Catabolism of taurine in Pseudomonas aeruginosa

Chilled Pacu (Piaractus mesopotamicus) fillets: Modeling Pseudomonas spp. and psychrotrophic bacteria growth and monitoring spoilage indicators by 1H NMR and GC-MS during storage

This study aimed to assess the growth of Pseudomonas spp. and psychrotrophic bacteria in chilled Pacu (Piaractus mesopotamicus), a native South American fish, stored under chilling conditions (0 to 10 °C) through the use of predictive models under isothermal and non-isothermal conditions. Growth kinetic parameters, maximum growth rate (μmax, 1/h), lag time (tLag, h), and (Nmax, Log10 CFU/g) were estimated using the Baranyi and Roberts microbial growth model. Both kinetic parameters, growth rate and lag time, were significantly influenced by temperature (P < 0.05). The square root secondary model was used to describe the bacteria growth as a function of temperature. Secondary models, √μ = 0.016 (T + 10.13) and √μ =0.017 (T + 9.91) presented a linear correlation with R2 values >0.97 and were further validated under non-isothermal conditions. The model's performance was considered acceptable to predict the growth of Pseudomonas spp. and psychrotrophic bacteria in refrigerated Pacu fillets with bias and accuracy factors between 1.24 and 1.49 (fail-safe) and 1.45-1.49, respectively. Fish biomarkers and spoilage indicators were assessed during storage at 0, 4, and 10 °C. Volatile organic compounds, VOCs (1-hexanol, nonanal, octenol, and indicators 2-ethyl-1-hexanol) showed different behavior with storage time (P > 0.05). 1H NMR analysis confirmed increased enzymatic and microbial activity in Pacu fillets stored at 10 °C compared to 0 °C. The developed and validated models obtained in this study can be used as a tool for decision-making on the shelf-life and quality of refrigerated Pacu fillets stored under dynamic conditions from 0 to 10 °C.

Taurine and Astrocytes: A Homeostatic and Neuroprotective Relationship

Taurine is considered the most abundant free amino acid in the brain. Even though there are endogenous mechanisms for taurine production in neural cells, an exogenous supply of taurine is required to meet physiological needs. Taurine is required for optimal postnatal brain development; however, its brain concentration decreases with age. Synthesis of taurine in the central nervous system (CNS) occurs predominantly in astrocytes. A metabolic coupling between astrocytes and neurons has been reported, in which astrocytes provide neurons with hypotaurine as a substrate for taurine production. Taurine has antioxidative, osmoregulatory, and anti-inflammatory functions, among other cytoprotective properties. Astrocytes release taurine as a gliotransmitter, promoting both extracellular and intracellular effects in neurons. The extracellular effects include binding to neuronal GABAA and glycine receptors, with subsequent cellular hyperpolarization, and attenuation of N-methyl-D-aspartic acid (NMDA)-mediated glutamate excitotoxicity. Taurine intracellular effects are directed toward calcium homeostatic pathway, reducing calcium overload and thus preventing excitotoxicity, mitochondrial stress, and apoptosis. However, several physiological aspects of taurine remain unclear, such as the existence or not of a specific taurine receptor. Therefore, further research is needed not only in astrocytes and neurons, but also in other glial cells in order to fully comprehend taurine metabolism and function in the brain. Nonetheless, astrocyte’s role in taurine-induced neuroprotective functions should be considered as a promising therapeutic target of several neuroinflammatory, neurodegenerative and psychiatric diseases in the near future. This review provides an overview of the significant relationship between taurine and astrocytes, as well as its homeostatic and neuroprotective role in the nervous system.

Insight Into the Diversity and Possible Role of Plasmids in the Adaptation of Psychrotolerant and Metalotolerant Arthrobacter spp. to Extreme Antarctic Environments

