Edwardsiella hoshinae,a new species of enterobacteriaceae

Eight strains isolated from birds, reptiles, and water constitute a new DNA hybridization group that is 37–58% related toEdwardsiella tarda and less than 10% related to other species of Enterobacteriaceae (SI nuclease method). This homogeneous group (78–100% relatedness within the group) constitutes a new species that is namedEdwardsiella hoshinae sp. nov. (type strain, CIP 78.56 ATCC 33379). Strains of this species produce acid fromd-mannitol, sucrose,d-trehalose, and salicin, and give a positive malonate test. Seven other strains that produced acid fromd-mannitol and sucrose (but not fromd-trehalose and salicin) and were malonate negative were found to belong to theEdwardsiella tarda DNA hybridization group. The base composition of the DNAs ofE. tarda andE. hoshinae is 55–58 mol% G+C.     

Evidence for NO-dependent vasodilation in the trout (Oncorhynchus mykiss ) coronary system

The effects of l-arginine, and its analogues N ^ω-nitro-l-arginine methyl ester and N ^ω-nitro-l-arginine on vascular resistance were investigated in the intact coronary system of an isolated non-working trout heart preparation. l-Arginine, at 10^–8 mol · l^–1induced a slight vasodilatory effect (max 10%). N ^ω-nitro-l-arginine methyl ester and N ^ω-Nitro-l-arginine in the range 10^–8–10^–4 mol · l^–1 caused dose-dependent increases in coronary resistance. The vasodilatory action of l-arginine was abolished when the preparation was pretreated with 10^–4 mol · l^–1 N ^ω-nitro-l-arginine or N ^ω-nitro-l-arginine methyl ester. Nitroprusside alone at 1 mmol · l^–1 induced a maximum vasodilation (30%) of the coronary system. Methylene blue a known inhibitor of guanylate cyclase, induced a strong vasoconstriction (already significant at 10^–5 mol · l^–1) and was able to overcome the vasodilative effect of nitroprusside. The endothelial nitric oxide agonists acetylcholine and serotonin, established in mammalian vessels, also mediate vasodilation in trout coronary system. In 50% of preparations, acetylcholine induced a biphasic response with vasodilation at low concentration (max 15% at 10^–8 mol · l^–1). Serotonin displayed a dose-response vasodilation in the range 10^–8–10^–4 mol · l^–1 (max 20%). These vasodilative effects were reduced or abolished by 10^–4 mol · l^–1 l-NA. These data support the existence of NO-mediated vasodilation mechanisms in the trout coronary system. Accepted: 1 July 1996     

Metabolic design in the amino-acid-producing bacteriumCorynebacterium glutamicum

The Gram-positive bacteriumCorynebacterium glutamicum is used for the industrial production of amino acids,e.g. ofl-glutamate andl-lysine. By cloning and expressing the various genes of thel-lysine pathway inC. glutamicum we could demonstrate that an increase of the flux ofl-4-aspartaldehydate tol-lysine could be obtained in strains with increased dihydro-dipicolinate synthase activity. Recently we detected that inC. glutamicum two pathways exist for the synthesis ofdl-2,6-diaminopimelate andl-lysine. Mutants defective in one pathway are still able to synthesize enoughl-lysine for growth but thel-lysine secretion is reduced to 50–70%. Using NMR-spectroscopy we could calculate how much of thel-lysine secreted into the medium is synthesizedvia the one and the other pathway. Amplification of the feedback-inhibition-insensitive-homoserine dehydrogenase and homoserine kinase in a highl-lysine-overproducing strain made it possible to channell of the carbon flow from the intermediate 4-aspartaldehydate toward homoserine, resulting in a high accumulation ofl-threonine. For a further flux froml-threonine tol-isoleucine the allosteric control of threonine dehydratase was eliminated. Dedicated to Dr. Z. Vaněk on the occasion of his 70th birthday Presented at theIUMS Congresses '94-7th International Congress of Bacteriology and Applied Microbiology Division, Prague, July 3–8, 1994 (Bacteriological Symposium BS-12Regulation of Microbial Product Overproduction).     

