The microbial community in eutrophic freshwater sediment was investigated from a 67-cm-deep sediment core collected from the Daechung Reservoir in South Korea, where cyanobacterial blooms have occurred annually for the past 30 years. The majority of core sediments were characterized by dark-grayish, fine-grained mud with abundant gas-escaped and thinly laminated layers. Intervals of summer and winter seasons were represented by periodic peaks of geochemical profiles of parameters such as grain size and relative carbon mass ratios to various nutrients such as nitrogen, sulfur, and phosphorus. In bacteria, Proteobacteria (66.6%) was the most prevalent phylum, followed by Chloroflexi (8.9%), Bacteroidetes (5.1%), and Spirochaetes (2.6%). Archaea were also abundant, representing approximately half of the total prokaryotes in the sediments. Notably, three Bacteria (Sulfuricurvum, Sideroxydans, and Gallionella) and one Archaea (Thermoplasmata) accounted for 43.4% and 38.4% of the total bacteria and archaea, respectively, implying that iron and sulfur oxidizing microorganisms dominate in this eutrophic freshwater sediment. These results indicate that 1) eutrophic freshwater lakes in monsoon climates undergo a stratified sedimentary process with seasonal and annual variations in geochemical and microbial profiles, and 2) the microbial oxidative metabolism of iron and sulfur is notably active in sediments from a eutrophic lake.

The Gram-stain-negative, aerobic, non-spore-forming, motile, with a single polar flagellum, or nonmotile (stalked) and rod-shaped bacteria, DS48-5-2T and DS48-6-3, were isolated from a sediment sample collected from a depth of 48 m taken The genus Caulobacter is well known to have a different reproductive mode of division into non-motile forms with prosthecae (Staley, 1968) and motile ones with a polar flagellum, which helps to disperse the population at each generation, minimizing competition for resources (Abraham et al., 1999). Since the first isolation of a species of the genus Caulobacter was reported by Löeffler (1890), the genus has undergone reclassification by Abraham et al. (1999) and Chen et al. Henrici & Johnson, 1935). This study describes two bacterial strains, DS48-5-2 T and DS48-6-3, and establishes their taxonomic positions using a polyphasic approach that includes determining their phenotypic and chemotaxonomic properties and a detailed phylogenetic investigation based on their 16S rRNA gene sequences.Strains DS48-5-2T and DS48-6-3 were isolated from a sediment sample collected at 48 m deep taken from Daechung Reservoir in South Korea. Sediments were sampled using a KB core sampler (Wildco) on a boat. Approximately 100 mg of the sediment was first serially diluted in 0.85 % saline solution, and then aliquots of each serial dilution were spread on an R2A agar (Difco) and incubated at 25 uC. After 6 days, two yellow colonies, designated DS48-5-2T and DS48-6-3, were isolated. The

Fructophilic behavior in microalgae is a rare trait that could benefit biorefineries by enabling substitution of carbon source with fructose, and our previous study identified that Ettlia sp. prefers fructose relative to glucose. In this study, by analyzing the transcription levels of genes related to sugar transport and the glycolysis pathway, the fructose utilization of Ettlia sp. was investigated. In a fructose‐containing medium, the expression levels of fructokinase (EttFRK3) and glucokinase (EttGCK1 and EttGCK2) genes were significantly upregulated in heterotrophic cultivation of Ettlia sp. under fructose supplementation conditions. Further, a sugar transporter (EttSTF11) was significantly upregulated by 3.2‐fold in 1 day, and this increase was analogous to the specific growth rate exhibited by the species. Subsequent cultivation tests with multi‐sugar sources also showed a significant upregulation of EttSTF11 relative to other treatments without fructose. A phylogenetic tree derived from the analysis of different transporters of interest identified that EttSTF11 was adjacent to reference fructose transporters with a high bootstrap value of 71. Given that the transmembrane domains of EttSTF11 were analogous to those of reference fructose transporter genes, EttSTF11 appeared to play a critical role in fructose consumption and metabolism in Ettlia sp.

Microalgae not only serve as raw materials for biofuel but also have uses in the food, pharmaceutical, and cosmetic industries. However, regulated gene expression in microalgae has only been achieved in a few strains due to the lack of genome information and unstable transformation. This study developed a species-specific transformation system for an oleaginous microalga, Ettlia sp. YC001, using electroporation. The electroporation was optimized using three parameters (waveform, field strength, and number of pulses), and the final selection was a 5 kV cm −1 field strength using an exponential decay wave with one pulse. A new strong endogenous promoter CRT (Pcrt) was identified using transcriptome and quantitative PCR analysis of highly expressed genes during the late exponential growth phase. The activities of this promoter were characterized using a codon optimized cyan fluorescent protein (CFP) as a reporter. The expression of CFP was similar under Pcrt and under the constitutive promoter psaD (PpsaD). The developed transformation system using electroporation with the endogenous promoter is simple to prepare, is easy to operate with high repetition, and utilizes a species-specific vector for high expression. This system could be used not only in molecular studies on microalgae but also in various industrial applications of microalgae.