Arthrobacter spp. are coryneform Gram-positive aerobic bacteria, belonging to the class Actinobacteria. Representatives of this genus have mainly been isolated from soil, mud, sludge or sewage, and are usually mesophiles. In recent years, the presence of Arthrobacter spp. was also confirmed in various extreme, including permanently cold, environments. In this study, 36 psychrotolerant and metalotolerant Arthrobacter strains isolated from petroleum-contaminated soil from the King George Island (Antarctica), were screened for the presence of plasmids. The identified replicons were thoroughly characterized in order to assess their diversity and role in the adaptation of Arthrobacter spp. to harsh Antarctic conditions. The screening process identified 11 different plasmids, ranging in size from 8.4 to 90.6 kb. A thorough genomic analysis of these replicons detected the presence of numerous genes encoding proteins that potentially perform roles in adaptive processes such as (i) protection against ultraviolet (UV) radiation, (ii) resistance to heavy metals, (iii) transport and metabolism of organic compounds, (iv) sulfur metabolism, and (v) protection against exogenous DNA. Moreover, 10 of the plasmids carry genetic modules enabling conjugal transfer, which may facilitate their spread among bacteria in Antarctic soil. In addition, transposable elements were identified within the analyzed plasmids. Some of these elements carry passenger genes, which suggests that these replicons may be actively changing, and novel genetic modules of adaptive value could be acquired by transposition events. A comparative genomic analysis of plasmids identified in this study and other available Arthrobacter plasmids was performed. This showed only limited similarities between plasmids of Antarctic Arthrobacter strains and replicons of other, mostly mesophilic, isolates. This indicates that the plasmids identified in this study are novel and unique replicons. In addition, a thorough meta-analysis of 247 plasmids of psychrotolerant bacteria was performed, revealing the important role of these replicons in the adaptation of their hosts to extreme environments.

Paracoccus denitrificans PD1222 utilizes hypotaurine via transamination followed by spontaneous desulfination to yield acetaldehyde and, finally, acetate for growth

Hypotaurine (HT; 2-aminoethane-sulfinate) is known to be utilized by bacteria as a sole source of carbon, nitrogen, and energy for growth, as is taurine (2-aminoethane-sulfonate); however, the corresponding HT degradation pathway has remained undefined. Genome-sequenced Paracoccus denitrificans PD1222 utilized HT (and taurine) quantitatively for heterotrophic growth and released the HT sulfur as sulfite (and sulfate) and HT nitrogen as ammonium. Enzyme assays with cell extracts suggested that an HT-inducible HT:pyruvate aminotransferase (Hpa) catalyzes the deamination of HT in an initial reaction step. Partial purification of the Hpa activity and peptide fingerprinting-mass spectrometry (PF-MS) identified the Hpa candidate gene; it encoded an archetypal taurine:pyruvate aminotransferase (Tpa). The same gene product was identified via differential PAGE and PF-MS, as was the gene of a strongly HT-inducible aldehyde dehydrogenase (Adh). Both genes were overexpressed in Escherichia coli. The overexpressed, purified Hpa/Tpa showed HT:pyruvate-aminotransferase activity. Alanine, acetaldehyde, and sulfite were identified as the reaction products but not sulfinoacetaldehyde; the reaction of Hpa/Tpa with taurine yielded sulfoacetaldehyde, which is stable. The overexpressed, purified Adh oxidized the acetaldehyde generated during the Hpa reaction to acetate in an NAD(+)-dependent reaction. Based on these results, the following degradation pathway for HT in strain PD1222 can be depicted. The identified aminotransferase converts HT to sulfinoacetaldehyde, which desulfinates spontaneously to acetaldehyde and sulfite; the inducible aldehyde dehydrogenase oxidizes acetaldehyde to yield acetate, which is metabolized, and sulfite, which is excreted.

Isethionate formation from taurine in Chromohalobacter salexigens: purification of sulfoacetaldehyde reductase

Bacterial generation of isethionate (2-hydroxyethanesulfonate) from taurine (2-aminoethanesulfonate) by anaerobic gut bacteria was established in 1980. That phenomenon in pure culture was recognized as a pathway of assimilation of taurine-nitrogen. Based on the latter work, we predicted from genome-sequence data that the marine gammaproteobacterium Chromohalobacter salexigens DSM 3043 would exhibit this trait. Quantitative conversion of taurine to isethionate, identified by mass spectrometry, was confirmed, and the taurine-nitrogen was recovered as cell material. An eight-gene cluster was predicted to encode the inducible vectorial, scalar and regulatory enzymes involved, some of which were known from other taurine pathways. The genes (Csal_0153-Csal_0156) encoding a putative ATP-binding-cassette (ABC) transporter for taurine (TauAB(1)B(2)C) were shown to be inducibly transcribed by reverse transcription (RT-) PCR. An inducible taurine : 2-oxoglutarate aminotransferase [EC 2.6.1.55] was found (Csal_0158); the reaction yielded glutamate and sulfoacetaldehyde. The sulfoacetaldehyde was reduced to isethionate by NADPH-dependent sulfoacetaldehyde reductase (IsfD), a member of the short-chain alcohol dehydrogenase superfamily. The 27 kDa protein (SDS-PAGE) was identified by peptide-mass fingerprinting as the gene product of Csal_0161. The putative exporter of isethionate (IsfE) is encoded by Csal_0160; isfE was inducibly transcribed (RT-PCR). The presumed transcriptional regulator, TauR (Csal_0157), may autoregulate its own expression, typical of GntR-type regulators. Similar gene clusters were found in several marine and terrestrial gammaproteobacteria, which, in the gut canal, could be the source of not only mammalian, but also arachnid and cephalopod isethionate.