Selection ofRhizopus strains forl(+)-lactic acid andγ-linolenic acid production

The production ofl(+)-lactic acid and formation ofγ-linolenic acid by 50Rhizopus strains growing on saccharidic substrates were investigated. Formation of acids was observed on solid cultivation media but mainly during submerged fermentation. Strains with the highest selectivity of bothl(+)-lactic acid production andγ-linolenic acid formation were tested in a laboratory fermenter. The best producer was treated by UV irradiation to increase the fatty acid content in the biomass, especially that ofγ-linolenic acid. The conversion of 10% saccharidic substrate by this newly prepared strainRhizopus arrhizus CCM 8109 results in more than 95% of theoretical yield ofl(+)-lactic acid and permits a volume productivity of 0.4 gγ-linolenic acid per liter.     

Yeast invertase: Subcellular distribution and possible relationship between the isoenzymes

The intracellular invertase ofSaccharomyces cerevisiae is mainly found in a soluble form (91–95%), while only minor amounts are found bound to the internal (4–8%) and plasma membranes (less than 1%). In the processes of derepression or repression, inhibition of RNA or protein synthesis, or in the presence of 2-deoxy-d-glucose, the levels of the membrane-bound and external activities are modified in a way in which their relation is clear, while the soluble enzyme does not change at all. These results, together with the fact that the membrane-bound and the external enzymes are glycoproteins, suggest a precursor-product relationship between the enzymic forms.     

Transport ofl-tryptophan inSaccharomyces cerevisiae

In addition to the general amino acid transport system (GAP) ofS. cerevisiae l-tryptophan is transported by another system with approximately 25% capacity of GAP, with aK _T of 0.41±0.08 mmol/L and with a similar specificity as GAP (lower inhibition by Met, Pro, Ser, Thr and 2-aminoisobutyric acid; greater inhibition by Glu and His). The pH optimum of this system is at 5.0–5.5, activation energy above the transition point (20°C) was 20 kJ/mol, below the transition point 55 kJ/mol. The transport by this system was virtually unidirectional, efflux amounting to at most 10% into a tryptophan-free medium. The transport itself was blocked by 2,4-dinitrophenol, antimycin A and uranyl nitrate. The system was synthesized de novo during preincubation with glucose=fructose>trehalose >ethanol within 30 min, and was degraded with a half-time of 15 min in the absence of further synthesis. The accumulation ratios ofl-tryptophan ingap1 mutants were concentration-dependent (200∶1 at 1 μmoll-Trp/L, 4∶1 at 2.5 mmoll-Trp/L) and decreased with increasing suspension density from 200∶1 to 5∶1 (for 10 μmoll-Trp/L). The involvement of hydrogen ions in the uptake was clearly demonstrated by the effect of D₂O even if it could not be established by either shifts of pH_out or membrane depolarization.     

Beobachtungen Beim Züchten VonPerillus Bioculatus (Fabr.) (Heteropt., Pentatomidae), Einem Aus Nordamerika Importierten Räuber des Kartoffelkäfers

