Ultrastructural characteristics of the salivary glands of of the tick Ixodes persulcatus. II. Type III alveoli of the sucking female

Electron microscope observations were conducted to study changes in the cellular structure of IIId type alveoli of feeding females of I. persulcatus. Within the first 1-2 days of feeding granulosecreting glandular cells "d" and "e" get free of secretory inclusions. After that cells "d" degenerate completely and cells "e" undergo morphological transformations and start to fulfil osmoregulatory functions. From the third day of feeding cytoplasm of cells "e" and basal intersticial cells form a complex labyrinth from a system of branching processes limiting intercellular space from the basal to apical surfaces of alveolar wall. Cells "e" of I. persulcatus in their structure and functional activity closely resemble the earlier described cells "f" in alveoli III of the tick Rhipicephalus appendiculatus.     

Redshift of the purple membrane absorption band and the deprotonation of tyrosine residues at high pH: Origin of the parallel photocycles of trans-bacteriorhodopsin

At high pH (> 8) the 570 nm absorption band of all-trans bacteriorhodopsin (bR) in purple membrane undergoes a small (1.5 nm) shift to longer wavelengths, which causes a maximal increase in absorption at 615 nm. The pK of the shift is 9.0 in the presence of 167 mM KCl, and its intrinsic pK is ~8.3. The red shift of the trans-bR absorption spectrum correlates with the appearance of the fast component in the light-induced L to M transition, and absorption increases at 238 and 297 nm which are apparently caused by the deprotonation of a tyrosine residue and red shift of the absorption of tryptophan residues. This suggests that the deprotonation of a tyrosine residue with an exceptionally low pK (pK_a ≈ 8.3) is responsible for the absorption shift of the chromophore band and fast M formation. The pH and salt dependent equilibrium between the two forms of bR, “neutral” and “alkaline,” bR ↔ bR_a, results in two parallel photocycles of trans-bR at high pH, differing in the rate of the L to M transition. In the pH range 10-11.8 deprotonation of two more tyrosine residues is observed with pK's ~ 10.3 and 11.3 (in 167 mM KCL). Two simple models discussing the role of the pH induced tyrosine deprotonation in the photocycle and proton pumping are presented.

It is suggested that the shifts of the absorption bands at high pH are due to the appearance of a negatively charged group inside the protein (tyrosinate) which causes electrochromic shifts of the chromophore and protein absorption bands due to the interaction with the dipole moments in the ground and excited states of bR (Stark effect). This effect gives evidence for a significant change in the dipole moment of the chromophore of bR upon excitation.

Under illumination alkaline bR forms, besides the usual photocycle intermediates, a long-lived species with absorption maximum at 500 nm (P500). P500 slowly converts into bR_a in the dark. Upon illumination P500 is transformed into an intermediate having an absorption maximum at 380 nm (P380). P380 can be reconverted to P500 by blue light illumination or by incubation in the dark.

     

The coevolution of ixodid ticks and terrestrial vertebrates

Paleontologic and zoogeographic data speak in favour of Mesozoic origin of ixodid ticks. The absence of strict restrictions for the feeding on unusual species of hosts has caused the domination of polyphagy and oligophagy over monophagy among ixodid ticks. The same peculiarities of ixodid ecology are responsible for a restricted part or absence of phylogenetic parallelism with hosts in their evolution. Primary food relations with reptiles are, apparently, preserved only in the genus Aponomma and in many species of Amblyomma while hosts for most species of other genera are mammals and, to a lesser extent, birds. The number of potential hosts in these species can be much greater than that of real ones. Restrictions in the distribution of some species are connected rather with direct effect of unfavourable environmental factors on their nonparasitic stages of the life cycle than with the absence of suitable hosts. During the evolution of natural landscapes and at a shorter stages under the influence of successions or anthropogenic factors ixodids easily adapt themselves to feeding on new species of hosts. So the differentiation of primary and secondary hosts of these parasites is rather difficult.     

