Description of two new actinosporean types from a brook of Fuji Mountain,Honshu, and from Chitose River,Hokkaido, Japan

Actinospore infection of oligochaetes living in the mud of 3 freshwater biotopes in Japan was studied. Using the cell-well plate method, a new aurantiactinomyxon type was found in 0.77% of the examined Tubifex tubifex oligochaete specimens from a brook near Yamanashi Prefectural Fisheries Experimental Station on Fuji Mountain. In 0.14% of Lumbriculus variagetus collected from Chitose River, near Chitose Salmon Hatchery, a new siedleckiella type was found, while at the same time 8.1% of the Lumbriculus spp. oligochaetes released triactinomyxons of Myxobolus arcticus. Of the examined Rhyacodrilus komarovi oligochaetes collected from the Mena River system, Hokkaido, 0.2, 0.6, 0.5 and 0.8% were infected with echinactinomyxon, neoactinomyxum and 2 types of triactinomyxon spores, respectively, and described in our previous paper. The oligochaetes released actinospores for several weeks. Actinospore infection showed high intensity in positive oligochaetes in the case of all the actinosporean types. Two of the actinospore types (aurantiactinomyxon and siedleckiella) presented here have not been previously described.     

Adaptation to fluctuations in temperature by nine species of bacteria

Rapid environmental fluctuations are ubiquitous in the wild, yet majority of experimental studies mostly consider effects of slow fluctuations on organism. To test the evolutionary consequences of fast fluctuations, we conducted nine independent experimental evolution experiments with bacteria. Experimental conditions were same for all species, and we allowed them to evolve either in fluctuating temperature alternating rapidly between 20°C and 40°C or at constant 30°C temperature. After experimental evolution, we tested the performance of the clones in both rapid fluctuation and in constant environments (20°C, 30°C and 40°C). Results from experiments on these nine species were combined meta‐analytically. We found that overall the clones evolved in the fluctuating environment had evolved better efficiency in tolerating fluctuations (i.e., they had higher yield in fluctuating conditions) than the clones evolved in the constant environment. However, we did not find any evidence that fluctuation‐adapted clones would have evolved better tolerance to any measured constant environments (20°C, 30°C, and 40°C). Our results back up recent empirical findings reporting that it is hard to predict adaptations to fast fluctuations using tolerance curves.     

Comparative genome analysis of potential regulatory elements in the ABCG5-ABCG8 gene cluster

The excretion of sterols from the liver and intestine is regulated by the ABCG5 and ABCG8 transporters. To identify potential regulatory elements, 152 kb of the human ABCG5-ABCG8 gene cluster was sequenced and comparative genome analysis was performed. The two genes are oriented in a head-to-head configuration and are separated by a 374-bp intergenic region, which is highly conserved among several species. Using a reporter construct, the intergenic region was found to act as a bidirectional promoter. A conserved GATA site in the intergenic region was shown by site-directed mutagenesis to act as a repressor for the ABCG5 promoter. The intergenic region was also shown to be partially responsive to treatment by LXR agonists. In summary, several potential regulatory elements were found for the ABCG5 and ABCG8 genes, and the intergenic region was found to act as a bidirectional promoter.     

A mechanism of regulating transmembrane potassium flux through a ligand-mediated conformational switch

The regulation of cation content is critical for cell growth. However, the molecular mechanisms that gate the systems that control K+ movements remain unclear. KTN is a highly conserved cytoplasmic domain present ubiquitously in a variety of prokaryotic and eukaryotic K+ channels and transporters. Here we report crystal structures for two representative KTN domains that reveal a dimeric hinged assembly. Alternative ligands NAD+ and NADH block or vacate, respectively, the hinge region affecting the dimer's conformational flexibility. Conserved, surface-exposed hydrophobic patches that become coplanar upon hinge closure provide an assembly interface for KTN tetramerization. Mutational analysis using the KefC system demonstrates that this domain directly interacts with its respective transmembrane constituent, coupling ligand-mediated KTN conformational changes to the permease's activity.     