Zusammenfassung Die PentatomidePerillus bioculatus (Fabr.), ein natürlicher Feind vonLeptinotarsa decemlineata (Say) in Nordamerika, wurde 1956 bis 1958 aus Kanada (Belleville) nach Deutschland (Darmstadt) geschickt und hier für eine sp?tere Verwendung zur biologischen Bek?mpfung des Kartoffelk?fers aufgezogen. Nach einer Schilderung der Lebensweise der einzelnen Entwicklungsstadien wird die Methode beschrieben, die sich beim Import der Wanzeneier aus Amerika und bei deren Versand nach Polen und Ungarn 1959 bew?hrt hat. Die bei der Durchführung von Gruppenzuchten und Massenzuchten erprobten K?figtypen und Verfahren werden geschildert. — Als mittlerer Nahrungsverbrauch eines Individuums w?hrend der Entwicklung zur Imago wurden entweder 285 Kartoffelk?fer-Eier oder 3,7 L₄ oder 5,1 K?fer dieser Art ermittelt. Das letzte (5.) Larvenstadium verbraucht dabei 69% der angegebenen Menge (Abb. 10). Für Erstlarven ist Saugen an Pflanzenstengeln lebenswichtig. Imagines nach der überwinterung verbrauchten meist 0,7–0,8 Kartoffelk?fer oder 0,5 L₄ am Tag. Ohne grosse Verluste k?nnen die Wanzen im Sommer 1–2 Monate hungern; gelegentlich tun sie das sogar spontan. Das Geschlechterverh?ltnis der Imagines betrug 1∶1. Die durchschnittliche Eizahl eines begatteten Weibchens wurde bei Ern?hrung mit Eiern oder Larven vonL. decemlineata mit 95–98 im Monat und mit sch?tzungsweise 100–120 im ganzen Leben ermittelt. Unbegattete oder nur mit K?fern ern?hrte Weibchen legten viel weniger Eier. Die Larvenentwicklung wird durch ungünstige Ern?hrung verlangsamt. Die Mortalit?t in den Zuchten war niedrig, wenn eine günstige Temperatur (tags über 25°C), eine hochwertige Ern?hrung (Eier und Larven des Kartoffelk?fers) und reichlich Versteckpl?tze in den K?figen zur Verfügung standen. Die praktische Durchführung einer Massenzucht wird geschildert, deren Ausbeute in 123 bzw. 91 Tagen das 45- bzw. 67 fache des Ausgangsbestandes war. Die überwinterung vonP. bioculatus ist unter allen bisher bekannten Bedingungen sehr verlustreich. Im Freiland konnte die Art bisher zweimal in Darmstadt überwintern. Obwohl warme Tage sie aus den Verstecken locken, gelang es in zahlreichen Versuchen bei hoher Temperatur und st?ndigem Futterangebot nicht, die Wanzen den Winter über sich fortpflanzen zu lassen; auch die Nahrung wurde monatelang nahezu ganz verweigert. Die Tiere sind im Winter nicht erstarrt, sondern nur lethargisch. — Als Vorbereitung für eine Freilassung der Raubwanze durchgeführte Versuche mit Pflanzenschutz-Mitteln, die auf Kartoffelfeldern weiterhin notwendig sein werden, wurde die verschiedenartige Empfindlichkeit vonP. bioculatus gegenüber einigen Insektiziden und Fungiziden bestimmt (Tab. 6). Besonders schonend waren Kalkarsen und die Phytophthora-Mittel Dithane, Maneb und Kupferoxydul.

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Summary The pentatomidPerillus bioculatus (Fabr.), a predator ofLeptinotarsa decemlineata (Say) in North America, was sent to Germany (Darmstadt) from Canada (Belleville) in 1956–1958 and reared there for later use in biological control against the Colorado potato beetle. After outlining the life history of the different instars a method of shipment is described which was successfully employed in transferring the eggs from America and to Hungary and Poland. Cages and methods used in group- and in mass-rearings are depicted. — The average food intake of one individual ofP. bioculatus during its development from the egg to the adult stage was either 285 eggs or 3,7 fourth instar larvae (L₄) or 5,1 adults ofL. decemlineata. The last larval instar (L₅) consumed approx. 69% of it (Fig. 10). For first instar larvae sucking on plants is obligatory. Adults after hibernation use mostly 0,7–0,8 adult potato beetle or 0,5 L₄ of the prey per day. The predator is able to starve without great losses 1–2 months during summer time; occasionally, this is done spontaneously. The sexual index of adultP. bioculatus was 1∶1. The average egg number per mated female was 95–98 per month when fed with eggs or larvae ofL. decemlineata amounting to approx. 100–120 eggs during lifetime. Unmated females or such fed with beetles only produced much less eggs. Larval development is retarded through unfavourable nourishment. Mortality in the rearings was low when favourable temperature (day-time above 25°C), good food (eggs and larvae ofL. decemlineata) and enough hiding places were available. A practical mass rearing method is described which yielded in 123 or 91 days an 45- or 67- fold increase respectively of the start population. Hibernation ofP. bioculatus results under all conditions so far studied in high mortality. The species hibernated successfully twice in Darmstadt. Although warm temperatures activate them in the field it was not possible to obtain permanent reproduction and food intake in the laboratory at high temperatures and long day conditions (after end of August). The bugs are not motion-less but only lethargic during winter. — In field experiments using pesticides which remain to be necessary on potato fields the differential susceptibility ofP. bioculatus was tested (Tab. 6). Most selective properties were shown by the stomac insecticide calcium arsenate and the fungicides Dithane, Maneb and cuprous oxide.

