Characterization and purification of bile salt hydrolase from Lactobacillus sp. strain 100-100.

We have characterized and purified the bile salt hydrolase from Lactobacillus sp. strain 100-100. Bile salt hydrolase from cells of the strain was purified with column and high-performance liquid chromatography. The activity was assayed in whole cells and cell-free extracts with either a radiochemical assay involving [14C]taurocholic acid or a nonradioactive assay involving trinitrobenzene sulfonate. The activity was detectable only in stationary-phase cells. Within 20 min after conjugated bile acids were added to stationary-phase cultures of strain 100-100, the activity in whole cells increased to levels three- to fivefold higher than in cells from cultures grown in medium free of bile salts. In cell-free extracts, however, the activity was about equal, 1.41 and 1.53 mumol/min per mg of protein, respectively, whether or not the cells have been grown with bile salts present. When supernatant solutions from cultures grown in medium containing taurocholic acid were used to suspend cells grown in medium free of the bile salt, the bile salt hydrolase activity detected in whole cells increased two- to threefold. Two forms of the hydrolase were purified from the cells and designated hydrolases A and B. They eluted from anion-exchange high-performance liquid chromatography in two sets of fractions, A at 0.15 M NaCl and B at 0.18 M NaCl. Their apparent molecular weights in nondenaturing polyacrylamide gel electrophoresis were 115,000 and 105,000, respectively. However, discrepancies existed in the apparent molecular weights and number of peptides detected in sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the two forms. Both had similar substrate specificities, highest on taurodeoxycholic and glycocholic acid, and pH optima between 3.8 and 4.5. The kinetic properties were also similar, with Vmaxs of 17 and 53 micromoles/min per mg of protein and Kms of 0.76 and 0.95 mM taurocholic acid for A and B, respectively. Therefore, whether the enzyme exists in two forms in the cells remains to be determined.     

Bile salt toxicity to some bifidobacteria strains: role of conjugated bile salt hydrolase and pH

The purpose of this work was to study some aspects of bile salt toxicity towards bifidobacteria. A strain (Bifidobacterium coryneforme ATCC 25911) was selected for its lack of conjugated bile salt hydrolase activity (CBSH-), and was used with three deconjugating strains (CBSH+), for study of their growth and viability in the presence of two dihydroxylated conjugated bile salts (tauro- and glyco-deoxycholic acids). The presence of the glycoconjugate induced a more significant growth inhibition for the four strains than the tauroconjugate. The viability of the strains was measured at several pH levels. Glycodeoxycholic acid, but not taurodeoxycholic acid, exerted a lethal effect, which increased at low pH. This phenomenon was more pronounced for the CBSH- strain. We explain some of these results using an hypothesis based on the consequence of dissociation of conjugated and deconjugated bile salts, and the value of their pKa.     

Identification of Genes Encoding Conjugated Bile Salt Hydrolase and Transport in Lactobacillus johnsonii 100-100

Cytosolic extracts of Lactobacillus johnsonii 100-100 (previously reported as Lactobacillus sp. strain 100-100) contain four heterotrimeric isozymes composed of two peptides, α and β, with conjugated bile salt hydrolase (BSH) activity. We now report cloning, from the genome of strain 100-100, a 2,977-bp DNA segment that expresses BSH activity in Escherichia coli. The sequencing of this segment showed that it contained one complete and two partial open reading frames (ORFs). The 3′ partial ORF (927 nucleotides) was predicted by BLAST and confirmed with 5′ and 3′ deletions to be a BSH gene. Thermal asymmetric interlaced PCR was used to extend and complete the 948-nucleotide sequence of the BSH gene 3′ of the cloned segment. The predicted amino acid sequence of the 5′ partial ORF (651 nucleotides) was about 80% similar to the C-terminal half of the largest, complete ORF (1,353 nucleotides), and these two putative proteins were similar to several amine, multidrug resistance, and sugar transport proteins of the major facilitator superfamily. E. coli DH5α cells transformed with a construct containing these ORFs, in concert with an extracellular factor produced by strain 100-100, demonstrated levels of uptake of [¹⁴C]taurocholic acid that were increased as much as threefold over control levels. [¹⁴C]Cholic acid was taken up in similar amounts by strain DH5α pSportI (control) and DH5α p2000 (transport clones). These findings support a hypothesis that the ORFs are conjugated bile salt transport genes which may be arranged in an operon with BSH genes.     

