Chryseobacterium culicis sp. nov., isolated from the midgut of the mosquito Culex quinquefasciatus

Culturable bacteria and fungi in Ixodes, Dermacentor, Amblyomma and Ornithodoros ticks

Ticks are ectoparasites harboring complex microbial communities, typically dominated by nutritional symbionts that produce B vitamins and sometimes including pathogens affecting human and animal health. However, ticks also host a variety of commensal microbes whose diversity remains poorly documented. In this study, we isolated and identified culturable bacteria and fungi associated with various tick species from the genera Ixodes, Dermacentor, Amblyomma, and Ornithodoros, collected from their natural habitats or hosts in France and French Guiana. A total of 111 bacterial and 27 fungal isolates were obtained which were then identified using both molecular and morphological approaches. Substantial fungal diversity was observed in a few ticks, whereas culturable bacteria displayed a broader distribution and diversity across tick species. Interestingly, the diversity of culturable bacteria and fungi revealed a microbiome structure that reflected the ecological niches of the tick host, indicating habitat-specific microbial associations and a potential ecological role in tick biology. The isolation of common gut bacteria of other arthropods, as well as the isolation of a viable entomopathogenic fungus, underscores the potential influence of these microbes on tick biology.

Microbiome profile of South Korean vector mosquitoes

This research offers a comprehensive exploration of the microbial communities associated with vector mosquitoes from South Korea. Aedes albopictus, Anopheles sinensis, and Culex molestus are vectors of pathogens, and understanding the intricacies of their microbiome profile is paramount for unraveling their roles in disease transmission dynamics. In this study, we characterized the microbiome of the midguts of adult female vector mosquitoes collected from different locations in South Korea. After DNA extraction from dissected mosquito midguts, we used the Illumina MiSeq next-generation sequencing to obtain sequences spanning the V4 hypervariable region of the bacteria 16S rRNA. Morphological and molecular characterization using 506-bp mitochondrial 16S rRNA was used to identify the mosquito species before amplicon sequencing. Across the three vector mosquitoes surveyed, 21 bacteria genera belonging to 20 families and 5 phyla were discovered. Proteobacteria and Bacteriodota were the major phyla of bacteria associated with the three mosquito species. There were significant differences in the gut microbiome genera composition between the species and little variation in the gut microbiome between individuals of the same mosquito species. Wolbachia is the most dominant genus in Aedes while Aeromonas, Acinetobacter, and unassigned taxa are the most common in An. sinensis. In addition to that, Chromobacterium, Chryseobacterium, and Aeromonas are dominant in Cx. molestus. This study sheds light on the complex interactions between mosquitoes and their microbiome, revealing potential implications for vector competence, disease transmission, and vector control strategies.

Chryseobacterium metallicongregator, sp. nov., a bacterium possessing metallophore activity towards rare earth elements

A polyphasic taxonomic study was carried out on strain ES2T, isolated from sediment of a wetland created to remediate acid drainage from a coal mine. The rod-shaped bacterium formed yellow/orange pigmented colonies and produced the pigment flexirubin. The 16S rRNA gene sequence results assigned the strain to Chryseobacterium, with 98.9 and 98.3 % similarity to Chryseobacterium vietnamense and Chryseobacterium cucumeris, respectively. Computation of the average nucleotide identity and digital DNA-DNA hybridization values with the closest phylogenetic neighbours of ES2T revealed genetic differences at the species level, which were further substantiated by differences in several physiological characteristics. The dominant fatty acids of strain ES2T were iso-C15 : 0, iso-C17 : 1 ω9c, iso C17 : 0 3-OH, and iso-C15 : 0 2-OH. The DNA G+C content was 35.5 mol%. The major polar lipid was phosphatidylethanolamine while menaquinone-6 was the only menaquinone found. This bacterium has been previously shown to possess metallophore activity towards rare earth elements, and based on genome sequencing, possesses all required genes for siderophore production/activity, possibly identifying the source of this unique ability. On the basis of the results obtained here, this bacterium is assigned to the genus Chryseobacterium as representing a new species with the name Chryseobacterium metallicongregator sp. nov., type strain ES2T (=NRRL B-65679T=KCTC 102120T).

