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Asset Tag: Marine biology

July 7, 2019

Analysis of complete genome sequence and major surface antigens of Neorickettsia helminthoeca, causative agent of salmon poisoning disease.

Neorickettsia helminthoeca, a type species of the genus Neorickettsia, is an endosymbiont of digenetic trematodes of veterinary importance. Upon ingestion of salmonid fish parasitized with infected trematodes, canids develop salmon poisoning disease (SPD), an acute febrile illness that is particularly severe and often fatal in dogs without adequate treatment. We determined and analysed the complete genome sequence of N. helminthoeca: a single small circular chromosome of 884 232 bp encoding 774 potential proteins. N. helminthoeca is unable to synthesize lipopolysaccharides and most amino acids, but is capable of synthesizing vitamins, cofactors, nucleotides and bacterioferritin. N. helminthoeca is, however, distinct from majority of the family Anaplasmataceae to which it belongs, as it encodes nearly all enzymes required for peptidoglycan biosynthesis, suggesting its structural hardiness and inflammatory potential. Using sera from dogs that were experimentally infected by feeding with parasitized fish or naturally infected in southern California, Western blot analysis revealed that among five predicted N. helminthoeca outer membrane proteins, P51 and strain-variable surface antigen were uniformly recognized. Our finding will help understanding pathogenesis, prevalence of N. helminthoeca infection among trematodes, canids and potentially other animals in nature to develop effective SPD diagnostic and preventive measures. Recent progresses in large-scale genome sequencing have been uncovering broad distribution of Neorickettsia spp., the comparative genomics will facilitate understanding of biology and the natural history of these elusive environmental bacteria.© 2017 The Authors. Microbial Biotechnology published by John Wiley & Sons Ltd and Society for Applied Microbiology.

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July 7, 2019

The complete genome sequence of Exiguobacterium arabatum W-01 reveals potential probiotic functions.

Shrimp is extensively cultured worldwide. Shrimp farming is suffering from a variety of diseases. Probiotics are considered to be one of the effective methods to prevent and cure shrimp diseases. Exiguobacterium arabatum W-01, a gram-positive and orange-pigmented bacterium, was isolated from the intestine of a healthy Penaeus vannamei specimen. Whole-genome sequencing revealed a genome of 2,914,854 bp, with 48.02% GC content. In total, 3,083 open reading frames (ORFs) were identified, with an average length of 843.98 bp and a mean GC content of 48.11%, accounting for 89.27% of the genome. Among these ORFs, 2,884 (93.5%) genes were classified into Clusters of Orthologous Groups (COG) families comprising 21 functional categories, and 1,650 ORFs were classified into 83 functional Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. A total of 27 rRNA operons and 68 tRNAs were identified, with all 20 amino acids represented. In addition, 91 genomic islands, 68 potential prophages, and 33 tandem repeats, but no clustered regularly interspaced short palindromic repeats (CRISPRs), were found. No resistance genes and only one virulence gene were identified. Among the 150 secreted proteins of E. arabatum W-01, a variety of transport system substrate-binding proteins, enzymes, and biosynthetic proteins, which play important roles in the uptake and metabolism of nutrients, were found. Two adherence-related protein genes and 31 flagellum-related protein genes were also identified. Taken together, these results indicate potential probiotic functions for E. arabatum W-01.© 2017 The Authors. MicrobiologyOpen published by John Wiley & Sons Ltd.

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July 7, 2019

Complete genome sequence of Photobacterium damselae subsp. piscicida strain OT-51443 isolated from yellowtail (Seriola quinqueradiata) in Japan.

Pseudotuberculosis caused by infection of Photobacterium damselae subsp. piscicida has caused serious economic damages to aquaculture farms worldwide. Here, the whole-genome sequence of P. damselae subsp. piscicida strain OT-51443, isolated in Japan, was determined and suggests that this genome consists of two chromosomes and five plasmids. Copyright © 2017 Aoki et al.

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July 7, 2019

Isolation of a novel ‘atypical’ Brucella strain from a bluespotted ribbontail ray (Taeniura lymma).

