Effect of growth at low pH on the cell surface properties of a typical strain of Lactobacillus casei group

BACKGROUND AND OBJECTIVES

Although members of the Lactobacillus casei group are known to survive under acidic conditions, the underlying mechanisms of growth at acidic condition and the impact of low pH on the relative level of protein expression at the cell surface remain poorly studied.

MATERIAL AND METHODS

After confirming the taxonomy of L. casei strain GCRL 12 which was originally isolated from cheese and confirmed by 16S rRNA sequence analysis, the impact of acidic pH on growth rate was determined.

RESULTS

Late log-phase cells cultured at pH 4.0 showed obvious changes in Gram staining properties while transmission electron microscopy analysis revealed evidence of structural distortions of the cell surface relative to the controls cultured at pH 6.5. When comparing cytosolic or whole cell preparations on SDS-PAGE, few changes in protein profiles were observed under the two growth conditions. However, analysis of surface protein extracted by 5M LiCl demonstrated changes in the proportions of proteins present in the molecular weight range of 10 to 80 kDa, with some proteins more dominant at pH 6.5 and other at pH 4.

CONCLUSION

These data suggest that surface proteins of this strain are associated with growth and survival at low pH. The function of these proteins is subject to further investigation.

Metabolite repression inhibits degradation of benzo[a]pyrene and dibenz[a,h]anthracene by Stenotrophomonas maltophilia VUN 10,003

Large inocula of Stenotrophomonas maltophilia VUN 10,003 were used to investigate bacterial degradation of benzo[a]pyrene and dibenz[a,h]anthracene. Although strain VUN 10,003 was capable of degrading 10-15 mg (-1) of the five-ring compounds in the presence of pyrene after 63 days, further addition of pyrene after degradation of the five-ring polycyclic aromatic hydrocarbons (PAHs) ceased did not stimulate significant decreases in the concentration of benzo[a]pyrene or dibenz[a,h]anthracene. However, pyrene was degraded to undetectable levels 21 days after its addition. The amount of benzo[a]pyrene and dibenz[a,h]anthracene degraded by strain VUN 10,003 was not affected by the initial concentration of the compounds when tested at 25-100 mg l(-1), by the accumulation of by-products from pyrene catabolism or a loss of ability by the cells to catabolise benzo[a]pyrene or dibenz[a,h]anthracene. Metabolite or by-product repression was suspected to be responsible for the inhibition: By-products from the degradation of the five-ring compounds inhibited their further degradation.

Microbial degradation and detoxification of high molecular weight polycyclic aromatic hydrocarbons by Stenotrophomonas maltophilia strain VUN 10,003

The ability of Stenotrophomonas maltophilia strain VUN 10,003 to degrade and detoxify high molecular weight polycyclic aromatic hydrocarbons (PAHs) was evaluated in a basal liquid medium. Using high cell density inocula of strain VUN 10,003, the concentration of pyrene, fluoranthene, benz[a]anthracene, benzo[a]pyrene, dibenz[a, h]anthracene and coronene decreased by 98, 45, 26, 22, 22 and 55% over periods ranging from 5 to 42 d. When a PAH mixture containing three- to seven-ring compounds was used, degradation of both low and high molecular weight compounds occurred concurrently. Mutagenicity assays (Ames Test) demonstrated a decrease in the mutagenic potential of dichloromethane culture extracts from all cultures containing single PAH over the incubation period, corresponding to the decrease in the concentration of the PAH. These observations indicate that strain VUN 10,003 could be used for the detoxification of PAH-contaminated wastes.

