Robust immobilization techniques that preserve the activity of biomolecules have many potential applications. Silicates, primarily in the form of sol-gel composites or functionalized mesoporous silica, have been used to encapsulate a wide variety of biomolecules but the harsh conditions required for chemical synthesis limit their applicability. Silaffin polypeptides from diatoms catalyze the formation of silica in vitro at neutral pH and ambient temperature and pressure. Here we show that butyrylcholinesterase entrapped during the precipitation of silica nanospheres retained all of its activity. Ninety percent of the soluble enzyme was immobilized, and the immobilized enzyme was substantially more stable than the free enzyme. The mechanical properties of silica nanospheres facilitated application in a flow-through reactor. The use of biosilica for enzyme immobilization combines the excellent support properties of a silica matrix with a benign immobilization method that retains enzyme activity.

Nitroaromatic compounds are released into the biosphere almost exclusively from anthropogenic sources. Some compounds are produced by incomplete combustion of fossil fuels; others are used as synthetic intermediates, dyes, pesticides, and explosives. Recent research revealed a number of microbial systems capable of transforming or biodegrading nitroaromatic compounds. Anaerobic bacteria can reduce the nitro group via nitroso and hydroxylamino intermediates to the corresponding amines. Isolates of Desulfovibrio spp. can use nitroaromatic compounds as their source of nitrogen. They can also reduce 2,4,6-trinitrotoluene to 2,4,6-triaminotoluene. Several strains of Clostridium can catalyze a similar reduction and also seem to be able to degrade the molecule to small aliphatic acids. Anaerobic systems have been demonstrated to destroy munitions and pesticides in soil. Fungi can extensively degrade or mineralize a variety of nitroaromatic compounds. For example, Phanerochaete chrysosporium mineralizes 2,4-dinitrotoluene and 2,4,6-trinitrotoluene and shows promise as the basis for bioremediation strategies. The anaerobic bacteria and the fungi mentioned above mostly transform nitroaromatic compounds via fortuitous reactions. In contrast, a number of nitroaromatic compounds can serve as growth substrates for aerobic bacteria. Removal or productive metabolism of nitro groups can be accomplished by four different strategies. (a) Some bacteria can reduce the aromatic ring of dinitro and trinitro compounds by the addition of a hydride ion to form a hydride-Meisenheimer complex, which subsequently rearomatizes with the elimination of nitrite. (b) Monooxygenase enzymes can add a single oxygen atom and eliminate the nitro group from nitrophenols. (c) Dioxygenase enzymes can insert two hydroxyl groups into the aromatic ring and precipitate the spontaneous elimination of the nitro group from a variety of nitroaromatic compounds. (d) Reduction of the nitro group to the corresponding hydroxylamine is the initial reaction in the productive metabolism of nitrobenzene, 4-nitrotoluene, and 4-nitrobenzoate. The hydroxylamines undergo enzyme-catalyzed rearrangements to hydroxylated compounds that are substrates for ring-fission reactions. Potential applications of the above reactions include not only the biodegradation of environmental contaminants, but also biocatalysis and synthesis of valuable organic molecules.