Comparative global transcription analysis of sodium hypochlorite, peracetic acid, and hydrogen peroxide on Pseudomonas aeruginosa

Disinfectants are routinely used in hospitals and health care facilities for surface sterilization. However, the mechanisms by which these disinfectants kill and the extent to which bacteria, including Pseudomonas aeruginosa, are resistant remains unclear. Consequently, P. aeruginosa nosocomial infections result in considerable casualties and economic hardship. Previously, DNA microarrays were utilized to analyze the genome-wide transcription changes in P. aeruginosa after oxidative antimicrobial (sodium hypochlorite, peracetic acid, and hydrogen peroxide) exposure. Simultaneous analysis of these transcriptome datasets provided a comprehensive understanding of the differential responses to these disinfectants. An analysis of variance, functional classification analysis, metabolic pathway analysis, Venn diagram analysis, and principal component analysis revealed that sodium hypochlorite exposure resulted in more genome-wide changes than either peracetic acid or hydrogen peroxide exposures.

Toxicogenomic analysis of sodium hypochlorite antimicrobial mechanisms in Pseudomonas aeruginosa

Sodium hypochlorite (bleach) is routinely used in hospitals and health care facilities for surface sterilization; however, the mechanism of action by which this disinfectant kills and the extent to which Pseudomonas aeruginosa is resistant to sodium hypochlorite have not been elucidated. Consequently, nosocomial infections from P. aeruginosa result in considerable casualties and economic hardship. We report the genome-wide transcriptome response of P. aeruginosa to sodium hypochlorite-induced oxidative stress via the use of DNA microarrays. In addition to a general oxidative stress response, our data revealed a downregulation of virtually all genes related to oxidative phosphorylation and electron transport and an upregulation of many organic sulfur transport and metabolism genes.

Phototrophic utilization of taurine by the purple nonsulfur bacteria Rhodopseudomonas palustris and Rhodobacter sphaeroides

Taurine metabolism by two phototrophically grown purple nonsulfur bacteria enrichment isolates has been examined.Rhodopseudomonas palustris(strain Tau1) grows with taurine as a sole electron donor, sulfur and nitrogen source during photoautotrophic growth.Rhodobacter sphaeroides(strain Tau3) grows on the compound as sole electron donor, sulfur and nitrogen source, and partial carbon source, in the presence of CO2during photoheterotrophic growth. Both organisms utilize an inducible taurine–pyruvate aminotransferase and a sulfoacetaldehyde acetyltransferase. The products of this metabolism are bisulfite and acetyl phosphate. Bisulfite ultimately was oxidized to sulfate, but this was not an adequate source of electrons for photometabolism. Experiments using either [U-14C]taurine or14CO2demonstrated thatRb. sphaeroidesTau3 assimilated the carbon from approximately equimolar amounts of taurine and exogenous CO2. The taurine-carbon assimilation was not diminished by excess non-radioactive bicarbonate. Malate synthase (but not isocitrate lyase) was induced in these taurine-grown cells. It is concluded that assimilation of taurine carbon occurs through an intermediate other than CO2. Similar labelling experiments withRp. palustrisTau1 determined that taurine is utilized only as an electron donor for the reduction of CO2, which contributes all the cell carbon. Photoautotrophic metabolism was confirmed in this organism by the absence of either malate synthase or isocitrate lyase in taurine+CO2-grown cells. Culture collection strains of these two bacteria did not utilize taurine in these fashions.