The first proof of a possibility of change of temperature norms of insect development as a result of artificial selection for rapid or slow development by the example of the red soldier bug Pyrrhocoris apterus (Heteroptera: Pyrrhocoridae)

For 3-4 generations, selection of the most rapidly and slowly developing nymphs at 28 degrees C was performed on four families of the red soldier bug Pyrrhocoris apterus L. In each generation, duration of development of nymphs was determined at 5 constant temperatures from 20 degrees C to 28 degrees C. From these data there were calculated the linear regression coefficient of the development rate for temperature (the coefficient of the thermolability of development) and the temperature development threshold for each generation. As a result of the selection the mean duration of the nymph development was shortened or increased statistically significantly depending on its direction. The artificial selection for the development duration has been established to change not only this parameter, but also the temperature norms of the insect development. At selection for rapid development the regression line scope (i. e., the regression coefficient value) increased statistically significantly, i. e., development became more dependent on temperature. The temperature threshold of development increased. At selection for slow development the values of the regression coefficient and of the threshold decrease, but these differences were not statistically significant. The effect of artificial selection for duration of development on temperature norms of insect development has been revealed for the first time.     

Xanthorhodopsin: a bacteriorhodopsin-like proton pump with a carotenoid antenna

Xanthorhodopsin is a light-driven proton pump like bacteriorhodopsin, but made more effective for collecting light by its second chromophore, salinixanthin, a carotenoid. Action spectra for transport and fluorescence of the retinal upon excitation of the carotenoid indicate that the carotenoid functions as an antenna to the retinal. The calculated center-to-center distance and angle of the transition moments of the two chromophores are 11 A and 56 degrees , respectively. As expected from their proximity, the carotenoid and the retinal closely interact: tight binding of the carotenoid, as indicated by its sharpened vibration bands and intense induced circular dichroism in the visible, is removed by hydrolysis of the retinal Schiff base, and restored upon reconstitution with retinal. This antenna system, simpler than photosynthetic complexes, is well-suited to study features of excited-state energy migration.     

Mistranslation induced by streptomycin provokes a RecABC/RuvABC-dependent mutator phenotype in Escherichia coli cells.

Translational stress-induced mutagenesis (TSM) refers to the mutator phenotype observed in Escherichia coli cells expressing a mutant allele (mutA or mutC) of the glycine tRNA gene glyV (or glyW). Because of an anticodon mutation, expression of the mutA allele results in low levels of Asp-->Gly mistranslation. The mutA phenotype does not require lexA-regulated SOS mutagenesis functions, and appears to be suppressed in cells defective for RecABC-dependent homologous recombination functions. To test the hypothesis that the TSM response is mediated by non-specific mistranslation rather than specific Asp-->Gly misreading, we asked if streptomycin (Str), an aminoglycoside antibiotic known to promote mistranslation, can provoke a mutator phenotype. We report that Str induces a strong mutator phenotype in cells bearing certain alleles of rpsL, the gene encoding S12, an essential component of the ribosomal 30 S subunit. The phenotype is strikingly similar to that observed in mutA cells in its mutational specificity, as well as in its requirement for RecABC-mediated homologous recombination functions. Expression of Str-inducible mutator phenotype correlates with mistranslation efficiency in response to Str. Thus, mistranslation in general is able to induce the TSM response. The Str-inducible mutator phenotype described here defines a new functional class of rpsL alleles, and raises interesting questions on the mechanism of action of Str, and on bacterial response to antibiotic stress.     

Fertility of triploid hybrids of Prussian carp (<Emphasis Type="Italic">Carassius gibelio</Emphasis>) with common carp (<Emphasis Type="Italic">Cyprinus carpio</Emphasis> L.)

Fertility of backcross triploid hybrids containing one genome of Prussian carp and two genomes of common carp is investigated. The females of hybrids of Prussian carp and common carp (Prussian × common carp) are prolific and produce diploid gametes. Since males of such hybrids are sterile, their reproduction is realized by means of induced gynogenesis. Triploid progeny is obtained by backcrossing female Prussian × common carp with carp males. Among triploids obtained from hybrids F₁ and among hybrids of the first gynogenetic generation, there were no prolific specimens. However, in reproduction of diploid hybrids by means of gynogenesis during six generations, the female fertility in the backcross progeny is restored. From backcross triploid females (daughters of Prussian × common carp of the sixth gynogenetic generation), a viable triploid gynogenetic progeny and a tetraploid backcross (by carp) progeny are obtained. The obtained data may be considered as the experimental proof of the hypothesis of reticular speciation.     

