A taxonomic study was carried out on bacterial strain H3^T, which was isolated from the toxic marine diatom Pseudo-nitzschia multiseries. Cells of strain H3^T were Gram-stain-negative, rod-shaped, non-motile and capable of reducing nitrate to nitrite, but not denitrification. Growth was observed at NaCl concentrations of 1–9 %, pH 6–12 and 10–37 °C. It was unable to degrade aesculin or gelatin. The dominant fatty acids (>10 %) were C_18 : 1ω7c/ω6c (summed feature 8) and C_16 : 0. The respiratory ubiquinone was Q10. The major lipids were phosphatidylethanolamine, phosphatidylglycerol, an aminolipid and one unknown lipid, and the minor lipids were two phospholipids and three unknown lipids. The G+C content of the chromosomal DNA was 61.7 mol%. 16S rRNA gene sequence comparison showed that strain H3^T was related most closely to Sulfitobacter donghicola DSW-25^T (97.3 % similarity) and levels of similarity with other species of the genus Sulfitobacter were 95.1–96.9 %. The mean (±sd) DNA–DNA hybridization value between strain H3^T and Sulfitobacter donghicola DSW-25^T was 18.0±2.25 %. The average nucleotide identity between strain H3^T and Sulfitobacter donghicola DSW-25^T was 70.45 %. Phylogenetic analyses based on 16S rRNA gene sequences showed that strain H3^T formed a separate clade close to the genus Sulfitobacter and was distinguishable from phylogenetically related species by differences in several phenotypic properties. On the basis of the phenotypic and phylogenetic data, strain H3^T represents a novel species of the genus Sulfitobacter , for which the name Sulfitobacter pseudonitzschiae is proposed (type strain H3^T = DSM 26824^T = MCCC 1A00686^T).

Global warming will be combined with predicted increases in thermal variability in the future surface ocean, but how temperature dynamics will affect phytoplankton biology and biogeochemistry is largely unknown. Here, we examine the responses of the globally important marine coccolithophore Emiliania huxleyi to thermal variations at two frequencies (1 d and 2 d) at low (18.5 ^∘C) and high (25.5 ^∘C) mean temperatures. Elevated temperature and thermal variation decreased growth, calcification and physiological rates, both individually and interactively. The 1 d thermal variation frequencies were less inhibitory than 2 d variations under high temperatures, indicating that high-frequency thermal fluctuations may reduce heat-induced mortality and mitigate some impacts of extreme high-temperature events. Cellular elemental composition and calcification was significantly affected by both thermal variation treatments relative to each other and to the constant temperature controls. The negative effects of thermal variation on E. huxleyi growth rate and physiology are especially pronounced at high temperatures. These responses of the key marine calcifier E. huxleyi to warmer, more variable temperature regimes have potentially large implications for ocean productivity and marine biogeochemical cycles under a future changing climate.