Dissimilation of the C2 sulfonates

Organosulfonates are widespread in the environment, both as natural products and as xenobiotics; and they generally share the property of chemical stability. A wide range of phenomena has evolved in microorganisms able to utilize the sulfur or the carbon moiety of these compounds; and recent work has centered on bacteria. This Mini-Review centers on bacterial catabolism of the carbon moiety in the C2-sulfonates and the fate of the sulfonate group. Five of the six compounds examined are subject to catabolism, but information on the molecular nature of transport and regulation is based solely on sequencing data. Two mechanisms of desulfonation have been established. First, there is the specific monooxygenation of ethanesulfonate or ethane-1,2-disulfonate. Second, the oxidative, reductive and fermentative modes of catabolism tend to yield the intermediate sulfoacetaldehyde, which is now known to be desulfonated to acetyl phosphate by a thiamin-diphosphate-dependent acetyltransferase. This enzyme is widespread and at least three subgroups can be recognized, some of them in genomic sequencing projects. These data emphasize the importance of acetyl phosphate in bacterial metabolism. A third mechanism of desulfonation is suggested: the hydrolysis of sulfoacetate.

Biochemical and molecular characterization of taurine:pyruvate aminotransferase from the anaerobe Bilophila wadsworthia

Bilophila wadsworthia RZATAU is a Gram-negative bacterium which converts the sulfonate taurine (2-aminoethanesulfonate) to ammonia, acetate and sulfide in an anaerobic respiration. Taurine:pyruvate aminotransferase (Tpa) catalyses the initial metabolic reaction yielding alanine and sulfoacetaldehyde. We purified Tpa 72-fold to apparent homogeneity with an overall yield of 89%. The purified enzyme did not require addition of pyridoxal 5'-phosphate, but highly active enzyme was only obtained by addition of pyridoxal 5'-phosphate to all buffers during purification. SDS/PAGE revealed a single protein band with a molecular mass of 51 kDa. The apparent molecular mass of the native enzyme was 197 kDa as determined by gel filtration, which indicates a homotetrameric structure. The kinetic constants for taurine were: Km = 7.1 mM, Vmax = 1.20 nmol.s-1, and for pyruvate: Km = 0.82 mM, Vmax = 0.17 nmol.s-1. The purified enzyme was able to transaminate hypotaurine (2-aminosulfinate), taurine, beta-alanine and with low activity cysteine and 3-aminopropanesulfonate. In addition to pyruvate, 2-ketobutyrate and oxaloacetate were utilized as amino group acceptors. We have sequenced the encoding gene (tpa). It encoded a 50-kDa peptide, which revealed 33% identity to diaminopelargonate aminotransferase from Bacillus subtilis.

Riding the sulfur cycle--metabolism of sulfonates and sulfate esters in gram-negative bacteria

Sulfonates and sulfate esters are widespread in nature, and make up over 95% of the sulfur content of most aerobic soils. Many microorganisms can use sulfonates and sulfate esters as a source of sulfur for growth, even when they are unable to metabolize the carbon skeleton of the compounds. In these organisms, expression of sulfatases and sulfonatases is repressed in the presence of sulfate, in a process mediated by the LysR-type regulator protein CysB, and the corresponding genes therefore constitute an extension of the cys regulon. Additional regulator proteins required for sulfonate desulfonation have been identified in Escherichia coli (the Cbl protein) and Pseudomonas putida (the AsfR protein). Desulfonation of aromatic and aliphatic sulfonates as sulfur sources by aerobic bacteria is oxygen-dependent, carried out by the alpha-ketoglutarate-dependent taurine dioxygenase, or by one of several FMNH(2)-dependent monooxygenases. Desulfurization of condensed thiophenes is also FMNH(2)-dependent, both in the rhodococci and in two Gram-negative species. Bacterial utilization of aromatic sulfate esters is catalyzed by arylsulfatases, most of which are related to human lysosomal sulfatases and contain an active-site formylglycine group that is generated post-translationally. Sulfate-regulated alkylsulfatases, by contrast, are less well characterized. Our increasing knowledge of the sulfur-regulated metabolism of organosulfur compounds suggests applications in practical fields such as biodesulfurization, bioremediation, and optimization of crop sulfur nutrition.

