There is a paucity of knowledge on microbial community diversity and naturally occurring seasonal variations in agricultural soil. For this purpose the soil microbial community of a wheat field on an experimental farm in The Netherlands was studied by using both cultivation-based and molecule-based methods. Samples were taken in the different seasons over a 1-year period. Fatty acid-based typing of bacterial isolates obtained via plating revealed a diverse community of mainly gram-positive bacteria, and only a few isolates appeared to belong to the Proteobacteria and green sulfur bacteria. Some genera, such as Micrococcus, Arthrobacter, and Corynebacterium were detected throughout the year, while Bacillus was found only in July. Isolate diversity was lowest in July, and the most abundant species, Arthrobacter oxydans, and members of the genus Pseudomonas were found in reduced numbers in July. Analysis by molecular techniques showed that diversity of cloned 16S ribosomal DNA (rDNA) sequences was greater than the diversity among cultured isolates. Moreover, based on analysis of 16S rDNA sequences, there was a more even distribution among five main divisions, Acidobacterium, Proteobacteria, Nitrospira, cyanobacteria, and green sulfur bacteria. No clones were found belonging to the gram-positive bacteria, which dominated the cultured isolates. Seasonal fluctuations were assessed by denaturing gradient gel electrophoresis. Statistical analysis of the banding patterns revealed significant differences between samples taken in different seasons. Cluster analysis of the patterns revealed that the bacterial community in July clearly differed from those in the other months. Although the molecule- and cultivation-based methods allowed the detection of different parts of the bacterial community, results from both methods indicated that the community present in July showed the largest difference from the communities of the other months. Efforts were made to use the sequence data for providing insight into more general ecological relationships. Based on the distribution of 16S rDNA sequences among the bacterial divisions found in this work and in literature, it is suggested that the ratio between the number of Proteobacteria and Acidobacterium organisms might be indicative of the trophic level of the soil.

Diversity and Seasonal Fluctuations of the Dominant Members of the Bacterial Soil Community in a Wheat Field as Determined by Cultivation and Molecular Methods

The commercial use of entomopathogenic fungi and their products as mycoinsecticides necessitates their registration. Worldwide, several registration guidelines are available, however, most of them focus on similar or even the same safety issues. With respect to the two entomopathogenic fungi, Beauveria bassiana (Bals.-Criv.) Vuill. and Beauveria brongniartii (Sacc.) Petch, many commercial products have been developed, and numerous papers on different biological, environmental, toxicological and other safety aspects have been published during the past 30–40 years. The aim of the present review is to summarise these data. The following safety issues are presented: (1) identity of Beauveria spp.; (2) biological properties of Beauveria spp. (history, natural occurrence and geographical distribution, host range, mode of action, production of metabolites/toxins, effect of environmental factors); (3) analytical methods to determine and quantify residues; (4) fate and behaviour in the environment (mobili...

Review on safety of the entomopathogenic fungi Beauveria bassiana and Beauveria brongniartii

The entomopathogenic fungus Metarhizium anisopliae (Metschn.) Sorokin is widely used for biocontrol of pest insects, and many commercial products are on the market or under development. The aim of this review is to summarise all relevant safety data of this fungus, which are necessary for the commercialisation and registration process. The review contains the following sections: (1) identity, (2) biological properties (history, natural occurrence and geographical distribution, host range, mode of action, production of metabolites/toxins, effect of environmental factors), (3) methods to determine and quantify residues, (4) fate and behaviour in the environment (mobility and persistence in air, water and soil), (5) effects on non-target organisms (microorganisms, plants, soil organisms, aquatic organisms, predators, parasitoids, honey bees, earth worms, etc.), (6) effects on vertebrates (fish, amphibia, reptiles, and birds), and (7) effects on mammals and human health (allergy, pathogenicity/toxici...

Review on safety of the entomopathogenic fungus Metarhizium anisopliae

Coprinus cinereus has two main types of mycelia, the asexual monokaryon and the sexual dikaryon, formed by fusion of compatible monokaryons. Syngamy (plasmogamy) and karyogamy are spatially and temporally separated, which is typical for basidiomycetous fungi. This property of the dikaryon enables an easy exchange of nuclear partners in further dikaryotic-monokaryotic and dikaryotic-dikaryotic mycelial fusions. Fruiting bodies normally develop on the dikaryon, and the cytological process of fruiting-body development has been described in its principles. Within the specialized basidia, present within the gills of the fruiting bodies, karyogamy occurs in a synchronized manner. It is directly followed by meiosis and by the production of the meiotic basidiospores. The synchrony of karyogamy and meiosis has made the fungus a classical object to study meiotic cytology and recombination. Several genes involved in these processes have been identified. Both monokaryons and dikaryons can form multicellular resting bodies (sclerotia) and different types of mitotic spores, the small uninucleate aerial oidia, and, within submerged mycelium, the large thick-walled chlamydospores. The decision about whether a structure will be formed is made on the basis of environmental signals (light, temperature, humidity, and nutrients). Of the intrinsic factors that control development, the products of the two mating type loci are most important. Mutant complementation and PCR approaches identified further genes which possibly link the two mating-type pathways with each other and with nutritional regulation, for example with the cAMP signaling pathway. Among genes specifically expressed within the fruiting body are those for two galectins, β-galactoside binding lectins that probably act in hyphal aggregation. These genes serve as molecular markers to study development in wild-type and mutant strains. The isolation of genes for potential non-DNA methyltransferases, needed for tissue formation within the fruiting body, promises the discovery of new signaling pathways, possibly involving secondary fungal metabolites.