Aerobic bacteria that grow on vinyl chloride (VC) have been isolated previously, but their diversity and distribution are largely unknown. It is also unclear whether such bacteria contribute to the natural attenuation of VC at chlorinated-ethene-contaminated sites. We detected aerobic VC biodegradation in 23 of 37 microcosms and enrichments inoculated with samples from various sites. Twelve different bacteria (11 Mycobacterium strains and 1 Nocardioides strain) capable of growth on VC as the sole carbon source were isolated, and 5 representative strains were examined further. All the isolates grew on ethene in addition to VC and contained VC-inducible ethene monooxygenase activity. The Mycobacterium strains (JS60, JS61, JS616, and JS617) all had similar growth yields (5.4 to 6.6 g of protein/mol), maximum specific growth rates (0.17 to 0.23 day ؊1 ), and maximum specific substrate utilization rates (9 to 16 nmol/min/mg of protein) with VC. The Nocardioides strain (JS614) had a higher growth yield (10.3 g of protein/mol), growth rate (0.71 day ؊1 ), and substrate utilization rate (43 nmol/min/mg of protein) with VC but was much more sensitive to VC starvation. Half-velocity constant (K s ) values for VC were between 0.5 and 3.2 M, while K s values for oxygen ranged from 0.03 to 0.3 mg/liter. Our results indicate that aerobic VC-degrading microorganisms (predominantly Mycobacterium strains) are widely distributed at sites contaminated with chlorinated solvents and are likely to be responsible for the natural attenuation of VC.Vinyl chloride (VC) is a common groundwater contaminant (49) which is of concern due to its carcinogenicity (7). Although VC can be produced naturally at very low levels in some soils (32), the industrial synthesis of polyvinyl chloride plastics (27 million tons per year globally [33]) and the bacterial metabolism of chlorinated solvents (36, 41) are the most problematic sources of VC contamination. Many anaerobic bacteria can reductively dechlorinate the widely used solvents tetrachloroethene (PCE) and trichloroethene (TCE), producing cis-dichloroethene (cDCE), VC, or ethene (ETH) (19,30,35,40,59). However, microbes capable of reducing VC to ETH are often absent or inactive in subsurface ecosystems, and thus, VC commonly accumulates as an end product of anaerobic dechlorination (17,37,39).VC can be oxidized to CO 2 under anaerobic conditions in the presence of Fe(III) or humic acids (4, 5), but the microbiology and biochemistry of such anaerobic oxidations have not been investigated. Aerobic bacteria can catalyze the cometabolic oxidation of VC in the presence of monooxygenase inducers such as methane (18), ethane (20), ETH (34), propane (38), propene (15), isoprene (16), toluene (48), and ammonia (56). Bioremediation strategies based on aerobic cometabolism have been examined for VC and other chlorinated ethenes (36, 47), but there are several problems with cometabolic systems-electron donors are required (2), the growth-supporting substrate and the pollutant compete for the same enzymes (1...

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N]-RDX, the [M-H] appeared at 120 Da, indicating that two of the three N atoms in the metabolite originated from the ring in RDX. When [U-14 C]-RDX was used in the experiment, 64% of the original radioactivity in RDX incorporated into the metabolite with a molecular weight (MW) of 119 (high-pressure LC/radioactivity) and 30% in 14 CO 2 (mineralization) after 4 days of incubation, suggesting that one of the carbon atoms in RDX was converted to CO 2 and the other two were incorporated in the ring cleavage product with an MW of 119. Based on the above stoichiometry, we propose a degradation pathway for RDX based on initial denitration followed by ring cleavage to formaldehyde and the dead end product with an MW of 119.The two cyclic nitramine explosives hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) are powerful energetic compounds that are commonly used in conventional munitions and various military applications. Activities associated with manufacturing, training, waste disposal, and closures of bases have resulted in severe soil and groundwater contamination with the two explosives (9, 14, 21). RDX and HMX are both toxic (25, 29), thus necessitating their removal from the environment.Previous studies have focused on the degradation of RDX by microorganisms under anaerobic conditions (1,17,18,20,24,30). McCormick et al. (20) reported the formation of the three nitroso derivatives, hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine (MNX), hexahydro-1,3-dinitroso-5-nitro-1,3,5-triazine (DNX), and hexahydro-1,3,5-trinitroso-1,3,5-triazine (TNX), which after further reduction to the corresponding hydroxylamines undergo ring cleavage to produce hydrazine, dimethyl hydrazine, and methanol, respectively. No microorganisms or enzymes were identified in the study by McCormick et al. (20). Recently, Kitts et al. (19) reported the involvement of a type I nitroreductase in the degradation of RDX, but no products were identified. Using anaerobic sludge, Hawari et al.(11) reported that in addition to the occurrence of a ring cleavage via the nitroso route, other ring cleavage pathways, such as direct ring cleavage and/or denitration followed by ring cleavage, might be possible. In the latter study, several key intermediate ring cleavage products, including bis(hydroxymethyl)nitramine, methylenedinitramine (MEDINA), nitrous oxide, and formaldehyde, accumulated, but hydrazines were not detected (11, 12).Several groups described RDX biodegradation under aerobic conditions, but little information was provided on the degradation pathway (5,6,16,27). Products from biodegradation of cyclic nitramine explosives under aerobic conditions are poorly understood, particularly ring cleavage products (5, 10). Jones et al. (16) isolated a Rhodococcus sp. strain A from explosives-contaminated soil and demonstrated its potential for the degradation of RDX but did not report any products. Coleman et al. (6) reported the isolation and characterization of another Rhodococcus sp. strain DN22,...