The actinobacterial diversity of Arctic marine sediments was investigated using culture-dependent and culture-independent approaches. A total of 152 strains were isolated from seven different media; 18 isolates were selected for phylogenetic analysis on the basis of their 16S rRNA gene sequences. Results showed that the 18 isolates belonged to a potential novel genus and 10 known genera including Actinotalea, Arthrobacter, Brachybacterium, Brevibacterium, Kocuria, Kytococcus, Microbacterium, Micrococcus, Mycobacterium, and Pseudonocardia. Subsequently, 172 rDNA clones were selected by restriction fragment length polymorphism analysis from 692 positive clones within four actinobacteria-specific 16S rDNA libraries of Arctic marine sediments, and then these 172 clones were sequenced. In total, 67 phylotypes were clustered in 11 known genera of actinobacteria including Agrococcus, Cellulomonas, Demequina, Iamia, Ilumatobacter, Janibacter, Kocuria, Microbacterium, Phycicoccus, Propionibacterium, and Pseudonocardia, along with other, unidentified actinobacterial clones. Based on the detection of a substantial number of uncultured phylotypes showing low BLAST identities (<95 %), this study confirms that Arctic marine environments harbour highly diverse actinobacterial communities, many of which appear to be novel, uncultured species.

Upwelling and internal waves are known to affect the physical and chemical characteristics of marine ecosystems, yet the processes and mechanisms by which internal waves influence phytoplankton biomass and community composition in upwelling regions are still unclear. In this study, a 72‐h time series of observations was conducted in an upwelling system in the northern South China Sea during the summer of 2014. The results showed that the intensity of upwelling was affected by internal waves, which caused nutrient fluctuations in the upper water column. The phytoplankton total chlorophyll a responded positively to the increase of nutrient concentrations, but only after a time lag of 12–16 h. This overall response was the net result of four different types of responses displayed by nine specific phytoplankton groups. All groups that displayed immediate positive responses continued to respond positively at least 12 h later, whereas all groups that responded negatively showed no time‐lagged responses. Based on the vertical distributions of the nine phytoplankton groups and their known physiological traits, we suggest that these different types of response were the net result of a rapid physical transport effect and a time‐lagged, physiological effect via bottom‐up control.

A new Gram-stain-positive, aerobic, non-motile and rod-shaped actinobacterium, designated O1T, was isolated from a deep-sea sediment of the Western Pacific Ocean. Strain O1T showed optimal growth at 30 °C, between pH 6.0 and 8.0, and in the presence of 1–5 % (w/v) NaCl. The predominant menaquinone was MK-8 (H2), and anteiso-C15 : 0 and anteiso-C17 : 0 were the major fatty acids. The diagnostic diamino acid in the cell-wall peptidoglycan was meso-diaminopimelic acid. The major polar lipids were diphosphatidylglycerol, phosphatidylglycerol and one unknown glycolipid. The DNA G+C content of strain O1T was 64.9 mol% and the genome size was 4.17 Mb. Based on a similarity search and phylogenetic analysis of the 16S rRNA gene sequence, strain O1T belonged to the genus Brevibacterium . The values of average nucleotide identity and in silico DNA–DNA hybridization between strain O1T and its close relatives were well below the thresholds used for the delineation of a new species. On the basis of the morphological and chemotaxonomic characteristics, as well as the genotypic data, it is proposed that strain O1T represents a novel species of the genus Brevibacterium , for which the name Brevibacterium profundi sp. nov. is proposed. The type strain is O1T (=JCM 33845T=MCCC 1A16744T).