Sphingobium cyanobacteriorum sp. nov., isolated from fresh water.

A novel Gram-stain-negative, yellow-pigmented, short rod-shaped bacterial strain, HBC34T, was isolated from a freshwater sample collected from Daechung Reservoir, Republic of Korea. The results of 16S rRNA gene sequence analysis indicated that HBC34T was affiliated with the genus Sphingobium and shared the highest sequence similarity to the type strains of Sphingobium vermicomposti (98.01 %), Sphingobium psychrophilum (97.87 %) and Sphingobium rhizovicinum (97.59 %). The average nucleotide identity (ANI) and digital DNA-DNA hybridisation (dDDH) values between HBC34T and species of the genus Sphingobium with validly published names were below 84.01 and 28.1 %, respectively. These values were lower than the accepted species-delineation thresholds, supporting its recognition as representing a novel species of the genus Sphingobium. The major fatty acids (>10 % of the total fatty acids) were identified as summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c) and summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c). The main polar lipids were phosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, two phospholipids and two unidentified polar lipids. The respiratory quinone was Q-10. The genomic DNA G+C content of HBC34T was 64.04 %. The polyphasic evidence supports the classification of HBC34T as the type strain of a novel species of the genus Sphingobium, for which the name Sphingobium cyanobacteriorum sp. nov is proposed. The type strain is HBC34T (= KCTC 8002T= LMG 33140T).

Biotechnological approaches for suppressing Microcystis blooms: insights and challenges.

Cyanobacterial harmful algal blooms, particularly those dominated by Microcystis, pose significant ecological and health risks worldwide. This review provides an overview of the latest advances in biotechnological approaches for mitigating Microcystis blooms, focusing on cyanobactericidal bacteria, fungi, eukaryotic microalgae, zooplankton, aquatic plants, and cyanophages. Recently, promising results have been obtained using cyanobactericidal bacteria: not through the inoculation of cultured bacteria, but rather by nurturing those already present in the periphyton or biofilms of aquatic plants. Fungi and eukaryotic microalgae also exhibit algicidal properties; however, their practical applications still face challenges. Zooplankton grazing on Microcystis can improve water quality, but hurdles exist because of the colonial form and toxin production of Microcystis. Aquatic plants control blooms through allelopathy and nutrient absorption. Although cyanophages hold promise for Microcystis control, their strain-specificity hinders widespread use. Despite successful laboratory validation, field applications of biological methods are limited. Future research should leverage advanced molecular and bioinformatic techniques to understand microbial interactions during blooms and offer insights into innovative control strategies. Despite progress, the efficacy of biological methods under field conditions requires further verification, emphasizing the importance of integrating advanced multi-meta-omics techniques with practical applications to address the challenges posed by Microcystis blooms. KEY POINTS: • A diverse range of biotechnological methods is presented for suppressing Microcystis blooms. • Efficacy in laboratory experiments needs to be proved further in field applications. • Multi-meta-omics techniques offer novel insights into Microcystis dynamics and interactions.

Response of particle-attached and free-living bacterial communities to Microcystis blooms.

The massive proliferation of Microcystis threatens freshwater ecosystems and degrades water quality globally. Understanding the mechanisms that contribute to Microcystis growth is crucial for managing Microcystis blooms. The lifestyles of bacteria can be classified generally into two groups: particle-attached (PA; > 3 µm) and free-living (FL; 0.2-3.0 µm). However, little is known about the response of PA and FL bacteria to Microcystis blooms. Using 16S rRNA gene high-throughput sequencing, we investigated the stability, assembly process, and co-occurrence patterns of PA and FL bacterial communities during distinct bloom stages. PA bacteria were phylogenetically different from their FL counterparts. Microcystis blooms substantially influenced bacterial communities. The time decay relationship model revealed that Microcystis blooms might increase the stability of both PA and FL bacterial communities. A contrasting community assembly mechanism was observed between the PA and FL bacterial communities. Throughout Microcystis blooms, homogeneous selection was the major assembly process that impacted the PA bacterial community, whereas drift explained much of the turnover of the FL bacterial community. Both PA and FL bacterial communities could be separated into modules related to different phases of Microcystis blooms. Microcystis blooms altered the assembly process of PA and FL bacterial communities. PA bacterial community appeared to be more responsive to Microcystis blooms than FL bacteria. Decomposition of Microcystis blooms may enhance cooperation among bacteria. Our findings highlight the importance of studying bacterial lifestyles to understand their functions in regulating Microcystis blooms. KEY POINTS: • Microcystis blooms alter the assembly process of PA and FL bacterial communities • Microcystis blooms increase the stability of both PA and FL bacterial communities • PA bacteria seem to be more responsive to Microcystis blooms than FL bacteria.

