Effect of rainfall in shaping microbial community during Microcystis bloom in Nakdong River, Korea

Various environmental factors play a role in the formation and collapse of Microcystis blooms. This study investigates the impact of heavy rainfall on cyanobacterial abundance, microbial community composition, and functional dynamics in the Nakdong River, South Korea, during typical and exceptionally rainy years. The results reveal distinct responses to rainfall variations, particularly in cyanobacterial dominance and physicochemical characteristics. In 2020, characterized by unprecedented rainfall from mid-July to August, Microcystis blooms were interrupted significantly, exhibiting lower cell densities and decreased water temperature, compared to normal bloom patterns in 2019. Moreover, microbial community composition varied, with increases in Gammaproteobacteria and notably in genera of Limnohabitans and Fluviicola. These alterations in environmental conditions and bacterial community were similar to those of the post-bloom period in late September 2019. It shows that heavy rainfall during summer leads to changes in environmental factors, consequently causing shifts in bacterial communities akin to those observed during the autumn-specific post-bloom period in typical years. These changes also accompany shifts in bacterial functions, primarily involved in the degradation of organic matter such as amino acids, fatty acids, and terpenoids, which are assumed to have been released due to the significant collapse of cyanobacteria. Our results demonstrate that heavy rainfall in early summer induces changes in the environmental factors and subsequently microbial communities and their functions, similar to those of the post-bloom period in autumn, leading to the earlier breakdown of Microcystis blooms.

Microbiome dataset of bacterial and fungal communities in anthosphere of twelve different wild plants in South Korea

This dataset provides detailed profiles of bacterial and fungal communities associated with flowers (anthosphere) of 12 different plant species collected from remote and secluded locations characterized by a flourishing and diverse plant ecosystem. In total, 144 flower samples were collected from 12 different wild plants. Bacterial 16S rRNA and fungal ITS genes obtained using the Illumina Miseq approach were used to describe the anthosphere. Metadata and raw sequences obtained in this study are available from the National Center for Biotechnology Information (BioProject ID: PRJNA983070). Amplicon Sequence Variants (ASVs) of bacteria and fungi were analyzed using the DADA2 pipeline. After quality filtering, trimming, and removing the chimeric sequences, 2076 bacterial and 2152 fungal ASVs were identified in the anthosphere. Burkholderiales and Enterobacterales in bacteria, and Pleosporales in fungi were the predominant groups in the anthosphere regardless of the plant species. Among the twelve different plant species, Forsythia koreana exhibited the highest abundance of both bacterial and fungal groups. This dataset represents a detailed exploration of the anthosphere in the most abundant and commonly observed plant species in South Korea, and provides new insights into the microbial communities and interactions of the anthosphere.

Vegetation as a key driver of the distribution of microbial generalists that in turn shapes the overall microbial community structure in the low Arctic tundra

Understanding the variability of microbial niches and their interaction with abiotic and biotic factors in the Arctic can provide valuable insights into microbial adaptations to extreme environments. This study investigates the structure and diversity of soil bacterial communities obtained from sites with varying vegetation coverage and soil biogeochemical properties in the low Arctic tundra and explores how bacteria interact under different environmental parameters. Our findings reveal differences in bacterial composition and abundance among three bacterial niche breadths (specialists, common taxa, and generalists). Co-occurrence network analysis revealed Rhizobiales and Ktedonobacterales as keystone taxa that connect and support other microbes in the habitat. Low-elevation indicators, such as vascular plants and moisture content, were correlated with two out of three generalist modular hubs and were linked to a large proportion of generalists' distribution (18%). Structural equation modeling revealed that generalists' distribution, which influenced the remaining microbial communities, was mainly regulated by vegetation coverage as well as other abiotic and biotic factors. These results suggest that elevation-dependent environmental factors directly influence microbial community structure and module formation through the regulation of generalists' distribution. Furthermore, the distribution of generalists was mainly affected by macroenvironment filtering, whereas the distribution of specialists was mainly affected by microenvironment filtering (species-engineered microbial niche construction). In summary, our findings highlight the strong top-down control exerted by vegetation on generalists' distribution, which in turn shapes the overall microbial community structure in the low Arctic tundra.

Organic Connection of Holobiont Components and the Essential Roles of Core Microbes in the Holobiont Formation of Feral Brassica napus