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Herr Dr.A. Szmidt vom Forstschutz-Institut in Posen (Katedra Ochrony Lasu, Poznań, Polen) arbeitete von M?rz bis Oktober 1959 als Stipendiat der Rockefeller-Foundation in Darmstadt.     

Glucose-2-oxidase activity and accumulation of D-arabino-2-hexosulose in cultures of the basidiomyceteOudemansiella mucida

Submerged cultures of the basidiomyceteOudemansiella mucidd, strain III, accumulate D-arabino-2-hexosulose. The maximum yields during cultivations in shaker flasks or in a laboratory fermentor are 6–12 and 15 mg/ml, respectively (20–50 % conversion of substrate glucose). The accumulation is transient, the aldoketose being again utilized after glucose exhaustion. Its production is stimulated by fluoride ions. The enzyme responsible for the C₍₂₎-specific oxidation ofd-glucose acts as an intracellular oxidase with a maximum activity in the exponential phase of growth.d-arabino-2-Hexosulose was also detected in the cultivation medium of the wood-rotting fungiPleurotus ostreatus, Laetiporus sulphureus, andPhellinus abietis. Part III of the series Enzymatic activity of Basidiomycetes; part II:Folia Microbiol. 13, 334 (1968).     

The genusCandida Berkhout

Glucose and mannose were demonstrated by chromatography in polysaccharides isolated by alkaline and acid extraction from cell walls. A mannan composed ofd-mannopyranose units bound by α(1–2) and α(1–6) bonds was isolated from the polysaccharides of the strainsCandida guilliermondii (Cast.) Langeron et Guerra andCandida guilliermondii var.membranaefaciens. Mannans isolated from these two strains have the same chemical structure and immunochemical properties. The polysaccharide isolated from cell walls of the strainCandida guilliermondii var.nitratophila has a different chemical structure and different immunochemical properties.     

Resting cysts of someChaetoceros species,identified and figured by A. Van der Werff

This note is dedicated to Albert van der Werff (1903–1991), the Dutch diatom expert, distributing his extended knowledge to numerous students interested in aquatic ecology. His drawings of the resting cysts ofChaetoceros affine Lauder andCh. constrictum Gran, not figured in his diatom flora (van der werff andhuls, 1957–1974), are published and discussed. The figures represent a valuable contribution to taxonomical literature. Publication no. 661 Netherlands Institute of Ecology, Centre for Estuarine and Coastal Ecology, Yerseke, The Netherlands.     

Insectivory and its significance to langur diets

Earlier studies on Hanuman langurs (Presbytis entellus) around Jodhpur found them entirely vegetarian (Mohnot, 1974;Winkler, 1988). However, recent observations in the open scrub forests of Jodhpur reveal that scale insects may constitute a regular part of their diet and that insectivory is particularly prevalent in the monsoon months July – September. The insect eating in this habitat seems to support the “Energy/nutrient maximization” hypothesis ofHamilton andBusse (1978).     

Different affinities of the α- and β-anomers ofD-glucose,D-mannose andD-xylose for the glucose uptake system of baker’s yeast

A recording technique for measuring the sugar uptake by cell suspensions using a polarimeter is described. The method makes it possible to calculate the uptake rates of the α-and β-anomers. The constitutive monosaccharide transport system ofSaccharomyces cerevisiae andSaccharomyces fragilis exhibits a higher affinity for the α-anomers ofd-glucose,d-manose andd-xylose than for the corresponding β-anomers, this resulting in a preferential uptake of the α-anomers from a mixture. The α-anomer ofd-xylose is preferred both during influx and efflux. The membrane transport ofd-xylose inSaccharomyces cerevisiae is not associated with a change of the anomer configuration. The facilitated diffusion system appears to possess a regulatory role for the utilization ofd-glucose andd-mannose in both yeast species investigated.     