Undibacterium cyanobacteriorum sp. nov., an auxin-producing bacterium isolated from fresh water during cyanobacterial bloom period.

A novel Gram-negative, white-pigmented, and auxin-producing strain, 20NA77.5T, was isolated from fresh water during cyanobacterial bloom period. Pairwise comparison of the 16S rRNA gene sequences showed that strain 20NA77.5T belonged to the genus Undibacterium and exhibited the highest sequence similarity to the type strains of Undibacterium danionis (98.00%), Undibacterium baiyunense (97.93%), Undibacterium macrobrachii (97.92%), and Undibacterium fentianense (97.71%). The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between strain 20NA77.5T and its related type strains were below 79.93 and 23.80%, respectively. The predominant fatty acids (> 10% of the total fatty acids) were C16:0 and summed feature 3 (C16:1ω7c and/or C16:1ω6c). The genomic DNA G + C content of strain 20NA77.5T was found to be 48.61%. Based on the phylogenetic distinctness, chemotaxonomic features, and phenotypic features, strain 20NA77.5T is considered to represent a novel species of the genus Undibacterium, for which the name Undibacterium cyanobacteriorum sp. nov is proposed. The type strain is 20NA77.5T (= KCTC 8005T = LMG 33136T).

Microcystis abundance is predictable through ambient bacterial communities: A data-oriented approach.

The number of cyanobacterial harmful algal blooms (cyanoHABs) has increased, leading to the widespread development of prediction models for cyanoHABs. Although bacteria interact closely with cyanobacteria and directly affect cyanoHABs occurrence, related modeling studies have rarely utilized microbial community data compared to environmental data such as water quality. In this study, we built a machine learning model, the multilayer perceptron (MLP), for the prediction of Microcystis dynamics using both bacterial community and weekly water quality data from the Daechung Reservoir and Nakdong River, South Korea. The modeling performance, indicated by the R2 value, improved to 0.97 in the model combining bacterial community data with environmental factors, compared to 0.78 in the model using only environmental factors. This underscores the importance of microbial communities in cyanoHABs prediction. Through the post-hoc analysis of the MLP models, we revealed that nitrogen sources played a more critical role than phosphorus sources in Microcystis blooms, whereas the bacterial amplicon sequence variants did not have significant differences in their contribution to each other. Similar to the MLP model results, bacterial data also had higher predictability in multiple linear regression (MLR) than environmental data. In both the MLP and MLR models, Microscillaceae showed the strongest association with Microcystis. This modeling approach provides a better understanding of the interactions between bacteria and cyanoHABs, facilitating the development of more accurate and reliable models for cyanoHABs prediction using ambient bacterial data.

How do freshwater microalgae and cyanobacteria respond to antibiotics?

Antibiotic pollution is an emerging environmental challenge. Residual antibiotics from various sources, including municipal and industrial wastewater, sewage discharges, and agricultural runoff, are continuously released into freshwater environments, turning them into reservoirs that contribute to the development and spread of antibiotic resistance. Thus, it is essential to understand the impacts of antibiotic residues on aquatic organisms, especially microalgae and cyanobacteria, due to their crucial roles as primary producers in the ecosystem. This review summarizes the effects of antibiotics on major biological processes in freshwater microalgae and cyanobacteria, including photosynthesis, oxidative stress, and the metabolism of macromolecules. Their adaptive mechanisms to antibiotics exposure, such as biodegradation, bioadsorption, and bioaccumulation, are also discussed. Moreover, this review highlights the important factors affecting the antibiotic removal pathways by these organisms, which will promote the use of microalgae-based technology for the removal of antibiotics. Finally, we offer some perspectives on the opportunities for further studies and applications.

