3-Methylindole (skatole) and indole production by mixed populations of pig fecal bacteria.

Pig fecal slurries converted added L-tryptophan either to indole without detectable intermediates or to 3-methylindole (skatole) via indole-3-acetate. The initial rate of production of 3-methylindole was greatest at pH 6.5 and less at pH 5.0 and 8.0; the initial rates of indole production were similar at pH 6.5 and 8.0. More than 80% of the tryptophan added was converted to 3-methylindole at pH 5.0; at pH 8.0 85% was converted to indole. Both pathways had similar Km values for tryptophan and similar maximum rates. Indole-3-carbinol and indole-3-acetonitrile completely inhibited the production of 3-methylindole from indole-3-acetate but had no effect on the reactions involving L-tryptophan.     

Dissimilation of Tryptophan and Related Indolic Compounds by Ruminal Microorganisms In Vitro

Intraruminal doses of L-tryptophan cause acute pulmonary edema and emphysema in cattle. The D and L isomers of tryptophan and 22 related indolic compounds were incubated with ruminal microorganisms in vitro. Incubation of L-[U-benzene ring-(14)C]tryptophan with ruminal microorganisms for 24 h resulted in 39% of the added radioactivity being incorporated into skatole, 7% into indole, and 4% into indoleacetate (IAA). D-Tryptophan was not degraded to any of these metabolites. The major pathway of skatole formation from L-tryptophan appeared to be by the decarboxylation of IAA. Incubation of [2-(14)C]IAA with ruminal microorganisms for 24 h resulted in 38% incorporation into skatole. L-[5-Hydroxy]tryptophan was degraded to 5-hydroxyskatole and 5-hydroxyindole, whereas 5-hydroxyindoleacetate was degraded to only 5-hydroxyskatole. Incubation of indolepyruvate, indolelactate, and indolealdehyde with ruminal microorganisms resulted in the formation of both skatole and indole. Under similar conditions, indoleacetaldehyde was converted to IAA and tryptophol. The addition of increasing concentrations of glucose (0 to 110 mM) reduced the formation of both skatole and indole from L-tryptophan and resulted in the accumulation of IAA. Antibiotics reduced the degradation of L-tryptophan to skatole and indole, with kanamycin and neomycin particularly effective in reducing the decarboxylation of IAA to skatole.     

A comparison of features and the microbial constitution of the fresh feces of pigs fed diets supplemented with or without dietary microbes

The features and the constitution of the microbial population of fresh feces were compared between pigs fed a diet supplemented with dietary microbes and pigs given nonsupplemented diets. The former were reared on farm C and the latter on farms A and B. The concentrations of ammonia-N, indole, and skatole of fresh feces were not significantly different between pigs reared on farm C and those raised on farms A and B, but the concentrations of ammonia-N and the skatole of fresh feces were significantly different between pigs reared on farms A and B. The total VFA (volatile fatty acids) concentration of fresh feces in pigs on farm C was slightly lower than in those on farms A and B. Moreover, the molar proportion of the acetic acid in feces in pigs on farm C was lower; inversely, that of propionic and butyric acids was higher in comparison with those on farms A and B. No differences were evident in the total viable counts of feces among pigs reared on the three different farms. Clostridium perfringens was abundant in feces of pigs raised on farms A and B, but it was not detected in pigs reared on farm C. Megasphaerae, bifidobacteria, and clostridia except for C. perfringens were more abundant in the feces of pigs fed a diet supplemented with dietary microbes on farm C, compared with pigs given the nonsupplemented diets on farms A and B.     

Enzymatic production of L-tryptophan from DL-serine and indole by a coupled reaction of tryptophan synthase and amino acid racemase

Enzymatic production of L-tryptophan from DL-serine and indole by a coupled reaction of tryptophan synthase and amino acid racemase was studied. The tryptophan synthase (EC 4.2.1.20) of Escherichia coli catalyzed beta-substitution reaction of L-serine into L-tryptophan and the amino acid racemase (EC 5.1.1.10) of Pseudomonas putida catalyzed the racemization of D-serine simultaneously in one reactor. Under optimal conditions established for L-tryptophan production, a large-scale production of L-tryptophan was carried out in a 200-liter reactor using intact cells of E. coli and P. putida. After 24 h of incubation with intermittent indole feeding, 110 g liter-1 of L-tryptophan was formed in molar yields of 91 and 100% for added DL-serine and indole, respectively. Continuous production of L-tryptophan was also carried out using immobilized cells of E. coli and P. putida. The maximum concentration of L-tryptophan formed was 5.2 g liter-1 (99% molar yield for indole), and the concentration decreased to 4.2 g liter-1 after continuous operation for 20 days.     