Impact of transgenerational host switch on gut bacterial assemblage in generalist pest, Spodoptera littoralis (Lepidoptera: Noctuidae)

Diet composition is vital in shaping gut microbial assemblage in many insects. Minimal knowledge is available about the influence of transgenerational diet transition on gut microbial community structure and function in polyphagous pests. This study investigated transgenerational diet-induced changes in Spodoptera littoralis larval gut bacteriome using 16S ribosomal sequencing. Our data revealed that 88% of bacterial populations in the S. littoralis larval gut comprise Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes. The first diet transition experiment from an artificial diet (F0) to a plant diet (F1), cabbage and cotton, caused an alteration of bacterial communities in the S. littoralis larval gut. The second transgenerational diet switch, where F1 larvae feed on the same plant in the F2 generation, displayed a significant variation suggesting further restructuring of the microbial communities in the Spodoptera larval gut. F1 larvae were also challenged with the plant diet transition at the F2 generation (cabbage to cotton or cotton to cabbage). After feeding on different plant diets, the microbial assemblage of F2 larvae pointed to considerable differences from other F2 larvae that continued on the same diet. Our results showed that S. littoralis larval gut bacteriome responds rapidly and inexplicably to different diet changes. Further experiments must be conducted to determine the developmental and ecological consequences of such changes. Nevertheless, this study improves our perception of the impact of transgenerational diet switches on the resident gut bacteriome in S. littoralis larvae and could facilitate future research to understand the importance of symbiosis in lepidopteran generalists better.

In vitro assays reveal inherently insecticide-tolerant termite symbionts

Introduction: Termite symbionts are well known for conferring a myriad of benefits to their hosts. Bacterial symbionts are repeatedly associated with increased fitness, nutritional supplementation, pathogen protection, and proper development across insect taxa. In addition, several recent studies link bacterial symbionts to reduced insecticide efficacy. This has important implications both in pest control management and environmental bioremediation efforts. Insects' guts may be a valuable resource for microbes with broad application given their unique niches and metabolic diversity. Though insecticide resistance in termites is considered unlikely due to their life history, the close association of termites with a multitude of bacteria raises the question: is there potential for symbiont-mediated pesticide tolerance in termites? Methods and results: We identified a candidate that could grow in minimal medium containing formulated pesticide. This bacterial isolate was then subjected to continuous culture and subsequently demonstrated improved performance in the presence of pesticide. Isolates subjected to continuous culture were then grown at a range of concentrations from 1-10X the formulation rate. After constant exposure for several generations, isolates grew significantly better. Conclusion: Here we demonstrate that naïve insect hosts can harbor symbionts with inherent insecticide tolerance capable of rapid adaptation to increasing insecticide concentrations overtime. This has broad implications for both pest control and environmental cleanup of residual pesticides.

Chryseobacterium oryctis sp. nov., isolated from the gut of the beetle Oryctes rhinoceros, and Chryseobacterium kimseyorum sp. nov., isolated from a stick insect rearing cage

Two strains of Chryseobacterium identified from different experiments are proposed to represent new species. Strain WLa1L2M3T was isolated from the digestive tract of an Oryctes rhinoceros beetle larva. Strain 09-1422T was isolated from a cage housing the stick insect Eurycantha calcarata. Sequence analysis of the 16S rRNA and rpoB genes found both strains to be similar but not identical to other Chryseobacterium species. Whole-genome sequencing suggested the isolates represent new species, with average nucleotide identity values ranging from 74.6 to 80.5 %. Genome-to-genome distance calculations produced values below 25.3 %, and digital DNA-DNA hybridization values were 13.7-29.9 %, all suggesting they are distinct species. The genomic DNA G+C content of WLa1L2M3T is approximately 32.53 %, and of 09-1422T is approximately 35.89 %. The predominant cellular fatty acids of strain WLa1L2M3T are C15 : 0 iso, summed feature 9 (C16 : 0 10OH or C17 : 1 iso ω6c), C17 : 0 iso 3OH, summed feature 3 (C16 : 1 ω7c and/or C16 : 1 ω6c), C15 : 0 iso 3OH, C15 : 0 anteiso and C13 : 0 iso, and those of strain 09-1422T are C15 : 0 iso, summed feature 3 (C16 : 1 ω7c and/or C16 : 1 ω6c), C17 : 0 iso 3OH, C15 : 0 anteiso, C15 : 0 iso 3OH, C16 : 1 ω7c, C17 : 0 2OH and C18 : 0. In addition, physiological and biochemical tests revealed phenotypic differences from related Chryseobacterium type strains. These cumulative data indicate that the two strains represent novel species of the genus Chryseobacterium for which the names Chryseobacterium oryctis sp. nov. and Chryseobacterium kimseyorum sp. nov. are proposed with WLa1L2M3T (=BCRC 81350T=JCM 35215T=CIP 112035T) and 09-1422T (=UCDFST 09-1422T=BCRC 81359T=CIP 112165T), as type strains, respectively.