Degradation of p-toluenesulfonate by immobilized Comamonas testosteroni BS1310 (pBS1010) cells

Parameters of degradation of p-toluenesulfonate (TS) by free and agar-embedded Comamonas testosteroni BS1310 (pBS1010) cells were determined. The maximum rate of TS degradation was 25% lower in by immobilized than free cells, equaling 11 nmol x min(-1) x mg(-1) cells. Degradation of TS by both free and immobilized cells was associated with molecular oxygen consumption (molar ratio, 1 : 2). In a plug-flow reactor, the degradation rate was 10.4 nmol x min(-1) x mg(-1) cells. The results can be applied to designing reactors for TS degradation in sewage and developing biosensors.     

Ecological niches of ectoparasites

On mammals and birds communities of ectoparasites are present, which can include scores of ticks, mites and insects species. The parasitizing of arthropods terrestrial vertebrates appeared as far back a the Cretaceous period, and after 70-100 mil. years of the coevolution ectoparasites have assimilated all food resources and localities of the hosts' bodies. To the present only spatial and (to the less extent) trophic niches of parasitic insects, ticks and mites are studied completely enough. The main results these investigations are discussed in the present paper. A high abundance of the communities is reached because of their partition into the number of ecological niches. Host is complex of ecological niches for many ectoparasites species. These niches reiterate in the populations of a species closely related species of hosts and repeat from generation to generation. The each part of host (niche) being assimilated be certain parasite species is available potentially for other species. The partition of host into ecological niches is clearer than the structure of ecosystems including free-living organisms. A real extent of the ecological niches occupation by different species of ticks, mites and insects is considerably lower than a potential maximum. The degree of ecological niches saturation depends on the history of the coevolution of parasites community components, previous colonization be new ectoparasite species and many other ecological factors affecting host-parasite system. The use of the ecological niche conception in parasitology is proved to be rather promising. Ectoparasites communities because of their species diversity, different types of feeding and a number of habitats on host represent convenient models and study of them can contribute significantly to the developmeht of the general conception of ecological niche.     

Water molecule rearrangements around Leu93 and Trp182 in the formation of the L intermediate in bacteriorhodopsin's photocycle

After the chromophore's isomerization in the initial photochemical event in bacteriorhodopsin, the primary photoproduct K makes a thermal transition to the L intermediate, which prepares the pigment for Schiff base deprotonation in the following step (L --> M). Substantial changes in the hydrogen bonding of internal water molecules take place upon L formation. Some of these mobile waters are probably involved in changing the pK of the Schiff base and perhaps that of the proton acceptor Asp85 to allow proton movement [Maeda, A. (2001) Biochemistry (Moscow) 66, 1555-1569]. Here we show that mutations of Leu93 and Trp182, residues close to the 13-methyl group of the chromophore, allow the formation of L at much lower temperatures than in the wild type (80 K instead of 140 K). Moreover, an intense band due to weakly bound water that is peculiar for L was already present in the initial (unphotolyzed) state of each mutant at 2632 cm(-1) (in D2O) but not in the wild type. This unique, intense water band is shifted compared to the L band at 2589 cm(-1) but coincides with the band seen in L', the all-trans photoproduct of wild-type L formed at 80 K. We propose that the L93M and W182F mutations induce changes in the hydrogen bonding of one or more water molecules in the unphotolyzed states of these pigments, which are similar to those H-bonding changes that take place upon formation of L in the wild type, and thus facilitate the formation of L even at 80 K. We infer that L formation involves perturbation of a site which includes retinal, Trp182, and Leu93, and this structure is temporarily stabilized by rearranged hydrogen bonds with water molecules.