Degradation of and sensitivity to cholate in Pseudomonas sp. strain Chol1

Abstract

A facultative anaerobic bacterium, Pseudomonas sp. strain Chol1, degrading cholate and other bile acids was isolated from soil. We investigated how strain Chol1 grew with cholate and whether growth was affected by the toxicity of this compound. Under anoxic conditions with nitrate as electron acceptor, strain Chol1 grew by transformation of cholate to 7,12-dihydroxy-1,4-androstadiene-3,17-dione (DHADD) as end product. Under oxic conditions, strain Chol1 grew by transformation of cholate to 3,7,12-trihydroxy-9, 10-seco-1,3,5(10)-androstatriene-9,17-dione (THSATD), which accumulated in the culture supernatant before its further oxidation to CO 2 . Strain Chol1 converted DHADD into THSATD by an oxygenase-dependent reaction. Addition of cholate ( ‡10 mM) to cell suspensions of strain Chol1 caused a decrease of optical density and viable counts but aerobic growth with these toxic cholate concentrations was possible. Addition of CCCP or EDTA strongly increased the sensitivity of the cells to 10 mM cholate. EDTA also increased the sensitivity of the cells to DHADD and THSATD ( £ 1.7 mM). The toxicity of cholate and its degradation intermediates with a steroid structure indicates that strain Chol1 requires a strategy to minimize these toxic effects during growth with cholate. Apparently, the proton motive force and the outer membrane are necessary for protection against these toxic effects.

Different bacterial strategies to degrade taurocholate

“…3, chromatogram t5). These intermediates, presumably representing compounds reported elsewhere (Philipp et al 2006), were absent at the beginning of the experiment (Fig. 3, chromatogram t0) and had disappeared by the end of growth (Fig.…”

“…Reversed phase HPLC was used to quantify taurine after derivatisation with 2,4-dinitroXuorobenzene (DNFB) (Laue et al 1997), or to quantify cholate and taurocholate. The method of Philipp et al (2006) to determine cholate, isocratic elution from a reversed-phase column with a neutral mobile phase and UV detection at 195 nm, was modiWed to gradient elution with acetonitrile (20-60% over 9 min) as the organic modiWer in an acidic mobile phase (10 mM potassium phosphate buVer, pH 2.0) (Fig. 3).…”

“…The data represent three samples taken during growth, at zero time (t0), at 5 h (t5) and at 9 h (t9) not individual species but communities will be involved in the dissimilation of taurocholate. Little work has been done on the catabolism of taurocholate: it is only recently that the analytical chemical tools (Philipp et al 2006 and our modiWcation to separate cholate and taurocholate) have become available to approach the problem quantitatively.…”

“…However, an understanding of taurine degradation in other organisms has proceeded further (Cook andDenger 2002, 2006;Denger et al 2006;Gorzynska et al 2006;Cook et al 2007): relevant pathway variants have been found in Delftia acidovorans SPH-1 and in C. testosteroni KF-1 (see below). An understanding of cholate degradation is also being developed (Philipp et al 2006).…”

Degradation of the Acyl Side Chain of the Steroid Compound Cholate in Pseudomonas sp. Strain Chol1 Proceeds via an Aldehyde Intermediate

“…1) by Pseudomonas sp. strain Chol1 (15). Bile salts are surface-active steroid compounds that aid the digestion of lipophilic nutrients in the digestive tracts of vertebrates and enter the environment in significant amounts by excretion (16,17).…”