A novel binary pesticidal protein from Chryseobacterium arthrosphaerae controls western corn rootworm by a different mode of action to existing commercial pesticidal proteins

The western corn rootworm (WCR) Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae) remains one of the economically most important pests of maize (Zea mays) due to its adaptive capabilities to pest management options. This includes the ability to develop resistance to some of the commercial pesticidal proteins originating from different strains of Bacillus thuringiensis. Although urgently needed, the discovery of new, environmentally safe agents with new modes of action is a challenge. In this study we report the discovery of a new family of binary pesticidal proteins isolated from several Chryseobacterium species. These novel binary proteins, referred to as GDI0005A and GDI0006A, produced as recombinant proteins, prevent growth and increase mortality of WCR larvae, as does the bacteria. These effects were found both in susceptible and resistant WCR colonies to Cry3Bb1 and Cry34Ab1/Cry35Ab1 (reassigned Gpp34Ab1/Tpp35Ab1). This suggests GDI0005A and GDI0006A may not share the same binding sites as those commercially deployed proteins and thereby possess a new mode of action. This paves the way towards the development of novel biological or biotechnological management solutions urgently needed against rootworms.

The mosquito microbiome includes habitat-specific but rare symbionts

Microbial communities are known to influence mosquito lifestyles by modifying essential metabolic and behavioral processes that affect reproduction, development, immunity, digestion, egg survival, and the ability to transmit pathogens. Many studies have used 16S rRNA gene amplicons to characterize mosquito microbiota and investigate factors that influence host-microbiota dynamics. However, a relatively low taxonomic resolution due to clustering methods based on arbitrary threshold and the overall dominance of Wolbachia or Asaia symbionts obscured the investigation of rare members of mosquito microbiota in previous studies. Here, we used high resolution Shannon entropy-based oligotyping approach to analyze the microbiota of Culex pipiens, Culex quinquefasciatus and Aedes individuals from continental Southern France and overseas Guadeloupe as well as from laboratories with or without antibiotics treatment. Our experimental design that resulted in a series of mosquito samples with a gradient of Wolbachia density and relative abundance along with high-resolution analyses of amplicon sequences enabled the recovery of a robust signal from typically less accessible bacterial taxa. Our data confirm species-specific mosquito-bacteria associations with geography as a primary factor that influences bacterial community structure. But interestingly, they also reveal co-occurring symbiotic bacterial variants within single individuals for both Elizabethkingia and Erwinia genera, distinct and specific Asaia and Chryseobacterium in continental and overseas territories, and a putative rare Wolbachia variant. Overall, our study reveals the presence of previously overlooked microdiversity and multiple closely related symbiotic strains within mosquito individuals with a remarkable habitat-specificity.

Analysis of 1,000 Type-Strain Genomes Improves Taxonomic Classification of Bacteroidetes

Although considerable progress has been made in recent years regarding the classification of bacteria assigned to the phylum Bacteroidetes, there remains a need to further clarify taxonomic relationships within a diverse assemblage that includes organisms of clinical, piscicultural, and ecological importance. Bacteroidetes classification has proved to be difficult, not least when taxonomic decisions rested heavily on interpretation of poorly resolved 16S rRNA gene trees and a limited number of phenotypic features. Here, draft genome sequences of a greatly enlarged collection of genomes of more than 1,000 Bacteroidetes and outgroup type strains were used to infer phylogenetic trees from genome-scale data using the principles drawn from phylogenetic systematics. The majority of taxa were found to be monophyletic but several orders, families and genera, including taxa proposed long ago such as Bacteroides, Cytophaga, and Flavobacterium but also quite recent taxa, as well as a few species were shown to be in need of revision. According proposals are made for the recognition of new orders, families and genera, as well as the transfer of a variety of species to other genera. In addition, emended descriptions are given for many species mainly involving information on DNA G+C content and (approximate) genome size, both of which can be considered valuable taxonomic markers. We detected many incongruities when comparing the results of the present study with existing classifications, which appear to be caused by insufficiently resolved 16S rRNA gene trees or incomplete taxon sampling. The few significant incongruities found between 16S rRNA gene and whole genome trees underline the pitfalls inherent in phylogenies based upon single gene sequences and the impediment in using ordinary bootstrapping in phylogenomic studies, particularly when combined with too narrow gene selections. While a significant degree of phylogenetic conservation was detected in all phenotypic characters investigated, the overall fit to the tree varied considerably, which is one of the probable causes of misclassifications in the past, much like the use of plesiomorphic character states as diagnostic features.