Importance of microbial defence systems to bile salts and mechanisms of serum cholesterol reduction

An important feature of the intestinal microbiota, particularly in the case of administered probiotic microorganisms, is their resistance to conditions in the gastrointestinal tract, particularly tolerance to and growth in the presence of bile salts. Bacteria can use several defence mechanisms against bile, including special transport mechanisms, the synthesis of various types of surface proteins and fatty acids or the production of exopolysaccharides. The ability to enzymatically hydrolyse bile salts occurs in a variety of bacteria. Choloylglycine hydrolase (EC 3.5.1.24), a bile salt hydrolase, is a constitutive intracellular enzyme responsible for the hydrolysis of an amide bond between glycine or taurine and the steroid nucleus of bile acids. Its presence was demonstrated in specific microorganisms from several bacterial genera (Lactobacillus spp., Bifidobacterium spp., Clostridium spp., Bacteroides spp.). Occurrence and gene arrangement encoding this enzyme are highly variable in probiotic microorganisms. Bile salt hydrolase activity may provide the possibility to use the released amino acids by bacteria as sources of carbon and nitrogen, to facilitate detoxification of bile or to support the incorporation of cholesterol into the cell wall. Deconjugation of bile salts may be directly related to a lowering of serum cholesterol levels, from which conjugated bile salts are synthesized de novo. Furthermore, the ability of microorganisms to assimilate or to bind ingested cholesterol to the cell wall or to eliminate it by co-precipitation with released cholic acid was also documented. Some intestinal microflora produce cholesterol reductase that catalyses the conversion of cholesterol to insoluble coprostanol, which is subsequently excreted in faeces, thereby also reducing the amount of exogenous cholesterol.     

植物乳杆菌JPP2胆盐水解酶相关基因克隆和表达

通过PCR方法从植物乳杆菌JPP2中扩增出胆盐水解酶（BSH）相关基因bsh3,利用中间克隆载体pMD19-T将其构建于表达载体pET-28b上,并转化入表达宿主菌E．coli BL21（DE3）,成功构建重组BSH的工程菌。核苷酸及推导的氨基酸序列分析表明,正确克隆出目的基因。诱导表达后,SDS-PAGE电泳结果显示出特异性蛋白质条带,其分子量约为38kDa。此单克隆体系的构建为进一步研究BSH的功能奠定基础。     

Bile Salt Hydrolase Activity and Resistance to Toxicity of Conjugated Bile Salts Are Unrelated Properties in Lactobacilli

Bacteria of numerous species isolated from the human gastrointestinal tract express bile salt hydrolase (BSH) activity. How this activity contributes to functions of the microorganisms in the gastrointestinal tract is not known. We tested the hypothesis that a BSH protects the cells that produce it from the toxicity of conjugated bile salts. Forty-nine strains of numerous Lactobacillus spp. were assayed to determine their capacities to express BSH activities (taurodeoxycholic acid [TDCA] hydrolase and taurocholic acid [TCA] hydrolase activities) and their capacities to resist the toxicity of a conjugated bile acid (TDCA). Thirty of these strains had been isolated from the human intestine, 15 had been recovered from dairy products, and 4 had originated from other sources. Twenty-six of the strains expressed both TDCA hydrolase and TCA hydrolase activities. One strain that expressed TDCA hydrolase activity did not express TCA hydrolase activity. Conversely, in one strain for which the assay for TDCA hydrolase activity gave a negative result there was evidence of TCA hydrolase activity. Twenty-five of the strains were found to resist the toxicity of TDCA. Fourteen of these strains were of human origin, nine were from dairy products, and two were from other sources. Of the 26 strains expressing both TDCA hydrolase and TCA hydrolase activities, 15 were resistant to TDCA toxicity, 6 were susceptible, and 5 gave inconclusive results. Of the 17 strains that gave negative results for either of the enzymes, 7 were resistant to the toxicity, 9 were susceptible, and 1 gave inconclusive results. These findings do not support the hypothesis tested. They suggest, however, that BSH activity is important at some level for lactobacillus colonization of the human intestine.     