Brassica napus (Rapeseed) is an econfomically important oil-producing crop. The microbial interactions in the plant holobiont are fundamental to the understanding of plant growth and health. To investigate the microbial dynamics in the holobiont of feral B. napus, a total of 215 holobiont samples, comprised of bulk soil, primary root, lateral root, dead leaf, caulosphere, basal leaf, apical leaf, carposphere, and anthosphere, were collected from five different grassland sites in South Korea. The soil properties differed in different sampling sites, but prokaryotic communities were segregated according to plant holobiont components. The structures of the site-specific SparCC networks were similar across the regions. Recurrent patterns were found in the plant holobionts in the recurrent network. Ralstonia sp., Massilia sp., and Rhizobium clusters were observed consistently and were identified as core taxa in the phyllosphere, dead leaf microbiome, and rhizosphere, respectively. Arthropod-related microbes, such as Wolbachia sp., Gilliamella sp., and Corynebacteriales amplicon sequence variants, were found in the anthosphere. PICRUSt2 analysis revealed that microbes also possessed specific functions related to holobiont components, such as functions related to degradation pathways in the dead leaf microbiome. Structural equation modeling analysis showed the organic connections among holobiont components and the essential roles of the core microbes in the holobiont formations in natural ecosystem. Microbes coexisting in a specific plant showed relatively stable community structures, even though the regions and soil characteristics were different. Microbes in each plant component were organically connected to form their own plant holobiont. In addition, plant-related microbes, especially core microbes in each holobiont, showed recurrent interaction patterns that are essential to an understanding of the survival and coexistence of plant microbes in natural ecosystems.

Ecological network analysis reveals distinctive microbial modules associated with heavy metal contamination of abandoned mine soils in Korea

Heavy metal pollution in soil around abandoned mine sites is one of the most critical environmental issues worldwide. Soil microbes form complex communities and perform ecological functions individually or in cooperation with other organisms to adapt to harsh environments. In this study, we investigated the distribution patterns of bacterial and fungal communities in non-contaminated and heavy metal-contaminated soil of the abandoned Samkwang mine in Korea to explore microbial interaction mechanisms and their modular structures. As expected, the bacterial and fungal community structures showed large differences depending on the degree of heavy metal contamination. The microbial network was divided into three modules based on the levels of heavy metal pollution: heavy metal-tolerant (HM-Tol), heavy metal-mid-tolerant (HM-mTol), and heavy metal-sensitive (HM-Sens) modules. Taxonomically, microbes assigned to Vicinamibacterales, Pedosphaeraceae, Nitrosomonadaceae, and Gemmatimonadales were the major groups constituting the HM-Tol module. Among the detected heavy metals (As, Pb, Cd, Cu, and Zn), copper concentrations played a key role in the formation of the HM-Tol module. In addition, filamentous fungi (Fusarium and Mortierella) showed potential interactions with bacteria (Nitrosomonadaceae) that could contribute to module stability in heavy metal-contaminated areas. Overall, heavy metal contamination was accompanied by distinct microbial communities, which could participate in the bioremediation of heavy metals. Analysis of the microbial interactions among bacteria and fungi in the presence of heavy metals could provide fundamental information for developing bioremediation mechanisms for the recovery of heavy metal-contaminated soil.

Aquariibacter albus gen. nov., sp. nov., a new member of the order Burkholderiales, isolated from a freshwater aquarium

A novel bacterium, strain SJAQ100^T, was isolated from a freshwater aquarium and was characterized taxonomically and phylogenetically. Strain SJAQ100^T was a Gram-stain-negative, aerobic, rod-shaped and non-motile bacterium. The strain grew optimally with 0 % NaCl and at 25-37 °C on Reasoner's 2A agar. Phylogenetic analysis based on the 16S rRNA gene sequences revealed that the strain SJAQ100^T clustered with members of Burkholderiales incertae sedis in the order Burkholderiales, but sequence similarities to known species were less than 96.5 %. The genomic DNA G+C content of strain SJAQ100^T was 71.2 mol%. Genomic comparisons of strain SJAQ100^T with species in the order Burkholderiales were made using the Genome-to-Genome Distance Calculator, average nucleotide identity and average amino acid identity analyses (values indicated ≤22.1, ≤78.1, and ≤68.1 % respectively). Strain SJAQ100^T contained C_16 : 0 and C_16 : 1  ω7c/C_16 : 1  ω6c as major fatty acids and Q-8 as the major quinone. The major polyamines were putrescine and cadaverine. Strain SJAQ100^T contained phosphatidylethanolamine and diphosphatidylglycerol as major polar lipids. Based on the genotypic, chemotaxonomic and phenotypic results, strain SJAQ100^T represents a novel genus and species, Aquariibacter albus gen. nov., sp. nov., which belongs to order Burkholderiales and the class Betaproteobacteria. The type strain is SJAQ100^T (=KCTC 72203^T=CGMCC 1.18869^T=MCC 4385^T).