Degradation and mineralization of high-molecular-weight polycyclic aromatic hydrocarbons by defined fungal-bacterial cocultures

This study investigated the biodegradation of high-molecular-weight polycyclic aromatic hydrocarbons (PAHs) in liquid media and soil by bacteria (Stenotrophomonas maltophilia VUN 10,010 and bacterial consortium VUN 10,009) and a fungus (Penicillium janthinellum VUO 10, 201) that were isolated from separate creosote- and manufactured-gas plant-contaminated soils. The bacteria could use pyrene as their sole carbon and energy source in a basal salts medium (BSM) and mineralized significant amounts of benzo[a]pyrene cometabolically when pyrene was also present in BSM. P. janthinellum VUO 10,201 could not utilize any high-molecular-weight PAH as sole carbon and energy source but could partially degrade these if cultured in a nutrient broth. Although small amounts of chrysene, benz[a]anthracene, benzo[a]pyrene, and dibenz[a,h]anthracene were degraded by axenic cultures of these isolates in BSM containing a single PAH, such conditions did not support significant microbial growth or PAH mineralization. However, significant degradation of, and microbial growth on, pyrene, chrysene, benz[a]anthracene, benzo[a]pyrene, and dibenz[a,h]anthracene, each as a single PAH in BSM, occurred when P. janthinellum VUO 10,201 and either bacterial consortium VUN 10,009 or S. maltophilia VUN 10,010 were combined in the one culture, i.e., fungal-bacterial cocultures: 25% of the benzo[a]pyrene was mineralized to CO(2) by these cocultures over 49 days, accompanied by transient accumulation and disappearance of intermediates detected by high-pressure liquid chromatography. Inoculation of fungal-bacterial cocultures into PAH-contaminated soil resulted in significantly improved degradation of high-molecular-weight PAHs, benzo[a]pyrene mineralization (53% of added [(14)C]benzo[a]pyrene was recovered as (14)CO(2) in 100 days), and reduction in the mutagenicity of organic soil extracts, compared with the indigenous microbes and soil amended with only axenic inocula.

Surfactant-enhanced biodegradation of high molecular weight polycyclic aromatic hydrocarbons by stenotrophomonas maltophilia

The objectives of this study were to isolate and evaluate microorganisms with the ability to degrade high molecular weight polycyclic aromatic hydrocarbons (PAHs) in the presence of synthetic surfactants. Stenotrophomonas maltophilia VUN 10,010, isolated from PAH-contaminated soil, utilized pyrene as a sole carbon and energy source and also degraded other high molecular weight PAHs containing up to seven benzene rings. Various synthetic surfactants were tested for their ability to improve the PAH degradation rate of strain VUN 10,010. Anionic and cationic surfactants were highly toxic to this strain, and the Tween series was used as a growth substrate. Five nonionic surfactants (Brij 35, Igepal CA-630, Triton X-100, Tergitol NP-10, and Tyloxapol) were not utilized by, and were less toxic to, strain VUN 10,010. MSR and log Km values were determined for fluoranthene, pyrene, and benzo[a]pyrene in the presence of these nonionic surfactants and their apparent solubility was increased by a minimum of 250-fold in the presence of 10 g L-1 of all surfactants. The rate of pyrene degradation by strain VUN 10,010 was enhanced by the addition of four of the nonionic surfactants (5-10 g L-1); however, 5 g L-1 Igepal CA-630 inhibited pyrene degradation and microbial growth. The specific growth rate of VUN 10,010 on pyrene was increased by 67% in the presence of 10 g L-1 Brij 35 or Tergitol NP-10. The addition of Brij 35 and Tergitol NP-10 to media containing a single high molecular weight PAH (four and five benzene rings) as the sole carbon source increased the maximum specific PAH degradation rate and decreased the lag period normally seen for PAH degradation. The addition of Tergitol NP-10 to VUN 10,010 cultures which contained a PAH mixture (three to seven benzene rings) substantially improved the overall degradation rate of each PAH and increased the specific growth rate of VUN 10,010 by 30%. Evaluation of the use of VUN 10,010 for degrading high molecular weight PAHs in leachates from surfactant-flushed, weathered, PAH-contaminated sites is warranted. Copyright 1998 John Wiley & Sons, Inc.

