may permeabilize fungal spores and inhibit their germination.

Influence of elevated CO(2) on the fungal community in a coastal scrub oak forest soil investigated with terminal-restriction fragment length polymorphism analysis

Sixteen open-top chambers (diameter, 3.66 m) were established in a scrub oak habitat in central Florida where vegetation was removed in a planned burn prior to chamber installation. Eight control chambers have been continuously exposed to ambient air and eight have been continuously exposed to elevated CO(2) at twice-ambient concentration (approximately 700 ppm) for 5 years. Soil cores were collected from each chamber to examine the influence of elevated atmospheric CO(2) on the fungal community in different soil fractions. Each soil sample was physically fractionated into bulk soil, rhizosphere soil, and roots for separate analyses. Changes in relative fungal biomass were estimated by the ergosterol technique. In the bulk soil and root fractions, a significantly increased level of ergosterol was detected in the elevated CO(2) treatments relative to ambient controls. Fungal community composition was determined by terminal-restriction fragment length polymorphism (T-RFLP) analysis of the internal transcribed spacer (ITS) region. The specificities of different ITS primer sets were evaluated against plant and fungal species isolated from the experimental site. Changes in community composition were assessed by principal component analyses of T-RFLP profiles resolved by capillary electrophoresis. Fungal species richness, defined by the total number of terminal restriction fragments, was not significantly affected by either CO(2) treatment or soil fraction.

Effect of pollutants on the ergosterol content as indicator of fungal biomass

Ergosterol content was determined in 20 white-rot fungi isolates and the values ranged from 2380 to 13060 microg g(-1) fungal biomass. Significant changes of ergosterol content according the physiological stage for Bjerkandera adusta 4312 and Coriolopsis gallica 8260 were found, showing the highest values during the stationary phase. However, in the case of Phanerochaete chrysosporium 3642, no changes were detected during growth. The effect of pollutants, such as heavy metals and fungicides, on the ergosterol content of C. gallica was determined. Heavy metals (Cu 80 ppm, Zn 50 ppm or Cd 10 ppm) and fungicides (thiram 3 ppm or pentachlorophenol 1.5 ppm) at concentrations that reduce the metabolic activity between 18% and 53% (pollutant-stressed cultures) did not affect the ergosterol content. Only the fungicide zineb (25 ppm) reduced significantly the ergosterol content in biomass basis. In soil experiments with Cu (80 ppm) or thiram (10 ppm) after 15 and 30 days of incubation, the ergosterol content in soil was linearly correlated to the fungal biomass C in both polluted and control soil cultures. The ergosterol content was independent of the presence or the absence of pollutants. Thus, these results indicate that ergosterol can be a useful indicator for fungal biomass in polluted soils, and can be applied for monitoring bioremediation processes.

Predictive modelling approach applied to spoilage fungi: growth of Penicillium brevicompactum on solid media

Growth of Penicillium brevicompactum was examined on five solid media. Fungal growth was established by diameter measurements up to 50 days. Seventy experimental curves were fitted by Baranyi's primary predictive model. The growth rates were then analysed by non-parametric statistical methods. Penicillium brevicompactum could colonize the surface of solid media containing up to 700 g l-1 of sugar (50% glucose-50% fructose) with a growth rate of 0.9 mm day-1 (median values). Fitting curves by non-linear models followed by a non-parametric multiple comparison seems to be a convenient method for detecting differences in fungal growth on solid media. These two methods would be useful for studying fungal spoilage of bakery products with intermediate water activity.

Ergosterol content in various fungal species and biocontaminated building materials

