Distribution and bioaccumulation of butyltins in the edible gastropod Odontocymbiola magellanica

Butyltins (BTs) were found in sediments and body tissues of the edible gastropod Odontocymbiola magellanica, in which imposex has been recorded since 2000. BTs in sediments ranged from < MDL to 174.8?ng (Sn) g^?1 for TBT, < MDL to 19.2?ng (Sn) g^?1 for DBT, and < MDL to 71.8?ng (Sn) g^?1 for MBT. In body tissues BTs varied from??1 for TBT, DBT and MBT, respectively. BT concentrations were higher in gonads and digestive glands than in the albumen gland and foot (edible). The highest concentrations of BTs in both sediments and gastropods were found in the harbour area, decreasing with distance to the harbour and areas with less maritime traffic. The Biota-Sediment Accumulation Factor (BSAF) in the different organs was between 0.02–0.42, 0.09–0.35 and 0.08–5.25 for TBT, DBT and MBT, respectively. There were positive correlations between concentrations of BTs in sediments and gastropod body tissues, suggesting that xenobiotic accumulation in O. magellanica occurs mainly through contaminated sediments, rather than water or the food chain. Considering current sediment quality guidelines, our results indicate that acute toxic effects would be expected from TBT exposure, which represents a serious environmental threat for the benthic community. Although the levels of BTs found in the foot of this edible gastropod did not exceed the recommended Tolerable Daily Intake in polluted areas, they should be monitored to ensure the safety of seafood consumers. The alternative antifouling biocides Irgarol and Diuron were not detected in sediments.     

Effects of Rhamnolipids from Pseudomonas aeruginosa DS10-129 on Luminescent Bacteria: Toxicity and Modulation of Cadmium Bioavailability

In this study, the mixture of mono- and di-rhamnolipids produced by Pseudomonas aeruginosa DS10-129 was characterized for its toxicity and modulatory effects on Cd availability to different bacteria. Gram-negative naturally bioluminescent Vibrio fischeri and recombinant bioluminescent Pseudomonas fluorescens, P. aeruginosa, Escherichia coli, and Gram-positive Bacillus subtilis were used as model organisms. Rhamnolipids reduced the bioluminescence of these bacteria in less than a second of exposure even in relatively low concentrations (30-min EC₅₀ 45–167 mg l⁻¹). Toxicity of Cd to Gram-negative bacteria (30-min EC₅₀ values 0.16 mg l⁻¹ for E. coli, 0.96 mg l⁻¹ for P. fluorescens, and 4.4 mg l⁻¹ for V. fischeri) was remarkably (up to 10-fold) reduced in the presence of 50 mg l⁻¹ rhamnolipids. Interestingly, the toxicity of Cd to Gram-positive B. subtilis (30-min EC₅₀ value 0.49 mg l⁻¹) was not affected by rhamnolipids. Rhamnolipids had an effect on desorption of Cd from soil: 40 mg l⁻¹ rhamnolipids increased the water-extracted fraction of Cd twice compared with untreated control. However, this additionally desorbed fraction of Cd remained bound with rhamnolipids and was not available to bacteria. Hence, in carefully chosen concentrations (still effectively complexing heavy metals but not yet toxic to soil bacteria), rhamnolipids could be applied in remediation of polluted areas.     

Additions to the fungi of Jabalpur (madhya pradesh) V

Summary The present paper includes ten parasitic fungi occurring at Jabalpur. These include three new species viz.Hendersonia syzygii Hasija onSyzygium cumini, Phoma ixorae Hasija onIxora sp. andPhyllosticta agarwalii Hasija onDalbergia paniculata. Colletotrichum truncatum (Schw.)Andrus &Moore onAlysicarpus bupleurifolius andPiricularia zingiberi onHedychium sp. are new fungus records for the country.Grewia hirsuta forPhyllosticta sedgwickii DaCosta &Mundkur,Lagerstroemia speciosa forPestalotiopsis versicolor (Speg.)Stey.,Zingiber officinale forCurvularia lunata (Wakker)Boedijn,Musa paradisiaca forDeightoniella torulosa (Syd.)Ellis andFlacourtia ramontchi forAlternaria tenuis Nees exPers. are new hosts record from Jabalpur, India.     