Detection of heavy metal ion resistance genes in gram-positive and gram-negative bacteria isolated from a lead-contaminated site

Resistance to a range of heavy metal ions was determined for lead-resistant and other bacteria which had been isolated from a battery-manufacturing site contaminated with high concentration of lead. Several Gram-positive (belonging to the genera Arthrobacter and Corynebacterium) and Gram-negative (Alcaligenes species) isolates were resistant to lead, mercury, cadmium, cobalt, zinc and copper, although the levels of resistance to the different metal ions were specific for each isolate. Polymerase chain reaction, DNA-DNA hybridization and DNA sequencing were used to explore the nature of genetic systems responsible for the metal resistance in eight of the isolates. Specific DNA sequences could be amplified from the genomic DNA of all the isolates using primers for sections of the mer (mercury resistance determinant on the transposon Tn501) and pco (copper resistance determinant on the plasmid pRJ1004) genetic systems. Positive hybridizations with mer and pco probes indicated that the amplified segments were highly homologous to these genes. Some of the PCR products were cloned and partially sequenced, and the regions sequenced were highly homologous to the appropriate regions of the mer and pco determinants. These results demonstrate the wide distribution of mercury and copper resistance genes in both Gram-positive and Gram-negative isolates obtained from this lead-contaminated soil. In contrast, the czc (cobalt, zinc and cadmium resistance) and chr (chromate resistance) genes could not be amplified from DNAs of some isolates, indicating the limited contribution, if any, of these genetic systems to the metal ion resistance of these isolates.

Analysis of nucleotide methylation in DNA from Corynebacterium glutamicum and related species

Plasmid DNA (pCSL17) isolated from Corynebacterium glutamicum transformed recipient McrBC+ strains of Escherichia coli with lower efficiency than McrBC- strains, confirming a previous report by Tauch et al. (FEMS Microbiol. Lett. 123 (1994) 343-348) which inferred that C. glutamicum DNA contains methylcytidine. Analysis of nucleotides in C. glutamicum-derived chromosomal and plasmid DNA failed to detect significant levels of methylated adenosine, but methylated cytidine was readily detected. Restriction enzymes which are inhibited by the presence of methylcytidine in their recognition sequence failed to cut pCSL17 from C. glutamicum, whereas enzymes which require methylation at adenosine in GATC sequences failed to cut. Failure of HaeIII to cut two specific sites of C. glutamicum-derived pCSL17 identified the first cytidine in the sequence GGCCGC as one target of methylation in this species, which contains the methyltransferase recognition sequence. Although Brevibacterium lactofermentum-derived DNA showed a similar methylation pattern by HPLC analysis, HaeIII cleaved these GGCCGC sites, suggesting differences in the specificity of methylation between these two species. Results for all analyses of B. flavum DNA were identical to those for C. glutamicum.

Partial purification and characterization of two enzymes involved in isovaleric acid synthesis in Clostridium bifermentans

Conversion of leucine to isovaleric acid by Clostridium bifermentans is achieved by the action of at least two enzymes. One is a transaminase producing alpha-ketoisocaproic acid, which was purified 30-fold from osmotic lysates of late-exponential phase cells by repeated chromatography on DEAE-Sepharose C16B and Sephacryl S300: this represented a 147-fold purification of activity found in sonically disrupted cells. This enzyme had an apparent molecular weight of approximately 190000 and was composed of six identically sized sub-units (molecular weight 31000 +/- 1000). Transamination required pyridoxal phosphate and pyruvate and was optimal at pH 8.6; the apparent Km for leucine was 7.0 mM. Activity was totally inhibited by 1 mM-p-chloromercuribenzoate and partially inhibited by other thiol reagents. The second enzyme decarboxylated alpha-ketoisocaproic acid to form isovaleric acid and was also partially purified by chromatography on DEAE-Sepharose C16B and Sephacryl S300. It has an apparent molecular weight of 240000 and required FAD and coenzyme A for activity; the Km for alpha-ketoisocaproic acid was 4.2 mM and activity was optimal around pH 8.0. This enzyme was a flavoprotein with absorption maxima at 280, 320 and 400 nm, and a fluorescent maximum at 500 nm. The prosthetic group, FAD, dissociated from the protein during purification resulting in an inactive apoenzyme which was only partially re-activated by FAD. Activity was completely inhibited by several thiol reagents tested at 1 mM.