Untersuchungen zur Apfelwicklerbekämpfung (Carpocapsa pomonella (L.)) mit Hilfe vonTrichogramma embryophagum hartig

Summary In the investigations described the number of parasites (Trichogramma embryophagum hartig (var.cacoeciae marchal)) released on each tree was determined in relation to the size of the trees. Since the sectional area of the trunks, measured below the ramification, is fairly well correlated with the size of the crowns, we correlated the number ofTrichogramma to the sectional area of the trunks. In 1961 we released a number which generally corresponded to 40 wasps for each square centimeter of the sectional area of the trunks. On the trees of one orchardTrichogramma in larval und pupal stage (in eggs ofSitotroga cerealella (oliv.)) were released in small pipes closed with wiregauze; so big predators could not enter and destroy the unhatchedTrichogramma. An apparatus, named by us “Dosierungs-Trommel” (dose drum) (described and illustrated in the text) makes it possible to spray a definite amount of parasitized and unparasitized eggs (ofAnagasta kuehniella) on the crowns of apple trees. The release ofTrichogramma in this way gave better results than the release of the same amount of wasps from containers fastened to the trunks of apple trees.

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Vortrag anl?sslich des Kolloquiums der “Internationalen Arbeitsgruppe für integrierte Sch?dlingsbek?mpfung der C.I.L.B.” — Wageningen (Holland), 5–9 Sept. 1961.     

Développement endoparasitaire et croissance pondérale larvaire du parasitoïdeLixophaga diatraeae [Dip.: Tachinidae] dans un hôte de substitution:Galleria mellonella [Lep.: Pyralidae]

Résumé L'étude du développement endoparasitaire deLixophaga diatraeae (Towns.) dans un h?te de substitutionGalleria mellonella L. a été effectuée par dissections d'h?tes hébergeant des parasito?des d'age connu. Les résultats mentionnés sont obtenus avec en movenge 2.6 parasito?des par h?te. Les élevages ont lieu à 22.5±0.5°C et 85±5 % H.R. avec une photophase de 12 h pourL. diatraeae et à 28±1°C à l'obscurité pourG. mellonella. La croissance pondérale larvaire suit une loi exponentielle et correspond à un temps de doublement du poids de 0,65 j pour les stades 1 et 2 et environ 0,8 j pour le stade 3. Le développement larvaire complet requiert 7,5 j en moyenne. Les stades 1,2 et 3 durent en moyenne respectivement 2,9, 2,5 et 2,1 j. La mue larvaire L₁–L₂ intervient vers 0,23 mg et la mue L₂–L₃ vers 3,2 mg. La larve nouvelle née pèse 12,3 μg et la croissance larvaire représente un facteur multiplicatif maximum d'environ 2 500 fois. Le poids moyen des pupes obtenues est de 14,2 mg.

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Summary Endoparasitic development ofLixophaga diatraeae (Towns.) reared in a substitution hostGalleria mellonella L. was studied by dissections of hosts containing known aged parasitoids. The exposed results are obtained with an average of 2,6 parasitoids per host. Rearing ofL. diatraeae was performed at 22.5±0.5°C and 85±5% R.H. with 12 light hours and rearing ofG. mellonella at 28±1°C in darkness. The larval weight growth is exponential and exhibits a doubling time of 0.65 day for the 1st and 2nd stages and around 0.8 d. for the 3rd stage. Mean complete larval development time is 7.5 days. The 1, 2 and 3 stages last respectively 2.9, 2.5 and 2.1 days. Larval moulting 1–2 happens around 0.23 mg and moulting 2–3 around 3.2 mg. New hatched larva weights 12.3 μg and during larval growth multiplicates its weight by about 2,500. The mean pupal weight is 14.2 mg.

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Nous remercionsColette Ogier pour sa collaboration technique,P. Laviolette etG. Bonnot pour leur lecture critique du manuscrit.     