Chryseobacterium mulctrae sp. nov., isolated from raw cow's milk

A Gram-stain-negative bacterial strain, designated CA10^T, was isolated from bovine raw milk sampled in Anseong, Republic of Korea. Cells were yellow-pigmented, aerobic, non-motile bacilli and grew optimally at 30 °C and pH 7.0 on tryptic soy agar without supplementation of NaCl. Phylogenetic analysis based on the 16S rRNA gene sequences revealed that strain CA10^T belonged to the genus Chryseobacterium, family Flavobacteriaceae, and was most closely related to Chryseobacterium indoltheticum ATCC 27950^T (98.75 % similarity). The average nucleotide identity and digital DNA-DNA hybridization values of strain CA10^T were 94.4 and 56.9 %, respectively, relative to Chryseobacterium scophthalmum DSM 16779^T, being lower than the cut-off values of 95-96 and 70 %, respectively. The predominant respiratory quinone was menaquinone-6; major polar lipid, phosphatidylethanolamine; major fatty acids, iso-C_15 : 0, summed feature 9 (iso-C_17 : 1ω9c and/or C_16 : 0 10-methyl), summed feature 3 (iso-C_15 : 0 2-OH and/or C_16 : 1ω7c) and iso-C_17 : 0 3-OH. The results of physiological, chemotaxonomic and biochemical analyses suggested that strain CA10^T is a novel species of genus Chryseobacterium, for which the name Chryseobacterium mulctrae sp. nov. is proposed. The type strain is CA10^T (=KACC 21234^T=JCM 33443^T).

Phylogenetic insights into the diversity of Chryseobacterium species

The genus Chryseobacterium was formally established in 1994 and contains 112 species with validly published names. Most of these species are yellow or orange coloured, and contain a flexirubin-type pigment. The genomes of 83 of these 112 species have been sequenced in view of their importance in clinical microbiology and potential applications in biotechnology. The National Center for Biotechnology Information taxonomy browser lists 1415 strains as members of the genus Chryseobacterium, of which the genomes of 94 strains have been sequenced. In this study, by comparing the 16S rDNA and the deduced proteome sequences, at least 20 of these strains have been proposed to represent novel species of the genus Chryseobacterium. Furthermore, a yellow-coloured bacterium isolated from dry soil in the USA (and identified as Flavobacterium sp. strain B-14859) has also been reconciled as a novel member of the genus Chryseobacterium based on the analysis of 16S rDNA sequences and the presence of flexirubin. Yet another bacterium (isolated from a water sample collected in the Western Ghats of India and identified as Chryseobacterium sp. strain WG4) was also found to represent a novel species. These proposals need to be validated using polyphasic taxonomic approaches.

Chryseobacterium aureum sp. nov., isolated from the Han River, Republic of Korea

A Gram-stain-negative, yellow-pigmented, non-motile, non-spore-forming, aerobic and rod-shaped bacterial strain, designated 17S1E7^T, was isolated from the Han River, Republic of Korea, and characterized by polyphasic taxonomy analyses. Strain 17S1E7^T grew optimally on tryptic soy agar at 37 °C and pH 7.0 in the absence of NaCl. Phylogenetic analysis based on the 16S rRNA gene sequence indicated that strain 17S1E7^T belonged to the genus Chryseobacterium and was most closely related to Chryseobacterium culicis DSM 23031^T (98.54 %). The average nucleotide identity value of strain 17S1E7^T was 91.1 % to Chryseobacterium culicis DSM 23031^T, which was lower than the cut-off of 95-96 %. The DNA G+C content of strain 17S1E7^T was 37.4 mol%. Flexirubin-type pigments were produced. The predominant respiratory quinone was menaquinone 6. The major fatty acids of strain 17S1E7^T were iso-C15 : 0, summed feature 9 (iso-C17 : 1ω9c and/or C16 : 0 10-methyl), iso-C17 : 0 3-OH and summed feature 3 (iso-C15 : 0 2-OH and/or C16 : 1ω7c). The predominant polar lipid was phosphatidylethanolamine. Based on polyphasic taxonomy data, strain 17S1E7^T represents a novel species of the genus Chryseobacterium, for which the name Chryseobacterium aureum sp. nov. is proposed. The type strain is 17S1E7^T (=KACC 19920^T=JCM 33165^T).

Comparison of the Vitek MS and Bruker Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry Systems for Identification of Chryseobacterium Isolates from Clinical Specimens and Report of Uncommon Chryseobacterium Infections in Humans

Matrix-assisted laser desorption ionization-time of flight mass spectrometry is becoming more popular and is replacing traditional identification methods in the clinical microbiology laboratory. We aimed to compare the Vitek mass spectrometry (MS) and Bruker Biotyper systems for the identification of Chryseobacterium isolated from clinical specimens and to report uncommon Chryseobacterium infections in humans. The microbial database from a hospital was searched for records between 2005 and 2016 to identify cultures that yielded Chryseobacterium Species identification by the Vitek MS and Bruker Biotyper systems was compared to identification by 16S rRNA gene sequencing. Over the study period, 140 Chryseobacterium isolates were included. Based on 16S rRNA gene sequencing, 78 isolates were C. indologenes, 39 were C. gleum, 12 were uncommon Chryseobacterium species (C. arthrosphaerae, C. culicis, C. cucumeris, C. bernardetii, C. artocarpi, and C. daecheongense), and the remaining 11 isolates were only identified at the genus level. The Vitek MS and Bruker Biotyper systems correctly identified 98.7% and 100% of C. indologenes isolates, respectively. While the Bruker Biotyper accurately identified 100% of C. gleum isolates, the Vitek MS system correctly identified only 2.6% of isolates from this species. None of the uncommon Chryseobacterium species were successfully identified by either of these two systems. The overall accuracies of Chryseobacterium identification at the species level by the Vitek MS and Bruker Biotyper systems were 60.5% and 90.7%, respectively. An upgrade and correction of the Vitek MS and Bruker Biotyper databases is recommended to correctly identify Chryseobacterium species.