The Speciation of Organotin Compounds in Sediment and Water Samples from the Port of Gdynia

Organotin compounds (OTC) are toxic towards all living organisms. The application of organitin-based antifouling systems is becoming the main source of OTC in the ocean. Harbor sediments and water contain large deposits of organotin compounds due to application of antifouling systems in the shipping industry. OTC contamination presents a potential risk to the marine environment.

Sediment and water samples were collected in 2009 from Gdynia Harbor. For all the analyzed organotin compounds, the mean concentration values were determined: water samples monobutyltin (MBT): 13.2, dibutyltin (DBT): 16.7, tributyltin (TBT): 60.7 (ng cation dm^?3), and sediment samples MBT: 261.4, DBT: 751.9, TBT: 2148.2 (ng cation g^?1 d.w.). The estimated content of monophenyltin (MPhT), diphenyltin (DPhT), triphenyltin (TPhT), monooctyltin (MOT), dioctyltin (DOT), and tricyclohexyltin (TCHT) were below the detection limit of the applied method. It was found that the content of organic matter, the amount of fine fraction, and the pH all play a significant role in the distribution and sorption process of OTC between the water and the sediment on the bottom. Compared to an earlier study, the concentrations of all OTC are much lower, confirming that the applied legislation has had a positive impact.     

Bioconversion of L-tyrosine to L-DOPA by a novel bacterium Bacillus sp. JPJ

l-DOPA is an amino acid derivative and most potent drug used against Parkinson’s disease, generally obtained from Mucuna pruriens seeds. In present communication, we have studied the in vitro production of l-DOPA from l-tyrosine by novel bacterium Bacillus sp. JPJ. This bacterium produced 99.4% of l-DOPA from l-tyrosine in buffer (pH 8) containing 1 mg ml⁻¹ cell mass incubated at 40°C for 60 min. The combination of CuSO₄ and l-ascorbic acid showed the inducing effect at concentrations of 0.06 and 0.04 mg ml⁻¹, respectively. The activated charcoal 2 mg ml⁻¹ was essential for maximum bioconversion of l-tyrosine to l-DOPA and the crude tyrosinase activity was 2.7 U mg⁻¹ of tyrosinase. Kinetic studies showed significant values of Y _p/s (0.994), Q _s (0.500) and q _s (0.994) after optimization of the process. The production of l-DOPA was confirmed by analytical techniques such as HPTLC, HPLC and GC–MS. This is the first report on rapid and efficient production of l-DOPA from l-tyrosine by bacterial source which is more effective than the plant, fungal and yeast systems.     

Additions to the fungi of Jabalpur. (Madhya Pradesh) - I

Summary The present paper describes eight Foliicolous Fungi imperfecti from Jabalpur (India). These include four new species viz.Ramularia alangii Hasija onAlangium lamarckii, Colletotrichum holopteleae Hasija onHoloptelea integrifolia, Gloeosporium wendlandiae Hasija onWendlandia exserta andPhyllosticta macropycnidiai Hasija onSolanum melongena. Discosia artocreas Tode exFr. onTerminalia sp. is a new fungus record for the country raising the total number ofDiscosia from India to five.Heteropogon contortus forCurvularia lunata (Wakker)Boed. andBarleria priniotes forCercospora barlericola Payak &Thirum. are new hosts record from India, andCercospora tridacis-procumbentis Govindu &Thirum. onTridax procumbens is a new record for the state.     

