Trypanosoma cruzi: identification of specific epimastigote antigens by human immune sera

Soluble antigens from epimastigotes of Trypanosoma cruzi were analyzed by western blot in terms of their reactivity with sera from patients with Chagas' disease. In addition, sera from patients with visceral (AVL) and tegumental leishmaniasis (ATL) were also tested in order to identify cross-reactivities with Trypanosoma cruzi antigens. Twenty eight polypeptides with molecular weights ranging from 14 kDa to 113 kDa were identified with sera from Chagas' disease patients. An extensive cross-reactivity was observed when sera from human visceral leishmaniasis were used, while only a slight cross-reaction was observed with sera from tegumental leishmaniasis. On the other hand, 10 polypeptides specifically reacting with sera from Chagas' disease patients were identified. Among them, the antigens with molecular weights of 46 kDa and 25 kDa reacted with all sera tested and may be good candidates for specific immunodiagnosis of Chagas' disease.     

Stimulation by calcium and carbamoylcholine of the ouabain-sensitive uptake of 86Rb+ in isolated rat pancreatic acinar cells

The uptake of 86Rb+ was assayed in isolated rat pancreatic acinar cells to determine the effect of calcium and carbamoylcholine on the ouabain-sensitive and ouabain-insensitive components. The presence of calcium in the medium bathing the cells during the preincubation and the main incubation periods was needed to preserve in optimum conditions the uptake of 86Rb+, the stimulation by carbamoylcholine and the sensitivity to ouabain. In the presence of calcium, the ouabain-sensitive component of 86Rb+ uptake was higher than the ouabain-insensitive. The ouabain-sensitive component was 3-times lower in cells incubated in a medium lacking calcium and containing 1 mM EGTA, as compared to cells incubated in the presence of calcium. Carbamoylcholine, at 5 X 10(-4) M, stimulated the uptake of 86Rb+ and this effect depended on the presence of calcium in the bathing medium. Maximal stimulation by carbamoylcholine was reached at 0.2 mM calcium. The nett stimulation by carbamoylcholine was inhibited up to 85% by 1 mM ouabain. As judged by digitonin-disruption of plasma membrane, the above-indicated effects were limited to a cytoplasmic pool of 86Rb+ and a leaky plasma membrane could be ruled out. The results suggest that in rat pancreatic acinar cells, carbamoylcholine stimulated the ouabain-sensitive uptake of 86Rb+ and required the presence of calcium in the bathing medium.     

Brief communication: Possible third molar impactions in the hominid fossil record

Impacted third molars affect 15%–20% of modern Americans and Western Europeans. In contrast, third molar impactions have not been reported in the early hominid fossil record. It is uncertain whether the lack of reports reflects an absence of impactions or a failure to recognize them. This communication is intended to raise awareness of the possibility of impactions by describing the appearance of impacted teeth and by noting two possible instances of impaction in early hominids. Specifically, the mandibular third molars of the Sterkfontein specimen, STS52b (Australopithecus africanus), and the left maxillary third molar of the Lake Turkana specimen, KNM-WT17400 (Australopithecus boisei), are positioned in a manner which suggests that they would not have erupted normally. Both specimens also exhibit strong crowding of the anterior dentition, providing further support for the view that these individuals lacked sufficient space for normal eruption of the third molars. Other published reports of dental crowding in the hominid fossil record are noted, and it is suggested that more attention be paid to dental impaction and dental crowding in hominid evolution. © 1993 Wiley-Liss, Inc.     

Coevolution of species colonisation rates controls food-chain length in spatially structured food webs

How the complexity of food webs depends on environmental variables is a long-standing ecological question. It is unclear though how food-chain length should vary with adaptive evolution of the constitutive species. Here we model the evolution of species colonisation rates and its consequences on occupancies and food-chain length in metacommunities. When colonisation rates can evolve, longer food-chains can persist. Extinction, perturbation and habitat loss all affect evolutionarily stable colonisation rates, but the strength of the competition-colonisation trade-off has a major role: weaker trade-offs yield longer chains. Although such eco-evo dynamics partly alleviates the spatial constraint on food-chain length, it is no magic bullet: the highest, most vulnerable, trophic levels are also those that least benefit from evolution. We provide qualitative predictions regarding how trait evolution affects the response of communities to disturbance and habitat loss. This highlights the importance of eco-evolutionary dynamics at metacommunity level in determining food-chain length.     

