Is there a common water-activity limit for the three domains of life?

Archaea and Bacteria constitute a majority of life systems on Earth but have long been considered inferior to Eukarya in terms of solute tolerance. Whereas the most halophilic prokaryotes are known for an ability to multiply at saturated NaCl (water activity (a(w)) 0.755) some xerophilic fungi can germinate, usually at high-sugar concentrations, at values as low as 0.

The extreme xerophilic mould Xeromyces bisporus--growth and competition at various water activities.

Little is known about the mould, Xeromyces bisporus, unique in its strong xerophilicity and ability to grow at water activity (a(w)) 0.62, lower than for any other known organism. The linear growth rates of one fast and one slow-growing strain of X.

Effect of reduced water activity and reduced matric potential on the germination of xerophilic and non-xerophilic fungi.

Reduction in water activity (a(w)) is used as a microbiological hurdle to prevent food spoilage. To minimize the levels of salt and sugar, which are commonly used to reduce a(w), the potential of food structure as a microbiological hurdle needs to be assessed. The concept of matric potential (Psi(m)) is used to measure the effect of food structure on water movement.

Evaluation of the efficacy of four weak acids as antifungal preservatives in low-acid intermediate moisture model food systems.

The potential efficacy of four weak acids as preservatives in low-acid intermediate moisture foods was assessed using a glycerol based agar medium. The minimum inhibitory concentrations (MIC, % wt./wt.

Effect of agar concentration on the matric potential of glycerol agar media and the germination and growth of xerophilic and non-xerophilic fungi.

The concept of water activity (a(w)) does not differentiate between water status resulting from the interaction of water with solutes, and that from interaction of water with matrices, which is termed matric potential (psi(m)). This study reports the effect of agar concentration (1.5, 3.

Inactivation of food spoilage fungi by ultra violet (UVC) irradiation.

The effect of ultraviolet irradiation (254 nm, UVC) on Aspergillus flavus, Aspergillus niger, Penicillium corylophilum and Eurotium rubrum was investigated using three different exposure techniques. Survival was determined for spores suspended in liquid medium after 1, 2 and 3 min UVC exposure at 4644 J/m(2)/min. The same UVC dose was applied to spores on the surface of agar plates for 5, 10, 15, 30, 60 and 120 s.

Utility of microsatellite markers and amplified fragment length polymorphism in the study of potentially ochratoxigenic black aspergilli.

Microsatellite markers and the results of amplified fragment length polymorphism (AFLP) were compared in the characterization of 68 Aspergillus carbonarius and A. niger aggregate strains of differing ochratoxin-producing ability and from different geographic areas, isolated mainly from grapes and soil. AFLP was applied to both A.

Fungi and mycotoxins in vineyards and grape products.

Many fungi may occur on grapes during growth in the vineyard, but the main concern from the viewpoint of mycotoxin contamination is the black Aspergilli, Aspergillus carbonarius and A. niger. These fungi are capable of producing ochratoxin A (OA) which may contaminate grapes and grape products such as wine, grape juice and dried vine fruit.

Mycotoxins in Australia: biocontrol of aflatoxin in peanuts.

The major mycotoxin problem in Australia is the formation of aflatoxins in peanuts by Aspergillus flavus and A. parasiticus. This is controlled by good farm management practice, segregation into grades on aflatoxin content at intake to shelling facilities, colour sorting and aflatoxin assays.

Fate of ochratoxin A during vinification of Semillon and Shiraz grapes.

Semillon and Shiraz grapes containing ochratoxin A (OA) were obtained by inoculation of bunches on the vine with Aspergillus carbonarius. Citric acid content was greater in the inoculated grapes than in healthy grapes. Samples were collected throughout vinification of these grapes and the OA content was quantified using a stable isotope dilution liquid chromatographic-tandem mass spectrometric method.

Effect of temperature and water activity on growth and ochratoxin A production by Australian Aspergillus carbonarius and A. niger isolates on a simulated grape juice medium.

The effect of water activity (0.92, 0.95, 0.

Survival and growth of Aspergillus carbonarius on wine grapes before harvest.

Aspergillus carbonarius, the primary OTA-producing species in Australia, was inoculated onto the surface of Chardonnay and Shiraz bunches at pre-bunch closure, veraison and pre-harvest during the 2002-03 and 2003-04 seasons. Mean A. carbonarius counts decreased between pre-bunch closure and veraison, and increased between veraison and pre-harvest.

Diversity of the Trichocomaceae in the Katandra Nature Reserve, Central Coast, NSW, Australia.

The diversity of the family Trichocomaceae, which includes the major anamorph genera Aspergillus and Penicillium, was studied in the Katandra Nature Reserve, Central Coast, NSW, Australia. Soil, living leaves, leaf litter and detritus were examined by both direct and dilution plating techniques. Fungi were isolated on dichloran Rose Bengal chloramphenicol agar, and dichloran 18 % glycerol agar, media suitable for cultivation of many species within this family.

Tremor syndrome associated with a fungal toxin: sequelae of food contamination.

We report on an elderly couple who presented with a syndrome that included severe generalised tremor and incoordination after eating soup from a damaged can. Black mould contaminating the can was subcultured and the fungus Penicillium crustosum was identified. This fungus usually produces a potent neurotoxin called penitrem A.

Microbiology of wheat and flour milling in Australia.

A survey was undertaken to determine the microbiological status of Australian wheat and the distribution of microorganisms in the flour milling fractions and end products. A total of 650 milling process and end product samples was obtained from nine flour mills located in New South Wales (4), Queensland (2), Victoria (2) and Western Australia (1) during the 1997-1998 and 1998-1999 wheat seasons. Most frequent (modal) counts in wheat and flour were, respectively, as follows: aerobic mesophilic plate count, 10(5) and 10(2) colony forming units/gram (cfu/g); coliforms, 10 and 1 most probable number/gram (MPN/g); Bacillus spp.

Influence of temperature, water activity and pH on growth of some xerophilic fungi.

The combined effects of water activity (aw), pH and temperature on the germination and growth of seven xerophilic fungi important in the spoilage of baked goods and confectionery were examined. Eurotium rubrum, E. repens, Wallemia sebi, Aspergillus penicillioides, Penicillium roqueforti, Chrysosporium xerophilum and Xeromyces bisporus were grown at 25, 30 and 37 degrees C on media with pH values of 4.

Some Considerations When Analyzing Foods for the Presence of Xerophilic Fungi.

Foodborne fungi capable of growing at reduced water activity (a) are described as xerophilic. Some xerophilic fungi will not grow or grow very slowly at a values characteristic of media traditionally used to enumerate yeasts and molds in foods. Populations of xerophiles may therefore be underestimated or go undetected.