Draft Genome Sequence of Chryseobacterium Strain CBo1 Isolated from Bactrocera oleae

Bacteria of the genus Chryseobacterium have previously been identified as mutualists of plants and insects. Chryseobacterium strain CBo1 was cultured from the gut of the agricultural pest Bactrocera oleae and its whole genome sequenced. This genomic resource will aid investigations into the transition of microbes between plant and invertebrate hosts.

Chryseobacterium reticulitermitis sp. nov., isolated from the gut of Reticulitermes aculabialis

A Gram-stain-negative, non-motile, aerobic and rod-shaped bacterium, strain Ra1T, was isolated from the gut of a wood-feeding lower termite, Reticulitermes aculabialis. Phylogenetic analysis of 16S rRNA gene sequences showed that the strain was closely related to Chryseobacterium rigui JCM 18078T (96.7 % similarity). Growth was observed at 15-45 °C (optimum 30 °C), at pH 6.0-9.0 (optimum pH 8.0) and in the presence of 0-2 % (w/v) NaCl (optimum 0 %). The DNA G+C content of strain Ra1T was 39.9 mol%. Cells contained menaquinone MK-6 as the sole respiratory quinone and the major fatty acids were iso-C15 : 0, iso-C17 : 0, summed feature 3 (comprising C16 : 1ω6c and/or C16 : 1ω7c) and summed feature 9 (comprising C16 : 0 10-methyl and/or iso-C17 : 1ω9c). The predominant polyamine was sym-homospermidine. The cellular polar lipids consisted of one phosphatidylethanolamine, three unidentified aminolipids, one unidentified phospholipid and one unidentified lipid. Based on phenotypic, genotypic and phylogenetic studies, it is concluded that strain Ra1T represents a novel species of the genus Chryseobacterium, for which the name Chryseobacterium reticulitermitis sp. nov. is proposed. The type strain is Ra1T (=CCTCC AB 2015431T=KCTC 52230T).

Dental plaque bacteria with reduced susceptibility to chlorhexidine are multidrug resistant

BACKGROUND

Chlorhexidine (CHX) is used in oral care products to help control dental plaque. In this study dental plaque bacteria were grown on media containing 2 μg/ml chlorhexidine gluconate to screen for bacteria with reduced CHX susceptibility. The isolates were characterized by 16S rRNA gene sequencing and antibiotic resistance profiles were determined using the disc diffusion method.

RESULTS

The isolates were variably resistant to multiple drugs including ampicillin, kanamycin, gentamicin and tetracycline. Two species, Chryseobacterium culicis and Chryseobacterium indologenes were able to grow planktonically and form biofilms in the presence of 32 μg/ml CHX. In the CHX and multidrug resistant C. indologenes we demonstrated a 19-fold up-regulation of expression of the HlyD-like periplasmic adaptor protein of a tripartite efflux pump upon exposure to 16 μg/ml CHX suggesting that multidrug resistance may be mediated by this system. Exposure of biofilms of these resistant species to undiluted commercial CHX mouthwash for intervals from 5 to 60 s indicated that the mouthwash was unlikely to eliminate them from dental plaque in vivo.

CONCLUSIONS

The study highlights the requirement for increased vigilance of the presence of multidrug resistant bacteria in dental plaque and raises a potential risk of long-term use of oral care products containing antimicrobial agents for the control of dental plaque.

