Community structure and association network of prokaryotic community in surface sediments from the Bering-Chukchi shelf and adjacent sea areas.

The Bering-Chukchi shelf is one of the world's most productive areas and characterized by high benthic biomass. Sedimentary microbial communities play a crucial role in the remineralization of organic matter and associated biogeochemical cycles, reflecting both short-term changes in the environment and more consistent long-term environmental characteristics in a given habitat. In order to get a better understanding of the community structure of sediment-associated prokaryotes, surface sediments were collected from 26 stations in the Bering-Chukchi shelf and adjacent northern deep seas in this study. Prokaryote community structures were analyzed by metabarcoding of the 16S rRNA gene, and potential interactions among prokaryotic groups were analyzed by co-occurrence networks. Relationships between the prokaryote community and environmental factors were assessed. Gammaproteobacteria, Alphaproteobacteria, and Flavobacteriia were the dominant bacterial classes, contributing 35.0, 18.9, and 17.3% of the bacterial reads, respectively. The phototrophic cyanobacteria accounted for 2.7% of the DNA reads and occurred more abundantly in the Bering-Chukchi shelf. Prokaryotic community assemblages were different in the northern deep seas compared to the Bering-Chukchi shelf, represented by the lowered diversity and the increased abundant operational Taxonomic Units (OTU), suggesting that the abundant taxa may play more important roles in the northern deep seas. Correlation analysis showed that latitude, water depth, and nutrients were important factors affecting the prokaryote community structure. Abundant OTUs were distributed widely in the study area. The complex association networks indicated a stable microbial community structure in the study area. The high positive interactions (81.8-97.7%) in this study suggested that symbiotic and/or cooperative relationships accounted for a dominant proportion of the microbial networks. However, the dominant taxa were generally located at the edge of the co-occurrence networks rather than in the major modules. Most of the keystone OTUs were intermediately abundant OTUs with relative reads between 0.01 and 1%, suggesting that taxa with moderate biomass might have considerable impacts on the structure and function of the microbial community. This study enriched the understanding of prokaryotic community in surface sediments from the Bering-Chukchi shelf and adjacent sea areas.

Interspecies competition between Scrippsiella acuminata and three marine diatoms: Growth inhibition and allelopathic effects.

Interactions between Scrippsiella acuminata and three diatoms, Chaetoceros curvisetus, Phaeodactylum tricornutum, and Skeletonema dohrnii, were investigated using bi-algal co-cultures and cell-free and sonicated-cell filtrates in this study. Volatile aldehydes in sonicated filtrates of the three diatoms were analyzed by GC/MS. Furthermore, effects of 2E, 4E-decadienal (2,4-D) on the growth and the photosynthetic efficiency of the four microalgal species were studied. The growth of Sc. acuminata was significantly inhibited by the three diatoms in all co-cultures, and the inhibitory effects were higher under nutrient-rich conditions. Both cell-free and sonicated-cell filtrates of the three diatoms showed significant inhibitions on the growth of Sc. acuminata, which highlighted that diatoms produce allelopathic compounds not only to the surrounding environments but also inside the cells. Fifteen aldehydes were detected in the sonicated-cell filtrates of the three diatoms, and 5, 5, and 12 types of aldehydes were detected in C. curvisetus, P. tricornutum, and Sk. dohrnii, respectively. Polyunsaturated aldehydes (PUAs) composition differed among the three diatom species. Phenylglyoxal (C8H6O2) dominated in C. curvisetus, 2,4-D (C10H16O) predominated in P. tricornutum, and high proportions of 2-hexenal (C6H10O), 2E, 4E-heptadienal (C7H10O), and 2,4-D were detected in Sk. dohrnii. 2,4-D showed significantly inhibitory effects on the growth of algal cells including diatoms themselves in a dose-dependent manner, and photosynthetic efficiency was significantly decreased as well. Sc. acuminata was the most sensitive species. The 96 h EC50 values of 2,4-D on the growth of the four microalgae were 1.64 µmol/L for Sc. acuminata, 3.09 µmol/L for C. curvisetus, 4.93 µmol/L for P. tricornutum, and 8.54 µmol/L for Sk. dohrnii, respectively. The results suggest that PUAs produced by diatoms may help them to take the competitive advantages in phytoplankton community, and thus to sustain diatom-dominated community structure in nutrient rich coastal waters.

Characterization, relative abundances of mRNA transcripts, and subcellular localization of two forms of membrane progestin receptors (mPRs) in the common Chinese cuttlefish, Sepiella japonica.

The membrane progestin receptor (mPR) family has been characterized in several species, including fish, frogs, rats, and humans. Results of previous studies indicate mPRs mediate the rapid, nongenomic action of progestins. In this study, the full-length cDNA of Sepiella japonica mPR-beta (mPRß) and mPR-gamma (mPRγ) were characterized. Furthermore, sjmPR mRNA relative abundances were assessed for different tissues. There was also determination of the subcellular localization of mPRs, and investigation of the effect of sjmPRs on ovarian development via proximate actions on the brain and ovary of S. japonica. Results of tissue distribution assays indicated mPRß and mPRγ transcripts were present predominantly in the brain and ovary. As ovaries developed, the abundance of SjmPRs mRNA transcripts increased and peaked during the interstitial growth phase (III), followed by a marked decrease afterward in both the brain and ovary. In addition, confocal microscopy evaluations of HEK293 T cells expressing the mPRs-EGFP gene indicated both SjmPRß and SjmPRγ were localized in the plasma membrane of HEK293 T cells. Taken together, these findings indicate S. japonica protein is a membrane progestin receptor capable of inducing ovary maturation in cephalopods.