Isolation and characteristics of a skatole-producing Lactobacillus sp. from the bovine rumen.

A bacterium that is capable of decarboxylating indoleacetic acid to skatole (3-methylindole) has been isolated from an L-tryptophan enrichment of bovine rumen fluid. The bacterium is a gram-positive, nonmotile, nonsporeforming rod. It is an obligate anaerobe, and strains predominatly produce D-(-)-lactic acid, with smaller amounts of L-(+)-lactic acid and acetic acid, from sugar. All four strains isolated gave a negative reaction to the indole test because they cannot form skatole directly from tryptophan. This is the first report of indoleacetic acid decarboxylation to skatole in pure culture and the demonstration of skatole production by a Lactobacillus species.     

Production L-tryptophan by Escherichia coli cells

Whole cells of Escherichia coli B 10 having high tryptophan synthetase activity were used directly as an enzyme source to produce L-tryptophan from indole and L- or D,L-serine. This strain is tryptophan auxotrophic, which is tryptophanase negative and, in addition, L- and D-serine deaminase negative under production conditions. To avoid inhibition of tryptophan synthetase by a high concentration of indole, nonaqueous organic solvents, Amberlite XAD-2 adsorbent, and nonionic detergents were used as reservoirs of indole in the reaction mixture for the production of L-tryptophan. As a result, different effects were observed on the production of L-tryptophan. Particularly, among the nonionic detergents, Triton X-100 was very efficient. Using Triton X-100 for production of L-tryptophan from indole and L- or D,L-serine by whole cells of Escherichia coli B 10, 14.14 g/100 mL and 14.2 g/100 mL of L-tryptophan were produced at 37 degrees C for 60 h.     

Effects of Dietary Non-Digestible Oligosaccharides on Microbial Characteristics of Ileal Chyme and Faeces in Weaner Pigs

Fructooligosaccharides (FOS) and transgalactooligosaccharides (TOS), which are non-digestible oligosaccharides (NDO), were included at 10 and 40g/kg in an NDO-free control diet at the expense of purified cellulose. Each of the 5 diets was fed to 4 weaner pigs and microbial characteristics of their ileal chyme and faeces were assessed. The NDO-pigs had lower ileal pH than the control pigs. Dietary NDO did not affect the ileal volatile fatty acid concentration, though FOS-pigs had a higher concentration of lactic acid and relatively more iso-valeric acid and less acetic acid than TOS-pigs. The NDO-pigs had lower ileal aerobic bacterial counts than the control pigs, whilst the FOS-pigs had a larger ileal anaerobic bacterial counts than the TOS-pigs. The NDO-pigs had an higher faecal pH and their faecal volatile fatty acid pool contained relatively more iso-butyric acid and iso-valeric acid than the control pigs. The TOS-pigs tended to have higher faecal anaerobic bacterial counts and had a smaller concentration of faecal volatile fatty acid than the FOS-pigs. We concluded that whilst effects at the faecal level may have been partly due to a reduced intake of cellulose, dietary NDO can exert precaecal prebiotic effects in weaner pigs.     

Feeding dried chicory root to pigs decrease androstenone accumulation in fat by increasing hepatic 3β hydroxysteroid dehydrogenase expression

The present study investigated the in vivo effect of chicory root on testicular steroid concentrations and androstenone metabolizing enzymes in entire male pigs. Furthermore, the effect on skatole and indole concentrations in plasma and adipose tissue was investigated. The pigs were divided into two groups; one receiving experimental feed containing 10% dried chicory root for 16 days before slaughter, the control group was fed a standard diet. Plasma, adipose and liver tissue samples were collected at slaughter. Plasma was analyzed for the concentration of testosterone, estradiol, insulin-like growth factor 1 (IGF-1), skatole and indole. Adipose tissue was analyzed for the concentration of androstenone, skatole and indole, while the liver tissue was analyzed for mRNA and protein expressions of 3β-hydroxysteroid dehydrogenase (3β-HSD), sulfotransferase 2A1 and heat-shock protein 70 (HSP70). The results showed that the androstenone concentrations in the adipose tissue of chicory fed pigs were significantly (p<0.05) lower and indole concentrations were higher (p<0.05) compared to control fed pigs. Moreover the chicory root fed pigs had increased mRNA and protein expression of 3β-HSD and decreased HSP70 expression (p<0.05). Testosterone and IGF-1 concentrations in plasma as well as skatole concentrations in adipose tissue were not altered by dietary intake of chicory root. It is concluded that chicory root in the diet reduces the concentration of androstenone in adipose tissue via induction of 3β-HSD, and that these changes were not due to increased cellular stress.     