Immune tolerance to an intestine-adapted bacteria, Chryseobacterium sp., injected into the hemocoel of Protaetia brevitarsis seulensis

To explore the interaction of gut microbes and the host immune system, bacteria were isolated from the gut of Protaetia brevitarsis seulensis larvae. Chryseobacterium sp., Bacillus subtilis, Arthrobacter arilaitensis, Bacillus amyloliquefaciens, Bacillus megaterium, and Lysinibacillus xylanilyticus were cultured in vitro, identified, and injected in the hemocoel of P. brevitarsis seulensis larvae, respectively. There were no significant changes in phagocytosis-associated lysosomal formation or pathogen-related autophagosome in immune cells (granulocytes) from Chryseobacterium sp.-challenged larvae. Next, we examined changes in the transcription of innate immune genes such as peptidoglycan recognition proteins and antimicrobial peptides following infection with Chryseobacterium sp. PGRP-1 and -2 transcripts, which may be associated with melanization generated by prophenoloxidase (PPO), were either highly or moderately expressed at 24 h post-infection with Chryseobacterium sp. However, PGRP-SC2 transcripts, which code for bactericidal amidases, were expressed at low levels. With respect to antimicrobial peptides, only coleoptericin was moderately expressed in Chryseobacterium sp.-challenged larvae, suggesting maintenance of an optimum number of Chryseobacterium sp. All examined genes were expressed at significantly higher levels in larvae challenged with a pathogenic bacterium. Our data demonstrated that gut-inhabiting bacteria, the Chryseobacterium sp., induced a weaker immune response than other pathogenic bacteria, E. coli K12.

Chryseobacterium panacis sp. nov., isolated from ginseng soil

A novel strain, DCY107(T), was isolated from soil collected from a ginseng field in Gochang, Republic of Korea. Strain DCY107(T) is Gram-negative, yellow pigmented, non-motile, non-flagellate, rod-shaped and aerobic. The strain was found to grow optimally at 25-30 °C and pH 6.5-7. Phylogenetically, strain DCY107(T) is closely related to Chryseobacterium polytrichastri DSM 26899(T) (98.49 % 16S rRNA gene sequence similarity), Chryseobacterium yeoncheonense JCM 18516(T) (97.78 %), Chryseobacterium aahli LMG 27338(T) (97.74 %), Chryseobacterium limigenitum LMG28734(T) (97.74 %), Chryseobacterium ginsenosidimutans JCM 16719(T) (97.47 %) and Chryseobacterium gregarium LMG 24052(T) (97.31 %). The DNA-DNA relatedness values between strain DCY107(T) and reference strains were found to be clearly below 70 %. The DNA G+C content of strain DCY107(T) was determined to be 34.2 mol%. The predominant quinone was identified menaquinone 6 (MK-6). The major polar lipids were identified as phosphatidylethanolamine and unidentified lipids: aminolipids AL1, AL2 and lipid L2. C16:00, iso-C15:00, iso-C15:02OH, iso-C17:03OH and summed feature 9 (iso-C17:1 ω9c and/or C16:0 10-methyl) were identified as the major fatty acids present in strain DCY107(T). The results of physiological and biochemical tests allowed strain DCY107(T) to be differentiated phenotypically from other recognised species belonging to the genus Chryseobacterium. Therefore, it is suggested that the newly isolated organism represents a novel species, for which the name Chryseobacterium panacis sp. nov. is proposed, with the type strain designated as DCY107(T) (=CCTCC AB 2015195(T) = KCTC 42750(T)).

Chryseobacterium arachidiradicis sp. nov., isolated from the geocarposphere (soil around the peanut) of very immature peanuts (Arachis hypogaea)

A yellow-pigmented bacterial strain, 91A-612(T), isolated from the geocarposphere (soil around the peanut) of very immature peanuts (Arachis hypogaea) in Alabama, USA, was studied for its taxonomic position. Cells of the isolate were rod-shaped and stained Gram-negative. A comparison of the 16S rRNA gene sequence with the sequences of the type strains of the most closely related species showed that the strain belongs to the genus Chryseobacterium, showing the highest sequence similarities to the type strains of Chryseobacterium molle (98.4%), C. pallidum (98.3%) and C. hominis (97.8%). The 16S rRNA gene sequence similarities to the type strains of all other species of the genus Chryseobacterium were below 97.0%. The fatty acid profile of strain 91A-612(T) consisted of the major fatty acids iso-C15 : 0, summed feature 3 (iso-C15 : 0 2-OH/C16 : 1ω7c) and iso-C17 : 0 3-OH. Major compounds in the polar lipid profile were phosphatidylethanolamine and several unidentified lipids, including two lipids that did not contain a sugar moiety, an amino group or a phosphate group (L3, L8), and an aminolipid (AL1). The quinone system was composed mainly of MK-6. The polyamine pattern contained sym-homospermidine as the major compound and moderate amounts of spermidine and spermine. DNA-DNA hybridizations between strain 91A-612(T) and the type strains of C. molle, C. pallidum and C. hominis resulted in relatedness values well below 70%. These data and the differentiating biochemical and chemotaxonomic properties showed that isolate 91A-612(T) represents a novel species of the genus Chryseobacterium, for which we propose the name Chryseobacterium arachidiradicis sp. nov. (type strain 91A-612(T) = LMG 27814(T)= CCM 8490(T) = CIP 110647(T)).