A pleomorphic Gram-negative, motile coccobacillus was isolated from the gills of a wild-caught bluespotted ribbontail ray after its sudden death during quarantine. Strain 141012304 was observed to grow aerobically, to be clearly positive for cytochrome oxidase, catalase, urease and was initially identified as “Brucella melitensis” or “Ochrobactrum anthropi” by Matrix-assisted laser desorption/ionization-time of flight mass spectrometry and VITEK2-compact(®), respectively. Affiliation to the genus Brucella was confirmed by bcsp31 and IS711 PCR as well as by Brucella species-specific multiplex PCR, therein displaying a characteristic banding pattern recently described for Brucella strains obtained from amphibian hosts. Likewise, based on recA sequencing, strain 141012304 was found to form a separate lineage, within the so called ‘atypical’ Brucella, consisting of genetically more distantly related strains. The closest similarity was detected to brucellae, which have recently been isolated from edible bull frogs. Subsequent next generation genome sequencing and phylogenetic analysis confirmed that the ray strain represents a novel Brucella lineage within the atypical group of Brucella and in vicinity to Brucella inopinata and Brucella strain BO2, both isolated from human patients. This is the first report of a natural Brucella infection in a saltwater fish extending the host range of this medically important genus.

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July 7, 2019

Higher-order organisation of extremely amplified, potentially functional and massively methylated 5S rDNA in European pikes (Esox sp.).

Pikes represent an important genus (Esox) harbouring a pre-duplication karyotype (2n?=?2x?=?50) of economically important salmonid pseudopolyploids. Here, we have characterized the 5S ribosomal RNA genes (rDNA) in Esox lucius and its closely related E. cisalpinus using cytogenetic, molecular and genomic approaches. Intragenomic homogeneity and copy number estimation was carried out using Illumina reads. The higher-order structure of rDNA arrays was investigated by the analysis of long PacBio reads. Position of loci on chromosomes was determined by FISH. DNA methylation was analysed by methylation-sensitive restriction enzymes.The 5S rDNA loci occupy exclusively (peri)centromeric regions on 30-38 acrocentric chromosomes in both E. lucius and E. cisalpinus. The large number of loci is accompanied by extreme amplification of genes (>20,000 copies), which is to the best of our knowledge one of the highest copy number of rRNA genes in animals ever reported. Conserved secondary structures of predicted 5S rRNAs indicate that most of the amplified genes are potentially functional. Only few SNPs were found in genic regions indicating their high homogeneity while intergenic spacers were more heterogeneous and several families were identified. Analysis of 10-30 kb-long molecules sequenced by the PacBio technology (containing about 40% of total 5S rDNA) revealed that the vast majority (96%) of genes are organised in large several kilobase-long blocks. Dispersed genes or short tandems were less common (4%). The adjacent 5S blocks were directly linked, separated by intervening DNA and even inverted. The 5S units differing in the intergenic spacers formed both homogeneous and heterogeneous (mixed) blocks indicating variable degree of homogenisation between the loci. Both E. lucius and E. cisalpinus 5S rDNA was heavily methylated at CG dinucleotides.Extreme amplification of 5S rRNA genes in the Esox genome occurred in the absence of significant pseudogenisation suggesting its recent origin and/or intensive homogenisation processes. The dense methylation of units indicates that powerful epigenetic mechanisms have evolved in this group of fish to silence amplified genes. We discuss how the higher-order repeat structures impact on homogenisation of 5S rDNA in the genome.

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July 7, 2019

Population genomics of picophytoplankton unveils novel chromosome hypervariability.

Tiny photosynthetic microorganisms that form the picoplankton (between 0.3 and 3 µm in diameter) are at the base of the food web in many marine ecosystems, and their adaptability to environmental change hinges on standing genetic variation. Although the genomic and phenotypic diversity of the bacterial component of the oceans has been intensively studied, little is known about the genomic and phenotypic diversity within each of the diverse eukaryotic species present. We report the level of genomic diversity in a natural population of Ostreococcus tauri (Chlorophyta, Mamiellophyceae), the smallest photosynthetic eukaryote. Contrary to the expectations of clonal evolution or cryptic species, the spectrum of genomic polymorphism observed suggests a large panmictic population (an effective population size of 1.2 × 10(7)) with pervasive evidence of sexual reproduction. De novo assemblies of low-coverage chromosomes reveal two large candidate mating-type loci with suppressed recombination, whose origin may pre-date the speciation events in the class Mamiellophyceae. This high genetic diversity is associated with large phenotypic differences between strains. Strikingly, resistance of isolates to large double-stranded DNA viruses, which abound in their natural environment, is positively correlated with the size of a single hypervariable chromosome, which contains 44 to 156 kb of strain-specific sequences. Our findings highlight the role of viruses in shaping genome diversity in marine picoeukaryotes.

