Two strains of Pseudomonasputida, S3 and P3, were shown to contain dehalogenase activity against monochloroacetate, dichloroacetate, 2-monochloropropionate and 2,2'-dichloropropionate but differed markedly in their levels of enzyme activity. Strain S3 had activities of less than 1 pmol substrate converted (mg protein)-l h-l and was unable to grow on any of nine chlorinated compounds tested. Strain P3 had enzyme activities 10 to 40 times greater than those of strain S3 but was capable of growth only on 2-monochloropropionate and 2,2'-dichloropropionate. In strain P3, dehalogenase activity was induced by a number of chlorinated compounds other than those that acted as growth substrates. Strain P3 dehalogenase activity dehalogenated C-2 substituted compounds. The evidence of the dehalogenase activity profiles in chemostat cultures and from thermal denaturation experiments suggested that there was more than one dehalogenase enzyme in P . putida strain P3. In crude extract, the enzyme activity was optimal at pH 7.9 to 8.1 and apparent K, values were in the millimolar range for the four major substrates, monochloroacetate, dichloroacetate, 2-monochloropropionate and 2,2'-dichloropropionate.

A seven-membered microbial community capable of utilising the herbicide Dalapon has been isolated by continuous-flow enrichment culture. The composition of this community has remained remarkably stable over thousands of hours in a Dalapon-limited chemostat. During this period, however, one member of the community, Pseudomonas putida, acquired the ability to grow on Dalapon through the evolution of an extant dehalogenase.

Biochar -charcoal used to amend land and sequester carbon -is attracting considerable interest. Its distinctive physical/chemical/biological properties, including high water-holding capacity, large surface area, cation exchange capacity, elemental composition and pore size/volume/distribution, effect its recognised impacts, especially on microbial communities. These are explored in the context of agriculture, composting and land remediation/restoration. Considerable focus is given to mycorrhizal associations, which are central to exploitation in environmental technologies involving biochar. The characteristics of biochar, its availability for nutrient cycling, including the beneficial and potentially negative/inhibitory impacts, and the requisite multidisciplinary analysis (physico-chemical, microbiological and molecular) to study these in detail, are explored.

As confidence in gas biofiltration efficacy grows, ever more complex malodorant and toxic molecules are ameliorated. In parallel, for many countries, emission control legislation becomes increasingly stringent to accommodate both public health and climate change imperatives. Effective gas biofiltration in biofilters and biotrickling filters depends on three key bioreactor variables: the support medium; gas molecule solubilization; and the catabolic population. Organic and inorganic support media, singly or in combination, have been employed and their key criteria are considered by critical appraisal of one, char. Catabolic species have included fungal and bacterial monocultures and, to a lesser extent, microbial communities. In the absence of organic support medium (soil, compost, sewage sludge, etc.) inoculum provision, a targeted enrichment and isolation program must be undertaken followed, possibly, by culture efficacy improvement. Microbial community process enhancement can then be gained by comprehensive characterization of the culturable and total populations. For all species, support medium attachment is critical and this is considered prior to filtration optimization by water content, pH, temperature, loadings, and nutrients manipulation. Finally, to negate discharge of fungal spores, and/or archaeal and/or bacterial cells, capture/destruction technologies are required to enable exploitation of the mineralization product CO2.

The rates of sulfate reduction, methanogenesis, and methane loss were measured in saltmarsh sediment at monthly intervals. In addition, dissolved methane and sulfate concentrations together with pS2and pH were determined. Methane formation from carbon dioxide, but not from acetate, was detected within the same horizon of sediment where sulfate reduction was most active. Sulfate reduction was about three orders of magnitude greater than annual methanogenesis. The two processes were not separated either spatially or temporally, but occurred within the same layer of sediment at the same time of the year. Their coexistence did not seem to be the result of sulfate-depleted microenvironments within which methanogenesis could occur, but the methanogenic bacteria persisted at very low rates of activity within the same environment as the sulfate reducers. Sulfate reduction and methanogenesis are microbial processes of particular importance in anaerobic environments as they are major terminal oxidation steps in the flow of carbon and electrons. Cappenberg (8) demonstrated that the two processes were spatially separated in freshwater sediment, and Reeburgh and Heggie (21), in a review of the available data, reported that in marine sediments methane production occurred only at depths where sulfate reduction was limited by a depleted supply of available sulfate. Winfrey and Zeikus (26) showed that sulfate additions to freshwater sediment inhibited methanogenesis and hypothesized that this was possibly due to competition between the sulfatereducing and methanogenic bacteria for a common substrate. Laboratory studies by Abram and Nedwell (2, 3) confirmed that methanogens were outcompeted by sulfate-reducing bacteria for the limited amount of hydrogen produced in sediments, and suggested that this competition was a possible explanation for the apparent inhibition of methanogenesis in the presence of sulfate reduction. The present work was undertaken to investigate in greater detail the relationship between sulfate reduction and methanogenesis in East Coast, United Kingdom, saltmarsh sediment.