Screening studies with strict and facultative anaerobic bacteria showed that Clostridium app. and several other representatives of Bacillaceae and Enterobacteriaceae actively degraded gamma-hexachlorocyclohexane (gamma-HCH) under anaerobic conditions. Representatives of Lactobacillaceae and Propronibacterium were inactive. With 36Cl-labelled gamma-HCH a nearly complete dechlorination was shown to occur in 4--6 days by Clostridium butyricum, C. pasteurianum and Citrobacter freundii, while other facultative anaerobic species were less active. Aerobically grown facultative anaerobes also dechlorinated actively gamma-HCH during subsequent anaerobic incubation with glucose, pyruvate or formate as substrates. The alpha-, beta- and delta-HCH isomers were also, but more slowly, dechlorinated (gamma larger than alpha larger than beta larger than or equal to delta-HCH). All species active in anaerobic degradation of gamma-HCH formed gamma-tetrachlorocyclohexene (TCH) as the main intermediate metabolite and no gamma-pentachlorocyclohexene (PCH) or other isomers of TCH or PCH have been found. Small amounts of tri- and tetrachlorinated benzenes have been found too. The mechanism of dechlorination is discussed.

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No autotrophic nitrifying organisms were found in a podzolic brown earth forming nitrate. 350 fungi and aerobic heterotrophic bacteria were isolated from this soil and examined for their nitrifying abilities. About one quarter of the isolates produced 0.05–0.90 mg N·1−1 nitrite or nitrate in peptone solution, soil extract mixture or sterilised soil. The nitrification rate of the most active fungus, Verticillium lecanii, was highest at pH 3.5 in defined media. The results support the significance of heterotrophic nitrification in acid soils.

Recent field inoculation trials with Azospirillum and Azotobacter spp. applied to cereal and forage crops have shown extremely different results in yield response. Some aspects of bacteria‐plant interactions affecting yield response are discussed. These include provision of fixed nitrogen, specificity and adaptation to root habitat, influence of microbial metabolites, enhancement of VA‐mycorrhiza, displacement of deleterious rhizosphere microorganisms, differences between host plant genotypes, competitive ability and longevity of inoculants. Based on these considerations, needs for further research will be outlined.

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