Seasonal succession of microbes in different size-fractions and their modular structures determined by both macro- and micro-environmental filtering in dynamic coastal waters

Microbes interact with each other in response to various environmental changes in coastal marine ecosystems. To explore how the macroenvironment (environmental filtering) and species-engineered microenvironment (niche construction) affect the ecological network of the marine microbiome in the highly dynamic coastal waters of Korea, we analyzed the modular structures of the microbial community and identified microbial interconnections in different size fractions for a year. Fluctuations in the macroenvironment, such as temperature and nutrient concentrations driven by seasonal changes, are the major factors in determining successive microbial modules. Compared to particle-associated (PA) microbes, free-living (FL) microbes seemed to be more affected by macroenvironmental filtering. Modules related to nutrients were further divided into various modules according to different lifestyles. In addition, a large transient discharge of the Changjiang (Yangtze River) in summer also formed a distinct microbial module, which was related to the high ammonia concentration arising from phytoplankton degradation. Microbes belonging to the SAR11, SAR86, and SAR116 clades, Flavobacteriaceae, and MG IIa-L showed repeated interconnections in temperature-related modules, while the SAR202 clade, Marinimicrobia, DEV007 clade, and Arctic97B-4 and Sva0996 marine groups displayed repeated connections in nutrient-related modules. These 'skeleton'-forming microbes created species-engineered microenvironments, further fine-tuning microbial modular structures. Furthermore, they serve as keystone species for module stability by linking interdependent microbial partners within their own modules through universally beneficial metabolic activities. Therefore, they could reinforce the ecological resilience of microbial communities under abiotic and biotic perturbations in dynamic coastal waters. In conclusion, both macro- and micro-environmental filtering were important for determining the seasonal succession of microbial community structures.

Tabrizicola algicola sp. nov. isolated from culture of microalga Ettlia sp

A novel Gram-stain-negative, aerobic, non-spore-forming, non-motile, and rod-shaped bacterium, strain ETT8^T was isolated from a chemostat culture of microalga Ettlia sp. YC001. Optimal growth was with 0-2% NaCl and at 25-37 °C on R2A medium. Phylogenetic analysis based on the 16S rRNA gene and genome sequence showed that strain ETT8^T belongs to the genus Tabrizicola, with the close neighbours being T. sediminis DRYC-M-16^T (98.1 %), T. alkalilacus DJC^T (97.6 %), T. fusiformis SY72^T (96.9 %), T. piscis K13M18^T (96.8 %), and T. aquatica RCRI19^T (96.5 %). The genomic comparison of strain ETT8^T with type species in the genus Tabrizicola was analysed using the genome-to-genome distance calculator (GGDC), average nucleotide identity (ANI), and average amino acid identity (AAI) (values indicated ≤17.7, ≤75.4 and ≤71.9 %, respectively). The genomic DNA G+C content of strain ETT8^T was 64.4 %, plus C_18 : 1  ω6c and C_18 : 0-iso were the major fatty acids and Q-10 the major respiratory quinone. Strain ETT8^T contained diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine aminolipid, and four unidentified lipids as the major polar lipids. Based on the chemotaxonomic, genotypic, and phenotype results, strain ETT8^T was recognized as a novel species of the genus Tabrizicola for which the name Tabrizicola algicola sp. nov. is proposed. The type strain is ETT8^T (=KCTC 72206^T=JCM 31893^T=MCC 4339^T).

Distribution of Dimethylsulfoniopropionate Degradation Genes Reflects Strong Water Current Dependencies in the Sanriku Coastal Region in Japan: From Mesocosm to Field Study

Dimethyl sulfide (DMS) is an important component of the global sulfur cycle as it is the most abundant sulfur compound that is emitted via the ocean surface to the atmosphere. Dimethylsulfoniopropionate (DMSP), the precursor of DMS, is mainly produced by phytoplankton and is degraded by marine bacteria. To reveal the role of bacteria in the regulation of DMSP degradation and DMS production, mesocosm and field studies were performed in the Sanriku Coast on the Pacific Ocean in northeast Japan. The responsible bacteria for the transformation of DMSP to DMS and the assimilation of DMSP were monitored, and the genes encoding DMSP lyase (dddD and dddP) and DMSP demethylase (dmdA) were analyzed. The mesocosm study showed that the dmdA subclade D was the dominant DMSP degradation gene in the free-living (FL) and particle-associated (PA) fractions. The dddD gene was found in higher abundance than the dddP gene in all the tested samples. Most importantly, DMS concentration was positively correlated with the abundance of the dddD gene. These results indicated that bacteria possessing dmdA and dddD genes were the major contributors to the DMSP degradation and DMS production, respectively. The genes dmdA subclade D and dddP were abundant in the Tsugaru Warm (TW) Current, while the dmdA subclade C/2 and dddD genes were dominant in the Oyashio (OY) Current. Functional gene network analysis also showed that the DMSP degradation genes were divided into OY and TW Current-related modules, and genes sharing similar functions were clustered in the same module. Our data suggest that environmental fluctuations resulted in habitat filtering and niche partitioning of bacteria possessing DMSP degradation genes. Overall, our findings provide novel insights into the distribution and abundance of DMSP degradation genes in a coastal region with different water current systems.