Indicative profundal oligochaete assemblages in selected small Swedish lakes

Fifty-seven small- to middle-size lakes of Sweden (size-range from <0.1 to about 200 km²) representing different regions and lake-types were selected for the purpose of demonstrating the indicative value of profundal oligochaete communities also of relatively small lakes. It is well known since previously that profundal oligochaete assemblages of large lakes in Europe may be particularly indicative of the current trophic situation, but little has been known about smaller lakes in this respect. Characterizations based on oligochaete community structure in these lakes could be summarized in eight different groups: Characteristic oligochaete communities in oligotrophic lakes of relatively small size are Spirosperma ferox, Stylodrilus heringianus and Tubifex tubifex. Oligochaete species richness is low (1–3 species) and so is species abundance (<300 specimens m^–2). Very eutrophic lakes of the same size-range are largely dominated by the tubificids Limnodrilus hoffmeisteri and/or Potamothrix hammoniensis. Substitute or complementary species may be T. tubifex. Species richness is usually low (1–3 species), but abundance is high to very high (>5000 specimens m^–2). Mesotrophic to moderately eutrophic lakes of the same size categories contain more species than the above extremes, most of them being fairly tolerant to oxygene deficiency such as Tubifex ignotus, a number of species of the genera Aulodrilus and Limnodrilus and a variety of so-called Ponto-Caspian Potamothrix species, most of them having recently invaded south-eastern Sweden. Species richness is moderate to high (4–8 species), while abundance may vary considerably (range from about 300 to about 5000 specimens m^–2). In this respect, small- to middle-size lakes do not differ much from larger lakes. For the trophic characterization of lake water the mean concentrations of total-phosphorus (in g l^–1) is generally regarded to be the most appropriate measure. The match between characterizations based upon oligochaete community structure and total-phosphorus concentrations is generally very good for large lakes. The present study shows that this applies fairly well also to the majority of the small- to middle-size lakes selected for this study. This has not been shown before. Obvious deviations from this rule could be caused by a scarcity of reliable chemical data, or considerable seasonal shifts in the chemical composition ot the water, which in its turn may be caused by short water residence time. Littoral elements in the fauna, which are generally less indicative, or effects of local inflows may also be more frequent here than in lakes of larger size.     

The intrinsically disordered amino-terminal region of human RecQL4: multiple DNA-binding domains confer annealing,strand exchange and G4 DNA binding

Human RecQL4 belongs to the ubiquitous RecQ helicase family. Its N-terminal region represents the only homologue of the essential DNA replication initiation factor Sld2 of Saccharomyces cerevisiae, and also participates in the vertebrate initiation of DNA replication. Here, we utilized a random screen to identify N-terminal fragments of human RecQL4 that could be stably expressed in and purified from Escherichia coli. Biophysical characterization of these fragments revealed that the Sld2 homologous RecQL4 N-terminal domain carries large intrinsically disordered regions. The N-terminal fragments were sufficient for the strong annealing activity of RecQL4. Moreover, this activity appeared to be the basis for an ATP-independent strand exchange activity. Both activities relied on multiple DNA-binding sites with affinities to single-stranded, double-stranded and Y-structured DNA. Finally, we found a remarkable affinity of the N-terminus for guanine quadruplex (G4) DNA, exceeding the affinities for other DNA structures by at least 60-fold. Together, these findings suggest that the DNA interactions mediated by the N-terminal region of human RecQL4 represent a central function at the replication fork. The presented data may also provide a mechanistic explanation for the role of elements with a G4-forming propensity identified in the vicinity of vertebrate origins of DNA replication.     

Oligochaeta of Lake Taimyr: a preliminary survey

Lake Taimyr in Siberia is northernmost among the world's large lakes: 73°40–75°20N, 99–106°E. The lake area is up to 4650 km² in summer, with a maximum depth of 26 m and a mean depth of only 2.8 m. The ice-free period lasts about three months. The water level sinks 5.5–6 m during winter, so that 85% of the bottom surface is frozen into ice for some time and subjected to negative temperatures, probably down to –20 °C. In artificially melted sediment samples, 75–92% of animals survived. The average summer biomass of zoobenthos is about 1 g m^–2 wet weight, a half of this being formed by Oligochaeta. Altogether 76 samples with 3742 oligochaete specimens collected by V. N. Grëze in 1943–1944 were studied. At least 14 taxa of Tubificidae, Lumbriculidae, and Enchytraeidae were found in the lake, and some more enchytraeids in an adjacent river. Many immature animals could not be identified to species. Naididae were completely lacking probably due to the absence of macrovegetation. The shallow freezing zone is inhabited mostly by Alexandrovia ringulata. The profundal fauna is dominated by Lamprodrilus isoporus, Stylodrilus sp., and Isochaetides sp.