Localization and primary characterization of bile salt hydrolase from Lactobacillus reuteri

The bile salt hydrolase (BSH) of Lactobacillus reuteri CRL 1098 is a single, constitutive, intracellular enzyme which is only detectable in stationary phase cells. It has optimal activity at pH 4.5–5.5 and 37–45 °C. The enzyme (80 kDa apparent mass) has sulphydryl groups in the catalytic active site and hydrolyzes both glycine and taurine conjugated bile acids with higher affinity for glyco-conjugates.     

Bile salt hydrolase activity and resistance to toxicity of conjugated bile salts are unrelated properties in lactobacilli

Bacteria of numerous species isolated from the human gastrointestinal tract express bile salt hydrolase (BSH) activity. How this activity contributes to functions of the microorganisms in the gastrointestinal tract is not known. We tested the hypothesis that a BSH protects the cells that produce it from the toxicity of conjugated bile salts. Forty-nine strains of numerous Lactobacillus spp. were assayed to determine their capacities to express BSH activities (taurodeoxycholic acid [TDCA] hydrolase and taurocholic acid [TCA] hydrolase activities) and their capacities to resist the toxicity of a conjugated bile acid (TDCA). Thirty of these strains had been isolated from the human intestine, 15 had been recovered from dairy products, and 4 had originated from other sources. Twenty-six of the strains expressed both TDCA hydrolase and TCA hydrolase activities. One strain that expressed TDCA hydrolase activity did not express TCA hydrolase activity. Conversely, in one strain for which the assay for TDCA hydrolase activity gave a negative result there was evidence of TCA hydrolase activity. Twenty-five of the strains were found to resist the toxicity of TDCA. Fourteen of these strains were of human origin, nine were from dairy products, and two were from other sources. Of the 26 strains expressing both TDCA hydrolase and TCA hydrolase activities, 15 were resistant to TDCA toxicity, 6 were susceptible, and 5 gave inconclusive results. Of the 17 strains that gave negative results for either of the enzymes, 7 were resistant to the toxicity, 9 were susceptible, and 1 gave inconclusive results. These findings do not support the hypothesis tested. They suggest, however, that BSH activity is important at some level for lactobacillus colonization of the human intestine.     

Molecular cloning,characterization and comparison of bile salt hydrolases from Lactobacillus johnsonii PF01

Aims

To clone, characterize and compare the bile salt hydrolase (BSH) genes of Lactobacillus johnsonii PF01.

Methods and Results

The BSH genes were amplified by polymerase chain reaction (PCR) using specific oligonucleotide primers, and the products were inserted into the pET21b expression vector. Escherichia coli BLR (DE3) cells were transformed with pET21b vectors containing the BSH genes and induced using 0·1 mmol l^?1 isopropylthiolgalactopyranoside. The overexpressed BSH enzymes were purified using a nickel–nitrilotriacetic acid (Ni²⁺‐NTA) agarose column and their activities characterized. BSH A hydrolysed tauro‐conjugated bile salts optimally at pH 5·0 and 55°C, whereas BSH C hydrolysed glyco‐conjugated bile salts optimally at pH 5·0 and 70°C. The enzymes had no preferential activities towards a specific cholyl moiety.

Conclusions

BSH enzymes vary in their substrate specificities and characteristics to broaden its activity. Despite the lack of conservation in their putative substrate‐binding sites, these remain functional through motif conservation.

Significance and Impact of the Study

This is to our knowledge the first report of isolation of BSH enzymes from a single strain, showing hydrolase activity towards either glyco‐conjugated or tauro‐conjugated bile salts. Future structural homology studies and site‐directed mutagenesis of sites associated with substrate specificity may elucidate specificities of BSH enzymes.     