Purification and molecular properties of ferredoxin-glutamate synthase from Chlamydomonas reinhardii

Ferredoxin-glutamate synthase (EC 1.4.7.1) from Chlamydomonas reinhardii has been purified to electrophoretic homogeneity, with a specific activity of 10.4 units mg^-1 protein, by a method which included chromatography on diethylaminoethyl sephacel and hydroxylapatite, and ferredoxin-sepharose affinity treatment. The enzyme is a single polypeptide chain of M _r 146000 dalton which shows an absorption spectrum with maxima at 278, 377 and 437 nm, and an A₂₇₆/A₄₃₇ absorptivity ratio of 7.0. The anaerobic addition of dithionite results in the loss of the absorption peak at 437 nm, which is restored upon reoxidation of the enzyme with an excess of 2-oxoglutarate, alone or in the presence of glutamine. This indicates the presence in the enzyme of a flavin prosthetic group, which is functional during the catalysis. The ferredoxin-glutamate synthase can be assayed with methyl viologen, chemically reduced with dithionite, but it is unable to use reduced pyridine nucleotide. Azaserine, 6-diazo-5-oxo-norleucine, bromocresol green and p-hydroxymercuribenzoate are potent inhibitors of this activity, which, on the other hand, is stable upon heating at 45°C for 10 min.Abbreviations DEAE-sephacel diethylaminoethyl sephacel - Fd ferredoxin - GOGAT glutaniate synthase (glutamine: -ketoglutarate aminotransferase) - SDS sodium dodecyl sulfate     

Biochemical and genetic characterization of a carbamyl phosphate synthetase mutant of Escherichia coli K12.

An unusual Escherichia coli K12 mutant for carbamyl phosphate synthetase is described. The mutation was generated by bacteriophage MUI insertion and left a 5% residual activity of the enzyme using either ammonia or glutamine as donors. The mutation is recessive to the wild-type allele and maps at or near the pyrA gene, but the mutant requires only arginine and not uracil for growth. By a second block in the pyrB gene it was possible to shift the accumulated carbamyl phosphate to arginine biosynthesis. The Km values and the levels of ornithine activation and inhibition by UMP were normal in the mutant enzyme.     

Feather mites (Acari: Astigmata) and body condition of their avian hosts: a large correlative study

Feather mites are arthropods that live on or in the feathers of birds, and are among the commonest avian ectosymbionts. However, the nature of the ecological interaction between feather mites and birds remains unclear, some studies reporting negative effects of feather mites on their hosts and others reporting positive or no effects. Here we use a large dataset comprising 20 189 measurements taken from 83 species of birds collected during 22 yr in 151 localities from seven countries in Europe and North Africa to explore the correlation between feather mite abundance and body condition of their hosts. We predicted that, if wing‐dwelling feather mites are parasites, a negative correlation with host body condition should be found, while a mutualistic interaction should yield positive correlation. Although negative relationships between feather mite abundance and host body condition were found in a few species of birds, the sign of the correlation was positive in most bird species (69%). The overall effect size was only slightly positive (r =0.066). The effect of feather mite abundance explained <10% of variance in body condition in most species (87%). Results suggest that feather mites are not parasites of birds, but rather that they hold a commensalistic relationship where feather mites may benefit from feeding on uropygial gland secretions of their hosts and birds do not seem to obtain a great benefit from the presence of feather mites.     

Larval and early juvenile development of Lithodes santolla (Molina, 1782) (Decapoda: Anomura: Lithodidae) reared at different temperatures in the laboratory

The southern king crab, Lithodes santolla Molina, is distributed in cold-temperate and subantarctic waters ranging from the southeastern Pacific island of Chiloé (Chile) and the deep Atlantic waters off Uruguay, south to the Beagle Channel (Tierra del Fuego, Argentina/Chile). Recent investigations have shown that its complete larval development from hatching to metamorphosis, comprising three zoeal stages and a megalopa, is fully lecithotrophic, i.e. independent of food. In the present study, larvae were individually reared in the laboratory at seven constant temperatures ranging from 1 to 18 °C, and rates of survival and development through successive larval and early juvenile stages were monitored throughout a period of 1 year. The highest temperature (18 °C) caused complete mortality within 1 week; only a single individual moulted under this condition, 2 days after hatching, to the second zoeal stage, while all other larvae died later in the zoea I stage. At the coldest condition (1 °C), 71% of the larvae reached the zoea III stage, but none of these moulted successfully to a megalopa. A temperature of 3 °C allowed for some survival to the megalopa stage (17-33% in larvae obtained from two different females), but only a single individual passed successfully, 129 days after hatching, through metamorphosis to the first juvenile crab instar. At all other experimental conditions (6, 9, 12 and 15 °C), survival through metamorphosis varied among temperatures and two hatches from 29% to 90% without showing a consistent trend. The time of nonfeeding development from hatching to metamorphosis lasted, on average, from 19 days at 15 °C to 65 days at 6 °C. The relationship between the time of development through individual larval or juvenile stages (D) and temperature (T) was described as a power function (D=aT^b, or log[D]=log[a]blog[T]). The same model was also used to describe the temperature dependence of cumulative periods of development from hatching to later larval or juvenile stages. One year after hatching, the 7th (6 °C) to 9th (15 °C) crab instar was reached. Under natural temperature conditions in the region of origin of our material (Beagle Channel, Argentina), L. santolla should reach metamorphosis in October-December, i.e. ca. 2 months after hatching (taking place in winter and early spring). Within 1 year from hatching, the crabs should grow approximately to juvenile instars VII-VIII. Our results indicate that the early life-history stages of L. santolla tolerate moderate cold stress as well as planktonic food-limitation in winter, implying that this species is well adapted to subantarctic environments with low temperatures and a short seasonal plankton production.