Microbial desulfonation

Organosulfonates are widespread compounds, be they natural products of low or high molecular weight, or xenobiotics. Many commonly found compounds are subject to desulfonation, even if it is not certain whether all the corresponding enzymes are widely expressed in nature. Sulfonates require transport systems to cross the cell membrane, but few physiological data and no biochemical data on this topic are available, though the sequences of some of the appropriate genes are known. Desulfonative enzymes in aerobic bacteria are generally regulated by induction, if the sulfonate is serving as a carbon and energy source, or by a global network for sulfur scavenging (sulfate-starvation-induced (SSI) stimulon) if the sulfonate is serving as a source of sulfur. It is unclear whether an SSI regulation is found in anaerobes. The anaerobic bacteria examined can express the degradative enzymes constitutively, if the sulfonate is being utilized as a carbon source, but enzyme induction has also been observed. At least three general mechanisms of desulfonation are recognisable or postulated in the aerobic catabolism of sulfonates: (1) activate the carbon neighboring the C-SO3- bond and release of sulfite assisted by a thiamine pyrophosphate cofactor; (2) destabilize the C-SO3- bond by addition of an oxygen atom to the same carbon, usually directly by oxygenation, and loss of the good leaving group, sulfite; (3) an unidentified, formally reductive reaction. Under SSIS control, different variants of mechanism (2) can be seen. Catabolism of sulfonates by anaerobes was discovered recently, and the degradation of taurine involves mechanism (1). When anaerobes assimilate sulfonate sulfur, there is one common, unknown mechanism to desulfonate the inert aromatic compounds and another to desulfonate inert aliphatic compounds; taurine seems to be desulfonated by mechanism (1).

Phosphate starvation-independent 2-aminoethylphosphonic acid biodegradation in a newly isolated strain of Pseudomonas putida, NG2

A strain of Pseudomonas putida that utilized the biogenic organophosphonate 2-aminoethylphosphonic acid as sole carbon and energy, nitrogen and phosphorus source contained 2-aminoethylphosphonic acid: pyruvate aminotransferase and phosphonoacetaldehyde hydrolase (phosphonatase) activities which were inducible by the presence of 2-aminoethylphosphonic acid in the culture medium, regardless of the phosphate status of the cells. Neither of these activities were induced in their phosphate-free or phosphate-replete medium in the absence of 2-aminoethylphosphonic acid. Alkaline phosphatase activity was induced in phosphate limited medium, however, indicating a phosphate-starvation inducible response. In Enterobacter aerogenes IFO 12010, 2-aminoethylphosphonate: pyruvate aminotransferase and phosphonatase activities were induced only when cells were both phosphate limited and supplied with 2-aminoethylphosphonic acid as sole phosphorus source for growth. Neither enzyme activity was induced in phosphate-replete medium, or in medium where both 2-aminoethylphosphonic acid and inorganic phosphate were supplied as sources of phosphorus. The results point to the presence of a substrate inducible 2-aminoethylphosphonic acid biodegradation pathway in the isolated strain of Pseudomonas putida. Uniquely, therefore, the pathway is not under pho regulon control in this strain.

Conversion of taurine into N-chlorotaurine (taurine chloramine) and sulphoacetaldehyde in response to oxidative stress

N-Chlorotaurine (taurine chloramine), formed by treating taurine with hypochlorous acid, was shown to decompose to sulphoacetaldehyde with a first-order rate constant of 9.9+/-0.5 x 10(-4).h-1 at 37 degrees C in 0.1 M phosphate buffer, pH 7.4. Rat liver homogenates accelerated this decay in a process that was proportional to tissue-protein concentration and saturable, with maximum velocity (Vmax) and Km values of 0.28+/-0.01 nmol/min per mg of protein and 37+/-9 microM respectively. This activity was found to be lost on heat denaturation, but retained after dialysis. There was no detectable formation of sulphoacetaldehyde when taurine itself was incubated with the tissue homogenates under the same conditions. Activation of human neutrophils (1.67 x 10(6) cells/ml) with latex beads resulted in a respiratory burst of oxygen-radical production, the products of which were partially sequestered by 12.5 mM taurine. Under these conditions sulphoacetaldehyde was generated at a constant rate of 637+/-18 pmol/h per ml for over 7 h. A non-activated neutrophil suspension contained constant levels of 1.42+/-0.02 nmol/ml sulphoacetaldehyde, as did activated cells incubated in the absence of taurine, a basal level which may indicate a steady turnover of taurine in these cells. Such formation of chlorotaurine and its decay to the aldehyde may be the first steps in the metabolism of taurine to isethionate (2-hydroxyethanesulphonate) that has been demonstrated by various authors to occur in vivo.