Hydrolysis of Conjugated Bile Acids by Cell-Free Extracts from Aerobic Bacteria

By means of an aerobic enrichment culture technique, several bacteria that hydrolyze conjugated bile acids and modify the formed deconjugates were isolated from feces of man, rat, and chicken and from soil. Hydrolase activity was intracellular and extractable, and the yield of the enzymes was increased by adding the conjugated bile acids to the culture media. The hydrolase from bacterium of human origin was stable, having a pH optimum at about 7.0. All bile acid conjugates were hydrolyzed linearly as a function of time.     

Brucella abortus choloylglycine hydrolase affects cell envelope composition and host cell internalization

Choloylglycine hydrolase (CGH, E.C. 3.5.1.24) is a conjugated bile salt hydrolase that catalyses the hydrolysis of the amide bond in conjugated bile acids. Bile salt hydrolases are expressed by gastrointestinal bacteria, and they presumably decrease the toxicity of host's conjugated bile salts. Brucella species are the causative agents of brucellosis, a disease affecting livestock and humans. CGH confers Brucella the ability to deconjugate and resist the antimicrobial action of bile salts, contributing to the establishment of a successful infection through the oral route in mice. Additionally, cgh-deletion mutant was also attenuated in intraperitoneally inoculated mice, which suggests that CGH may play a role during systemic infection other than hydrolyzing conjugated bile acids. To understand the role CGH plays in B. abortus virulence, we infected phagocytic and epithelial cells with a cgh-deletion mutant (Δcgh) and found that it is defective in the internalization process. This defect along with the increased resistance of Δcgh to the antimicrobial action of polymyxin B, prompted an analysis of the cell envelope of this mutant. Two-dimensional electrophoretic profiles of Δcgh cell envelope-associated proteins showed an altered expression of Omp2b and different members of the Omp25/31 family. These results were confirmed by Western blot analysis with monoclonal antibodies. Altogether, the results indicate that Brucella CGH not only participates in deconjugation of bile salts but also affects overall membrane composition and host cell internalization.     

An active type IV secretion system encoded by the F plasmid sensitizes Escherichia coli to bile salts

F(+) strains of Escherichia coli infected with donor-specific bacteriophage such as M13 are sensitive to bile salts. We show here that this sensitivity has two components. The first derives from secretion of bacteriophage particles through the cell envelope, but the second can be attributed to expression of the F genes required for the formation of conjugative (F) pili. The latter component was manifested as reduced or no growth of an F(+) strain in liquid medium containing bile salts at concentrations that had little or no effect on the isogenic F(-) strain or as a reduced plating efficiency of the F(+) strain on solid media; at 2% bile salts, plating efficiency was reduced 10(4)-fold. Strains with F or F-like R factors were consistently more sensitive to bile salts than isogenic, plasmid-free strains, but the quantitative effect of bile salts depended on both the plasmid and the strain. Sensitivity also depended on the bile salt, with conjugated bile salts (glycocholate and taurocholate) being less active than unconjugated bile salts (deoxycholate and cholate). F(+) cells were also more sensitive to sodium dodecyl sulfate than otherwise isogenic F(-) cells, suggesting a selectivity for amphipathic anions. A mutation in any but one F tra gene required for the assembly of F pili, including the traA gene encoding F pilin, substantially restored bile salt resistance, suggesting that bile salt sensitivity requires an active system for F pilin secretion. The exception was traW. A traW mutant was 100-fold more sensitive to cholate than the tra(+) strain but only marginally more sensitive to taurocholate or glycocholate. Bile salt sensitivity could not be attributed to a generalized change in the surface permeability of F(+) cells, as judged by the effects of hydrophilic and hydrophobic antibiotics and by leakage of periplasmic beta-lactamase into the medium.     

