So-Ra Ko

Lipid droplet synthesis is limited by acetate availability in starchless mutant of Chlamydomonas reinhardtii

Phenotypic and genotypic changes in Chlamydomonas reinhardtii BafJ5, a starchless mutant, with respect to lipid metabolism was studied in different trophic states under nitrogen (N) sufficient and limited conditions. Interestingly, cellular lipid content increased linearly with input acetate concentration with highest lipid content (∼42%) under nitrogen limitation and mixotrophic state. RT‐qPCR studies indicate that key fatty acid biosynthesis genes are down‐regulated under N limitation but not under mixotrophic state, whereas, ACS2, encoding Acetyl‐CoA synthetase, and DGTT4, encoding Diacylglycerol O‐acyltransferase, are up‐regulated under all conditions. These results collectively indicate that acetate is the limiting factor and central molecule in lipid droplet synthesis. The study also provides further evidence of the presence of a chloroplast pathway for triacylglycerol synthesis in microalgae.

Annual variation of Microcystis genotypes and their potential toxicity in water and sediment from a eutrophic reservoir

The relative genetic diversity of microcystin-producing Microcystis in the water and sediment of the Daechung Reservoir, Korea, was investigated over an entire year, including the cyanobacterial bloom season. The cells of potentially toxic Microcystis strains containing mcyJ genotypes and cells containing the genus-specific cpcBA gene were quantified by a real-time PCR. The ratio of cells with mcyJ genotypes to the total Microcystis population in the water body was the highest (68.3%) in August when the cyanobacterial bloom reached its peak and the microcystin concentration in the water began to increase. A denaturing gradient gel electrophoresis profile analysis of the mcyJ genotypes performed to monitor any changes in the toxic Microcystis population showed the appearance of new genotypes and the disappearance of existing genotypes in the reservoir water collected during the summer months, when compared with the profile for the samples collected in spring and autumn. However, very little change was observed over the course of the year as regards the population diversity of the sediment samples.

Determination of Cyanobacterial Diversity during Algal Blooms in Daechung Reservoir, Korea, on the Basis of cpcBA Intergenic Spacer Region Analysis

ABSTRACT The detection and prevention of cyanobacterial blooms are important issues in water quality management. As such, the diversity and community dynamics of cyanobacteria during cyanobacterial bloom in the Daechung Reservoir, Korea, were studied by analyzing the intergenic spacer (IGS) region between phycocyanin subunit genes cpcB and cpcA (cpcBA IGS). To amplify the cpcBA IGS from environmental samples, new PCR primers that could cover a wider range of cyanobacteria than previously known primers were designed. In the samples taken around the bloom peak (2 September 2003), seven groups of cpcBA IGS sequences were detected, and none of the amplified cpcBA IGSs was closely related to the cpcBA IGS from chloroplasts. Apart from the Microcystis-, Aphanizomenon (Anabaena)-, Pseudanabaena-, and Planktothrix (Oscillatoria)-like groups, the three other groups of cpcBA IGS sequences were only distantly related to previously reported sequences (<85% similarity to their closest relatives). The most prominent changes during the bloom were the gradual decrease and eventual disappearance of the Aphanizomenon (Anabaena)-like group before the bloom peak and the gradual increase and sudden disappearance of Planktothrix (Oscillatoria)-like groups right after the bloom peak. The community succession profile obtained based on the cpcBA IGS analysis was also supported by a PCR-denaturing gradient gel electrophoresis analysis of the 16S rRNA genes.

Chelatococcus caeni sp. nov., isolated from a biofilm reactor sludge sample.

A polyphasic taxonomic study was carried out on strain EBR-4-1(T), which was isolated from a biofilm reactor in the Republic of Korea. The cells of the strain were Gram-stain-negative, non-spore-forming, motile and rod-shaped. Comparative 16S rRNA gene sequence studies showed a clear affiliation of this strain to the Alphaproteobacteria, and it was most closely related to Chelatococcus daeguensis CCUG 54519(T), Chelatococcus sambhunathii HT4(T), and Chelatococcus asaccharovorans DSM 6462(T) with 16S rRNA gene sequence similarities to the type strains of these species of 98.8 %, 98.7 %, and 96.3 %, respectively. The G+C content of the genomic DNA of strain EBR-4-1(T) was 68.7 mol%. Phenotypic and chemotaxonomic data [Q-10 as the major ubiquinone; C19 : 0cycloω8c, C18 : 1 2-OH, and summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c) as the major fatty acids] supported the affiliation of strain EBR-4-1(T) to the genus Chelatococcus. On the basis of the polyphasic evidence, it is proposed that strain EBR-4-1(T) should be assigned to a new species, Chelatococcus caeni sp. nov. The type strain is EBR-4-1(T) ( = KCTC 32487(T) = JCM 30181(T)).