Populationsdynamische Wirkung vonPerillus bioculatus (Fabr.) [Het. pentatomidae] auf den Kartoffelkäfer

Summary Trials to acclimatize the predatory pentatomidPerillus bioculatus (Fabr.) in Europe did not yet lead to establishment of the predator (Franz, 1966). Practical utilization of the pentatomid in the biological control of the Colorado potato beetle could, at present, only consist in an annual mass release of them for which a permanent mass rearing of the predator would be necessary. Such considerations caused an experiment to test which population density of the predator could lead to economic success. — The results as described above (see also figs. 1–3, tab. 1) show that even during a heavy infestation by the beetle, at a density of two adults per young potato plant, 2,6 L_2–4 ofP. bioculatus per plant would be sufficient to suppress the pest perfectly. To achieve this, large numbers of individuals of the predator would be required which are obtainable for small areas only. On the other hand, during integrated control also a smaller population ofP. bioculatus could be useful.      

Age and composition of carbonate shoreface sediments, Kailua Bay, Oahu, Hawaii

The origin, age, and dynamics of carbonate sediments in Kailua Bay on Oahu, Hawaii, are described. The shoreface (from shoreline to 4 km offshore) consists of a broad (5 km²) fringing coral reef ecosystem bisected by a sinuous, shore-normal, sand-filled paleostream channel 200–300 m wide. The median grain diameter of surface sands is finest on the beach face (<0.3 mm) and increases offshore along the channel axis. Kailua sands are >90% biogenic carbonate, dominated by skeletal fragments of coralline algae (e.g. Porolithon, up to 50%) followed by the calcareous green alga Halimeda (up to 32%), coral fragments (1–24%), mollusc fragments (6–21%), and benthic foraminifera (1–10%). Sand composition and age across the shoreface are correlated to carbonate production. Corals and coralline algae, principal builders of the reef framework, are younger and more abundant in sands along the channel axis and in offshore reefal areas, while Halimeda, molluscs, and foraminifera are younger and more dominant in nearshore waters shoreward of the main region of framework building. Shoreface sediments are relatively old. Of 20 calibrated radiocarbon dates on skeletal constituents of sand, only three are younger than 500 years b.p.; six are 500–1000 years b.p.; six are 1000–2000 years b.p.; and five are 2000–5000 years b.p. Dated fine sands are older than medium to coarse sands and hence may constitute a reservoir of fossil carbonate that is distributed over the entire shoreface. Dominance of fossiliferous sand indicates long storage times for carbonate grains, which tend to decrease in size with age, such that the entire period of relative sea-level inundation (∼5000 years) is represented in the sediment. Despite an apparently healthy modern coral ecosystem, the surficial sand pool of Kailua Bay is dominated by sand reflecting an antecedent system, possibly one that existed under a +1–2 m sea-level high stand during the mid- to late Holocene. Accepted: 20 December 1999     

Imitation of facial gestures by an infant chimpanzee

A nursery-reared infant chimpanzee (Pan troglodytes) was tested for the ability to imitate human facial gestures, following the procedure ofMeltzoff andMoore (1977). The subject was observed between 5 to 15 weeks of ages. The results showed that the subject could imitate tongue protrusion in the age of 5–10 weeks and mouth opening between the ages of 5–11 weeks. However, from 12 to 15 weeks, the infant did not imitate the facial gestures. The present study clearly demonstrated that the infant chimpanzee could imitate human facial gestures in a particular period.     

<Emphasis Type="Italic">Melanopsis</Emphasis> from Al-Qarn,Jordan Valley (Gastropoda: Cerithioidea)

Fossil species ofMelanopsis from a freshwater formation in the Jordan Valley (near Al-Qarn) were investigated and the deposits containing these species are formally described as Al-Qarn Formation. Four species were found:Melanopsis buccinoidea Olivier,M. tchernovi Heller & Sivan,M. costata Olivier andM. aaronsohni Blanckenhorn.Melanopsis costata was represented by two groups, “stepped” and “non-stepped”, the latter differing in its lower figurativity index. Intermediates were found betweenM. buccinoidea andM. tchernovi; they may be hybrids. TheMelanopsis assemblage bridges the faunal gap, in the Jordan Valley, between the 2 Ma lake of ‘Erq el Ahmar on the one hand and the 0.8–1.7 Ma lake of ‘Ubeidiya on the other. This suggests an early Pleistocene age of about 1.8 million years for the Al-Qarn Formation.     