https://mmbr.asm.org/content/mmbr/64/2/316.full.pdf

Life History and Developmental Processes in the Basidiomycete Coprinus cinereus

Much of the work regarding earthworm effects on other organisms has focused on the functional significance of microbial-earthworm interactions, and little is known on the effects of earthworms on microfloral and faunal diversity. Earthworms can affect soil microflora and fauna populations directly and indirectly by three main mechanisms: (1) comminution, burrowing and casting; (2) grazing; (3) dispersal. These activities change the soil's physico-chemical and biological status and may cause drastic shifts in the density, diversity, structure and activity of microbial and faunal communities within the drilosphere. Certain organisms and species may be enhanced, reduced or not be affected at all depending on their ability to adapt to the particular conditions of different earthworm drilospheres. A large host of factors (including CaCO3, enzymes, mucus and antimicrobial substances) influence the ability of preferentially or randomly ingested organisms to survive (or not) passage through the earthworm gut, and their resultant capacity to recover and proliferate (or not) in earthworm casts. Small organisms, particularly microflora and microfauna, with limited ability to move within the soil, may benefit from the (comparatively) long ranging movements of earthworms. Microflora and smaller fauna appear to be particularly sensitive to earthworm activities, and priming effects enhancing nutrient release, particularly in casts, are common. Larger fauna such as microarthropods, enchytraeids and Isopods may be enhanced under some conditions (e.g., in earthworm middens), but in other cases earthworm activity may lead to a decrease in their populations due to competition for food (microbes and organic materials), and spatial and temporal changes in food abundance. Nevertheless, considering the presently available data, the beneficial interactions of earthworms and microflora and fauna appear to far outweigh the potential negative effects. However, much is still unknown regarding the interactions of earthworms of different ecological categories on the diversity and function of microfloral and faunal communities, and much more interdisciplinary research is needed to assess the potential role of earthworms in regulating the diversity of microflora and fauna in soil systems and the potentially beneficial or harmful effects this regulation may have on ecosystem function and plant growth in different ecosystems.

How do earthworms affect microfloral and faunal community diversity

Studies on the Nutrition of Coprinus lagopus Fr., especially as affecting Fruiting

The fungus spore

The longevity of conidia of Beauveria bassiana, Paecilomyces farinosus and Metarrhizium anisopliae decreases as the temperature of storage is increased from 8 to 25°C., and is also reduced by exposure to light. Conidia of B. bassiana and P. farinosus lose the ability to germinate sooner at high storage humidities than at low. By contrast, those of M. anisopliae survive longest at high and low humidities and least at median humidities close to 45% r.h. If conidia of M. anisopliae are washed before storage, the least favourable storage humidity then rises to about 65% r.h. Very quick washing in water at 0° suffices to produce this change, which is independent of whether final equilibration with the storage humidity is achieved by loss or gain of water. The unfavourable effect of median humidities is reduced or suppressed in spores stored in air enriched with carbon dioxide or devoid of oxygen. The results are discussed in terms of the possible induction of differences in the rate or course of metabolism in the stored spores which might affect their viability.

The longevity of conidia of three insect-parasitizing hyphomycetes

Fungal Parasites of Insects

A standardised most-probable-number technique for estimating the number of myxomycete plasmodium-forming units (PFUs) in soils has been developed and tested experimentally. Application of the method to a local soil showed that the uppermost layers contained the most PFUs. Its application to 44 surface soils from various parts of the world detected myxomycetes in 36, of which 4 were desert soils. In general, highest numbers of PFUs (up to 9000·g−1 soil) were recorded in grassland and agricultural soils. The nature of the PFUs has not been definitely resolved but they are probably myxamoebae, myxoflagellates and microcysts.

M.F. Madelin

Papers

Studies on the Nutrition of Coprinus lagopus Fr., especially as affecting Fruiting

The fungus spore

The longevity of conidia of three insect-parasitizing hyphomycetes

Fungal Parasites of Insects

A method for the enumeration of myxomycetes in soils and its application to a wide range of soils