Biomedical subjects

Michihiko Ike

Publications and source records attributed to Michihiko Ike.

23 records · Page 2Linked to original sources

PubMed2003

Dissimilatory arsenate reduction by a facultative anaerobe, Bacillus sp. strain SF-1.

Bacillus sp. strain SF-1, isolated first as a selenate-reducing bacterium, was characterized as a novel arsenate-reducing bacterium. Strain SF-1 rapidly reduced 10 mM levels of arsenate to arsenite with concomitant cell growth and lactate oxidation under anoxic conditions, indicating that arsenate can act as the terminal electron acceptor for anaerobic respiration (dissimilatory arsenate reduction). Strain SF-1 can use various organic compounds including synthetic sewage mainly composed of peptone and meat extract as the electron donors for arsenate reduction. Although strain SF-1 can grow aerobically, which is very rare for dissimilatory arsenate-reducing bacteria, the presence of oxygen inhibited the arsenate reduction. On the other hand, the presence of nitrate or selenate, which can support the growth of strain SF-1 as electron acceptors, did not significantly inhibit the arsenate reduction. Arsenate-reducing activity, that is, arsenate reductase, was exhibited in strain SF-1 only when grown on arsenate, but the enzyme could not reduce other oxyanions including nitrate and selenate. It was presumed that arsenate reduction was carried out by an enzyme system separate from those of nitrate and selenate reduction, and the arsenate reductase was inducible and specific for arsenate. These results suggest that strain SF-1 may be utilized for extracting arsenic from contaminated soil for the purpose of bioremediation.

Journal Article↗

PubMed2002

Laboratory-scale continuous reactor for soluble selenium removal using selenate-reducing bacterium, Bacillus sp. SF-1.

A model continuous flow bioreactor (volume 0.5 L) was constructed for removing toxic soluble selenium (selenate/selenite) of high concentrations using a selenate-reducing bacterium, Bacillus sp. SF-1, which transforms selenate into elemental selenium via selenite for anaerobic respiration. Model wastewater contained 41.8 mg-Se/L selenate and excess lactate as the carbon and energy source; the bioreactor was operated as an anoxic, completely mixed chemostat with cell retention time between 2.2-95.2 h. At short cell retention times selenate was removed by the bioreactor, but accumulation of selenite was observed. At long cell retention times soluble selenium, both selenate and selenite, was successfully reduced into nontoxic elemental selenium. A simple mathematical model is proposed to evaluate Se reduction ability of strain SF-1. First-order kinetic constants for selenate and selenite reduction were estimated to be 2.9 x 10(-11) L/cells/h and 5.5 x 10(-13) L/cells/h, respectively. The yield of the bacterial cells by selenate reduction was estimated to be 2.2 x 10(9) cells/mg-Se.

Bacillus↗

PubMed2002

Acute toxicity, mutagenicity, and estrogenicity of bisphenol-A and other bisphenols.

Although abundant data are available on the toxicity of bisphenol-A (2,2-bis (4-hydroxydiphenyl)propane; BPA), little is known about the toxicities of the structurally similar compounds, namely bisphenols (BPs). A variety of BPs were examined for their acute toxicity against Daphnia magna, mutagenicity, and estrogenic activity using the Daphtoxkit (Creasel Ltd.), the umu test system, and the yeast two-hybrid system, respectively, in comparison with BPA. BPA was moderately toxic to D. magna (48-h EC50 was 10 mg/l) according to the current U.S. EPA acute toxicity evaluation standard, and it was weakly estrogenic with 5 orders of magnitude lower activity than that of the natural estrogen 17 beta-estradiol in the yeast screen, while no mutagenicity was observed. All seven BPs tested here showed moderate to slight acute toxicity, no mutagenicity, and weak estrogenic activity as well as BPA. Some of the BPs showed considerably higher estrogenic activity than BPA, and others exhibited much lower activity. Among the tested BPs, two compounds, i.e., bisphenol-S (bis(4-hydroxydiphenyl)sulfone) and bis(4-hydroxyphenyl)sulfide, have never been reported for their estrogenic activity previously.

Animals↗

PubMed2002

Acute toxicity, mutagenicity, and estrogenicity of biodegradation products of bisphenol-A.

Biodegradation of bisphenol-A (BPA), which is known as an estrogenic chemical, proceeds via complicated metabolic routes and leads to formation of several kinds of biodegradation products. Through the major route BPA can be completely mineralized; however, p-hydroxyacetophenone (p-HAP), p-hydroxybenzaldehyde (p-HBAL), and p-hydroxybenzoic acid (p-HBA) are transiently accumulated at relatively high concentrations. On the other hand, degradation of BPA through the minor route tends to cause the accumulation of 2,3-bis(4-hydroxyphenyl)-1,2-propanediol and p-hydroxyphenacyl alcohol as the dead-end products. To fully assess the impact of BPA discharge into the environment, the considerable BPA degradation products p-HAP, p-HBAL, and p-HBA and the mixture of the dead-end products were examined for their acute toxicity, mutagenicity, and estrogenicity using the Daphtoxkit (Creasel Ltd.), umu test system, and yeast two-hybrid system, respectively. BPA was moderately toxic to Daphnia magna (48-h EC(50) was 10 mg/L) and weakly estrogenic, with activity that was 5 orders of magnitude lower than that of 17beta-estradiol in the yeast screen, though no mutagenicity was observed. All the tested BPA biodegradation products showed very low acute toxicity compared with BPA, and none was mutagenic. A slight estrogenic activity was detected only for p-HAP among the tested degradation products. It was concluded that biodegradation can remarkably reduce the toxic effects of BPA.

Animals↗

PubMed2002

A reactor system combining reductive dechlorination with co-metabolic oxidation for complete degradation of tetrachloroentylene.

A laboratory sequential anaerobic-aerobic bioreactor system, which consisted of an anaerobic fixed film reactor and two aerobic chemostats, was set up to degrade tetrachloroethylene (PCE) without accumulating highly toxic degradation intermediates. A soil enrichment culture, which could reductively dechlorinate 900 microM (ca. 150 mg/L) of PCE stoichiometrically into cis-1,2-dichloroethylene (cis-DCE), was attached to ceramic media in the anaerobic fixed film reactor. A phenol degrading strain, Alcaligenes sp. R5, which can efficiently degrade cis-DCE by co-metabolic oxidation, was used as inoculum for the aerobic chemostats consisted of a transformation reactor and a growth reactor. The anaerobic fixed film bioreactor showed more than 99% of PCE transformation into cis-DCE in the range of influent PCE concentration from 5 microM to 35 microM at hydraulic retention time of 48 h. On the other hand, efficient degradation of the resultant cis-DCE by strain R5 in the following aerobic system could not be achieved due to oxygen limitation. However, 54% of the maximum cis-DCE degradation was obtained when 10 mumol of hydrogen peroxide (H2O2) was supplemented to the transformation reactor as an additional oxygen source. Further studies are needed to achieve more efficient co-metabolic degradation of cis-DCE in the aerobic reactor.

Aerobiosis↗