Mucilaginibacter straminoryzae sp. nov., isolated from rice straw used for growing periphyton.

A rod-shaped, non-motile, Gram-negative bacterium, strain RS28T, was isolated from rice straw used as material for periphyton growth. Phylogenetic analysis of the 16S rRNA gene sequence revealed that strain RS28T was affiliated with the genus Mucilaginibacter and had the highest sequence similarity to Mucilaginibacter ginkgonis HMF7856T (96.47 %) and Mucilaginibacter polytrichastri DSM 26907T (96.12 %). Strain RS28T was found to grow at pH 5.5-8.0, 17-40 °C and in the presence of 0-1.5 % (w/v) NaCl. Strain RS28T contained summed feature 3 (comprising C16 : 1 ω7c and/or C16 : 1 ω6c), iso-C15 : 0 and iso-C17 : 0 3-OH as the major fatty acids (> 10.0 %). The major polar lipids were phosphatidylethanolamine, two unidentified phospholipids, two unidentified aminophospholipids, three unidentified aminolipids and one unidentified lipid. The respiratory quinone was menaquinone 7. The genomic DNA G+C content was 44.7 mol%. Strain RS28T possessed six putative secondary metabolite gene clusters involved in the synthesis of resorcinol, NRPS-like, terpene, lassopeptide, T3PKS and arylpolyene. On the basis of the phenotypic, chemotaxonomic, and phylogenetic characteristics, strain RS28T represents a novel species of the genus Mucilaginibacter, for which the name Mucilaginibacter straminoryzae sp. nov. is proposed. The type strain is RS28T (=KCTC 92039T=LMG 32424T).

Novosphingobium cyanobacteriorum sp. nov., isolated from a eutrophic reservoir during the Microcystis bloom period.

A novel Gram-stain-negative, aerobic and rod-shaped bacterial strain, HBC54T, was isolated from periphyton during a Microcystis bloom. Based on the results of the 16S rRNA gene sequence analysis, strain HBC54T was closely related to Novosphingobium aerophilum 4Y4T (98.36 %), Novosphingobium aromaticivorans DSM 12444T (98.08 %), Novosphingobium huizhouense c7T (97.94 %), Novosphingobium percolationis c1T (97.65 %), Novosphingobium subterraneum DSM 12447T (97.58 %), Novosphingobium olei TW-4T (97.58 %) and Novosphingobium flavum UCT-28T (97.37 %). The average nucleotide identity and digital DNA-DNA hybridization values between HBC54T and its related type stains were below 78.97 and 23.7 %, which are lower than the threshold values for species delineation. The major fatty acids (>10.0 %) were identified as C14 : 0 2-OH, summed feature 3 (C16 : 1 ω7c and/or C16 : 1 ω6c) and summed feature 8 (C18 : 1 ω7c and/or C18 : 1 ω6c) and the respiratory quinone was ubiquinone Q-10. The main polar lipids detected in the strain were phosphatidylethanolamine, phosphatidylglycerol, phosphatidylcholine, diphosphatidylglycerol and three unidentified phospholipids. The genomic DNA G+C content was 64.8 mol%. Strain HBC54T is considered to represent a novel species within the genus Novosphingobium, for which the name Novosphingobium cyanobacteriorum sp. nov. is proposed. The type strain is HBC54T (=KCTC 92033T=LMG 32427T).

Panacibacter microcysteis sp. nov., isolated from a eutrophic reservoir during the Microcystis bloom period.

A Gram-stain-negative, rod-shaped bacterial strain DH6T was isolated from fresh water of the Daechung Reservoir during the Microcystis bloom period. The strain grew at pH 6.0-8.5, at temperature 17-40 °C, and at 0-1% (w/v) NaCl concentration. Comparison of 16S rRNA gene sequence indicated that strain DH6T exhibits the highest similarity with Panacibacter ginsenosidivorans Gsoil 1550T (96.6%). The average nucleotide identity (ANI), digital DNA-DNA hybridization (dDDH), and average amino acid identity (AAI) values of strain DH6T compared to its related type strains were below 74.2%, 22.3%, and 74.8%, respectively. The predominant fatty acids (> 5.0%) were identified as iso-C17:0 3-OH, iso-C13:0, iso-C15:0, C17:0 2-OH, iso-C11:0, anteiso-C13:0, and iso-C15:1 G. The polar lipid profile contained phosphatidylethanolamine, four unidentified aminolipids, and three unidentified lipids. The respiratory quinone was menaquinone 7 (MK-7). The genomic DNA G + C content was 42.6%. Collectively, strain DH6T should be classified as a novel species within the genus Panacibacter, for which the name Panacibacter microcysteis sp. nov. is proposed. The type strain is DH6T (= KCTC 82471T = LMG 32426T).