Characterization ofl-leucine transport in the opportunistic yeastsMalassezia furfur andMalassezia pachydermatis

The lipophilic yeastsMalassezia furfur andM. pachydermatis show an initial rapid uptake ofl-leucine followed by slower steady-state rates. At least two independent transport systems forl-leucine were present in both species. The high-affinity system forM. furfur had a K_T of 0.047 µM with a J_max of 222 fM/min/10⁶ cells (65 pM/min/mg dry weight), whereas forM. pachydermatis the K_T was 0.067 µM with a J_max of 709 fM/min/10⁶ cells (89 pM/min/dry weight). The low-affinity system forM. furfur had a K_T of 646 µM with a J_max of 1.62 pM/min/10⁶ cells (0.5 nM/min/mg dry weight) and that ofM. pachydermatis had a K_T of 3.3 µM with a J_max of 9.97 pM/min/10⁶ cells (1.3 nM/min/mg dry weight). Both transport systems were energy-dependent. Cells incubated with Tween 80 showedl-leucine uptake via both transport systems. Cells incubated with a combination of glucose (1%) and Tween 80 (0.01%) showed decreased transport rates for the high-affinity system for both species as compared with cells incubated only with glucose. The low-affinity transport system of both species in the presence of glucose plus Tween 80 showed an initial rapid uptake followed by greater efflux than influx ofl-leucine.l-Leucine demonstrated binding to Tween 80, but the major effect of Tween 80 on membrane transport inMalassezia appears to be on the efflux of transported molecules.     

Purification and properties of D-gluconate dehydratase fromAchromobacter

d-Gluconate dehydratase fromAchromobacter, grown ond-gluconate, was purified 100-fold by a procedure involving ammonium sulfate fractionation and preparative acrylamide gel electrophoresis. The purified enzyme appeared to be homogeneous by disc gel electrophoresis. It is an inducible enzyme with an optimal activity in the pH region 8.4–8.8, a Km value of 2.08 × 10^–2 m ford-gluconate and a molecular weight of 270,000 ± 25,000. Only C₅ and C₆ aldonic acids possessing al-threo configuration at C₂ and C₃ are dehydrated. The dehydration products ofd-gluconate,d-xylonate,d-galactonate,d-fuconate andl-arabonate were identified as 2-keto-3-deoxy compounds by specific colour reactions and thin layer chromatography. Onemm Mg^{+ +} is a powerful activator, 0.1 mm Mn^{+ +} activates poorly and EDTA inhibits. Glutatione, dithiothreitol and mercaptoethanol had no effect, althoughp-chloromercuribenzoate (0.01 mm) decreased enzyme activity.We wish to thank Mr D. Dewettinck for skilful technical assistance. The senior author (J.D.L.) is indebted to the Fonds voor Kollektief en Fundamenteel Onderzoek (Belgium) for research and personnel grants. J.K.-M. is indebted to the Belgian government for a travel and study grant.     

Toxicity of the new pyrethroid insecticide,deltamethrin, to Daphnia magna

The toxicity of deltamethrin, a synthetic pyrethroid insecticide, was determined under standardized conditions (ISO, 1982) in neonates and juveniles of Daphnia magna. Neonates (6 to 24 h old) were more sensitive than juveniles (48 to 72 h old). The 24- and 48-h EC₅₀s (immobilization) in neonates were 0.113 and 0.031 µg l^–1, respectively. The toxicity of deltamethrin was highly toxic. The 96-h EC₅₀ was in the ppt (µg l^–1) range. Toxicity tests with Daphnia may be used to detect toxic residues in water and sediment in areas treated with deltamethrin and other highly toxic pyrethroid pesticides.     

Determination of the isotope distribution in malate-14C with fumarase-negative lactic acid bacteria

No fumarase activity could be found in whole cells or in cell-free crude extracts from Leuconostoc mesenteroides or Lactobacillus curvatus. The degradation of l-malate-4-¹⁴C by these organisms yielded more than 95% of the label as ¹⁴CO₂. It is therefore recommended that these organisms, rather than Lactobacillus plantarum, should be used in the determination of isotope distribution in l-malate-¹⁴C, since L. plantarum exhibits a significant fumarase activity and thus randomizes malate prior to the decarboxylation of this substance by the malolactic enzyme.     