Production of L-tryptophan

A precursor method of L-tryptophan production using Corynebacterium glutamicum CCM 3358 resistant ot indole was developed. When the dissolved oxygen level was maintained optimal by a periodic pH adjustment and different doses of indole were added the mutant produced 10.5 g/l tryptophan after a 55-h cultivation.     

Feeding Jerusalem artichoke reduced skatole level and changed intestinal microbiota in the gut of entire male pigs

Different levels of dried Jerusalem artichoke were fed to entire male pigs 1 week before slaughter. The objective was to investigate the effect on skatole level in the hindgut and in adipose tissue, as well as the effect on microflora and short-chain fatty acids (SCFA) in the hindgut. Five experimental groups (n = 11) were given different dietary treatments 7 days before slaughtering: negative control (basal diet), positive control (basal diet + 9% chicory-inulin), basal diet + 4.1% Jerusalem artichoke, basal diet + 8.1% Jerusalem artichoke and basal diet + 12.2% Jerusalem artichoke. Samples from colon, rectum, faeces and adipose tissue were collected. Effect of dietary treatment on skatole, indole and androstenone levels in adipose tissue and on skatole, indole, pH, dry matter (DM), microbiota and SCFA in the hindgut was evaluated. Feeding increasing levels of Jerusalem artichoke to entire male pigs reduced skatole in digesta from colon and in faeces (linear, P < 0.01). There was also a tendency towards a decreased level of skatole in adipose tissue (linear, P = 0.06). Feeding Jerusalem artichoke decreased DM content in colon and faeces and pH in colon (linear, P < 0.01). Increasing levels of Jerusalem artichoke resulted in a reduced level of Clostridium perfringens in both colon and rectum (linear, P < 0.05) and a tendency towards decreased levels of enterobacteria in colon (linear, P = 0.05). Further, there was an increase in total amount of SCFA (linear, P < 0.05), acetic acid (linear, P < 0.05) and valerianic acid (linear, P < 0.01) in faeces. In conclusion, adding dried Jerusalem artichoke to diets for entire male pigs 1 week before slaughter resulted in a dose-dependent decrease in skatole levels in the hindgut and adipose tissue. The reduced skatole levels might be related to the decrease in C. perfringens and the increase in SCFA with subsequent reduction in pH.     

Beta-elimination of indole from L-tryptophan catalyzed by bacterial tryptophan synthase: a comparison between reactions catalyzed by tryptophanase and tryptophan synthase

Although tryptophan synthase catalyzes a number of pyridoxal phosphate dependent beta-elimination and beta-replacement reactions that are also catalyzed by tryptophanase, a principal and puzzling difference between the two enzymes lies in the apparent inability of tryptophan synthase to catalyze beta-elimination of indole from L-tryptophan. We now demonstrate for the first time that the beta 2 subunit and the alpha 2 beta 2 complex of tryptophan synthase from Escherichia coli and from Salmonella typhimurium do catalyze a slow beta-elimination reaction with L-tryptophan to produce indole, pyruvate, and ammonia. The rate of the reaction is about 10-fold higher in the presence of the alpha subunit. The rate of indole production is increased about 4-fold when the aminoacrylate produced is converted to S-(hydroxyethyl)-L-cysteine by a coupled beta-replacement reaction with beta-mercaptoethanol. The rate of L-tryptophan cleavage is also increased when the indole produced is removed by extraction with toluene or by condensation with D-glyceraldehyde 3-phosphate to form indole-3-glycerol phosphate in a reaction catalyzed by the alpha subunit of tryptophan synthase. The amount of L-tryptophan cleavage is greatest in the presence of both beta-mercaptoethanol and D-glyceraldehyde 3-phosphate, which cause the removal of both products of cleavage. The cleavage reaction is not due to contaminating tryptophanase since the activity is not inhibited by (3R)-2,3-dihydro-L-tryptophan, a specific inhibitor of tryptophanase, but is inhibited by (3S)-2,3-dihydro-L-tryptophan, a specific inhibitor of tryptophan synthase. The cleavage reaction is also inhibited by D-tryptophan, the product of a slow racemization reaction.(ABSTRACT TRUNCATED AT 250 WORDS)     

