Reductive dechlorination of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) was investigated in anaerobic sediments by non-adapted microorganisms and by microorganisms adapted to either 2,4- or 3,4-dichlorophenol (DCP). The rate of dechlorination of 2,4-D was increased by adaptation of sediment microorganisms to 2,4-DCP while dechlorination by sediment microorganisms adapted to 3,4-DCP displayed a lag phase similar to non-adapted sediment slurries. Both 2,4- and 3,4-DCP-adapted microorganisms produced 4-chlorophenoxyacetic acid by ortho-chlorine removal. Lag phases prior to dechlorination of the initial addition of 2,4,5-T by DCP-adapted sediment microorganisms were comparable to those from non-adapted sediment slurries. However, the rates of dechlorination increased upon subsequent additions of 2,4,5-T. Biodegradation of 2,4,5-T by sediment microorganisms adapted to 2,4- and/or 3,4-DCP produced 2,5-D as the initial intermediate followed by 3-chlorophenol and phenol indicating a para > ortho > meta order of dechlorination. Dechlorination of 2,4,5-T, by either adapted or non-adapted sediment microorganisms, progressed without detection of 2,4,5-trichlorophenol as an intermediate.

Soil microbiostasis inactivates microorganisms added to soil. Deficiency of nutrients also prevents added microorganisms from producing antibiotics in soil. Moreover, these microorganisms are too far away to exert any influence against plant pathogens in nature. Therefore, even those antagonistic microorganisms which can produce dramatic zones of inhibition in the laboratory are generally ineffective in controlling plant pathogens in nature when added directly to soil. The concept of primitive and advanced pathogens (or parasites) is very useful in determining which biological control measure should be used for a specific pathogen. Coating seeds with antagonistic microorganisms and planting seeds in a small amount of virgin soil are more suitable for controlling primitive pathogens than advanced ones. On the other hand, screening for resistance, crop rotation and organic amendment are more suitable for controlling advanced patogens. Rotation with crops cultivated on flooded soil, searching for decay crops or antagonistic plants, amending soil with organic materials mixed with antagonistic microorganisms, and exploration of suppressive soil are considered promising approaches to biological control of plant pathogens in the tropics

Soils from four sites, two with and two without previous exposure to sodium monofluoracetate (1080), in Western Australia were investigated to determine whether they contained microorganisms capable of defluorinating 1080. Most samples from these four sites showed microbial defluorination activity. A number of species of bacteria and fungi were isolated; Aspergillus fumigatus, Fusarium oxysporum, Pseudomonas acidovorans, Pseudomonas fluorescens 1, an unidentified Pseudomonas sp., Penicillium purpureseens and Penicillium restrictum. These seven microorganisms possessed the ability to defluorinate 1080 when grown in a 1080 solution, which was the sole carbon source, and also in autoclaved soil. The amount of defluorination varied with different species of microorganisms, ranging from 2 to 85% in soil and from 2 to 89% in 1080 solutions. A time-course experiment showed that some indigenous soil microflora were able to defluorinate over 50% and up to 87% of the 1080 within 5-9 days in soil with a moisture content of about 10% when kept at 28 degrees C (day) and 15 degrees C (night). Soils from four other arid or semiarid sites were also investigated for the presence of thermophilic microorganisms with 1080 defluorinating ability. No thermophilic microorganisms were isolated.

It is only recently that the implications of declining biodiversity for sustainable agricultural production and environmental protection have been recognized. However, while justifiable concern is expressed at the need to conserve and prevent from extinction the larger flora and fauna of the world, the importance of microorganisms and invertebrates in the stable functioning of ecosystems has attracted less overt attention. Nevertheless, the subject is now recognized as of major significance for a number of issues such as maintenance of soil fertility and the provision of natural enemies for the biological control of pests and pathogens. The biodiversity of microorganisms and invertebrates seeks to address a number of these key issues and is based on a workshop organized by CAB International in association with the Committee on the Application of Science to Agriculture Foresty and Aquaculture (CASAFA) of the International Council of Scientific Unions, the Commonwealth Science Council, and the Third World Academy of Sciences. Four main subject areas are covered: the importance of invertebrates and microorganisms as components of biodiversity; the importance of biodiversity in sustaining soil productivity, the importance of biodiversity to pest occurrence and management, and biotechnology and biodiversity among invertebrates and microorganisms. The biodiversity of microorganisms and invertebrates: its role in sustainable agriculture edited by D L Hawksworth 1991 302pp ISBN 0 85198 722 2 Hbk UKL40.00 CAB International, Wallingford Oxon OX10 ODE, UK | The biodiversity of microorganisms and invertebrates: its role in sustainable agriculture edited by D L Hawksworth 1991 302pp ISBN 0 85198 722 2 Hbk UKL40.00 CAB International, Wallingford Oxon OX10 ODE, UK

Nematodes recovered from the hindgut of zebras were examined with scanning and transmission electron microscopy for microorganisms. Microorganisms were observed attached to the posterior extremities of two groups of nematodes, atractids and cyathostomes. Novel techniques were used to culture the microorganisms, and these included rinses to reduce contamination from hindgut flora and the design of the culture media. Electron microscopy revealed a flat bacterium not previously observed, as well as small rods and segmented filamentous bacteria. Culturing techniques resulted in isolation of a Propionibacterium species.

