Planktotalea frisia gen. nov., sp. nov., isolated from the southern North Sea.

A heterotrophic, aerobic bacterium, designated strain SH6-1(T), was obtained from a seawater sample collected from the open North Sea during a phytoplankton bloom. Strain SH6-1(T) was isolated from a 10(-6) dilution culture, which indicated a high abundance of this organism in the environmental sample. 16S rRNA gene sequence comparison revealed that strain SH6-1(T) belonged to the marine Roseobacter clade (order Rhodobacterales) within the class Alphaproteobacteria. Pelagicola litoralis CL-ES2(T) was the closest phylogenetic neighbour (96.4% 16S rRNA gene sequence similarity). Cells of strain SH6-1(T) were small or elongated irregular rods. Optimal growth occurred between 20 and 25 °C and between pH 7.5 and 9.0 with peptone and yeast extract. On marine agar, the isolate formed non-pigmented, small, circular, convex colonies. For growth, cells required sodium ions and the vitamins pantothenic acid and nicotinic acid amide. The DNA G+C content was 53.8 mol%. The fatty acids (>1%) were C(10:0) 3-OH, C(16:0), C(12:1), C(12:1) 3-OH, C(18:0), C(18:1)ω7c, C(18:2) and 11-methyl C(18:1)ω7c. The polar lipid pattern indicated the presence of phosphatidylcholine, phosphatidylglycerol, an unidentified aminolipid and one unidentified phospholipid. The major respiratory lipoquinone was ubiquinone Q-10. Strain SH6-1(T) contained the genes pufLM, which code for the bacterial photosynthesis reaction centre; however, no bacteriochlorophyll a could be detected. Physiological, genotypic and phenotypic differences from P. litoralis support the description of a novel genus and species, for which we suggest the name Planktotalea frisia gen. nov., sp. nov; the type strain of the type species is SH6-1(T) (=DSM 23709(T)=LMG 25294(T)).

Combined Carbohydrates Support Rich Communities of Particle-Associated Marine Bacterioplankton.

Carbohydrates represent an important fraction of labile and semi-labile marine organic matter that is mainly comprised of exopolymeric substances derived from phytoplankton exudation and decay. This study investigates the composition of total combined carbohydrates (tCCHO; >1 kDa) and the community development of free-living (0.2-3 µm) and particle-associated (PA) (3-10 µm) bacterioplankton during a spring phytoplankton bloom in the southern North Sea. Furthermore, rates were determined for the extracellular enzymatic hydrolysis that catalyzes the initial step in bacterial organic matter remineralization. Concentrations of tCCHO greatly increased during bloom development, while the composition showed only minor changes over time. The combined concentration of glucose, galactose, fucose, rhamnose, galactosamine, glucosamine, and glucuronic acid in tCCHO was a significant factor shaping the community composition of the PA bacteria. The richness of PA bacteria greatly increased in the post-bloom phase. At the same time, the increase in extracellular ß-glucosidase activity was sufficient to explain the observed decrease in tCCHO, indicating the efficient utilization of carbohydrates by the bacterioplankton community during the post-bloom phase. Our results suggest that carbohydrate concentration and composition are important factors in the multifactorial environmental control of bacterioplankton succession and the enzymatic hydrolysis of organic matter during phytoplankton blooms.

Distinct seasonal growth patterns of the bacterium Planktotalea frisia in the North Sea and specific interaction with phytoplankton algae.

We investigated the occurrence of Planktotalea frisia strain SH6-1(T), a member of the Roseobacter clade, in the North Sea, and interactions with phytoplankton algae with a special emphasis on the carbohydrate metabolisms. This bacterium was present in May 2006 throughout the North Sea. Planktotalea frisia SH6-1 was further present in the German Bight between February and early July, with distinct peaks during and after phytoplankton blooms. The highest abundances, as detected by quantitative PCR, were 0.5-0.9% of total bacterial abundance. Comparison by catalyzed reporter deposition fluorescence in situ hybridization (CARD-FISH) with a set of highly specific probes confirmed the high values in one sample. Between mid-July and October, P. frisia SH6-1 was not detected throughout the North Sea. Experimental studies in which P. frisia SH6-1 was grown in the presence of axenic cultures of the algae Phaeocystis globosa, Leptocylindrus danicus and Thalassiosira rotula exhibited distinctly different responses, with the best growth together with P. globosa and T. rotula and very low growth together with L. danicus. The algae greatly differed in the composition of their exuded carbohydrates and in the fact that P. frisia SH6-1 was rather selective in consumption of algae, suggesting that the distinct carbohydrate metabolisms are a key feature to explain the seasonal occurrence of this bacterium in the North Sea.