Unique microbial module regulates the harmful algal bloom (Cochlodinium polykrikoides) and shifts the microbial community along the Southern Coast of Korea

Harmful algal blooms (HABs) of Cochlodinium (aka Margalefidinium) polykrikoides cause huge economic and ecological damages and thus are considered environmental problems. Previous studies uncovered that the formation and collapse of phytoplankton blooms could be closely related to their associated microbes although their roles in C. polykrikoides bloom have not been elucidated yet. To explore the potential interactions between C. polykrikoides and other microbes (archaea, bacteria, and phytoplankton), we collected water samples in the free-living (FL) (0.22 to 3 μm), nanoparticle-associated (NP) (3 to 20 μm), and microparticle-associated (MP) (>20 μm) fractions when C. polykrikoides blooms occurred from July to August in 2016, 2017, and 2018 in the South Sea of Korea. The microbial composition of the C. polykrikoides-associated microbial cluster (Module I) significantly differed from those of other modules associated with Alexandrium, Chaetoceros or Chattonella. Over half of the interspecies interactions in Module I occurred within the module. That is, specific microbial clusters were associated with the C. polykrikoides bloom. Structural equation modeling (SEM) further confirmed the stronger effects of Module I on C. polykrikoides blooms compared to environmental factors. Among the operational taxonomic units (OTUs) directly correlated with C. polykrikoides, Marine Group I was presumed to supply vitamin B₁₂, the essential element for C. polykrikoides growth, while the potential fish pathogens (Micrococcaceae and Piscirickettsiaceae) could contribute to the massive fish death together with C. polykrikoides itself. In addition, the zoospores of Syndiniales, a parasitoid to dinoflagellates, might be related to the sudden collapse of C. polykrikoides blooms. These microbial groups also contributed to significant alterations of the local microbial community structures. Collectively, network analysis and SEM revealed that the C. polykrikoides bloom is concomitant with distinct microbial communities, contributing to the rise and fall of the bloom, and finally determining the local microbial community structures.

Network analysis reveals succession of Microcystis genotypes accompanying distinctive microbial modules with recurrent patterns

Every member of the ecological community is connected via a network of vital and complex relationships, called the web of life. To elucidate the ecological network and interactions among producers, consumers, and decomposers in the Daechung Reservoir, Korea, during cyanobacterial harmful algal blooms (cyanoHAB), especially those involving Microcystis, we investigated the diversity and compositions of the cyanobacterial (16S rRNA gene), including the genotypes of Microcystis (cpcBA-IGS gene), non-cyanobacterial (16S), and eukaryotic (18S) communities through high-throughput sequencing. Microcystis blooms were divided into the Summer Major Bloom and Autumn Minor Bloom with different dominant genotypes of Microcystis. Network analysis demonstrated that the modules involved in the different phases of the Microcystis blooms were categorized into the Pre-Bloom, Bloom, Post-Bloom, and Non-Bloom Groups at all sampling stations. In addition, the non-cyanobacterial components of each Group were classified, while the same Group showed similarity across all stations, suggesting that Microcystis and other microbes were highly interdependent and organized into cyanoHAB-related module units. Importantly, the Microcystis genotype-based sub-network uncovered that Pirellula, Pseudanabaena, and Vampirovibrionales preferred to interact with specific Microcystis genotypes in the Summer Major Bloom than with other genotypes in the Autumn Minor Bloom, while the copepod Skistodiaptomus exhibited the opposite pattern. In conclusion, the transition patterns of cyanoHAB-related modules and their key components could be crucial in the succession of Microcystis genotypes and to enhance the understanding of microbial ecology in an aquatic environment.

Paraconexibacter algicola gen. nov., sp. nov., a novel actinobacterium isolated from a eutrophic lake during the end of cyanobacterial harmful algal blooms, and proposal of Paraconexibacteraceae fam. nov. in the order Solirubrobacterales

A novel bacterium, strain Seoho-28^T, was isolated from a shallow eutrophic lake during the end of cyanobacterial harmful algal blooms and was characterized taxonomically and phylogenetically. Strain Seoho-28^T was a Gram-stain-negative, aerobic, rod-shaped and non-motile bacterium. The strain grew optimally with 0 % NaCl and at 25-30 °C on Reasoner's 2A medium. The phylogenetic analysis based on 16S rRNA gene sequences positioned the novel strain among the order Solirubrobacterales, but sequence similarities to known species were less than 94.7 %. The genomic DNA G+C content of the strain Seoho-28^T was 74.2 mol%. Genomic comparisons of strain Seoho-28^T with families in the order Solirubrobacterales were made using the Genome-to-Genome Distance Calculator, average nucleotide identity and average amino acid identity analyses (values indicated ≤14.9, ≤73.5 and ≤57.8 %, respectively). Strain Seoho-28^T contained C_16 : 0-iso, C_18 : 1  ω9c and C_16 : 0 as major fatty acids and MK-7 (H₄) as the major quinone. Strain Seoho-28^T contained diphosphatidylglycerol, phosphatidylinositol and an unidentified phospholipid as major polar lipids. Meso- and ll-diaminopimelic acids were the diagnostic diamino acids in the cell-wall peptidoglycan. Based on the genotypic, chemotaxonomic and phenotypic results, strain Seoho-28^T represents a novel genus and species, Paraconexibacter algicola gen. nov., sp. nov., which belongs to a new family Paraconexibacteraceae in the order Solirubrobacterales and the class Thermoleophilia. The type strain is Seoho-28^T (=KCTC 39791^T=JCM 31881^T).