Biodiversity of human faecal bacteria isolated from phytic acid enriched chemostat fermenters

BACKGROUND: Myo-inositol hexaphosphate (IP6) or phytic acid is found mostly in cereals and legumes and is thought to possess anti-carcinogenic properties. AIM: To isolate and identify faecal bacteria capable of phytic acid metabolism and to assess the effectiveness of prebiotics (dietary oligosaccharides, metabolised by selective colonic bacteria) in preserving the integrity of phytic acid. METHODS: Faecal samples from three volunteers were used in continuous culture experiments under varying conditions of pH, substrate concentration and dilution rates, seventy three different isolates cultured at steady state were then screened for phytic acid metabolism and identified through partial sequencing of their 16S rRNA genes (16S ribosomal ribonucleic acid). Utilisation of phytic acid was also assessed in a continuous culture system enriched with prebiotic fructooligosaccharides (FOS). RESULTS: Bacteroides spp., Clostridium spp. and facultatively anaerobic bacteria generally appeared to maintain viable counts in the presence of phytic acid. Bifidobacterium spp. and Lactobacillus spp. appeared less able to maintain viable counts in the presence of phytic acid. These results were confirmed by an increase in viable counts of Bacteroides spp., Clostridium spp. and a decrease in viable counts of Bifidobacterium spp. and Lactobacillus spp. once phytic acid was introduced to a FOS enriched continuous culture. CONCLUSIONS: The phytate metabolising biodiversity from the human large intestine does not appear to encompass major bacterial genera associated with beneficial or benign health effects (e.g. Lactobacillus spp. and Bifidobacterium spp).     

Effect of L-tryptophan supplementation on eosinophils and eotaxin in guinea pigs

Eosinophilia Myalgia Syndrome is a hypereosinophilic disorder that appears to result from the ingestion of the dietary supplement L-tryptophan by susceptible individuals. It is unclear if this disease results from tryptophan, contaminants found in tryptophan, individual predisposition (such as immune status and allergies), or some combination of effects. To evaluate effects of L-tryptophan on eosinophil migration, guinea pigs were compared with or without supplemental tryptophan (0.4 g/kg/day), with or without immune sensitization, and with or without immune challenge. Eosinophil counts were obtained from bone marrow, blood, lung, and bronchial alveolar lavage fluid (BAL). Lung cells were obtained to measure eotaxin concentrations in supernates and lysates with or without antigen and calcium ionophore challenge using direct ELISA. Skin biopsies were taken from both non-injected and antigen injection sites. The tryptophan supplemented, antigen-sensitized/antigen-challenged guinea pigs showed a significant decrease in blood eosinophils, compared to control (cellulose) supplemented antigen-sensitized/antigen-challenged guinea pigs [(0.086 +/- 0.023) x 10(6) vs (0.147 +/- 0.021) x 10(6) eosinophils/ml recovered, respectively] with a significant increase in BAL eosinophils [(0.052 +/- 0.008) x 10(6) vs (0.033 +/- 0.005) x 10(6) eosinophils/ml recovered, respectively]. Unchallenged lung cell lysates from tryptophan-supplemented guinea pigs contained significantly less eotaxin compared to cellulose-supplemented guinea pigs regardless of whether they were sensitized (0.006 +/- 0.002 vs 0.027 +/- 0.008 ng/10(6) cells, respectively). No differences were observed in skin biopsies between cellulose and tryptophan groups. These results suggest that L-tryptophan-supplemented guinea pigs have altered eotaxin regulation, a potential mechanism by which human overconsumption of tryptophan dietary supplements could lead to hypereosinophilic disorders in susceptible individuals.     