The alternative<Emphasis Type="SmallCaps"> d</Emphasis>-galactose degrading pathway of<Emphasis Type="Italic"> Aspergillus nidulans</Emphasis> proceeds via<Emphasis Type="SmallCaps"> l</Emphasis>-sorbose

The catabolism of d-galactose in yeast depends on the enzymes of the Leloir pathway. In contrast, Aspergillus nidulans mutants in galactokinase (galE) can still grow on d-galactose in the presence of ammonium—but not nitrate—ions as nitrogen source. A. nidulans galE mutants transiently accumulate high (400 mM) intracellular concentrations of galactitol, indicating that the alternative d-galactose degrading pathway may proceed via this intermediate. The enzyme degrading galactitol was identified as l-arabitol dehydrogenase, because an A. nidulans loss-of-function mutant in this enzyme (araA1) did not show NAD⁺-dependent galactitol dehydrogenase activity, still accumulated galactitol but was unable to catabolize it thereafter, and a double galE/araA1 mutant was unable to grow on d-galactose or galactitol. The product of galactitol oxidation was identified as l-sorbose, which is a substrate for hexokinase, as evidenced by a loss of l-sorbose phosphorylating activity in an A. nidulans hexokinase (frA1) mutant. l-Sorbose catabolism involves a hexokinase step, indicated by the inability of the frA1 mutant to grow on galactitol or l-sorbose, and by the fact that a galE/frA1 double mutant of A. nidulans was unable to grow on d-galactose. The results therefore provide evidence for an alternative pathway of d-galactose catabolism in A. nidulans that involves reduction of the d-galactose to galactitol and NAD⁺-dependent oxidation of galactitol by l-arabitol dehydrogenase to l-sorbose.     

The effect of polyamines on tyrosine hydroxylase and L-Aromatic amino acid decarboxylase

The polyamines stimulated tyrosine hydroxylase in whole homogenates of bovine caudate nuclei approximately 2 fold. TheV _max forl-tyrosine increased by 2.3 fold while theK _m s forl-tyrosine and for the cofactor (DMPH₄) were unchanged.l-Aromatic amino acid decarboxylase from whole rat brain homogenate was stimulated by about 40% in the presence of polyamines. These findings suggest that increased polyamine levels associated with increased cellular synthetic activity can modify the synthesis of neurotransmitters.     

Uptake of amino acids by actidione-treated yeast cells

Uptake of glyeine,l-cysteine,l-leucine,l-methionine,l-aspartic acid andl-lysine was investigated in resting cells ofSaccharomyces cerevisiae treated with 0.3mm actidione for blocking protein synthesis. The amino acids were taken up against substantial concentration gradients (up to nearly 1,000∶1 for μm l-cysteine and glycine). They were present in the free form inside the cells. Their unidirectional transmembrane fluxes were under a negative feedback control by the intracellular concentration of the amino acid involved. The amino acids tested apparently employed more than one transport agéncies for their membrane passage, the half-saturation constants being 6.2–7.7×10⁻⁴ m for glycine, 2.5×10⁻⁴ m forl-cysteine, 6×10⁻⁵ and 4×10⁻⁴ m forl-lysine, 3×10⁻⁵ and 6×10⁻⁴ m forl-methionine, 7–18×10⁻⁵ and 1.6×10⁻³ m forl-aspartic acid and 6×10⁻⁵ and 2×10⁻³ m forl-leucine. The specificities of the transport systems are overlapping but there emerges a wide-affinity transport system for glycine, alanine, leucine, methionine, serine, cysteine, phenylalanine, aspartic acid, asparagine, glutamic acid and tryptophan (and possibly for other amino acids), and more specific systems for each of the following: glycine, lysine, methionine, histidine, arginine, and aspartic and glutamic acids. Proline had the peculiar effect of stimulating the transport of all the amino acids tested. The amino acids apparently interacted in the uptake not only by competition for the binding site but also by allotopic inhibition (e.g.l-cysteine) and possibly stimulation (l-proline). The initial rate of uptake of amino acids and their steady-state level of distribution were characterized by identical activation energies: 7.5 kcal/mole forl-lysine, 6.9 kcal/mole forl-aspartic acid, and 13.2 kcal/mole for glycine.     