Characterization of Distinct CyanoHABs-Related Modules in Microbial Recurrent Association Network

To elucidate the interspecies connectivity between cyanobacteria and other bacteria (non-cyanobacteria) during cyanobacterial harmful algal blooms (cyanoHABs), samples were collected from the Nakdong River, Korea, from June 2016 to August 2017, and microbial recurrent association network (MRAN) analysis was performed to overcome the limitations of conventional network analysis. Microcystis blooms were tightly linked with Pseudanabaena in summer and were accompanied by significant changes in the non-cyanobacterial community composition (nCCC) compared to non-bloom period. Riverine bacterial communities could be clearly separated into modules that were involved in the formation, maintenance, and decomposition of cyanoHABs. Roseomonas and Herbaspirillum were directly linked with major cyanobacteria and assigned to connector and module hub in cyanoHABs-related modules, respectively. The functional profiles of the cyanoHABs-related modules suggested that nitrate reduction, aerobic ammonia oxidation, fermentation, and hydrocarbon degradation could be increased during the Microcystis bloom periods. In conclusion, MRAN analysis revealed that specific bacteria belonging to cyanoHABs-related module, including connectors and module hubs, appeared to contribute to the development and collapse of cyanoHABs. Therefore, to understand cyanoHABs, a modular microbial perspective may be more helpful than a single bacterial species perspective.

Bacterial community enhances flocculation efficiency of Ettlia sp. by altering extracellular polymeric substances profile

This study examined the effects of a bacterial community and extracellular polymeric substances (EPS) on Ettlia sp. flocculation. The growth rate, flocculation efficiency (FE), bacterial community, and EPS profile of axenic and xenic Ettlia cultures were monitored during 46 days of cultivation. For the xenic culture, with a great abundance of growth-promoting and flocculation-inducing bacteria, the biomass density was 18.75% higher and its FE reached 100% in the mid-stationary phase. Moreover, microscopic observation and a quantitative analysis of the EPS revealed the exclusive presence of long filamentous EPS and more compact structure in the xenic Ettlia culture, possibly explaining its better FE. Notwithstanding, for the axenic culture, despite a lower biomass density and reduced abundance of EPS, its FE reached 92.54% in the mid-stationary phase. Thus, the role of the bacterial community was found to be supportive rather than vital for the high settleability of the self-flocculating Ettlia microalgal culture.

Nevskia lacus sp. nov., a gammaproteobacterium isolated from a eutrophic lake

A novel Gram-stain negative, rod-shaped and motile bacterial strain, designated strain Seoho-38^T, was isolated from a eutrophic lake in South Korea. Polyphasic taxonomic studies were performed to investigate the taxonomic position of the new isolate. The phylogenetic analysis based on the 16S rRNA gene sequences revealed that strain Seoho-38^T formed a distinct cluster with Nevskia ramosa Soe1^T, Nevskia persephonica G6M-30^T, Nevskia soli GR15-1^T, Nevskia terrae KIS13-15^T and Nevskia aquatilis F2-63^T with bootstrap resampling value of 100%. Of those Nevskia strains, the new isolate shows high sequence similarity with N. ramosa Soe1^T (98.7%) and N. persephonica G6M-30^T (97.2%), and values lower than 96.5% with the other type strains. The new isolate was observed to grow aerobically in 0-1.5% (w/v) NaCl (optimum 0%), at pH 7.0-9.0 (optimum pH 7.0) and temperature 15-36 °C (optimum 20-30 °C) on R2A medium. DNA-DNA relatedness values between strain Seoho-38^T and the type strains of reference species in the genus Nevskia were < 24%. The genomic DNA G + C content was determined to be 67.4 mol%. Ubiquinone-8 (Q-8) (95%) and ubiquinone-7 (Q-7) (5%) were identified as the respiratory quinones. The cellular polar lipids were identified as diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, a phosphoaminolipid, two glycolipids, an aminolipid and four unidentified lipids. The major fatty acid components were found to include summed feature 3 (C_16:1ω7c and/or C_16:1ω6c), summed feature 8 (C_18:0ω7c and/or C_18:0ω6c), C_16:0 and C_14:0. Based on the above polyphasic evidence, strain Seoho-38^T (= KCTC 52221^T = JCM 31888^T) represents a new species of the genus Nevskia, for which the name Nevskia lacus sp. nov. is proposed.