Chryseobacterium shandongense sp. nov., isolated from soil

YF-3T is a Gram-stain-negative, non-motile, non-spore-forming, yellow-orange, rod-shaped bacterium. Optimal growth conditions were at 30 °C, pH 7.0 and 1 % (w/v) NaCl. Phylogenetic analysis, on the basis of the 16S rRNA gene sequence, showed that strain YF-3T was closely related to the strains Chryseobacterium hispalense AG13T and Chryseobacterium taiwanense Soil-3-27T with 98.71 % and 96.93 % sequence similarity, respectively. Strain YF-3T contained MK-6 as the main menaquinone and had a polyamine pattern with sym-homospermidine as the major component. Its major polar lipid was phosphatidylethanolamine. The dominant fatty acids of strain YF-3T were iso-C15 : 0, iso-C17 : 0 3-OH, summed feature 9 (comprising iso-C17 : 1ω9c and/or C16 : 0 10-methyl) and summed feature 3 (comprising C16 : 1ω7c and/or C16 : 1ω6c). The DNA G+C content of strain YF-3T was 37 mol%. The DNA-DNA relatedness levels between strain YF-3T and the most closely related strains, C. hispalense AG13T and C. taiwanense Soil-3-27T, were 31.7 ± 2.1 % and 28.4 ± 5.4 %, respectively. Based on these results, a novel species named Chryseobacterium shandongense sp. nov. is proposed. The type strain is YF-3T ( = CCTCC AB 2014060T = JCM 30154T).

Emerging flavobacterial infections in fish: A review

Flavobacterial diseases in fish are caused by multiple bacterial species within the family Flavobacteriaceae and are responsible for devastating losses in wild and farmed fish stocks around the world. In addition to directly imposing negative economic and ecological effects, flavobacterial disease outbreaks are also notoriously difficult to prevent and control despite nearly 100 years of scientific research. The emergence of recent reports linking previously uncharacterized flavobacteria to systemic infections and mortality events in fish stocks of Europe, South America, Asia, Africa, and North America is also of major concern and has highlighted some of the difficulties surrounding the diagnosis and chemotherapeutic treatment of flavobacterial fish diseases. Herein, we provide a review of the literature that focuses on Flavobacterium and Chryseobacterium spp. and emphasizes those associated with fish.

Simultaneous heterotrophic nitrification and aerobic denitrification by Chryseobacterium sp. R31 isolated from abattoir wastewater

A heterotrophic carbon utilizing microbe (R31) capable of simultaneous nitrification and denitrification (SND) was isolated from wastewater of an Indian slaughterhouse. From an initial COD value of 583.0 mg/L, 95.54% was removed whilst, from a starting NH₄⁺-N concentration of 55.7 mg/L, 95.87% was removed after 48 h contact. The concentrations of the intermediates hydroxylamine, nitrite, and nitrate were low, thus ensuring nitrogen removal. Aerobic denitrification occurring during ammonium removal by R31 was confirmed by utilization of both nitrate and nitrite as nitrogen substrates. Glucose and succinate were superior while acetate and citrate were poor substrates for nitrogen removal. Molecular phylogenetic identification, supported by chemotaxonomic and physiological properties, assigned R31 as a close relative of Chryseobacterium haifense. The NH₄⁺-N utilization rate and growth of strain R31 were found to be higher at C/N = 10 in comparison to those achieved with C/N ratios of 5 and 20. Monod kinetic coefficients, half saturation concentration (K_s), maximum rate of substrate utilization (k), yield coefficient, (Y) and endogenous decay coefficient (K_d) indicated potential application of R31 in large-scale SND process. This is the first report on concomitant carbon oxidation, nitrification, and denitrification in the genus Chryseobacterium and the associated kinetic coefficients.

Chryseobacterium gallinarum sp. nov., isolated from a chicken, and Chryseobacterium contaminans sp. nov., isolated as a contaminant from a rhizosphere sample