Sodium gradient- and sodium plus potassium gradient-dependentl-glutamate uptake in renal basolateral membrane vesicles

Summary A membrane preparation enriched in the basolateral segment of the plasma membrane was isolated from the rat renal cortex by a procedure that included separation of particulates on a self-generating Percoll gradient. The uptake ofl-glutamate by the basolateral membrane vesicles was studied. A Na⁺ gradient ([Na⁺] _o >[Na⁺] _i ) stimulated the uptake ofl-glutamate and provided the driving force for the uphill transport of the acidic amino acid, suggesting a Na⁺-l-glutamate cotransport system in the basolateral membrane. A K⁺ gradient ([K⁺] _i >[K⁺] _o ) increased the uptake additionally. This effect was specific for K⁺ (Rb⁺). The action of the K⁺ gradient in enhancing the uptake ofl-glutamate had an absolute requirement for Na⁺. In the presence of Na⁺, but in the absence of a Na⁺ gradient. i.e., [Na⁺] _o =[Na⁺] _i , the K⁺ gradient also energized the concentrative uptake ofl-glutamate. This effect of the K⁺ gradient was not attributable to an alteration in membrane potential. The finding of a concentrative uptake system forl-glutamate energized by both Na⁺ ([Na⁺] _o >[Na⁺] _i and K⁺ ([K⁺] _i >[K⁺] _o ) gradients in the basolateral membrane, combined with previous reports of an ion gradient-dependent uphill transport system for this amino acid in the brush border membrane, suggests a mechanism by whichl-glutamate is accumulated intracellularly in the renal proximal tubule to extraordinarily high concentrations.     

Substrate regulation of ascorbate transport activity in astrocytes

Astrocytes possess a concentrativel-ascorbate (vitamin C) uptake mechanism involving a Na⁺-dependentl-ascorbate transporter located in the plasma membrane. The present experiments examined the effects of deprivation and supplementation of extracellularl-ascorbate on the activity of this transport system. Initial rates ofl-ascorbate uptake were measured by incubating primary cultures of rat astrocytes withl-[¹⁴C]ascorbate for 1 min at 37°C. We observed that the apparent maximal rate of uptake (V _max) increased rapidly (<1 h) when cultured cells were deprived ofl-ascorbate. In contrast, there was no change in the apparent affinity of the transport system forl-[¹⁴C]ascorbate. The increase inV _max was reversed by addition ofl-ascorbate, but notD-isoascorbate, to the medium. The effects of external ascorbate on ascorbate transport activity were specific in that preincubation of cultures withl-ascorbate did not affect uptake of 2-deoxy-D-[³H(G)]glucose. We conclude that the astroglial ascorbate transport system is modulated by changes in substrate availability. Regulation of transport activity may play a role in intracellular ascorbate homeostasis by compensating for regional differences and temporal fluctuations in external ascorbate levels.     

Biotransformation of phenylpyruvic acid to l-phenylalanine using a strain of Pseudomonas fluorescens ATCC 11250 with high transaminase activity

The rate of l-phenylalanine production from phenylpyruvic acid by whole cells of Pseudomonas fluorescens strain ATCC 11250 was greater than 3 g·l^-1 h^-1. Synthesis of transaminase was constitutive but activity was greatest in medium containing d- or l- phenylalanine as sole nitrogen source. Maximum conversion was observed at 34–40° C and at alkaline pH, with over six times initial rate of conversion at pH 12 than at pH 5. The optimum catalyst (cell) concentration was between 10–20 mg ml^-1 dry weight. The initial rate of conversion was directly proportional to phenylpyruvate concentration, up to 4%, but the conversion yield steadily decreased between 2% and 4% substrate concentration. The rate of conversion, as expected, increased as the concentration of glutamate increased. Whole cells were still capable of over 63% conversion after 40 days providing reactions were supplemented with pyridoxal phosphate. Immobilisation of cells in calcium alginate and operation of a packed bed bioreactor enabled the continuous production of l-phenylalanine in concentrations greater than 15 g·l^-1 after 60 days operation.     