Hymenobacter cyanobacteriorum sp. nov., isolated from a freshwater reservoir during the cyanobacterial bloom period.

A Gram-negative, red-colored, and rod-shaped bacterial strain, DH14T, was isolated from a eutrophic reservoir. The 16S rRNA gene sequence analysis showed that strain DH14T was most closely related to Hymenobacter terrigena (98.3% similarity) and Hymenobacter terrae (98.1%). The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between strain DH14T and its related type strains were below 82.9% and 27.2%, respectively. Strain DH14T contained iso-C15:0 (32.6%), anteiso-C15:0 (14.0%), and summed feature 3 (C16:1 ω6c and/or C16:1 ω7c) (25.8%) as major cellular fatty acids. The main polar lipids were phosphatidylethanolamine, two unidentified aminophospholipids, and one unidentified lipid. The respiratory quinone was menaquinone 7 (MK-7). The genomic DNA G + C content was 62.1%. These evidences support the classification of strain DH14T as a novel species in the genus Hymenobacter, for which the name Hymenobacter cyanobacteriorum sp. nov. is proposed. The type strain is DH14T (= KCTC 92040T = LMG 32425T).

New Multidrug Efflux Systems in a Microcystin-Degrading Bacterium Blastomonas fulva and Its Genomic Feature.

A microcystin-degrading bacterial strain, Blastomonas fulva T2, was isolated from the culture of a microalgae Microcystis. The strain B. fulva T2 is Gram-stain-negative, non-motile, aerobic, non-spore-forming and phototrophic. The cells of B. fulva T2 are able to grow in ranges of temperature from 15 to 37 °C, with a pH of 6 to 8 and a salinity of 0 to 1% NaCl. Here, we sequenced the complete genome of B. fulva T2, aiming to better understand the evolutionary biology and the function of the genus Blastomonas at the molecular level. The complete genome of B. fulva T2 contained a circular chromosome (3,977,381 bp) with 64.3% GC content and a sizable plasmid (145.829 bp) with 60.7% GC content which comprises about 3.5% of the total genetic content. A total of 3842 coding genes, including 46 tRNAs and 6 rRNAs, were predicted in the genome. The genome contains genes for glycolysis, citric acid cycle, Entner-Doudoroff pathways, photoreaction center and bacteriochlorophylla synthesis. A 7.9 K gene cluster containing mlrA, mlrB, mlrC and mlrD1,2,3,4 of microcystin-degrading enzymes was identified. Notably, eight different efflux pumps categorized into RND, ABC and MFS types have been identified in the genome of strain T2. Our findings should provide new insights of the alternative reaction pathway as well as the enzymes which mediated the degradation of microcystin by bacteria, as well as the evolution, architectures, chemical mechanisms and physiological roles of the new bacterial multidrug efflux system.

Mariniflexile maritimum sp. nov., isolated from seawater of the South Sea in the Republic of Korea.