Effect of faecal soiling on skatole and androstenone occurrence in organic entire male pigs

Production of entire male pigs could be a future strategy for organic pig production. However, production of entire males leads to increased risk of carcasses with elevated boar taint levels. It is hypothesized that skatole levels in pig meat are affected by faecal soiling and that organic housing facilities can increase the risk of pigs being heavily soiled. Therefore, the overall aim of this study was to investigate if increased pig and pen soiling increases skatole concentration in entire male pigs. In five herds, 1174 organic entire male pigs were reared in four batches across two seasons, summer and winter. Measurements of pig and pen soiling, as well as fat skatole and androstenone concentration and human nose sensory tests of fat odour, were performed. Skatole and androstenone concentrations varied greatly within and between herds with a 10% and 90% percentile for the overall population of 0.02 and 2.25 µg/g for skatole and 0.53 and 4.84 µg/g for androstenone. Human nose positive tests averaged 18.3% with great variation between herds and seasons. Pen soiling had significant effects on pig soiling. Moreover, outdoor pen soiling significantly affected skatole concentration in interactions with herd and season (P<0.001 and P=0.003) and affected human nose positive risk in interaction with herd (P=0.005). Soiling on indoor pen areas did not affect skatole levels and no effect on androstenone was found for any pen area. Soiling of pigs affected both skatole and androstenone levels, with the size of the head and abdomen body areas covered in manure showing significant positive effects on skatole concentration. No effect of density of the manure layer was found on either boar taint measure. Herd significantly affected both skatole and androstenone in fat as well as the human nose positive risk. The human nose test revealed no effect from pig soiling. A large variation in the different boar taint measures was found for both high and low scores of pen and pig soiling, and only a small difference in skatole and androstenone concentrations between the high and low soiling categories was found. Therefore, while increasing the hygiene management could be a strategy for reducing boar taint in production of organic entire male pigs, it should be emphasized that other factors would also need to be considered.     

Post-processing microflora and the shelf stability of gari marketed in Port Harcourt

Gari was examined for its post-processing microbial content. Aerobic mesophilic bacteria and fungi were isolated from all samples. The total viable bacterial counts ranged from 2.0 X 10(2) to 8.0 X 10(4) cfu/g. Fungal counts ranged from 1.0 X 10(2) to 1.5 X 10(4) cfu/g. The total viable counts of fresh samples were much lower than those of market and packaged samples. Bacillus, Micrococcus and Proteus spp. were the bacteria isolated, Aspergillus niger, Aspergillus flavus and Penicillium spp. the fungi. Food borne parasites and pathogens such as Staph. aureus and Clostridium perfringens were not found. The gari samples were quite stable, having a shelf life of 3-6 months. The water activities of the samples ranged from 0.52 to 0.68. Based on the microbial counts of the samples, the critical upper limit for the safety of gari was set at 10(4) cfu/g dry sample.     

Production of indole-3-acetic acid and related indole derivatives from L-tryptophan by <Emphasis Type="Italic">Rubrivivax benzoatilyticus</Emphasis> JA2

Rubrivivax benzoatilyticus JA2 produces indoles with simultaneous utilization of L-tryptophan. Fifteen chromatographically distinct indole derivatives were detected from the L-tryptophan-supplemented cultures of R. benzoatilyticus JA2. Nine of these were identified as, indole 3-acetamide, Methoxyindole-3-aldehyde, indole 3-aldehyde, methoxyindole-3-acetic acid, indole 3-acetic acid, indole-3-carboxylic acid, indole-3-acetonitrile, indole, and trisindoline. Tryptophan stable isotope feeding confirmed the indoles produced are from the supplemented L-tryptophan. Indole 3-acetic acid is one of the major products of L-tryptophan catabolism by R. benzoatilyticus JA2 and its production was influenced by growth conditions. Identification of indole 3-acetamide and tryptophan monooxygenase activity suggests indole 3-acetamide routed IAA biosynthesis in R. benzoatilyticus JA2. The study also indicated the possible multiple pathways of IAA biosynthesis in R. benzoatilyticus JA2.     

Production of indolic compounds by rumen bacteria isolated from grazing ruminants

AIM: To screen rumen bacterial cultures and fresh ruminal isolates for indole and skatole production. METHODS AND RESULTS: Culture collection strains and fresh bacterial isolates from rumen contents of sheep and dairy cows were screened for the production of indolic compounds. Clostridium aminophilum FT, Peptostreptococcus ssp. S1, Fusobacterium necrophorum D4 produced indole and Clostridium sticklandii SR produced indoleacetic acid. Fresh isolates from sheep (TrE9262 and TrE7262) and dairy cows (152R-1a, 152R-1b, 152R-3 and 152R-4) produced indole, indolepropionic acid, tryptophol and skatole from the fermentation of tryptophan and indoleacetic acid. Glucose altered the indolic compounds produced in some, but not all, isolates. TrE7262 and 152R-4 were identified as Clostridium sporogenes and 152R-1b as a new Cl. aminophilum strain. Isolates TrE9262, 152R-1a and 152R-3 were not closely related to any described species but belong to Megasphaera, Prevotella and Actinomyces genera, respectively. CONCLUSIONS: Rumen bacteria that produced a range of indolic compounds were identified. Some isolates are distinct from the previously described bacteria and may represent novel species. SIGNIFICANCE AND IMPACT OF THE STUDY: These observations will contribute to understanding skatole and indole formation in the rumen and will lead to methods that control the formation of indolic compounds in pasture-grazed ruminants.     