Effector molecules from antitumor macrophages induced with OK-432 and cyclophosphamide

Summary The present study was designed to determine whether antitumor activity of macrophages induced with OK-432 and cyclophosphamide was mainly dependent on their ability to produce a soluble factor, that is,l-arginine-dependent nitric oxide as measured by nitrite concentration. Nitrite production by peritoneal macrophages from NIH Swiss mice pretreated with OK-432 (125 KE/kg) i.p. twice at 1-week intervals and with cyclophosphamide (200 mg/kg) i.p. 2 days before the second OK-432 treatment, increased with time for 24 h, and proportionally depended on macrophage numbers. Nitrite production was inhibited by actinomycin D and puromycin but not by mitomycin C.N ^G-Monomethyl-l-arginine, a specific competitive inhibitor ofl-arginine-dependent nitric oxide synthesis, also inhibited production. There was a close correlation between nitrite production and antitumor activity in macrophages from mice pretreated with either OK-432 and cyclophosphamide, OK-432, or thioglycolate broth. OK-432 increased both nitrite production and antitumor activities when added to the macrophage from mice pretreated with OK-432 but not with thioglycolate broth. Both activities of macrophages from mice pretreated with OK-432 and cyclophosphamide were enhanced with increasing concentrations ofl-arginine (0.125–1 mM) in the culture medium.d-Arginine, however, did not substitute forl-arginine. Neither activity was affected by contact between the macrophage and the EL4 cell. The macrophage showed antitumor activity through a membrane filter though the activity was greatly reduced. This antitumor activity of macrophages through a membrane was also inhibited byN ^G-Monomethyl-l-arginine, and increased by OK-432. However, conditioned media, obtained by culturing macrophages induced with OK-432 and cyclophosphamide, inhibited growth of EL4 cells. This activity was carried out by dialysable and non-dialysable factors. One of the dialysable factors was nitrite, an oxidized product of nitric oxide. The antitumor activity of non-dialysable factors was heat-stable and production of factors was increased byN ^G-Monomethyl-l-arginine and OK-432. Also, non-dialysable factors increased both antitumor and nitrite production activities of OK-432-elicited macrophages, when incubated with factors. Such activity of factors was also heat-stable. The production of factors increased with incubation time of macrophages, and was not inhibited byN ^G-Monomethyl-l-arginine. These results indicate that in vitro antitumor activity of macrophages induced with OK-432 and cyclophosphamide was mainly dependent onl-arginine-dependent nitric oxide, and that macrophageassociated soluble factors other than nitric oxide were also needed to inhibit fully tumor growth in vitro.     

Tributyltin and triphenyltin inhibit osteoclast differentiation through a retinoic acid receptor-dependent signaling pathway

Organotin compounds, such as tributyltin (TBT) and triphenyltin (TPT), have been widely used in agriculture and industry. Although these compounds are known to have many toxic effects, including endocrine-disrupting effects, their effects on bone resorption are unknown. In this study, we investigated the effects of organotin compounds, such as monobutyltin (MBT), dibutyltin (DBT), TBT, and TPT, on osteoclast differentiation using mouse monocytic RAW264.7 cells. MBT and DBT had no effects, whereas TBT and TPT dose-dependently inhibited osteoclast differentiation at concentrations of 3-30 nM. Treatment with a retinoic acid receptor (RAR)-specific antagonist, Ro41-5253, restored the inhibition of osteoclastogenesis by TBT and TPT. TBT and TPT reduced receptor activator of nuclear factor-kappaB ligand (RANKL) induced nuclear factor of activated T cells (NFAT) c1 expression, and the reduction in NFATc1 expression was recovered by Ro41-5253. Our results suggest that TBT and TPT suppress osteoclastogenesis by inhibiting RANKL-induced NFATc1 expression via an RAR-dependent signaling pathway.     