A novel Gram-stain-negative, rod-shaped, aerobic, non-motile bacterial strain, designated M5A1MT, was isolated from seawater collected from the South Sea of the Republic of Korea. Based on 16S rRNA gene sequence similarity, strain M5A1MT was closely related to Mariniflexile gromovii KMM 6038T (95.3 %), Mariniflexile fucanivorans SW5T (95.2 %), Mariniflexile soesokkakense RSSK-9T (95.1 %), Yeosuana aromativorans GW1-1T (94.6 %) and Confluentibacter lentus HJM-3T (94.6 %). Genome-based phylogenetic analyses revealed that strain M5A1MT formed a distinct cluster with the type strains of the genus Mariniflexile. The major cellular fatty acid constituents (>5 % of the total fatty acids) were iso-C15:0, anteiso-C15 : 0, iso-C15 : 0 3-OH, iso-C15 : 1 G, iso-C16:03-OH and iso-C17 : 0 3-OH. The respiratory quinone was identified as MK-6. The major polar lipids were phosphatidylethanolamine and one unidentified polar lipid. The genomic DNA G+C content of strain M5A1MT was determined to be 37.7 mol%. On the basis of its phenotypic, phylogenetic and chemotaxonomic characteristics, strain M5A1MT is considered to represent a novel species within the genus Mariniflexile, for which the name Mariniflexile maritimum sp. nov. is proposed. The type strain is M5A1MT (=KCTC 72895T=JCM 33982T).

Cochlodiniinecator piscidefendens gen. nov., sp. nov., an algicidal bacterium against the ichthyotoxic dinoflagellate Cochlodinium polykrikoides.

Harmful algal blooms caused by Cochlodinium polykrikoides result in enormous economic damage to the aquaculture industry. Biological control methods have attracted wide attention due to their environmental-friendliness. In this study, a novel algicidal bacterium, designated strain M26A2MT, was determined for its taxonomic position and was evaluated for its potential to mitigate C. polykrikoides blooms. Strain M26A2MT exhibited the highest 16S rRNA gene sequence similarity to the type strains of Planktotalea lamellibrachiae (97.3%), Halocynthiibacter namhaensis (97.2%), Pseudohalocynthiibacter aestuariivivens (96.8%) and Halocynthiibacter arcticus (96.4%) in the family Rhodobacteraceae. The predominant fatty acids were C10 : 0 3-OH and summed feature 8 (comprising C18 : 1 ω7c and/or C18 : 1 ω6c). The major polar lipids were phosphatidylcholine, phosphatidylglycerol, phosphatidylethanolamine, one unidentified aminolipid and three unidentified lipids. Q-10 was the respiratory quinone. Strain M26A2MT exerted significant algicidal activity against C. polykrikoides cells by destroying the membrane integrity and the photosynthetic system. Our findings suggest that strain M26A2MT shows a high potential to control outbreaks of C. polykrikoides. Based on the polyphasic characterization, strain M26A2MT is considered to represent a novel species within a novel genus of the family Rhodobacteraceae, for which the name Cochlodiniinecator piscidefendens gen. nov., sp. nov. is proposed. The type strain is M26A2MT (=KCTC 82083T=JCM 34119T).

Novosphingobium aquimarinum sp. nov., isolated from seawater.

A novel Gram-stain-negative, aerobic, and rod-shaped bacterial strain, M24A2MT, was isolated from seawater in the Republic of Korea. On the basis of the 16S rRNA gene phylogeny, strain M24A2MT was found to be closely related to Novosphingobium pentaromativorans US6-1T and Novosphingobium mathurense SM117T with pair-wise sequence similarities of 97.4 and 96.9 %, respectively. Phylogenetic analysis of 16S rRNA sequences indicated that M24A2MT formed a branch with Novosphingobium pentaromativorans US6-1T and represented a member of the genus Novosphingobium. The predominant cellular fatty acids were C14 : 0 2-OH, summed feature 3 (C16 : 1 ω7c and/or C16 : 1 ω6c), and summed feature 8 (C18 : 1 ω7c and/or C18 : 1 ω6c). The polar lipids of strain M24A2MT consisted mainly of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylcholine, one unidentified phospholipid, and two unidentified lipids. The respiratory quinone was ubiquinone Q-10. The genomic DNA G+C content was 63.9 %. Given the phenotypic characteristics along with the phylogenetic distinctness and chemotaxonomic features, strain M24A2MT is considered to represent a novel species within the genus Novosphingobium, for which the name Novosphingobium aquimarinum sp. nov. is proposed. The type strain of Novosphingobium aquimarinum sp. nov. is M24A2MT (=KCTC 72894T=JCM 33983T).

Genomic insights into a novel species Rhodoferax aquaticus sp. nov., isolated from freshwater.