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July 7, 2019

Complete genome sequence of Marinifilaceae bacterium strain SPP2, isolated from the Antarctic marine sediment

Marinifilaceae bacterium strain SPP2 is a Gram-negative facultative anaerobe, isolated from the Antarctic marine sediment. Here, we present the complete genome sequence of Marinifilaceae bacterium strain SPP2, which consists of 5,718,991 bp with a G + C content of 35.99%. The genome data provides insights of microbial evolution and adaption in the Antarctic marine ecosystem.

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July 7, 2019

Plasmid composition in Aeromonas salmonicida subsp. salmonicida 01-B526 unravels unsuspected type three secretion system loss patterns.

Aeromonas salmonicida subsp. salmonicida is a ubiquitous psychrophilic waterborne bacterium and a fish pathogen. The numerous mobile elements, especially insertion sequences (IS), in its genome promote rearrangements that impact its phenotype. One of the main virulence factors of this bacterium, its type three secretion system (TTSS), is affected by these rearrangements. In Aeromonas salmonicida subsp. salmonicida most of the TTSS genes are encoded in a single locus on a large plasmid called pAsa5, and may be lost when the bacterium is cultivated at a higher temperature (25 °C), producing non-virulent mutants. In a previous study, pAsa5-rearranged strains that lacked the TTSS locus on pAsa5 were produced using parental strains, including 01-B526. Some of the generated deletions were explained by homologous recombination between ISs found on pAsa5, whereas the others remained unresolved. To investigate those rearrangements, short- and long-read high-throughput sequencing technologies were used on the A. salmonicida subsp. salmonicida 01-B526 whole genome.Whole genome sequencing of the 01-B526 strain revealed that its pAsa5 has an additional IS copy, an ISAS5, compared to the reference strain (A449) sequence, which allowed for a previously unknown rearrangement to occur. It also appeared that 01-B526 bears a second large plasmid, named pAsa9, which shares 40 kbp of highly similar sequences with pAsa5. Following these discoveries, previously unexplained deletions were elucidated by genotyping. Furthermore, in one of the derived strains a fusion of pAsa5 and pAsa9, involving the newly discovered ISAS5 copy, was observed.The loss of TTSS and hence virulence is explained by one consistent mechanism: IS-driven homologous recombination. The similarities between pAsa9 and pAsa5 also provide another example of genetic diversity driven by ISs.

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July 7, 2019

Whole-genome sequence of Photobacterium damselae subsp. piscicida strain 91-197, isolated from hybrid striped bass (Morone sp.) in the United States.

Photobacterium damselae subsp. piscicida is a causative bacterium of fish pasteurellosis, which has caused serious economic damage to aquaculture farms worldwide. Here, the whole-genome sequence of P. damselae subsp. piscicida 91-197, isolated in the United States, suggests that this genome consists of two chromosomes and two plasmids. Copyright © 2017 Teru et al.

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July 7, 2019

Complete genome of a metabolically-diverse marine bacterium Shewanella japonica KCTC 22435T.

Shewanella japonica KCTC 22435Tis a facultatively anaerobic, Gram-negative, mesophilic, rod-shaped bacterium isolated from sea water at the Pacific Institute of Bio-organic Chemistry of the Marine Experimental Station, Troitza Bay, Gulf of Peter the Great, Russia. Here, we report the complete genome of S. japonica KCTC 22435T, which consists of 4,975,677bp (G+C content of 40.80%) with a single chromosome, 4036 protein-coding genes, 97 tRNAs and 8 rRNA operons. Genes detected in the genome reveal that the strain possesses a type II secretion system, cytochrome c family proteins with various numbers of heme-binding motifs, and metabolic pathways for utilizing diverse carbon sources, supporting the potential of KCTC 22435Tto generate electricity in salinity culture conditions. Copyright © 2017 Elsevier B.V. All rights reserved.

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July 7, 2019

Plasmid dynamics in Vibrio parahaemolyticus strains related to shrimp Acute Hepatopancreatic Necrosis Syndrome (AHPNS).

