Kazuo Shoji

Corrosion by bacteria of concrete in sewerage systems and inhibitory effects of formates on their growth

Not only sulfur-oxidizing bacteria but also an acidophilic iron-oxidizing bacterium (or bacteria) were found in the corroded concrete from several sewerage systems in Japan. The surface pH of concrete test piece exposed to an atmosphere containing hydrogen sulfide of the concentrations more than 600 ppm in the systems was usually below 2 after a month. This was attributable to ability of the sulfur-oxidizing bacteria to grow in the thin water layer which contained hydrogen sulfide and covered the piece even when the surface pH of concrete was 12-13. When the sulfuroxidizing bacteria grew in the surface of concrete and produced sulfuric acid, the pH of the inner parts of concrete was lowered where the bacteria were hardly found. Probably, sulfuric acid formed by the bacteria in the surface parts penetrated into the inner parts. The different species of sulfur-oxidizing bacteria were found in different sewerage systems. The growth of the sulfur-oxidizing and acidophilic iron-oxidizing bacteria was completely inhibited by formates, especially by calcium formate of concentrations more than 50 mM. Calcium formate can protect concrete in sewerage systems from bacterial corrosion.

Direct interaction of natural and synthetic catechins with signal transducer activator of transcription 1 affects both its phosphorylation and activity

Our previous studies showed that (−)‐epigallocatechin‐3‐gallate (EGCG) inhibits signal transducer activator of transcription 1 (STAT1) activation. Since EGCG may be a promising lead compound for new anti‐STAT1 drug design, 15 synthetic catechins, characterized by the (−)‐gallocatechin‐3‐gallate stereochemistry, were studied in the human mammary MDA‐MB‐231 cell line to identify the minimal structural features that preserve the anti‐STAT1 activity. We demonstrate that the presence of three hydroxyl groups of B ring and one hydroxyl group in D ring is essential to preserve their inhibitory action. Moreover, a possible molecular target of these compounds in the STAT1 pathway was investigated. Our results demonstrate a direct interaction between STAT1 protein and catechins displaying anti‐STAT1 activity. In particular, surface plasmon resonance (SPR) analysis and molecular modeling indicate the presence of two putative binding sites (a and b) with different affinity. Based on docking data, site‐directed mutagenesis was performed, and interaction of the most active catechins with STAT1 was studied with SPR to test whether Gln518 on site a and His568 on site b could be important for the catechin–STAT1 interaction. Data indicate that site b has higher affinity for catechins than site a as the highest affinity constant disappears in the H568A‐STAT1 mutant. Furthermore, Janus kinase 2 (JAK2) kinase assay data suggest that the contemporary presence in vitro of STAT1 and catechins inhibits JAK2‐elicited STAT1 phosphorylation. The very tight catechin–STAT1 interaction prevents STAT1 phosphorylation and represents a novel, specific and efficient molecular mechanism for the inhibition of STAT1 activation.

Involvement of Sulfur- and Iron-Transforming Bacteria in Heaving of House Foundations

About 1,000 houses built on excavated nonweathered mudstone sediments, originally deposited in the Neogene, have been damaged by microbially induced heaving of foundations. The maximal height of the heaving was 48 cm. The presence of sulfate-reducing, sulfur-oxidizing, and acidophilic iron-oxidizing bacteria in the mudstone indicated that the joint activity of these three types of bacteria could account for the heaving. A hypothesis is presented in which, first, the temperature of the newly exposed mudstone sediments increased above 25 °C, which stimulated the sulfate-reducing bacteria in the mudstone to actively reduce sulfate to hydrogen sulfide. The mudstone sediments under the houses gradually dried, and became permeable to air. Consequently, sulfur-oxidizing bacteria oxidized the hydrogen sulfide to sulfuric acid and the environmental pH decreased to approximately 3. Next, the acidophilic iron-oxidizing bacteria actively oxidized the sulfur in pyrite to produce much more acid. The resulting sulfuric acid reacted with calcium carbonate and with ferric and potassium ions to produce gypsum and jarosite, respectively. A combination of the increased volume of gypsum and jarosite crystals and the production of CO 2 as a by-product of their formation made the mudstone sediments bulky. The end result was widespread heaving.

The Regulation by ATP of the Catalytic Activity and Molecular State of Thiobacillus novellus Cytochrome c Oxidase

Thiobacillus novellus cytochrome c oxidase has one heme a molecule and one copper atom in the minimal structural unit consisting of one molecule each of two subunits (32 and 23 kDa). The oxidase occurs as a monomer of the unit in the presence of 0.5% n-octyl-β-D-thioglucoside and as a dimer of the unit in the presence of 0.5% Tween 20. The heme molecule in the monomer is completely reactive with CO, that is, the monomeric oxidase appears to be cytochrome a3, while one of the two heure molecules in the dimer reacts with CO, that is, the dimeric oxidase appears to be cytochrome aa3. The [s]-v curve in the oxidation of ferrocytochrome c catalyzed by the dimeric oxidase is sigmoidal. On addition of ATP, the molecular mass of the dimeric oxidase becomes half and the [s]-v curve changes to a hyperbola from a sigmoid. Thus, ATP regulates the molecular states and catalytic properties of the oxidase.