Lipolytic enzymes of the human pancreas. II. Purification and properties of cholesterol ester hydrolase

Cholesterol ester hydrolase (sterol-ester acylhydrolase, EC 3.1.1.13) was purified from human pancreatic tissue by column chromatography and acetone precipitation, leading to a 400-fold enrichment. Isoelectric focusing of this product reveals a double-band at pH 4.5 and 4.6. The molecular weight was estimated at 320 kDa by means of Sephadex filtration on calibrated columns. Obviously these large molecules represent a tetrameric form of the monomeric subunit (molecular mass 76-80 kDa), which is also enzymatically active. It was found together with the dimeric form in pancreatic juice, where the tetrameric enzyme is responsible for the major part of the hydrolytic activity, splitting cholesterol ester as well as synthetic substrates, such as fluorescein or p-nitrophenyl esters. Attempts to split the tetrameric cholesterol ester hydrolase, isolated from pancreatic tissue, into active subunits found additionally in pancreatic juice by the influence of bile acids and proteolytic enzymes failed. The spectral shift method using Rhodamine fluorescence was employed in order to prove that fluorescein dilaurate forms micellar solutions and mixed micelles when bile salts are present.     

Molecular characterization of bile salt hydrolase from Bifidobacterium animalis subsp. lactis Bi30

The present work describes the identification, purification, and characterization of bile salt hydrolase (BSH) from Bifidobacterium animalis subsp. lactis. The enzyme was purified to electrophoretic homogeneity by hydrophobic chromatography, ion-exchange chromatography and ultrafiltration. SDS-PAGE analysis of putative BSH and gel filtration revealed that the analyzed protein is presumably a tetramer composed of four monomers each of about 35 kDa. The purified enzyme was analyzed by liquid chromatography coupled to LTQ FT ICR mass spectrometry and unambiguously identified as a bile salt hydrolase from B. animalis. The isoelectric point of the studied protein was estimated to be around pH 4.9. The pH optimum of the purified BSH is between 4.7 to 6.5, and the temperature optimum is around 50 degrees C. The BSH of B. animalis could deconjugate all tested bile salts, with clear preference for glycine-conjugated bile salts over taurine-conjugated forms. Genetic analysis of the bsh showed high similarity to the previously sequenced bsh gene from B. animalis and confirmed the usefulness of bile salt hydrolase as a genetic marker for B. animalis identification.     

Hydrolysis of retinyl palmitate by enzymes of rat pancreas and liver. Differentiation of bile salt-dependent and bile salt-independent, neutral retinyl ester hydrolases in rat liver

Previous studies have demonstrated that homogenates of the livers of rats contain a neutral retinyl ester hydrolase activity that requires millimolar concentrations of bile salts for maximal in vitro activity. The enzymatic properties of this neutral, bile salt-dependent retinyl ester hydrolase activity in liver homogenates are nearly identical to those observed in the present report for the in vitro hydrolysis of retinyl palmitate by purified rat pancreatic cholesteryl ester hydrolase (EC 3.1.1.13). Moreover, anti-rat pancreatic cholesteryl ester hydrolase IgG completely inhibits the bile salt-dependent retinyl ester hydrolase activity of rat liver homogenates whereas normal rabbit IgG does not. We also show that liver homogenates contain a neutral, bile salt-independent retinyl ester hydrolase activity that differs from the bile salt-dependent activity in that 1) its absolute activity does not vary markedly among individual rats, 2) it is not inhibited by antibodies to pancreatic cholesteryl ester hydrolase, and 3) it is localized in the microsomal fraction of liver homogenates. Subfractionation of microsomes demonstrates that the neutral, bile salt-independent retinyl ester hydrolase activity is associated with liver cell plasma membranes and thus may play a role in the hydrolysis of retinyl esters delivered to the liver by chylomicron remnants.     