A novel non-phototrophic member of the genus Rhodoferax was obtained from freshwater. The purpose of this study was to analyse the genome of a nonphototrophic strain and propose a new species based on its phylogenetic, genomic, physiological and chemotaxonomic characteristics. The results of phylogenetic analysis based on 16S rRNA gene sequences supports that the strain, designated Gr-4T, has a close relationship to the genus Rhodoferax. The observed average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between strain Gr-4T and its closest related strains were 72.3-74.6 % and 21.9-22.8 %, respectively. These values were much lower than the species separation thresholds for ANI or dDDH of 95-96 and 70 %, respectively, and in fact fall in the intergeneric range. Strain Gr-4T does not contain RuBisCO-related genes, but does contain GS/GOGAT pathway-related genes enabling nitrate ammonification. A polyphasic study and a genomic-level investigation were done to establish the taxonomic status of strain Gr-4T. Based on the phylogenetic, genomic and physiological differences, it is proposed that the isolate be classified to the genus Rhodoferax as Rhodoferax aquaticus sp. nov. with isolate Gr-4T (=KCTC 32394T=JCM 19166T) as the type strain.

Mucilaginibacter inviolabilis sp. nov., isolated from the phycosphere of Haematococcus lacustris NIES 144 culture.

A Gram-stain-negative, non-motile, rod-shaped, aerobic bacterial strain, designated HC2T, was isolated from the phycosphere of Haematococcus lacustris NIES 144 culture. Strain HC2T was able to grow at pH 4.5-8.0, at 4-32 °C and in the presence of 0-2 % (w/v) NaCl. Phylogenetic analysis of the 16S rRNA gene sequence revealed that strain HC2T was affiliated to the genus Mucilaginibacter and shared the highest sequence similarity with Mucilaginibacter lappiensis ANJKI2T (98.20 %) and Mucilaginibacter sabulilitoris SMS-12T (98.06 %). Strain HC2T contained summed feature 3 (C16 : 1 ω7c and/or C16 : 1 ω6c) and iso-C15 : 0 as the major fatty acids (>10.0 %). The major polar lipids were phosphatidylethanolamine, one unidentified aminophospholipid, one unidentified phospholipid, two unidentified aminolipids and four unidentified lipids. The respiratory quinone was menaquinone 7 (MK-7). The genomic DNA G+C content was 42.0 %. On the basis of the phenotypic, chemotaxonomic and phylogenetic characteristics, strain HC2T represents a novel species of the genus Mucilaginibacter, for which the name Mucilaginibacter inviolabilis sp. nov. is proposed. The type strain is HC2T (=KCTC 82084T=JCM 34116T).

Description of novel members of the family Sphingomonadaceae: Aquisediminimonas profunda gen. nov., sp. nov., and Aquisediminimonas sediminicola sp. nov., isolated from freshwater sediment.

Two Gram-stain-negative bacterial strains, DS48-3T and CH68-4T, were isolated from freshwater sediment taken from the Daechung Reservoir, Republic of Korea. Cells of strains DS48-3T and CH68-4T were aerobic, non-motile, non-spore-forming and rod-shaped. Strain DS48-3T was isolated from a sediment surface sample at a depth of 48 m from the Daechung Reservoir and was most closely related to the genus Sphingopyxis according to 16S rRNA gene sequence analysis (94.5-95.9 % similarity). Strain CH68-4T was isolated from the very bottom of a 67-cm-long sediment core collected from Daechung Reservoir at a water depth of 17 m and was most closely related to the genus Sphingopyxis (16S rRNA gene sequence similarity of 93.7-95.0 %). Phylogenetic analysis based on 16S rRNA gene sequencing indicated that the two strains formed a separate lineage within the order Sphingomonadales showing similarity values below 95.9 % with their closest phylogenetic neighbours, and sharing 97.3 % similarity with each other. The combined genotypic and phenotypic data showed that strains DS48-3T and CH68-4T could be distinguished from all genera within the family Sphingomonadaceae and represented two distinct species of a novel genus, Aquisediminimonas profunda gen. nov., sp. nov. (type strain DS48-3T=KCTC 52068T=CCTCC AB 2018061T) and Aquisediminimonas sediminicola sp. nov. (type strain CH68-4T=KCTC 62205T=CCTCC AB 2018062T).