This paper reports the ergosterol content for microbial cultures of six filamentous fungi, three yeast species, and one actinomycete and the ergosterol levels in 40 samples of building materials (wood chip, gypsum board, and glass wool) contaminated by microorganisms. The samples were hydrolyzed in alkaline methanol, and sterols were silylated and analyzed by gas chromatography-mass spectrometry. The average ergosterol content varied widely among the fungal species over the range of 2.6 to 42 &mgr;g/ml of dry mass or 0.00011 to 17 pg/spore or cell. Ergosterol could not be detected in the actinomycete culture. The results for both the fungal cultures and building material samples supported the idea that the ergosterol content reflects the concentration of filamentous fungi but it underestimates the occurrence of yeast cells. The ergosterol content in building material samples ranged from 0.017 to 68 &mgr;g/g of dry mass of material. A good agreement between the ergosterol concentration and viable fungal concentrations was detected in the wood chip (r > 0.66, P </= 0.009) and gypsum board samples (r > 0.48, P </= 0.059), whereas no relationship between these factors was observed in the glass wool samples. For the pooled data of the building materials, the ergosterol content correlated significantly with the viable fungal levels (r > 0.63, P < 0.0001). In conclusion, the ergosterol concentration could be a suitable marker for estimation of fungal concentrations in contaminated building materials with certain reservations, including the underestimation of yeast concentrations.

Pichia anomalaas a biocontrol agent ofPenicillium roquefortiin high-moisture wheat, rye, barley, and oats stored under airtight conditions

Pichia anomala inhibits growth of Penicillium roqueforti in high-moisture winter wheat, barley, and oats in cases where a malfunctioning airtight feed-storage system allows air to leak in. To imitate air leakage to such a storage system, grain was inoculated, packed in glass tubes with a restricted air supply, and incubated at 25°C. Yeast and mold colony-forming units (CFU) were counted on selective media after 14 days. Pichia anomala reached a density of about 5 x 107CFU/g on all tested cereals except in spring wheat (cv. Dragon), where a density of 109CFU/g was reached. In winter wheat (cv. Kosack), Penicillium roqueforti reached a density of 106CFU/g in grain that had not been inoculated with yeast and 105CFU/g in co-culture with 5 x 103CFU/g of Pichia anomala. At 5 x 104Pichia anomala, growth of Penicillum roqueforti was totally inhibited. Similar results were obtained with spring wheat (cv. Dragon), barley (cv. Golf), and oats (cv. Svea). However, spring wheat cv. Dragon was generally much less conducive to growth of Penicillium roqueforti. On rye (cv. Motto), Penicillium roqueforti did not grow in monoculture or when co-cultured with Pichia anomala. No differences in antagonistic activity of Pichia anomala or sensitivity of Penicillium roqueforti, respectively, were found between the three isolates tested of each species.Key words: biological control, postharvest, mold, cereal grain, storage.

Quantification of ergosterol and 3-hydroxy fatty acids in settled house dust by gas chromatography-mass spectrometry: comparison with fungal culture and determination of endotoxin by a Limulus amebocyte lysate assay

Ergosterol and 3-hydroxy fatty acids, chemical markers for fungal biomass and the endotoxin of gram-negative bacteria, respectively, may be useful in studies of health effects of organic dusts, including domestic house dust. This paper reports a method for the combined determination of ergosterol and 3-hydroxy fatty acids in a single dust sample and a comparison of these chemical biomarkers determined by gas chromatography-mass spectrometry with results from fungal culture and Limulus assay. Analyses of replicate house dust samples resulted in correlations of 0.91 (ergosterol in six replicates; P < 0.01) and 0.94 (3-hydroxy fatty acids in nine replicates; P < 0.001). The amounts of ergosterol (range, 2 to 16.5 ng/mg of dust) correlated with those of total culturable fungi (range, 6 to 1,400 CFU/mg of dust) in 17 samples, (r = 0.65; P < 0.005). The amounts of endotoxin (range, 11 to 243 endotoxin units/mg of dust) measured with a modified chromogenic Limulus assay correlated with those of lipopolysaccharide (LPS) determined from 3-hydroxy fatty acid analysis of 15 samples. The correlation coefficient depended on the chain lengths of 3-hydroxy acids used to compute the LPS content. The correlation was high (r = 0.88 +/- 0.01; P < 0.001) when fatty acid chains of 10 to 14 carbon atoms were included; the correlation was much lower when hydroxy acids of 16- or 18-carbon chains were included. In conclusion, the results of the described extraction and analysis procedure for ergosterol and 3-hydroxy fatty acids are reproducible, and the results can be correlated with fungal culture and endotoxin activity of organic dust samples.