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Marine microbial eukaryotes are ubiquitous, comprised of phylogenetically diverse groups and play key roles in microbial food webs and global biogeochemical cycling. However, their vertical distribution in the deep sea has received little attention. In this study, we investigated the composition and diversity of the eukaryotes of both 0.2–3 μm and >3 μm size fractions from the surface to the hadal zone (8727 m) of the Mariana Trench using Illumina MiSeq sequencing for the 18S rDNA. The microbial eukaryotic community structure differed substantially across size fractions and depths. Operational taxonomic unit (OTU) richness in the >3 μm fraction was higher than that in the 0.2–3 μm fraction at the same depth. For the 0.2–3 μm fraction, sequences of Retaria (Rhizaria) were most abundant in the surface water (53.5%). Chrysophyceae (Stramenopiles) sequences dominated mostly in the samples from water depths below 1795 m. For the >3 μm fraction, sequences of Dinophyceae (Alveolata) were most abundant in surface waters (49.3%) and remained a significant proportion of total sequences at greater depths (9.8%, on average). Retaria sequences were abundant in samples of depths ≥1000 m. Amoebozoa and Apusozoa sequences were enriched in the hadal sample, comprising 38 and 20.4% of total sequences, respectively. Fungi (Opisthokonta) sequences were most abundant at 1759 m in both size fractions. Strong positive associations were found between Syndiniales (mainly MALV-I and MALV-II) and Retaria while negative associations were shown between MALV-II and Fungi in a co-occurrence analysis. This study compared the community structure of microbial eukaryotes in different zones in the deep sea and identified a distinct hadal community in the larger size fraction, suggesting the uniqueness of the eukaryotes in the biosphere in the Mariana Trench. [ABSTRACT FROM AUTHOR]

Phage J2-1 was isolated from surface coastal seawater off Qingdao, China in July 2015. It is the first time that a phage active against Pseudoalteromonas phenolica CECT 7645(T) has been isolated. Morphological analysis using transmission electron microscopy revealed that phage J2-1 has an 87 ± 3 nm head, a 111 ± 3 nm long tail and appears to belong to the family Myoviridae . Genomic analysis of J2-1 revealed a genome size of 142,204 bp with 37.92% G + C content and 180 ORFs. Overall the ORF sequences accounted for 89% of the genome sequence. A genome comparison using the BLASTN tool in the NCBI database found no obvious similarity between J2-1 and other known phages. [ABSTRACT FROM AUTHOR]

• Characterize the composition and distribution of picoeukaryotes in the Nordic Seas. • Exhibit spatial patterns of picoeukaryotic community structures. • Investigate linkages between community structures and different ocean currents. • Using picoeukaryotic communities indicate the environmental heterogeneity. Picoeukaryotes are an important, diverse and spatially variable component of marine microbial communities. However, little is known of their distribution in response to environmental heterogeneity. In this study, to understand the Nordic Seas picoeukaryotic community, eleven surface samples from different water bodies were collected in June 2015. Archaeplastida, mainly Prasinophyceae, was present in all samples and was the largest component in cold waters, while Rhizaria and Alveoata were most abundant in the samples influenced by warm waters. Multivariate analyses showed that samples could be discriminated into groupings, each with its specific dominant species and community structure could precisely reflect the environmental heterogeneity caused by different water masses. This study details the relationships between the picoeukaryotes and complex currents in the Nordic Seas, and provides insight for application of using picoeukaryotes as indicator in future bioassessment for arctic or boreal waters. [ABSTRACT FROM AUTHOR]