Characterization of latent and active forms of cartilage proteinases produced by normal immature rabbit articular cartilage in tissue culture

Cultured tissue slices from normal immature rabbit articular cartilage released latent neutral metalloproteinases into serum-free medium. On activation with 4-aminophenylmercuric acetate, these metalloproteinases could degrade collagen, proteoglycan, and gelatin. Also produced were an acid proteinase with the properties of cathepsin D and an inhibitor of the neutral metalloproteinases. The appearance of both the proteinases and the inhibitor in the culture medium could be prevented by incubation of cultures with cycloheximide. The active and latent forms of the proteinases were characterized using Ultrogel AcA 54 chromatography.

Subcellular location of enzymes involved in leucine dissimilation in Clostridium bifermentans

Conversion of leucine to isovaleric (iV) and isocaproic (iC) acids by cell-free extracts of Clostridium bifermentans was demonstrated using two lysis procedures. Sonication resulted in an extract which had the enzymes to convert leucine to alpha-ketoisocaproic acid (alpha-kiC) and thence iV, but failed to produce iC. Extracts prepared by osmotic lysis, which contained intact membranes, could convert leucine to both iV and iC. The enzyme which converts leucine to alpha-kiC was solubilized during osmotic lysis, whereas the decarboxylase and leucine reductase system remained membrane bound. Osmotic lysis also released at least two small molecular weight, heat-stable, anionic components (3500 greater than molecular weight greater than or equal to 1000), which stimulated decarboxylase activity.

Isolation and properties of metronidazole-resistant mutants of Clostridium perfringens

Clostridium perfringens strains resistant to metronidazole and tinidazole were isolated from the sensitive parent strain CM288 after mutagenesis with N-methyl-N'-nitro-N-nitrosoguanidine. Strain CM288 was already resistant to rifampicin and nalidixic acid; these genetic markers helped to confirm the identity of mutants. All mutants showed similar characteristics: they grew more slowly than the parent strain and failed to reach the same maximum turbidity; uptake of metronidazole and tinidazole from culture fluids was slow and end products of glucose metabolism were different from those of the parent. Pyruvate dehydrogenase activity was not detected in broken cell preparations of the mutant strains although this enzyme was readily detected in the parent strain. Changes in end products of glucose metabolism were consistent with the absence of pyruvate dehydrogenase activity because pyruvate was accumulated during growth and lactate levels were higher whereas acetate, CO2 and ethanol levels were diminished.

Leucine dissimilation to isovaleric and isocaproic acids by cell suspensions of amino acid fermenting anaerobes: the Stickland reaction revisited

Freshly compared cell suspensions of clostridia (Clostridium bifermentans, C. botulinum proteolytic type A, C. difficile, C. sordellii, and C. sporogenes) and Peptostreptococcus anaerobius converted leucine to isovaleric (iV) and isocaproic (iC) acids in the absence of other amino acids. The optimal pH for conversion was between 8 and 9 at 37 degrees C. The stoichiometry of reaction was compatible with that expected for the Stickland reaction, as the ratio of iV to iC was 1:2, the amount of CO2 produced was equivalent to that of iV, and ammonium ion concentrations were equal to the total C5 and C6 acids formed. The presence of alanine and valine (proton donors in the Stickland reaction) in incubations effectively increased the concentration of iC at the expense of iV production, implying that leucine acted there primarily as a proton acceptor. Glycine and proline (proton acceptors) stimulated both iV and iC production from leucine, but increases in iV concentrations were proportionately greater than for iC so that leucine was primarily a proton donor in the presence of proton acceptors. Glucose stimulated the conversion of leucine to volatile fatty acids but favoured iC production. Production of iC from leucine was inhibited by surface active compounds (cetyltrimethylammonium bromide and desoxycholate) as well as arsenite and iodoacetate. The redox dyes methyl viologen and phenosafranine inhibited iC production more severely than iV production, as did the nitroimidazole antimicrobial agent, metronidazole.