Improving water quality using settleable microalga Ettlia sp. and the bacterial community in freshwater recirculating aquaculture system of Danio rerio

A highly settleable microalga, Ettlia sp., was applied to a freshwater recirculating aquaculture system (RAS) of Danio rerio to improve the treatment of nitrogenous compounds. The growth characteristics of the microalgae, water quality parameters, and bacterial communities were monitored for 73 days. In the treatment RAS, the inoculated Ettlia sp. grew up to 1.26 g/L and dominated (>99%) throughout the experiment, whereas naturally occurring microalgae grew to 0.57 g/L in the control RAS. The nitrate, nitrite, and ammonium concentrations in the treatment RAS were reduced by 50.1%, 73.3%, and 24.2%, respectively, compared to the control RAS. A bacterial community analysis showed that Rhodospirillales, Phycisphaerae, Chlorobiales, and Burkholderiales were the major bacterial groups in the later phase of the treatment RAS. Meanwhile, a network analysis among the Ettlia sp., bacterial groups, and environmental parameters, revealed that the bacterial groups played key roles in both water quality improvement and Ettlia sp. growth. In conclusion, the inoculation and growth of the Ettlia sp. and its associated bacteria in the RAS produced beneficial effects on the water quality by reducing the nitrogenous compounds and providing a favorable environment for certain bacterial groups to further improve water quality.

Floating rice-culture system for nutrient remediation and feed production in a eutrophic lake

The increased inputs of nutrients have been demonstrated to be a major contributing factor to the eutrophication of lakes and reservoirs which can lead to the production of harmful algal/cyanobacterial blooms and deleteriously affect the aesthetics of water-bodies. Floating plant-culture systems have been widely used for the ecological remediation of eutrophic water in a cost-effective manner. We investigated the applicability of Korean japonica rice variety 'Nampyeong' in a floating-culture system in a eutrophic lake for nutrient uptake and biomass production. Chemical and organic compound compositions were analyzed two times during the growth stages of the rice plant: 98 DAT (days after transplanting) and 165 DAT. Total nitrogen and phosphorus contributed around 1.36 and 0.15 (% dry weight), respectively, in rice plant components at 165 DAT. Crude protein, lipids, fiber and ash were 4.35, 1.91, 23.66 and 5.55 (% dry weight), respectively. In addition, microcystin levels in the rice plant components ranged from 0.0008 to 0.002 μg/g and did not exceed the recommended tolerable limits. These results suggested that the developed floating rice-culture system showed a good potential as a holistic management approach in terms of nutrient reduction, rice production for further use as feed and for bloom control.

Periphyton effects on bacterial assemblages and harmful cyanobacterial blooms in a eutrophic freshwater lake: a mesocosm study

Periphyton comprises a broad range of autotrophic and heterotrophic organisms that grow on submerged surfaces in aquatic environments. To investigate the ecological roles of periphyton and their symbiotic bacterial assemblages related to the control of cyanobacterial blooms, mesocosm experiments were performed in a eutrophic lake that is usually infested with harmful cyanobacterial blooms. Our results showed that periphyton, together with their symbionts, reduced Chl-a concentrations (up to 94%), improved water clarity and effectively controlled cyanobacterial blooms in the treatment mesocosm. Planktonic bacterial compositions varied greatly in the pre-bloom/bloom/post-bloom periods in both mesocosms and were mainly influenced by total dissolved nitrogen (TDN) concentrations. The phylum Cyanobacteria was the major component in the water samples until bloom peak, but it was replaced by Actinobacteria in the post-bloom period. However, periphyton niches were dominated by Alphaproteobacteria throughout the experiments, Cyanobacteria proportion being lower. Overall, the results indicated that periphyton and their unique bacterial partners could effectively compete with cyanobacteria and improve water quality. Their underlying interaction mechanism was also suggested to explain how periphyton and their symbionts can reduce cyanobacterial blooms in eutrophic water.

Parasympathetic and sympathetic control of the pancreas: a role for the suprachiasmatic nucleus and other hypothalamic centers that are involved in the regulation of food intake

To reveal brain regions and transmitter systems involved in control of pancreatic hormone secretion, specific vagal and sympathetic denervation were combined with injection of a retrograde transsynaptic tracer, pseudorabies virus (PRV), into the pancreas. After sympathetic or vagal transsection first-order neurons were revealed in the dorsal motor nucleus of the vagus (DMV) or in preganglionic spinal cord neurons (SPN), respectively. Careful timing of the survival of the animals allowed the detection of cell groups in immediate control of these DMV or SPN neurons. A far larger number of cell groups is involved in the control of DMV than of SPN neurons. Examples are given of a high level of interaction between the sympathetic and parasympathetic nervous system. Several cell groups project to both branches of the autonomic nervous system, sometimes even the same neurotransmitter is used, e.g., oxytocin neurons in the paraventricular nucleus and melanin-concentrating hormone and orexin neurons in the lateral hypothalamus project to both the DMV and SPN neurons. Moreover, the appearance of third-order neurons located in the sympathetic SPN after complete sympathectomy and in the DMV after complete vagotomy illustrates the possibility that motor neurons of the sympathetic and parasympathetic system may exchange information by means of interneurons. The presence of second-order neurons in prefrontal, gustatory, and piriform cortex may provide an anatomic basis for the involvement of these cortices in the cephalic insulin response. The observation that second-order neurons in both vagal and sympathetic control of the pancreas contain neuropeptides that are known to play a role in food intake indicates a direct association between behavioral and autonomic functions. Finally, the observation of third-order neurons in the suprachiasmatic nucleus and ventromedial hypothalamus shows the modulatory action of the time of the day and metabolic state, respectively.