Bioflocculation in natural and engineered systems: current perspectives.

Microorganisms have the tendency to accumulate at interfaces through the release of extracellular polymeric substances to form aggregates such as films or flocs. This physical association leads to different modes of interactions among cells and the subsequent development of functionally and metabolically diverse consortia. Aggregation of cells in aqueous suspensions often results in the formation of flocs, which are hotspots of enhanced microbial processes. This has important implications for the dynamics of organic and inorganic matter in varied ecosystems. These microbial flocs are not only important components in nutrient turnover, decomposition, and sinking flux but also facilitate contaminant removal and treatment of wastewater and biomass harvesting. Greater insight into the multitude of interactions between microorganisms in flocs would be useful to enhance the efficiency of bioflocculation processes. This review covers the fundamental aspects and outlines the role of bioflocculation in controlled industrial processes and in nature.

Description of Hymenobacter daejeonensis sp. nov., isolated from grass soil, based on multilocus sequence analysis of the 16S rRNA gene, gyrB and tuf genes.

A polyphasic taxonomic study was carried out on strains PB105T and PB108 isolated from a grass soil in Korea. The cells of the strains were Gram-stain negative, non-spore-forming, non-motile, and rod-shaped. Comparative 16S rRNA gene sequence studies showed a clear affiliation of these strains with Bacteroidetes, which showed high pairwise sequence similarities with Hymenobacter algoricola VUG-A23aT (99.2%), Hymenobacter fastidiosus VUG-A124aT (97.4%), and Hymenobacter daecheongensis Dae14T (96.9%). The phylogenetic analysis based on 16S rRNA gene sequences showed that the strains formed a clear phylogenetic lineage with the genus Hymenobacter. The major fatty acids were identified as C15:0 iso, C15:0 anteiso, C16:1 ω5c, C15:0 iso 3-OH, C17:0 iso 3-OH, summed feature 3 (C16:1 ω6c and/or C16:1 ω7c/t), and summed feature 4 (C17:1 anteiso B and/or C17:1 iso I). The major cellular polar lipids were identified as phosphatidylethanolamine, an unidentified aminolipid, and two unidentified lipids. The respiratory quinone was identified as MK-7 and the genomic DNA G+C content was determined to be 64.5 mol% for strain PB105T and 64.1 mol% for strain PB108. DNA-DNA hybridization value of type strain PB105T with H. algoricola VUG-A23aT was 32.3% (reciprocal 39.2). Based on the combined genotypic and phenotypic data, we propose that strains PB105T and PB108 represent a novel species of the genus Hymenobacter, for which the name Hymenobacter daejeonensis sp. nov. is proposed. The type strain is PB105T (= KCTC 52579T = JCM 31885T).

Asprobacter aquaticus gen. nov., sp. nov., a prosthecate alphaproteobacterium isolated from fresh water.

A novel Gram-negative bacterium strain, DRW22-8T, was isolated from fresh water taken at a depth of 22 m at Daechung Reservoir, Republic of Korea. The cells of strain DRW22-8T were aerobic and motile with a single polar flagellum or non-motile (stalked), and formed creamy-white colonies on R2A agar. The phylogenetic analysis based on 16S rRNA gene sequencing indicated that the strain formed a separate lineage within the order Rhodobacterales, showing similarity values under 91.8 % with its closest phylogenetic neighbours, Hirschia litorea, Hirschia baltica and Hirschia maritima. The chemotaxonomic results showed Q-10 as the predominant respiratory ubiquinone, three unidentified glycolipids, an unidentified lipid and phosphatidylglycerol as the major polar lipids, and C16 : 0, 11-methyl C18 : 1, C18 : 1 ω7c and/or C18 : 1 ω6c as the major fatty acids. The DNA G+C content was 64.4 mol%. The combined genotypic and phenotypic data showed that strain DRW22-8T could be distinguished from all genera within the family Hyphomonadaceae and represented a novel genus, Asprobacter gen. nov., with the name Asprobacter aquaticus sp. nov., in the family Hyphomonadaceae. The type strain is DRW22-8T (=KCTC 42356T=JCM 30469T).