Ecology of Fusarium udum was studied in relation to fungistasis of antagonistic microorganisms of the root region of pigeon-pea for biological control of its wilt disease. The microorganisms were screened for their antagonistic potential and were used for elevating the level of fungistasis of soil against the pathogen. Bacillus subtilis, Cephalosporium roseo-griseum and Trichoderma harzianum were found to be highly effective for suppressing the population of F. udum in soil as well as in the root region of pigeon-pea. This was correlated with the elevated level of soil fungistasis due to these microorganisms. Other microorganisms - Cladiosporium cladosporioides, Aspergillus fumigatus, Papulaspora sp. and Penicillium decumbers - also possessed strong fungistatic effects against F. udum but failed to exhibit a significant effect on the population of F. udum and on wilt incidence

Effects of rhizosphere microorganisms on Fe uptake by oat (Avena sativa) and maize (Zea mays) were studied in short-term (10 h) nutrient solution experiments. Fe was supplied either as microbial siderophores (pseudobactin [PSB] or ferrioxamine B [FOB]) or as phytosiderophores obtained as root exudates from barley (epi-3-hydroxy-mugineic acid [HMA]) under varied population densities of rhizosphere microorganisms (axenic, uninoculated, or inoculated with different microorganism cultures). When maize was grown under axenic conditions and supplied with FeHMA, Fe uptake rates were 100 to 300 times higher compared to those in plants supplied with Fe siderophores. Fe from both sources was taken up without the involvement of an extracellular reduction process. The supply of FeHMA enhanced both uptake rate and translocation rate to the shoot (more than 60% of the total uptake). However, increased density of microorganisms resulted in a decrease in Fe uptake rate (up to 65%), presumably due to microbial degradation of the FeHMA. In contrast, when FeFOB or FePSB was used as the Fe source, increased population density of microorganisms enhanced Fe uptake. The enhancement of Fe uptake resulted from the uptake of FeFOB and FePSB by microorganisms adhering to the rhizoplane or living in the free space of cortical cells. The microbial apoplastic Fe pool was not available for root to shoot transport or, thus, for utilization by the plants. These results, in addition to the low uptake rate under axenic conditions, are in contrast to earlier hypotheses suggesting the existence of a specific uptake system for Fe siderophores in higher plants. The bacterial siderophores PSB and FOB were inefficient as Fe sources for plants even when supplied by stem injection. It was concluded that microorganisms are involved in degradation processes of microbial siderophores, as well as in competition for Fe with higher plants.

Effects of rhizosphere microorganisms on Fe uptake by oat (Avena sativa) and maize (Zea mays) were studied in short-term (10 h) nutrient solution experiments. Fe was supplied either as microbial siderophores (pseudobactin [PSB] or ferrioxamine B [FOB]) or as phytosiderophores obtained as root exudates from barley (epi-3-hydroxy-mugineic acid [HMA]) under varied population densities of rhizosphere microorganisms (axenic, uninoculated, or inoculated with different microorganism cultures). When maize was grown under axenic conditions and supplied with FeHMA, Fe uptake rates were 100 to 300 times higher compared to those in plants supplied with Fe siderophores. Fe from both sources was taken up without the involvement of an extracellular reduction process. The supply of FeHMA enhanced both uptake rate and translocation rate to the shoot (more than 60% of the total uptake). However, increased density of microorganisms resulted in a decrease in Fe uptake rate (up to 65%), presumably due to microbial degradation of the FeHMA. In contrast, when FeFOB or FePSB was used as the Fe source, increased population density of microorganisms enhanced Fe uptake. The enhancement of Fe uptake resulted from the uptake of FeFOB and FePSB by microorganisms adhering to the rhizoplane or living in the free space of cortical cells. The microbial apoplastic Fe pool was not available for root to shoot transport or, thus, for utilization by the plants. These results, in addition to the low uptake rate under axenic conditions, are in contrast to earlier hypotheses suggesting the existence of a specific uptake system for Fe siderophores in higher plants. The bacterial siderophores PSB and FOB were inefficient as Fe sources for plants even when supplied by stem injection. It was concluded that microorganisms are involved in degradation processes of microbial siderophores, as well as in competition for Fe with higher plants.