Effect of bilateral lesions of the suprachiasmatic nucleus on hyperglycemia caused by 2-deoxy-D-glucose and vasoactive intestinal peptide in rats

In mammals, the brain usually uses glucose as a sole energy source. Thus, under a central glucopenic condition after intracranial injection of 2-deoxy-D-glucose (2DG), an inhibitor of glucose utilization, it has been shown that rats elevate their blood glucose level through excitation of the sympathetic nerves. Experiments were conducted with rats to examine the role of the hypothalamic suprachiasmatic nucleus (SCN) in the hyperglycemic response to intracerebroventricular injection of either 2DG or vasoactive intestinal peptide (VIP). It was observed that, (1) intracerebroventricular injection of a VIP-antagonist inhibited the hyperglycemic and hyperglucagonemic responses to the intracranial injection of 2DG; (2) bilateral electrolytic lesioning of the SCN suppressed the hyperglycemic and hyperglucagonemic responses to intracranial injection of 2DG, and intracerebroventricular injection of VIP restored these responses to 2DG; and (3) bilateral electrolytic lesioning of the SCN also suppressed the hyperglycemic and hyperglucagonemic responses to the VIP injection, and additional intracerebroventricular injection of 2DG caused hyperglycemia. These findings indicate that in rats with bilateral lesions of the SCN intracranial injection of 2DG is able to elicit hyperglycemia when VIP was administered intracranially, and suggest that neurons containing VIP-like immunoreactive substance (VIP-neurons) in the SCN have an important role in the mechanism of hyperglycemia elicitation following intracranial injection of 2DG. Moreover, these findings show that 2DG and VIP are able to realize their functions through acting on the brain sites outside the SCN.

Effect of intravenous administration of melatonin on the efferent activity of the adrenal nerve

The effect of intravenous administration of melatonin on the efferent activity of the adrenal nerve was investigated in the rat. Intravenous infusion of 1 or 2 ng melatonin resulted in a decrease, and 10 or 20 ng or larger amount of melatonin caused an increase in the efferent activity of the adrenal nerve. The least effective dose for the suppressive activity of melatonin was 100 pg and the response is dose-related. Administration of either 1 ng or 10 ng of melatonin did not change the plasma glucose concentration until 30 min after the administration. Hepatic vagotomy eliminates the inhibitory effect of melatonin. These results suggest that melatonin sensors in the hepato-portal region and melatonin receptors in the SCN play important roles in the regulation of sympathetic outflow to the adrenal medulla.

Melatonin suppresses hyperglycemia caused by intracerebroventricular injection of 2-deoxy-D-glucose in rats

To elucidate the role of melatonin (MT), we examined the effects of intracranial injection of MT and an MT-antagonist (S20928) on the hyperglycemic response to intracranial injection of 2-deoxy-D-glucose (2DG) in rats. The hyperglycemic and hyperglucagonemic responses caused by intracerebroventricular injection of 2DG were inhibited by intracerebroventricular co-injection of MT, but enhanced by co-injection of the MT-antagonist. Intraperitoneal injection of MT also inhibited the hyperglycemic response, though the inhibition seemed to be less than that after intracranial injection of MT. These results suggest that MT plays an endogenously suppressive role in the hyperglycemia caused by 2DG, possibly through a brain site.

Inheritance of dsRNAs in the rice blast fungus, Magnaporthe grisea

The 1.6 and 1.8 kbp dsRNAs have been found in the rice blast fungus, Magnaporthe grisea strain MG01. These dsRNA molecules are located in cytoplasm of the fungal cells and maintained stably during vegetative growth. Three crosses between dsRNA free and dsRNA containing strains including a parental cross, sib-mating and back cross were made to follow the inheritance of dsRNAs during sexual reproduction. Approximately 10% of ascospore progenies (11 out of 105) contained dsRNAs from all three crosses. These data indicate that dsRNAs of M. grisea are inherited at a low frequency and not in a Mendelian fashion.

Roles of the suprachiasmatic nucleus and vasoactive intestinal peptide in the response of plasma arginine vasopressin to osmotic challenge

To clarify the role of neurons containing a vasoactive intestinal peptide (VIP)-like substance (VIP neurons) in the hypothalamic suprachiasmatic nucleus (SCN) in regulation of the plasma arginine vasopressin (AVP) concentration, we examined the effects of bilateral lesions of the SCN and intracranial injection of VIP on the increase in the plasma AVP concentration caused by ip injection of hypertonic (3.6%) saline in rats. The increase in the plasma AVP concentration after ip injection of hypertonic saline was significantly suppressed in rats with bilateral lesions of the SCN. Furthermore, the increase in the plasma AVP concentration elicited by ip injection of hypertonic saline was enhanced by intracerebro-ventricular injection of VIP and suppressed by a VIP antagonist, [Lys1,Pro2,5,Arg3.4,Tyr6]VIP. However, the same dose of VIP injected into the heart had no effect on the increase in the plasma AVP concentration caused by ip injection of hypertonic saline. These results suggest that the SCN and intracranial VIP play important roles in the regulation of the plasma AVP concentration and support the possibility that VIP neurons in the SCN enhance the response of plasma AVP to osmotic challenge.

