A thermophilic, obligately chemolithoautotrophic H2-oxidizing bacterium, Hydrogenobacter thermophilus TK-6 can utilize O2 or NO3- as an electron acceptor. Here we show that this bacterium can grow autotrophically by the reduction of Fe(III)-EDTA or Fe(III)-DTPA (diethylene-triamine-pentaacetic acid) as an electron acceptor, through oxidation of H2 as an electron donor. A 7.6 kDa c-type cytochrome was purified from soluble fraction as the iron reducing protein and the protein was identified as cytochrome c-552. A rate constant for the reduction of Fe(III)-EDTA by the cytochrome was kinetically determined to be 1.73 × 107 s-1 by stopped-flow spectrophotometry, which is more than 20-fold higher than the constants of other iron reductases. The redox potential was measured as E = +0.27 V (vs NHE [Normal Hydrogen Electrode]), which is high enough to reduce Fe(III)-EDTA. These results suggest that cytochrome c-552 works as a terminal electron donor for Fe(III) in the periplasmic space.

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We isolated an extreme thermophilic bacterium strain SS, which grew between 55 and 82°C (optimum 70°C), from sewage sludge in Kagoshima City, Japan. Morphological and physiological properties, as well as 16S rRNA gene sequence indicated that strain SSbelongs to the genus Thermaerobacter. To confirm the distribution of Thermaerobacter spp. in sewage sludge, genus-specific detection by nested PCR of 16S rRNA gene was performed. As a result, the existence of Thermaerobacter spp. in six sewage sludge samples including composted sludge was demonstrated by sequencing of the nested PCR products. However, enrichment cultures with sewage sludge were needed to detect the target products, indicating that population of Thermaerobacter spp. may be significantly low. As far as we know, this is the first report on occurrence of extreme thermophilic bacteria in a municipal wastewater treatment process under mesophilic condition.

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A chitinase (ChiN1) from Halobacterium salinarum NRC-1 belongs to the glycoside hydrolase family 18. According to the three-dimensional structure model of ChiN1, Asn239 and Gln242 on a small helix between Phe237 and Arg247 were targeted for mutagenesis. Mutants N239D (Asn239 was replaced by Asp) and Q242E (Gln242 was replaced by Glu) were expressed in Haloarcula japonica and then characterized. Characterization of the mutants revealed that halotolerancy could be improved by introducing an acidic amino acid on the surface of ChiN1.

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Acid-extractable cellular polyamines of thermophilic Caldisericum exile belonging to a new bacterial phylum, Caldiserica were analyzed by HPLC and GC. The coexistence of an unusual tertiary brancehed tetra-amine, N4 -aminopropylspermidine with spermine, a linear tetra-amine, as the major polyamines in addition to putrescine and spermidine, is first reported in the moderate thermophile isolated from a terrestrial hot spring in Japan. Linear and branched penta-amines were not detected. The novel cellular polyamine profile found in the moderate thermophile has never been observed within various bacteria and archaea previously analyzed.

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