Belnapia soli sp. nov., a proteobacterium isolated from grass soil

A Gram-negative, aerobic, non-motile, non-spore-forming, cocci-shaped, red-pigmented bacterium, designated strain PB-K8(T), was isolated from grass soil sampled in Daejeon, Republic of Korea. Comparative 16S rRNA gene sequence studies showed that the isolate was clearly affiliated with the class Alphaproteobacteria, and was most closely related to Belnapia moabensis DSM 16746(T) and Belnapia rosea DSM 23312(T), showing a 16S rRNA gene sequence similarity to the type strains of each species of 98.4 and 97.2%, respectively. The cells of strain PB-K8(T) formed red colonies on R2A agar, contained Q-9 as the predominant ubiquinone and included summed feature 3 (C16:1ω7c C16:1ω6c), C16:0, summed feature 8 (C18:1ω7c/C18:1ω6c), C18:1 2-OH and C19:0 cyclo ω8c as the major fatty acids. The G+C content of the genomic DNA of strain PB-K8(T) was 72.1 mol%. Thus, the combined genotypic and phenotypic data supported the conclusion that strain PB-K8(T) represents a novel species of the genus Belnapia, for which the name Belnapia soli sp. nov. is proposed. The type strain is PB-K8(T) (=KCTC 23765(T)=JCM 18033(T)).

Flaviflexus salsibiostraticola sp. nov., an actinobacterium isolated from a biofilm reactor.

A Gram-stain-positive, aerobic, non-motile, non-spore-forming, cocci-shaped actinobacterium, designated strain EBR4-1-2(T), was isolated from a biofilm reactor in Korea. Comparative 16S rRNA gene sequence studies showed the isolate was clearly affiliated with the class Actinobacteria, and was related most closely to Flaviflexus huanghaiensis H5(T), showing 98.9 % similarity. Cells of strain EBR4-1-2(T) formed yellow colonies on R2A agar, contained MK-9(H4) as the predominant menaquinone, and included C18 : 1ω9c, C16 : 0, C16 : 1ω9c and C14 : 0 as the major fatty acids. The cell-wall peptidoglycan type was A5α (l-Lys-l-Ala-l-Lys-d-Glu). The G+C content of the genomic DNA of strain EBR4-1-2(T) was 65.6 mol%. Thus, the combined genotypic and phenotypic data supported the conclusion that strain EBR4-1-2(T) represents a novel species of the genus Flaviflexus, for which the name Flaviflexus salsibiostraticola sp. nov. is proposed. The type strain is EBR4-1-2(T) ( = KCTC 33148(T) = JCM 19016(T)).

Microcystin Biosynthesis and mcyA Expression in Geographically Distinct Microcystis Strains under Different Nitrogen, Phosphorus, and Boron Regimes.

Roles of nutrients and other environmental variables in development of cyanobacterial bloom and its toxicity are complex and not well understood. We have monitored the photoautotrophic growth, total microcystin concentration, and microcystins synthetase gene (mcyA) expression in lab-grown strains of Microcystis NIES 843 (reference strain), KW (Wangsong Reservoir, South Korea), and Durgakund (Varanasi, India) under different nutrient regimes (nitrogen, phosphorus, and boron). Higher level of nitrogen and boron resulted in increased growth (avg. 5 and 6.5 Chl a mg/L, resp.), total microcystin concentrations (avg. 1.185 and 7.153 mg/L, resp.), and mcyA transcript but its expression was not directly correlated with total microcystin concentrations in the target strains. Interestingly, Durgakund strain had much lower microcystin content and lacked microcystin-YR variant over NIES 843 and KW. It is inferred that microcystin concentration and its variants are strain specific. We have also examined the heterotrophic bacteria associated with cyanobacterial bloom in Durgakund Pond and Wangsong Reservoir which were found to be enriched in Alpha-, Beta-, and Gammaproteobacteria and that could influence the bloom dynamics.