Biosynthesis of the nargenicin A<Subscript>1</Subscript> pyrrole moiety from <Emphasis Type="Italic">Nocardia</Emphasis> sp. CS682

A number of structurally diverse natural products harboring pyrrole moieties possess a wide range of biological activities. Studies on biosynthesis of pyrrole ring have shown that pyrrole moieties are derived from l-proline. Nargenicin A₁, a saturated alicyclic polyketide from Nocardia sp. CS682, is a pyrrole-2-carboxylate ester of nodusmicin. We cloned and identified a set of four genes from Nocardia sp. CS682 that show sequence similarity to the respective genes involved in the biosynthesis of the pyrrole moieties of pyoluteorin in Pseudomonas fluorescens, clorobiocin in Streptomyces roseochromogenes subsp. Oscitans, coumermycin A₁ in Streptomyces rishiriensis, one of the pyrrole rings of undecylprodigiosin in Streptomyces coelicolor, and leupyrrins in Sorangium cellulosum. These genes were designated as ngnN4, ngnN5, ngnN3, and ngnN2. In this study, we presented the evidences that the pyrrole moiety of nargenicin A₁ was also derived from l-proline by the coordinated action of three proteins, NgnN4 (proline adenyltransferase), NgnN5 (proline carrier protein), and NgnN3 (flavine-dependent acyl-coenzyme A dehydrogenases). Biosynthesis of pyrrole moiety in nargenicin A₁ is initiated by NgnN4 that catalyzes ATP-dependent activation of l-proline into l-prolyl-AMP, and the latter is transferred to NgnN5 to create prolyl-S-peptidyl carrier protein (PCP). Later, NgnN3 catalyzes the two-step oxidation of prolyl-S-PCP into pyrrole-2-carboxylate. Thus, this study presents another example of a pyrrole moiety biosynthetic pathway that uses a set of three genes to convert l-proline into pyrrole-2-carboxylic acid moiety.     

An evolvant ofEscherichia coli that employs thel-fucose pathway also for growth onl-galactose andd-arabinose

Summary l-Galactose,d-arabinose, andl-fucose form six-membered rings with identical stereoconfigurations. However, onlyl-fucose can serve as the sole carbon and energy source of wild-typeEscherichia coli K-12. A mutant that can grow onl-galactose andd-arabinose was isolated by alternate selection on the two sugars. Thel-fucose pathway became inducible by all three sugars. Transduction into the mutant of the wild-type fuc⁺ region containing both the regulatory and structural genes abolished the novel growth abilities onl-galactose andd-arabinose, whereas transduction into the mutant of a fuc deletion abolished the growth abilities on all three sugars. Introduction of the wild-type fucR⁺ (which encodes the activator protein for the fuc regulon) on a multicopy plasmid depressed the growth abilities of the mutant onl-galactose andd-arabinose, but not onl-fucose. The results suggest that the effector specificity of the activator protein in the mutant was broadened. It is proposed that an adaptive response of an activator-controlled system is more likely than that of a repressor-controlled system to achieve fixation in a population, because the first variant to emerge in response to a novel metabolic demand has a good chance of having an altered specificity of regulation. Such a change entails little or no metabolic liability during the absence of the novel substrate. In contrast, the first variant of a negatively controlled system to emerge has an overwhelming chance of being the result of a random mutation that destroys repressor function. Although negatively controlled systems can be more opportunistic in exploiting new conditions than positively controlled systems, an adaptive change is less likely to become fixed because of the cost associated with gratuitous constitutive gene expression in the absence of the substrate.