A mixed microbial culture capable of metabolizing the explosive RDX (hexahydro-1,3,5,-trinitro-1,3,5triazine) was obtained from soil enrichments under aerobic and nitrogen-limiting conditions. A bacterium, Stenotrophomonas maltophilia PB1, isolated from the culture used RDX as a sole source of nitrogen for growth. Three moles of nitrogen was used per mole of RDX, yielding a metabolite identified by mass spectroscopy and 1 H nuclear magnetic resonance analysis as methylene-N-(hydroxymethyl)-hydroxylamine-N-(hydroxymethyl) nitroamine. The bacterium also used s-triazine as a sole source of nitrogen but not the structurally similar compounds octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine, cyanuric acid, and melamine. An inducible RDXdegrading activity was present in crude cell extracts.

A mixed microbial culture capable of metabolizing the explosive pentaerythritol tetranitrate (PETN) was obtained from soil enrichments under aerobic and nitrogen-limiting conditions. A strain of Enterobacter cloacae, designated PB2, was isolated from this culture and was found to use PETN as a sole source of nitrogen for growth. Growth yields suggested that 2 to 3 mol of nitrogen was utilized per mol of PETN. The metabolites pentaerythritol dinitrate, 3-hydroxy-2,2-bis-[(nitrooxy)methyl]propanal, and 2,2-bis-[(nitrooxy)methyl]-propanedial were identified by mass spectrometry and 1 H-nuclear magnetic resonance. An NADPH-dependent PETN reductase was isolated from cell extracts and shown to liberate nitrite from PETN, producing pentaerythritol tri-and dinitrates which were identified by mass spectrometry. PETN reductase was purified to apparent homogeneity by ion-exchange and affinity chromatography. The purified enzyme was found to be a monomeric flavoprotein with a M r of approximately 40,000, binding flavin mononucleotide noncovalently. MATERIALS AND METHODS Chemicals. PETN, GTN, and EGDN were kindly provided by the Defence Research Agency (Fort Halstead, United Kingdom). Other chemicals were of analytical grade and were obtained from BDH Ltd. (Poole, United Kingdom), Sigma Chemical Company Ltd. (Poole, United Kingdom), or Aldrich (Gillingham, United Kingdom). Liquid chromatography. High-performance liquid chromatography (HPLC) measurements were performed with a Hewlett-Packard 1050 series component system consisting of a multiple wavelength detector, quaternary pump, and 21-vial autosampler. Integrations were performed by using Hewlett-Packard Chemstation software. Samples (15 l) were separated with a 10-m C 18 reversed-phase column (length, 25 cm; diameter, 4.6 mm; HPLC Technology Ltd., Macclesfield, United Kingdom). A reverse-phase isocratic mobile phase consisting of methanol-water (65:35, vol/vol) was delivered at a flow rate of 1.5 ml/min. PETN elution was monitored at 205 nm.

Interactions between element chemistry and the ambient geochemistry play a significant role in the control of radionuclide migration in the geosphere. These same interactions influence radionuclide release from near surface, low level radioactive waste, disposal sites once physical containment has degraded. In situations where LLW contains significant amounts of metal and organic materials such as cellulose, microbial degradation in conjunction with corrosion can significantly perturb the ambient geochemistry. These processes typically produce a transition from oxidising to reducing conditions and can influence radionuclide migration through changes in both the dominant radionuclide species and mineral phases. The DRINK (DRIgg Near field Kinetic) code is a biogeochemical transport code designed to simulate the long term evolution of the UK low level radioactive waste disposal site at Drigg. Drigg is the UK's principal solid low level radioactive waste disposal site and has been receiving waste since 1959. The interaction between microbial activity, the ambient geochemistry and radionuclide chemistry is central to the DRINK approach with the development of the ambient pH, redox potential and bulk geochemistry being directly influenced by microbial activity. This paper describes the microbial aspects of the code, site data underpinning the microbial model, the microbiology/chemistry interface and provides an example of the code in action.

Membrane-bound chitin synthase from FuscUium graminearum A315 had a pH optimum of 6.5, an apparent temperature optimum of 30 "C and an apparent K,,, for UDP-N-acetylglucosamine (UDP-GlcNAc) of 2.5 mM.Digitonin-solubilized chitin synthase had a lower (about 25% of the original activity) and more variable activity than the membrane-bound chitin synthase from which it was prepared. The activity of solubilized chitin synthase was stabilized by incorporating Allosamidin (a chitinase inhibitor) into the reaction mixture, and an approximately 3.6-fold increase in activity was observed when the reaction mixture contained dimyristoylphosphatidylcholine. Concentrations of the organophosphorus fungicide edifenphos (Hinosan) up to 25 p~ had no effect on the in vitro activity of membrane-bound chitin synthase, but between 25 and 145 p~, chitin synthase activity decreased with increase in fungicide concentration. Edifenphos caused non-competitive inhibition of chitin synthase activity with an apparent Ki of 50 PM. Membrane-bound chitin synthase preparations from cultures of F. graminearurn grown in 250 pM-edifenphos had a much lower in vitro activity than preparations from cultures grown in the absence of the fungicide. Pre-growth of F. grdnearum in 250 p~ (but not 80 p~) edifenphos also caused a reduction in incorporation of [3H]GlcNAc into chitin in uivo (washed biomass was incubated in [3H]GlcNAc-containing medium lacking fungicide).

The phosphatidylcholine (PC) content of Aspergillus nidulans choC was varied by growing the auxotroph in medium containing various concentrations of choline chloride. Direct linear correlations were observed between PC content and in vivo chitin synthase activity, between in vivo chitin synthase activity and mean hyphal extension rate, and between mean hyphal extension rate and hyphal growth unit length; hyphal growth unit length is a measure of hyphal branching. Further, there was a correlation between PC content and colony radial growth rate. Thus, membrane composition is an important determinant of both hyphal (and colony) extension rate and mycelial morphology.