Thirteen anaerobic bacteria capable of performing the 7a-dehydroxylation of both cholic acid and chenodeoxycholic acid were isolated from human feces and also from sewage. Ten organisms from heat-treated samples were species of Clostridium identical or closely related to the Clostridium bifermentans-C. sordellii group and consisted of four strains elaborating 7a-dehydroxylase alone and six strains capable of catalyzing both 7a-dehydrogenation and 7a-dehydroxylation. The remaining three organisms, recovered from fresh human feces, were gram-positive, nonflagellated, nonsporeforming, anaerobic rods and comprised two distinct species. Strain HD-17, still unidentified, had both activities, but was unique in that it exclusively 7a-dehydroxylated cholic acid while biotransforming chenodeoxycholic acid, preferably through 7a-dehydrogenation. Two unclassified strains, b-8 and c-25, metabolized both acids through 7a-dehydroxylation and 7adehydrogenation. Except for strains b-8 and c-25, all of the 7a-dehydroxylating bacteria split the conjugated bile acid series, and hydrolases were detected in cellfree filtrates of early stationary-phase broth cultures.

A group of fecal isolates identified as Eubacterium lentum elaborated 3a-, 7a-, and 12a-dehydrogenases and also an epimerizing enzyme(s) for the 3ahydroxy group. The activities of the enzymes, however, were variably manifested according to the kind of bile acid substrate and the oxygen tension under which the reaction occurred.

The Hokkaido Eastern Iburi earthquake (M JMA = 6.7) occurred on September 6, 2018, in the Hokkaido corner region where the Kurile and northeastern Japan island arcs meet. We relocated aftershocks of this intraplate earthquake immediately after the main shock by using data from a permanent local seismic network and found that aftershock depths were concentrated from 20 to 40 km, which is extraordinarily deep compared with other shallow intraplate earthquakes in the inland area of Honshu and Kyushu, Japan. Further, we found that the aftershock area consists of three segments. The first segment is located in the northern part of the aftershock area, the second segment lies in the southern part, and the third segment forms a stepover between the other two segments. The hypocenter of the main shock, from which the rupture initiated, is located on the stepover segment. The centroid moment tensor solution for the main shock indicates a reverse faulting, whereas the focal mechanism solution determined by using the first-motion polarity of the P wave indicates strike-slip faulting. To explain this discrepancy qualitatively, we present a model in which the rupture started as a small strike-slip fault in the stepover segment of the aftershock area, followed by two large reverse faulting ruptures in the northern and southern segments.

Thirty-five strains of Clostridium perfringens were examined for their ability to transform bile acids, both in growing cultures and by washed whole cells. All of the strains oxidized the 3a-hydroxy group to an oxo group, and all except three converted the same a-hydroxy group into a fl-configuration. The oxidative 3adehydrogenation was barely detectable under anaerobic cultural conditions but was clearly demonstrated in an aerated system using washed whole cells, with a pH optimum between 7.0 and 9.0. The epimerizing reaction amounting to 10 to 20% conversion was observed in anaerobic cultures and also with resting cells, irrespective of oxygen supply. Both reactions were carried out with seven conventional 3a-hydroxy bile acids, thus producing a series of 3-oxo and 3,B-hydroxy derivatives that could be examined for gas-liquid chromatographic and mass spectrometric behavior. No evidence for the occurrence of 7aand 12a-hydroxysteroid dehydrogenase activities among the test strains was found. A highly potent deconjugating hydrolase was elaborated by all of the strains.

Microbial transformation of cholic acid and chenodeoxycholic acid by anaerobic mixed cultures of human fecal microorganisms was investigated, and the results were examined in relation to the bile acid transforming activities of 75 bacterial strains isolated from the same fecal cultures. The reactions involved in the mixed cultures were dehydrogenation and dehydroxylation of the 7a-hydroxy group in both primary bile acids and epimerization of the 3a-hydroxy group in all metabolic bile acids. Extensive epimerization of the 7a-hydroxy group of chenodeoxycholic acid yielding ursodeoxycholic acid was also demonstrated by certain fecal samples. 7a-Dehydrogenase activity was widespread among the fecal isolates (88% of 16 facultative anaerobes and 51% of 59 obligate anaerobes), and 7a-dehydroxylase activity was revealed in one of the isolates, an unidentified gram-positive nonsporeforming anaerobic bacterium. 3a-Epimerization was effected by seven strains assigned to Eubacterium lentum, which were also active for 3a-and 7a-dehydrogenations. No microorganism accounting for 7a-epimerization was recovered among the isolates. Splitting of conjugated bile acid was demonstrated by the majority of obligate anaerobes but the activity was rare among facultative anaerobes.Most of the microbial transformations of bile acids in the intestinal tract are reproducible in in vitro cultures offecal microorganisms. The major reactions involved are splitting of conjugated bile acids (deconjugation), removal of the hydroxy group, mainly at C-7 (7a-dehydroxylation), oxidation of hydroxy groups at C-7, C-3, and C-12 (the respective dehydrogenations) and conversion of the hydroxy group at C-3 from a-to ,B-configuration (3a-epimerization) (19,20). With regard to the kinds of microorganisms responsible for the respective reactions, however, only a few systematic studies have been attempted. Midtvedt and Norman (17) investigated the bile acid transforming capacities of 61 laboratory strains of intestinal origin, and Dickinson et al (3) evaluated the activities of 112 isolates from the digestive tract of the rat. They found the deconjugating and dehydrogenating 271