Elucidation of the bacterial communities associated with the harmful microalgae Alexandrium tamarense and Cochlodinium polykrikoides using nanopore sequencing

Interactions between microalgae and bacteria are often obligatory for harmful algal blooms (HABs). Here, we investigated the specific bacterial communities associated with Alexandrium tamarense and Cochlodinium polykrikoides, which cause ecological and economic damage during their blooms. To this end, the bacterial metagenome was selectively isolated from the two dinoflagellates and subsequently used for 16S rRNA analysis via the Nanopore MinION and Illumina sequencing platforms. Although the full-length 16S rRNA reads from the MinION platform showed high correlation in higher taxonomic ranks to the partial-length 16S rRNA reads from the Illumina platform, there was less correlation at the genus and species levels. MinION reads that are similar in the V3-V4 hypervariable regions with Illumina reads are classified to different taxonomies due to the extra information encoded in the full-length 16S rRNA reads. This indicates that bias arising from the short length Illumina reads can be supplemented by MinION reads. Furthermore, integrated analysis of the Illumina and MinION data showed that A. tamarense was predominantly enriched in the Roseobacter clade and C. polykrikoides was enriched in Gammaproteobacteria and Alphaproteobacteria. These results suggest that the association of different bacterial communities with A. tamarense and C. polykrikoides may be required for HABs.

Silanimonas algicola sp. nov., isolated from laboratory culture of a bloom-forming cyanobacterium, Microcystis

A Gram-stain-negative, aerobic, rod-shaped and motile bacterium, designated M23T, was isolated from a laboratory culture of a bloom-forming cyanobacterium, Microcystis, which was isolated from a eutrophic lake in Korea. The strain grew optimally without NaCl and at 25-30 °C on R2A agar medium. Phylogenetic analysis based on 16S rRNA gene sequences positioned the novel strain among the genus Silanimonas, with the highest similarity to Silanimonas lenta DSM 16282T (98.5 %). DNA-DNA relatedness between strain M23T and the closely related species in the genus Silanimonas was <30 %. Strain M23T contained iso-C15 : 0, summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c) and iso-C16 : 0 as major fatty acids and ubiquinone-8 (Q-8) as the major quinone. Strain M23T contained diphosphatidylglycerol, phosphatidylethanolamine and phosphatidylmethylethanolamine as major polar lipids. The DNA G+C content of strain M23T was 69.6 mol%. On the basis of the genotypic, chemotaxonomic and phenotypic data, strain M23T represents a novel species in the genus Silanimonas, for which the name Silanimonas algicola sp. nov. is proposed. The type strain is M23T (=KCTC 52219T=JCM 31889T).

Actinotalea caeni sp. nov., isolated from a sludge sample of a biofilm reactor

A polyphasic taxonomic study was carried out on strain EBR-4-2T isolated from a biofilm reactor in Korea. Cells of the strain were Gram-stain-positive, non-spore-forming, non-motile and rod-shaped. Comparative 16S rRNA gene sequence studies showed the clear affiliation of this strain to the Actinobacteria, and it had the highest pairwise sequence similarities with Actinotalea suaedae EGI 60002T (98.7 %), Actinotalea ferrariae CF5-4T (96.3 %) and Actinotalea fermentans DSM 3133T (96.2 %). Phylogenetic analysis based on the 16S rRNA gene sequences showed that the strain formed a clear phylogenetic lineage with the genus Actinotalea. The major fatty acids were identified as C15 : 0 anteiso, C16 : 0, C16 : 0 N alcohol, C15 : 1 anteiso A and C15 : 0 iso. The major cellular polar lipids were diphosphatidylglycerol, phosphatidylinositol mannoside, phosphatidylinositol and glycolipid. The peptidoglycan type was A4β containing l-Orn-d-Glu. The whole-cell-wall sugars were glucose and ribose. The respiratory quinone was identified as menaquinone MK-10(H4), and the genomic DNA G+C content was determined to be 74.8 mol %. Based on evidence from this polyphasic study, it is proposed that strain EBR-4-2T should be designated as representing a novel species named Actinotalea caeni sp. nov. The type stain is EBR-4-2T (=KCTC 33604T=JCM 30447T).