Two yellow-pigmented bacterial strains (100T and C26T), showing 98.4 % 16S rRNA gene sequence similarity to each other and isolated from a chicken in Germany and as a contaminant from an agar plate of a rhizosphere sample in Alabama, were studied by using a polyphasic taxonomic approach. Cells of both isolates were rod-shaped and stained Gram-negative. A comparison of the 16S rRNA gene sequences of the two organisms with the sequences of the type strains of the most closely related species of the genus Chryseobacterium showed the highest sequence similarities of strains 100T and C26T to the type strains of Chryseobacterium joostei (respectively 97.5 and 98.2 %), C. viscerum (96.6, 97.8 %), C. gleum (97.1, 97.7 %), C. arthrosphaerae (97.3%, 97.7 %), C. indologenes (97.2, 97.7 %), C. tructae (96.6, 97.6 %), C. jejuense (97.0, 97.6 %) and C. oncorhynchi (96.3, 97.5 %); 16S rRNA gene sequence similarities to members of all other species of the genus Chryseobacterium were below 97.5 %. The fatty acid profiles of both strains consisted of the major fatty acids iso-C15 : 0, summed feature 3 (iso-C15 : 0 2-OH and/or C16 : 1ω7c), iso-C17 : 1ω9c and iso-C17 : 0 3-OH, but also showed slight differences (absence or presence of C16 : 0 3-OH and iso-C15 : 1 F). DNA–DNA hybridizations between the two strains and between the novel strains and the type strains of C. joostei , C. indologenes , C. jejuense , C. tructae and C. viscerum resulted in relatedness values clearly below 70 %. These DNA–DNA hybridization results and the differentiating biochemical and chemotaxonomic properties showed that both strains 100T and C26T represent novel species, for which the names Chryseobacterium gallinarum sp. nov. (type strain 100T = LMG 27808T = CCM 8493T) and Chryseobacterium contaminans sp. nov. (type strain C26T = LMG 27810T = CCM 8492T) are proposed.

Chryseobacterium hispalense sp. nov., a plant-growth-promoting bacterium isolated from a rainwater pond in an olive plant nursery, and emended descriptions of Chryseobacterium defluvii, Chryseobacterium indologenes, Chryseobacterium wanjuense and Chryseobacterium gregarium

A novel non-motile, Gram-staining-negative, yellow-pigmented bacterium, designated AG13(T), isolated from a rain water pond at a plant nursery in Spain and characterized as a plant-growth-promoting bacterium, was investigated to determine its taxonomic status. The isolate grew best over a temperature range of 15-40 °C, at pH 5.0-8.0 and with 0-4 % (w/v) NaCl. Chemotaxonomic and molecular characteristics of the isolate matched those described for members of the genus Chryseobacterium. The DNA G+C content of the novel strain was 37.2 mol%. The strain had a polyamine pattern with sym-homospermidine as the major compound and produced flexirubin-type pigments. MK-6 was the dominant menaquinone and the major cellular fatty acids were iso-C15 : 0, C17 : 1ω9c and iso-C17 : 0 3-OH. The main polar lipids were phosphatidylethanolamine, aminolipids and several unidentified lipids. The 16S rRNA gene showed 92.0-97.2 % sequence similarity with those of the members of the genus Chryseobacterium. Based on chemotaxonomic and phenotypic traits, and DNA-DNA hybridizations with the type strains of the most closely related species, the isolate is proposed to represent a novel species, Chryseobacterium hispalense, type strain AG13(T) ( = DSM 25574(T) = CCUG 63019(T)). Emended descriptions of the species Chryseobacterium defluvii, Chryseobacterium indologenes, Chryseobacterium wanjuense and Chryseobacterium gregarium are also provided.

Chryseobacterium viscerum sp. nov., isolated from diseased fish

A taxonomic study was carried out on five Gram-staining-negative, catalase- and oxidase-positive, rod-shaped bacteria isolated from the gills and livers of five diseased rainbow trout. The five novel isolates were designated strains 687B-08T, 445-08, 452-08, 453B-08 and 967B-08. In phylogenetic analyses based on 16S rRNA gene sequences, the five novel strains appeared almost identical (99.0–100 % sequence similarity) and to belong to the genus Chryseobacterium . Strain 687B-08T (the strain selected to represent the five novel isolates) was found to be most closely related to Chryseobacterium oncorhynchi 701B-08T (98.9 % sequence similarity), Chryseobacterium ureilyticum F-Fue-04IIIaaaaT (98.6 %), Chryseobacterium indologenes ATCC 29897T (98.3 %), Chryseobacterium jejuense JS17-8T (98.1 %) and Chryseobacterium gleum ATCC 35910T (98.1 %). In DNA–DNA hybridizations, DNA–DNA relatedness values of 99–100 % were recorded between the five novel strains. Lower DNA–DNA relatedness values (21–57 %) were recorded between strain 687B-08T and C. oncorhynchi 701B-08T, C. ureilyticum F-Fue-04IIIaaaaT and the type strains of other closely related, established species of the genus Chryseobacterium . The predominant respiratory quinone of strain 687B-08T was MK-6 and the major cellular fatty acids were iso-C15 : 0, iso-C17 : 1ω9c, iso-C17 : 0 3-OH and C16 : 1ω6c. The G+C content of the genomic DNA of strain 687B-08T was 38.6 mol%. Based on the phenotypic and genotypic evidence, the five novel strains isolated from rainbow trout represent a single, novel species of the genus Chryseobacterium , for which the name Chryseobacterium viscerum sp. nov. is proposed. The type strain is 687B-08T ( = CECT 7793T  = CCUG 60103T).