Metabolism of sulfoacetate by environmental Aureobacterium sp. and Comamonas acidovorans isolates

Newly isolated environmental strains of Comamonas acidovorans and Aureobacterium sp. were found to mineralize sulfoacetate at concentrations up to at least 50 mM. Transient sulfite release was detected during growth on sulfoacetate, with essentially quantitative accumulation of sulfate. Cell-free conversion of sulfoacetate could not be obtained, but resting-cell studies indicated that cleavage of the C-S bonds of both sulfoacetate and sulfoacetaldehyde was induced only when sulfoacetate was the sole carbon and energy source. A sulfite-oxidizing activity was also induced under these conditions. Sulfoacetaldehyde sulfo-lyase activity was demonstrated by in vitro assay and by gel zymography in extracts of cells grown on sulfoacetate as sole carbon source. This activity was not present in acetate-grown cells, or in cells grown on sulfoacetate as sole sulfur source. Results suggest that sulfoacetate mineralization in both isolates may proceed by a novel pathway which involves an initial reduction to sulfoacetaldehyde and subsequent cleavage of the C-S bond to yield sulfite and acetate. The proposed pathway may be of environmental significance in the mineralization of plant sulfolipid.

Taurine-sulfur assimilation and taurine-pyruvate aminotransferase activity in anaerobic bacteria

We demonstrated the ability of strictly fermentative, as well as facultatively fermentative, bacteria to assimilate sulfonate sulfur for growth. Taurine (2-aminoethanesulfonate) can be utilized by Clostridium pasteurianum C1 but does not support fermentative growth of two Klebsiella spp. and two different Clostridium spp. However, the latter are able to assimilate the sulfur of a variety of other sulfonates (e.g., cysteate, 3-sulfopyruvate, and 3-sulfolactate) anaerobically. A novel taurine-pyruvate aminotransferase activity was detected in cell extracts of C. pasteurianum C1 grown with taurine as the sole sulfur source. This activity was not detected in extracts of other bacteria examined, in C. pasteurianum C1 grown with sulfate or sulfite as the sulfur source, or in a Klebsiella isolate assimilating taurine-sulfur by aerobic respiration. More common aminotransferase activities (e.g., with aspartate or glutamate as the amino donor and pyruvate, oxalacetate, or (alpha)-ketoglutarate as the amino acceptor) were present, no matter what sulfur source was used for growth. Partial characterization of the taurine-pyruvate aminotransferase revealed an optimal temperature of 37(deg)C and a broad optimal pH range of 7.5 to 9.5.

Identification of sulfate starvation-regulated genes in Escherichia coli: a gene cluster involved in the utilization of taurine as a sulfur source

Genes whose expression is regulated by sulfate starvation in Escherichia coli were identified by generating random translational lacZ fusions in the chromosome with the lambda placMu9 system. Nine lacZ fusion strains which expressed beta-galactosidase after growth under sulfate starvation conditions but not after growth in the presence of sulfate were found. These included two strains with insertions in the dmsA and rhsD genes, respectively, and seven strains in which the insertions were located within a 1.8-kb region downstream of hemB at 8.5 minutes on the E. coli chromosome. Analysis of the nucleotide sequence of this region indicated the presence of four open reading frames designated tauABCD. Disruption of these genes resulted in the loss of the ability to utilize taurine (2-aminoethanesulfonate) as a source of sulfur but did not affect the utilization of a range of other aliphatic sulfonates as sulfur sources. The TauA protein contained a putative signal peptide for transport into the periplasm; the TauB and TauC proteins showed sequence similarity to ATP-binding proteins and membrane proteins, respectively, of ABC-type transport systems; and the TauD protein was related in sequence to a dichlorophenoxyacetic acid dioxygenase. We therefore suggest that the proteins encoded by tauABC constitute an uptake system for taurine and that the product of tauD is involved in the oxygenolytic release of sulfite from taurine. The transcription initiation site was detected 26 to 27 bp upstream of the translational start site of tauA. Expression of the tauD gene was dependent on CysB, the transcriptional activator of the cysteine regulon.

