Reproduction of the Androgenetic Population of the Asian Corbicula Clam (Bivalvia: Cyrenidae) in the Northern Dvina River Basin, Russia

The Corbicula clam is one of the most successful invaders of aquatic ecosystems and has invaded all continents except Antarctica. The natural dispersion of Corbicula seems to be limited by low winter temperatures that fall below the lower lethal temperatures (0 to +2 °C). However, Corbicula can be found in colder regions, taking refuge in waters heated by thermal power plants. The purpose of this investigation was to study the gonadal histology, reproductive cycle, and the seasonal changes of shell size structure of the Corbicula clam populations in the warm water discharge of the Arkhangelsk thermal power plant (Northwest Russia). Samples were collected monthly from January 2017 to December 2018 and processed using traditional histological and morphological techniques. The number of reproductive periods varied from year to year. It was established that the Corbicula clam has a continuous reproduction period which may be adaptive in unstable environmental conditions. This reproductive strategy is probably aimed at increasing the reproductive success of the population. Our data expand the understanding of reproductive features of the Corbicula clam in harsh environmental conditions. These results could be applied to control, monitoring, and management measures.

Purification and Characterization of Hemagglutinating Proteins from Poker-Chip Venus (Meretrix lusoria) and Corbicula Clam (Corbicula fluminea)

Hemagglutinating proteins (HAPs) were purified from Poker-chip Venus (Meretrix lusoria) and Corbicula clam (Corbicula fluminea) using gel-filtration chromatography on a Sephacryl S-300 column. The molecular weights of the HAPs obtained from Poker-chip Venus and Corbicula clam were 358 kDa and 380 kDa, respectively. Purified HAP from Poker-chip Venus yielded two subunits with molecular weights of 26 kDa and 29 kDa. However, only one HAP subunit was purified from Corbicula clam, and its molecular weight was 32 kDa. The two Poker-chip Venus HAPs possessed hemagglutinating ability (HAA) for erythrocytes of some vertebrate animal species, especially tilapia. Moreover, HAA of the HAP purified from Poker-chip Venus was higher than that of the HAP of Corbicula clam. Furthermore, Poker-chip Venus HAPs possessed better HAA at a pH higher than 7.0. When the temperature was at 4°C–10°C or the salinity was less than 0.5‰, the two Poker-chip Venus HAPs possessed better HAA compared with that of Corbicula clam.

Oscillibacter valericigenes gen. nov., sp. nov., a valerate-producing anaerobic bacterium isolated from the alimentary canal of a Japanese corbicula clam

A mesophilic, strictly anaerobic bacterium, strain Sjm18-20T, was isolated from the alimentary canal of a Japanese corbicula clam. Cells of strain Sjm18-20T were Gram-negative, non-sporulating, straight to slightly curved rods, 2.5–6.0 μm long, and were motile with oscillatory movements by means of peritrichous flagella. Cells elongated to 30 μm after prolonged cultivation. Optimum growth was observed at 30 °C and pH 6.0–6.5. Growth occurred below 4.0 % (w/v) NaCl. Strain Sjm18-20T produced acid from d-glucose and a few pentoses such as l-arabinose, d-ribose and d-xylose. n-Valeric acid was the major end product from glucose. The genomic DNA G+C content of strain Sjm18-20T was 52.9 mol%. Phylogenetic analysis based on the 16S rRNA gene revealed that strain Sjm18-20T could be accommodated in clostridial cluster IV of the low-G+C-content Gram-positive bacteria and that the closest neighbour of this organism (92.6–92.9 % similarity) was the cloned 16S rRNA gene sequence of a not-yet cultured bacterium, thought to represent Oscillospira guilliermondii. The nearest cultivated neighbours of strain Sjm18-20T were Clostridium orbiscindens DSM 6740T and Clostridium viride T2-7T, with sequence similarities of 91.3 and 89.1 %, respectively. On the basis of phenotypic features and phylogenetic position, it is proposed that this isolate represents a novel species in a new genus, Oscillibacter valericigenes gen. nov., sp. nov. The type strain of Oscillibacter valericigenes is Sjm18-20T (=NBRC 101213T =DSM 18026T).