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Extremophilic organisms require specialized enzymes for their exotic metabolisms. Acid-loving thermophilic Archaea that live in the mudpots of volcanic solfataras obtain their energy from reduced sulphur compounds such as hydrogen sulphide (H(2)S) and carbon disulphide (CS(2)). The oxidation of these compounds into sulphuric acid creates the extremely acidic environment that characterizes solfataras. The hyperthermophilic Acidianus strain A1-3, which was isolated from the fumarolic, ancient sauna building at the Solfatara volcano (Naples, Italy), was shown to rapidly convert CS(2) into H(2)S and carbon dioxide (CO(2)), but nothing has been known about the modes of action and the evolution of the enzyme(s) involved. Here we describe the structure, the proposed mechanism and evolution of a CS(2) hydrolase from Acidianus A1-3. The enzyme monomer displays a typical β-carbonic anhydrase fold and active site, yet CO(2) is not one of its substrates. Owing to large carboxy- and amino-terminal arms, an unusual hexadecameric catenane oligomer has evolved. This structure results in the blocking of the entrance to the active site that is found in canonical β-carbonic anhydrases and the formation of a single 15-Å-long, highly hydrophobic tunnel that functions as a specificity filter. The tunnel determines the enzyme's substrate specificity for CS(2), which is hydrophobic. The transposon sequences that surround the gene encoding this CS(2) hydrolase point to horizontal gene transfer as a mechanism for its acquisition during evolution. Our results show how the ancient β-carbonic anhydrase, which is central to global carbon metabolism, was transformed by divergent evolution into a crucial enzyme in CS(2) metabolism.

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The trace metal dynamics in anaerobic granular sludge bed reactors and their influence on reactor performance is reviewed in this paper. An insight into the metal dynamics is required from a practical point of view in order to be able to early recognize limitations for essential trace elements, viz., to know when dosing of these elements is required in full‐scale anaerobic bioreactor applications. Further such knowledge is indispensable for a rational dosage of these metals, e.g., to ensure maximum substrate conversion rates and to prevent disturbances in reactor performance using a minimum amount of metals. Therefore, the retention, accumulation and release of trace metals in anaerobic granular sludge and the factors affecting these processes need to be known.

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The effect of the trace metal cobalt on the conversion of methanol in an upflow anaerobic sludge bed (UASB) reactor was investigated by studying the effect of cobalt deprivation from the influent on the reactor efficiency and the sludge characteristics. A UASB reactor (30 degrees C; pH 7) was operated for 261 days at a 12-h hydraulic retention time (HRT). The loading rate was increased stepwise from 2.6 g chemical oxygen demand (COD) x L reactor(-1) x d(-1) to 7.8 g COD x L reactor(-1) x d(-1). Cobalt deprivation had a strong impact on the methanogenic activity of the sludge. In batch tests, the methanogenic activity of the sludge with methanol as the substrate increased 5.3 (day 28) and 2.1 (day 257) times by addition of 840 nM of cobalt. The sludge had an apparent K(m) for cobalt of 948 nM after 28 days of operation and 442 nM at the end of the run. Cobalt deprivation during 54 days of operation led to a methanol conversion efficiency of only 55%. Continuous addition of cobalt (330 nM) for 33 days improved the methanol removal efficiency to 100%. In this period of cobalt dosing, the cobalt concentration in the sludge increased 2.7 times up to 32 microg x g TSS(-1). Upon omission of the cobalt addition, cobalt washed-out at a stable rate of 0.1 microg x g VSS(-1) x d(-1). At the end of the run, the cobalt concentration of the sludge was similar to that of the seed sludge.

No abstract

The speciation of metals plays an important role in their bioavailability. In the case of anaerobic reactors for the treatment of wastewaters, the ubiquitous presence of sulfide leads to extensive precipitation of metals like nickel and cobalt, which are essential for the metabolism of the anaerobic microorganisms that carry out the mineralization of the pollutants present in the wastewater. In practice, nickel, cobalt, and iron are added in excessive amounts to full-scale installations. This study is concerned with the complexation of nickel and cobalt with yeast extract and its effect on the biogas production by methanogenic biomass. Adsorptive stripping voltammetry (AdSV) was used to get information about the stability and complexing capacity of the metal-yeast extract complexes formed. Nickel and cobalt form relatively strong organic complexes with yeast extract. The bioavailability of these essential metals in anaerobic batch reactors was dramatically increased by the addition of yeast extract. This is due to the formation of dissolved bioavailable complexes, which favors the dissolution of metals from their sulfides. Trace doses of yeast extract may be effective in keeping additions of essential metals to anaerobic reactors at a minimum.