Microbial degradation of taurine in fecal cultures from cats given commercial and purified diets

Freshly passed feces were collected from cats (n = 5-7) given cooked and uncooked commercial canned-type diets, casein and soy protein containing purified diets and a commercial extruded diet. The feces were anaerobically cultured in medium containing either taurine, taurocholic acid or [2-3H]taurine for 24 h at 37 degrees C. Taurine degradation in cultures was greatest for cultures from cats receiving diets reputed to cause taurine depletion. Diaminopimelic acid in feces indicated that differences in taurine degradation rate among groups was associated with differences in bacterial numbers in feces. After 6 h of incubation, < 10% of taurocholate and > 60% of taurine remained. Nearly all the tritium on the labeled taurine was recovered as water. These results indicate that deconjugation and deamination are the initial steps in microbial catabolism of taurocholic acid and that enteric microbial growth may be a major determinant of dietary taurine requirement of cats.

Comparative aspects of utilization of sulfonate and other sulfur sources by Escherichia coli K12

Selected biochemical features of sulfonate assimilation in Escherichia coli K-12 were studied in detail. Competition between sulfonate-sulfur and sulfur sources with different oxidation states, such as cysteine, sulfite and sulfate, was examined. The ability of the enzyme sulfite reductase to attack the C-S linkage of sulfonates was directly examined. Intact cells formed sulfite from sulfonate-sulfur. In cysteine-grown cells, when cysteine was present with either cysteate or sulfate, assimilation of both of the more oxidized sulfur sources was substantially inhibited. In contrast, none of three sulfonates had a competitive effect on sulfate assimilation. In studies of competition between different sulfonates, the presence of taurine resulted in a decrease in cysteate uptake by one-half, while in the presence of isethionate, cysteate uptake was almost completely inhibited. In sulfite-grown cells, sulfonates had no competitive effect on sulfite utilization. An E. coli mutant lacking sulfite reductase and unable to utilize isethionate as the sole source of sulfur formed significant amounts of sulfite from isethionate. In cell extracts, sulfite reductase itself did not utilize sulfonate-sulfur as an electron acceptor. These findings indicate that sulfonate utilization may share some intermediates (e.g., sulfite) and regulatory features (repression by cysteine) of the assimilatory sulfate reductive pathway, but sulfonates do not exert regulatory effects on sulfate utilization. Other results suggest that unrecognized aspects of sulfonate metabolism, such as specific transport mechanisms for sulfonates and different regulatory features, may exist.

4-Sulphobenzoate 3,4-dioxygenase. Purification and properties of a desulphonative two-component enzyme system from Comamonas testosteroni T-2

Cell-free extracts of Comamonas testosteroni T-2 grown in toluene-p-sulphonate/salts medium catalyse the conversion of p-sulphobenzoate (PSB) into protocatechuate and sulphite by an NADH-requiring and Fe2(+)-activated dioxygenase. Anion-exchange chromatography of extracts yielded red (A) and yellow (B) protein fractions, both of which were necessary for dioxygenative activity. Further purification of each fraction by hydrophobic interaction chromatography and gel filtration led to two homogeneous protein components (A and B), which together converted 1 mol each of PSB, O2 and NADH into 1 mol each of protocatechuate, sulphite and, presumably, NAD+. The system was named 4-sulphobenzoate 3,4-dioxygenase (PSB dioxygenase system). Monomeric component B (Mr 36,000) was determined to be a reductase that contained 1 mol of FMN and about 2 mol each of iron and inorganic sulphur per mol. This component transferred electrons from NADH to the oxygenase component (A) or to, e.g., cytochrome c. Homodimeric component A (subunit Mr 50,000) of the PSB dioxygenase system contained one [2Fe-2S] centre per subunit and its u.v.-visible-absorption spectrum corresponded to a Rieske-type iron-sulphur centre. The requirement for activation by iron was interpreted as partial loss of mononuclear iron during purification of component A. Component A could be reduced by dithionite or by NADH plus catalytic amounts of component B. The PSB dioxygenase system displayed a narrow substrate range: none of 18 sulphonated or non-sulphonated analogues of PSB showed significant substrate-dependent O2 uptake. The physical properties of the PSB dioxygenase system resemble those of other bacterial multi-component dioxygenase, especially phthalate dioxygenase. However, it differs from most characterized systems in its overall reaction; the product is a vicinal diphenol, and not a dihydrodiol.