Purification, characterization, and expression of rat intestinal alkaline sphingomyelinase

Intestinal alkaline sphingomyelinase (SMase) has physiological roles in the digestion of sphingomyelin (SM) and clinical implications in colonic carcinogenesis. In the present work, the enzyme from rat has been purified 1,589-fold with 11% recovery by elution of the intestine with bile salt, precipitation of the proteins by acetone, and several types of chromatographies. Its molecular mass was 58 kDa and optimal pH was 9 to 9.5. Under the optimal conditions, the V(max) was 930 micromol/h/mg and K(m) was about 1.25 mM. The enzyme could hydrolyze phosphatidylcholine at pH 7.4 in the presence of Ca2+; the rate was about 8% of that for SM. The activity against SM was dependent on bile salt. Taurine conjugated bile salts were much more effective than glycine conjugated ones, and the most effective bile salts were taurocholate and taurochenodeoxycholate. 3-[(3-Cholamidopropyl) dimethylammonio]-1-propanesulfonate (CHAPS) and Triton X100 (TX100) had no stimulatory effects. Unlike neutral SMase, intestinal alkaline SMase was not Mg2+ dependent, not inhibited by EDTA, and not inhibited by glutathione. The enzyme was stable during incubation with temperatures up to 50 degree C and in pHs from 7 to 10. Trypsin and chymotrypsin had no effects on its activity, and 10 mM dithiothreitol reduced its activity by 25%. A specific antibody against the enzyme was developed, and Western blot showed that the enzyme was expressed in the intestine but not in other organs. In conclusion, we purified a potentially important SMase in the intestine with several properties different from neutral SMase.     

The effect of bile salts on survival and morphology of a potential probiotic strain Lactobacillus acidophilus M92

Bile tolerance is an important criterion in the selection of microbial strains for probiotic use. The survival and morphological changes of a potential probiotic strain, Lactobacillus acidophilus M92, in the presence of bile salts were examined. Lactobacillus acidophilus M92 has shown a satisfactory degree of tolerance against oxgall and individual bile salts tested, especially to taurocholate. The higher resistance of L. acidophilus M92 against taurine-conjugated bile salts relative to deconjugated and glycine-conjugated bile salts was attributed to its reaction to the stronger acidity of the former. Furthermore, bile salt hydrolase (BSH) was active when L. acidophilus M92 was grown in the presence of sodium taurocholate. The rate of BSH activity was highest at the exponential growth phase. It was hypothesised that BSH activity may be important for the bile salt resistance of this strain. The colonial and cellular morphology may also be a valuable parameter in the selection of bile salt-resistant Lactobacillus strains for probiotic use. Smooth (S) and rough (R) colonies, appeared in the original L. acidophilus M92 bacterial culture and demonstrated a different degree of bile tolerance. Rough colonies were more sensitive to bile salts than smooth ones. The R colony cells assumed a round form, probably induced by gaps in the cell wall caused by the cytotoxicity of glycodeoxycholate. This revised version was published online in July 2006 with corrections to the Cover Date.     

Significance of bile salt hydrolytic activities of lactobacilli

Bile salt hydrolase (BSH) activity was shown to be constitutive and substrate-specific: the BSH isogenic Lactobacillus plantarum wild type (LP80 WT) and BSH overproducing LP80 (pCBH1) strains preferentially hydrolysed glycodeoxycholic acid (GDCA), whereas the hamster Lact. animalis isolates H362 and H364 showed a higher affinity for taurodeoxycholic acid (TDCA). In viability studies in the presence of nutrients, it was demonstrated that GDCA exerted a higher toxicity than TDCA in a pH-dependent manner. This toxicity was inversely proportionate to the BSH activity level of the strains tested, indicating that BSH activity contributed towards bile salt resistance when appropriate nutrients were available. The high toxicity of GDCA relative to TDCA was suggested to be caused by their weak and strong acid properties respectively. It was therefore hypothesized that the protonated form of bile salts exhibited toxicity as it imported protons in the cell. This puts an energy-burden on BSH⁻ lactobacilli which undergo intracellular acidification. BSH⁺ cells primarily protect themselves through the formation of the weaker DCA compound, which can help negate the pH-drop by recapturing and exporting the co-transported proton. However, since DCA is more toxic than its conjugated counterparts, an additional energy-dependent detoxification of DCA is suggested.