Increased Lipid Peroxidation and Ascorbic Acid Utilization in Testis and Epididymis of Rats Chronically Exposed to Lead

The hypothesis has been recently presented that lead may exert its negative effect at least partially through the increase of reactive oxygen species (ROS) level in tissues. However, little is known about the influence of lead intoxication on equilibrium between generation and elimination of ROS in the male reproductive system. Sexually mature male Wistar rats were given ad libitum 1% of aqueous solution of lead acetate (PbAc) for 9 months. Significantly higher lead concentrations were found in blood [median 7.03 (Q25–Q75: 2.99–7.65) versus 0.18 (0.12–0.99) μg dl⁻¹, P < 0.01], caput epididymis [median 5.51 (Q25–Q75: 4.31–7.83) versus 0.51 (0.11–0.80) μg g⁻¹ d.m., P < 0.001], cauda epididymis [median 5.88 (Q25–Q75: 4.06–8.37) versus 0.61 (0.2 – 1.08) μg g⁻¹ d.m., P < 0.001] and testis [median 1.81 (Q25–Q75: 0.94–2.31) versus 0.17 (0.03–0.3) μg g⁻¹ d.m., P < 0.01] of lead-intoxicated rats when compared to the control. The concentration of ascorbyl radical, generated in vitro from l-ascorbic acid (present in tissues in vivo) was measured by means of Electron Paramagnetic Resonance (EPR) spectroscopy. The EPR signal of ascorbyl radical in caput epididymis, cauda epididymis, testis and liver of lead acetate-treated animals revealed a significant decrease by 53%, 45%, 40% and 69% versus control tissues, respectively. Plasma l-ascorbic acid content measured by high performance liquid chromatography (HPLC) method and total antioxidant status (TAS) measured by means of spectrophotometry were also significantly lower in the intoxicated versus control animals (28% and 21%, respectively). In the group exposed to lead the concentration of lipid peroxide in homogenates of the reproductive system organs was significantly elevated versus control group. It can be assumed that the lower EPR signal was caused by decreased tissue concentrations of l-ascorbic acid. The latter may have resulted from consumption of ascorbic acid for scavenging of ROS excess in tissues of animals chronically exposed to lead.     

Isocitrate dehydrogenase and glyoxylate cycle enzyme activities in Bradyrhizobium japonicum under various growth conditions

Bradyrhizobium japonicum, the nitrogen-fixing symbiotic partner of soybean, was grown on various carbon substrates and assayed for the presence of the glyoxylate cycle enzymes, isocitrate lyase and malate synthase. The highest levels of isocitrate lyase [165–170 nmol min^–1 (mg protein)^–1] were found in cells grown on acetate or β-hydroxybutyrate, intermediate activity was found after growth on pyruvate or galactose, and very little activity was found in cells grown on arabinose, malate, or glycerol. Malate synthase activity was present in arabinose- and malate-grown cultures and increased by only 50–80% when cells were grown on acetate. B. japonicum bacteroids, harvested at four different nodule ages, showed very little isocitrate lyase activity, implying that a complete glyoxylate cycle is not functional during symbiosis. The apparent K _m of isocitrate lyase for d,l-isocitrate was fourfold higher than that of isocitrate dehydrogenase (61.5 and 15.5 μM, respectively) in desalted crude extracts from acetate-grown B. japonicum. When isocitrate lyase was induced, neither the V _max nor the d,l-isocitrate K _m of isocitrate dehydrogenase changed, implying that isocitrate dehydrogenase is not inhibited by covalent modification to facilitate operation of the glyoxylate cycle in B. japonicum. Received: 10 October 1997 / Accepted: 16 January 1998