The tryptophan synthase bienzyme complex transfers indole between the alpha- and beta-sites via a 25-30 A long tunnel

The bacterial tryptophan synthase bienzyme complexes (with subunit composition alpha 2 beta 2) catalyze the last two steps in the biosynthesis of L-tryptophan. For L-tryptophan synthesis, indole, the common metabolite, must be transferred by some mechanism from the alpha-catalytic site to the beta-catalytic site. The X-ray structure of the Salmonella typhimurium tryptophan synthase shows the catalytic sites of each alpha-beta subunit pair are connected by a 25-30 A long tunnel [Hyde, C. C., Ahmed, S. A., Padlan, E. A., Miles, E. W., & Davies, D. R. (1988) J. Biol. Chem. 263, 17857-17871]. Since the S. typhimurium and Escherichia coli enzymes have nearly identical sequences, the E. coli enzyme must have a similar tunnel. Herein, rapid kinetic studies in combination with chemical probes that signal the bond formation step between indole (or nucleophilic indole analogues) and the alpha-aminoacrylate Schiff base intermediate, E(A-A), bound to the beta-site are used to investigate tunnel function in the E. coli enzyme. If the tunnel is the physical conduit for the transfer of indole from the alpha-site to the beta-site, then ligands that block the tunnel should also inhibit the rate at which indole and indole analogues from external solution react with E(A-A). We have found that when D,L-alpha-glycerol 3-phosphate (GP) is bound to the alpha-site, the rate of reaction of indole and nucleophilic indole analogues with E(A-A) is strongly inhibited. These compounds appear to gain access to the beta-site via the alpha-site and the tunnel, and this access is blocked by the binding of GP to the alpha-site. However, when small nucleophiles such as hydroxylamine, hydrazine, or N-methylhydroxylamine are substituted for indole, the rate of quinonoid formation is only slightly affected by the binding of GP. Furthermore, the reactions of L-serine and L-tryptophan with alpha 2 beta 2 show only small rate effects due to the binding of GP. From these experiments, we draw the following conclusions: (1) L-Serine and L-tryptophan gain access to the beta-site of alpha 2 beta 2 directly from solution. (2) The small effects of GP on the rates of the L-serine and L-tryptophan reactions are due to GP-mediated allosteric interactions between the alpha- and beta-sites.(ABSTRACT TRUNCATED AT 400 WORDS)     

Post-processing microflora and the shelf stability of gari marketed in Port Harcourt

Gari was examined for its post-processing microbial content. Aerobic mesophilic bacteria and fungi were isolated from all samples. The total viable bacterial counts ranged from 2.0 × 10² to 8.0 × 10⁴ cfu/g. Fungal counts ranged from 1.0 × 10² to 1.5 × 10⁴ cfu/g. The total viable counts of fresh samples were much lower than those of market and packaged samples. Bacillus, Micrococcus and Proteus spp. were the bacteria isolated, Aspergillus niger, Aspergillus flavus and Penicillium spp. the fungi. Food borne parasites and pathogens such as Staph. aureus and Clostridium perfringens were not found. The gari samples were quite stable, having a shelf life of 3–6 months. The water activities of the samples ranged from 0.52 to 0.68. Based on the microbial counts of the samples, the critical upper limit for the safety of gari was set at 10⁴ cfu/g dry sample.     

Enzymatic synthesis of L-tryptophan from hair acid hydrolysis industries wastewater with tryptophan synthase

An effective method for production of L-tryptophan from hair acid hydrolysis wastewater (HHW) containing L-serine was developed by recombinant tryptophan synthase. This study provides us with an alternative HHW utilization strategy. Tryptophan synthase could efficiently convert L-serine contained in HHW to L-tryptophan at pH 8.0, 40°C and Tween-80 of 0.04%. The enzyme also showed high tolerance to ammonium chloride, a component in HHW. In a scale up study, L-serine conversion rate reach 95.1% with a final L-tryptophan concentration of 33.2 g l(-1).