Utilization of sulfonic acids as the only sulfur source for growth of photosynthetic organisms

Growth on ethanesulfonic acid as the only sulfur source was found to occur in ten of the 14 green algae tested and in three of the ten cyanobacteria analyzed. Similar growth could not be demonstrated in the higher plant Lemna minor, or in tissue cultures of anise, sunflower and tobacco.Organisms growing on sulfonic acids as the only sulfur source developed an uptake system for ethanesulfonate found neither in algae growing on sulfate nor in algae unable to utilize sulfonic acids for growth. The development of sulfonate transport was not caused by substrate induction, but by conditions of sulfate starvation. The presence of this uptake system was always correlated with an increased sulfate-uptake capacity. Enhanced sulfate uptake was found in all S-deficient and sulfonate-grown cultures tested, indicating sulfate limitation as the regulatory signal. A lag period of 2-2.5 h after transfer to sulfate deprivation was needed for expression of both enhanced sulfate uptake and ethanesulfonate uptake in case of the green alga Chlorella fusca.It is speculated that the availability of sulfate (pool size) or a metabolic product in equilibrium with oxidized sulfur compounds (sulfate ester? sulfolipids?) controls sulfate and sulfonate uptake systems. The principle of (coordinated) derepression by starvation is discussed as a general strategy in photosynthetic organisms.

Measurements of amino acid transport in internally dialyzed giant axons

It is shown that the axoplasmic composition of acidic and neutral amino acids can be controlled effectively by the method of internal dialysis. Direct assay for specific binding and measurement of diffusion coefficients in axoplasm show that there is no significant binding or compartmentalization of amino acids. The dependence of amino acid efflux on substrate concentration can be measured under well-defined, true steady-state conditions. The taurine efflux-concentration relation in the Myxicola giant axon conforms to a second-order Hill equation. This fact is consistent with either a cooperative process or a mechanism in which membrane translocation is not the rate-controlling step. The effluxes of taurine and glycine from squid axon are an order of magnitude smaller than in Myxicola. The efflux-concentration relations are essentially linear up to 200 mM substrate concentration. This result may be produced by specific transporters which have very high asymmetry, or by simple diffusive leak in the absence of specific transporters.

Biosynthesis of the sulfonolipid 2-amino-3-hydroxy-15-methylhexadecane-1-sulfonic acid in the gliding bacterium Cytophaga johnsonae

The biosynthesis of the sulfonolipid 2-amino-3-hydroxy-15-methylhexadecane-1-sulfonic acid (capnine) was studied by measuring the incorporation of possible precursors into the lipid by cells grown in the presence of precursors which were labeled with stable isotopes. Cells grown on yeast extract in the presence of DL-[3,3-2H2]serine contained 40.1 mol% of the protein-bound serine and 5.0 mol% of the protein-bound cysteine derived from the labeled serine. Cells grown in the presence of DL-[3,3-2H2]cystine acid contained 86.4 mol% of the molecules that had two deuteriums. These results are consistent with the possibility that biosynthesis of capnine occurs by the condensation of 13-methylmyristoyl-coenzyme A with cysteic acid, in a reaction analogous to the condensation of a palmitoyl-coenzyme A with serine to form 3-keto-sphinganine during the biosynthesis of sphingolipids.

Taurine catabolism. II. biochemical and genetic evidence for sulfoacetaldehyde sulfo-lyase involvement

Cell-free extracts of Pseudomonas aeruginosa. TAU-5 catalyze the cleavage of chemically or enzymatically synthesized sulfoacetaldehyde to form acetate and sulfite. The activity is enhanced by the presence of thiamine pyrophosphate. The sulfo-lyase responsible for this reaction has been partially purified 9-fold in order to separate it from taurine: pyruvate aminotransferase and to demonstrate its role in taurine catabolism. The sulfo-lyase is induced in organisms grown on taurine but not on other compounds tested. The induction occurs co-ordinately with the induction of the aminotransferase. Mutagenesis of the organism yielded a strain which lacks the sulfo-lyase and in incapable of growing on taurine. A revertant of this strain regained all the prototrophic characterics.