Bilateral lesions of the hypothalamic suprachiasmatic nucleus eliminated sympathetic response to intracranial injection of 2-deoxy-D-glucose and VIP rescued this response

We previously found that bilateral lesions of the suprachiasmatic nucleus abolished hyperglycemic response to intracranial injection of 2-deoxy-D-glucose in rats. Because the hyperglycemia due to 2-deoxy-D-glucose was shown to be dependent on the functions of the adrenal medulla and sympathetic nervous system, the effect of bilateral lesions of the suprachiasmatic nucleus on changes in the nervous activity of sympathetic efferents to the adrenal after intracranial injection of 2-deoxy-D-glucose was examined in rats. It was found that bilateral lesions of the nucleus eliminated the increase in neural activity of the sympathetic efferent that occurred after the injection of 2-deoxy-D-glucose. Because the suprachiasmatic nucleus possesses neurons containing a vasoactive intestinal polypeptide-like substance, the effects of vasoactive intestinal polypeptide and 2-deoxy-D-glucose, administered alone or in combination, on the sympathetic activity were examined in intact control rats and in rats with bilateral lesions of the suprachiasmatic nucleus. It was found that in the normal control rats, vasoactive intestinal polypeptide alone increased the sympathetic activity, whereas it dramatically enhanced the sympathetic response to 2-deoxy-D-glucose. However, in rats with bilateral lesions of the suprachiasmatic nucleus, vasoactive intestinal polypeptide alone elicited no increase in the nervous activity of the sympathetic efferents to the adrenal, but combined administration of vasoactive intestinal polypeptide and 2-deoxy-D-glucose caused an increase in the nervous activity of sympathetic efferents to the adrenal. These findings suggest that the suprachiasmatic nucleus is involved in the enhancement of sympathetic activity caused by intracranial injection of 2-deoxy-D-glucose, and that neurons containing a vasoactive intestinal polypeptide-like substance in the suprachiasmatic nucleus play an important role in the sympathetic enhancement that occurs after intracranial injection of 2-deoxy-D-glucose. This role might be a permissive and facilitative one.

Involvement of cerebral neurotensin in hyperglycemic response caused by 2-deoxy-D-glucose in rats

Previous studies have indicated that neurons containing a vasoactive intestinal polypeptide (VIP)-like immunoreactive substance (VIP neurons) in the suprachiasmatic nucleus (SCN) are involved in regulating glucose metabolism in rats. In this connection, it has been suggested that in rats, VIP neurons in the SCN have neurotensin (NT) receptors. To clarify the role of NT, we examined the effects of intracranial injection of NT and an NT-antagonist on the hyperglycemic response to intracranial injection of 2-deoxy-D-glucose (2DG) in rats. The hyperglycemic and hyperglucagonemic responses caused by intracerebroventricular injection of 2DG were significantly enhanced by intracerebroventricular co-injection of NT, but suppressed by co-injection of the NT-antagonist. Intraperitoneal injection of the NT-antagonist did not affect the hyperglycemic and hyperglucagonemic responses to 2DG. These results suggest that intracranial NT plays an endogenously enhancive role in the hyperglycemic and hyperglucagonemic responses caused by 2DG.

Suppressive effect of vasopressin on the hyperglycemic response to intracranial injection of 2-deoxy-D-glucose

Vasopressin (VP) is a peptide consisting of 9 amino acids which acts as a neurotransmitter or neuromodulator in the central nervous system. Neurons containing VP project to some nuclei in the hypothalamus that have a role in energy metabolism. To clarify the possible role of VP on glucose metabolism in the brain, we examined the effect of intracranial injection of VP on the hyperglycemia induced by 2-deoxy-D-glucose (2DG) and obtained the following results. The hyperglycemic and hyperglucagonemic responses induced by 2DG were significantly suppressed and enhanced by co-injections of VP and a VP-antagonist with 2DG, respectively. However, co-injections of either VP or a VP-antagonist with 2DG had no effect on the change in plasma insulin concentration. These findings suggest that central VP plays a suppressive role in the hyperglycemic and hyperglucagonemic responses to 2DG.

A synthetic study on cyclic phosphate derivatives of seconucleosides as potential antiviral agents (I). Synthesis of 3',5'-cyclic phosphates of 2'-substituted secouridines and secoribavirins

The synthetic study of 3',5-cyclic phosphates of 2'-substituted 2',3'-secouridines and 2',3'-secoribavirins toward development of new antiviral agents is described. These cyclic phosphates were synthesized from their respective 4-nitrophenyl 3',5'-cyclic phosphate triesters. These triesters were prepared from the corresponding 2'-azido and 2'-bromo 2',3'-seconucleosides.