Some properties of neutral proteinases from lysosomes of rabbit polymorphonuclear leucocytes

Neutral proteinases capable of degrading proteoglycan were found in lysosomes of rabbit polymorphonuclear leucocytes extracted with 0 . 01 M citric acid. Esterase activity against an elastase substrate was also present but chymotrypsin- and trypsin-like activities were not detected; azocasein-degrading activity was poor. Proteoglycanase activity was stimulated by high concentrations of salts (0 . 2 M KCl) and divalent cations (Ca, Mg, Mn, Zn) but was inhibited by Cu++. Elastase activity was also stimulated by high ionic strength buffers and KCl, but not as much by divalent cations, and was inhibited by Cu++. Proteoglycanase in crude extracts was inhibited by EDTA, phenylmethanesulphonylfluoride (Pms-F), cell cytosol, alpha 1-antitrypsin, gold thiomalate and N-acetyl-di-L-alanyl-L-propyl-L-valine chloromethyl ketone (AAAPVCK). Partial inhibition by N-alpha-p-tosyl-L-lysine chloromethyl ketone (TLCK) and L-l-tosylamide-2-phenylethyl chloromethyl ketone (TPCK) occurred. Elastase adsorbed to CM-cellulose and was eluted by 0 . 6-0 . 7 M NaCl; a metallo-proteinase failed to adsorb completely but was retarded by the CM-cellulose. Isoelectric focusing showed that the major proteinases had pI's of 5 . 5, 8 . 5 and 9 . 1; the activity with pI 8 . 5 was a metallo-proteinase, and the Pi 9 . 1 activity was an elastase. The apparent molecular weight of the elastase, determined on Sephadex G-100, was 8,000 and 11,000 daltons.

Isolation and properties of metronidazole-resistant mutants of Bacteroides fragilis

Metronidazole-resistant mutants of Bacteroides fragilis, isolated after mutagenesis, had diminished ability to take up and metabolize the drug. All the metronidazole-resistant strains had depressed levels of pyruvate dehydrogenase compared with parent cultures. Their end products of glucose metabolism also differed from normal B. fragilis products and were consistent with deficiencies in pyruvate dehydrogenase activity.

Chloramphenicol acetyltransferase of Bacteroides fragilis

Chloramphenicol-resistant strains of Bacteroides fragilis (minimum inhibitory concentration, 12.5 mug/ml) were isolated from a stool specimen which contained multiply resistant Escherichia coli. The enzyme responsible for resistance, chloramphenicol acetyltransferase, was produced constitutively by these strains; the specific activity was 10-fold lower than that of the E. coli enzymes. Similar activity was not detected in susceptible B. fragilis strains, nor could it be induced by growth in the presence of chloramphenicol or by mutagenesis. The enzyme had a pH optimum of 7.8 and a molecular weight of approximately 89,000. The K(m) for chloramphenicol was 5.2 muM, and the enzyme was sensitive to inhibition by 5,5'-dithiobis-2-nitrobenzoic acid. The enzyme produced by an E. coli strain isolated from the same specimen had a similar K(m) and sensitivity to 5,5'-dithiobis-2-nitrobenzoic acid.

Purification and properties of beta-lactamase from Bacteroides fragilis

Beta-Lactamase activity was detected either biologically or using the chromogenic cephalosporin 87/312 in 20 clinical isolates of Bacteroides fragilis with penicillin G minimal inhibitory concentrations of 10 to 100 micrograms/ml. Strain AM78 (minimal inhibitory concentration, greater than 1,000 micrograms/ml) was used to optimize the conditions for production, assay, and storage of the enzyme. The enzymes are cell associated, with less than 1% of activity being found in culture fluids during growth, and can be released from the cell surface by modified osmotic shock procedure. This procedure causes concomitant release of cyclic phosphodiesterase activity. Substrate profiles and the effects of inhibitors were determined for enzymes partially purified by osmotic shock release and gel filtration. The enzymes are cephalosporinases with some penicillinase activity and are inhibited by p-chloromercuribenzoate, cloxacillin, and carbenicillin. The molecular weight, as determined by gel filtration, is 29,000 to 31,000. A method for the purification of the beta-lactamase from strain AM78 is described: the specific activity of the purified enzyme was 3,424 U/mg, about 3,000-fold that of the crude, cell-associated enzyme.