Vibrio parahaemolyticus is a causative agent of acute hapatopancreatic necrosis syndrome (AHPNS) which causes early mortality in white shrimp. Emergence of AHPNS has caused tremendous economic loss for aquaculture industry particularly in Asia since 2010. Previous studies reported that strains causing AHPNS harbor a 69-kb plasmid with possession of virulence genes, pirA and pirB. However, genetic variation of the 69-kb plasmid among AHPNS related strains has not been investigated. This study aimed to analyze genetic composition and diversity of the 69-kb plasmid in strains isolated from shrimps affected by AHPNS. Plasmids recovered from V. parahaemolyticus strain VPE61 which represented typical AHPNS pathogenicity, strain VP2HP which did not represent AHPNS pathogenicity but was isolated from AHPNS affected shrimp and other AHPNS V. parahaemolyticus isolates in Genbank were investigated. Protein coding genes of the 69-kb plasmid from the strain VPE61 were identical to that of AHPNS strain from Vietnam except the inverted complement 3.4-kb transposon covering pirA and pirB. The strain VP2HP possessed remarkable large 183-kb plasmid which shared similar protein coding genes to those of the 69-kb plasmid from strain VPE61. However, the 3.4-kb transposon covering pirA and pirB was absent from the 183-kb plasmid in strain VP2HP. A number of protein coding genes from the 183-kb plasmid were also detected in other AHPNS strains. In summary, this study identified a novel 183-kb plasmid that is related to AHPNS causing strains. Homologous recombination of the 69-kb AHPNS plasmid and other naturally occurring plasmids together with loss and gain of AHPNS virulence genes in V. parahaemolyticus were observed. The outcome of this research enables understanding of plasmid dynamics that possibly affect variable degrees of AHPNS pathogenicity. Copyright © 2017 Elsevier B.V. All rights reserved.

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July 7, 2019

Complete genome sequence of a denitrifying bacterium, Pseudomonas sp. CC6-YY-74, isolated from Arctic Ocean sediment

Pseudomonas sp. CC6-YY-74, a psychrotrophic, denitrifying bacterium isolated from Arctic Ocean sediment, uses NO3- or NH4+ as the sole nitrogen source to grow at low temperatures. Here we described the complete genome of Pseudomonas sp. CC6-YY-74. The genome has one circular chromosome of 5,040,792 bp (61.73 mol% G + C content), consisting of 4747 coding genes, 68 tRNA genes, as well as six rRNA operons as 16S-23S-5S rRNA. According to the annotation results, strain CC6-YY-74 encodes 52 proteins related to nitrogen metabolism, including a complete denitrifying pathway, and more than 20 kinds of hydrolytic enzymes.

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July 7, 2019

Complete genome sequence and analysis of three kinds of ß-agarase of Cellulophaga lytica DAU203 isolated from marine sediment.

Cellulophaga lytica DAU203 (KACC 19187), isolated from the marine sediment in Korea, has a strong ability to degrade agar. The genome of C. lytica DAU203 contains a single chromosome that is 3,952,957bp in length, with 32.02% G+C contents. The genomic information predicted that the DAU203 has the potential to be utilized in various enzymatic industries. Copyright © 2017. Published by Elsevier B.V.

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July 7, 2019

Euglena gracilis genome and transcriptome: organelles, nuclear genome assembly strategies and initial features.

Euglena gracilis is a major component of the aquatic ecosystem and together with closely related species, is ubiquitous worldwide. Euglenoids are an important group of protists, possessing a secondarily acquired plastid and are relatives to the Kinetoplastidae, which themselves have global impact as disease agents. To understand the biology of E. gracilis, as well as to provide further insight into the evolution and origins of the Kinetoplastidae, we embarked on sequencing the nuclear genome; the plastid and mitochondrial genomes are already in the public domain. Earlier studies suggested an extensive nuclear DNA content, with likely a high degree of repetitive sequence, together with significant extrachromosomal elements. To produce a list of coding sequences we have combined transcriptome data from both published and new sources, as well as embarked on de novo sequencing using a combination of 454, Illumina paired end libraries and long PacBio reads. Preliminary analysis suggests a surprisingly large genome approaching 2 Gbp, with a highly fragmented architecture and extensive repeat composition. Over 80% of the RNAseq reads from E. gracilis maps to the assembled genome sequence, which is comparable with the well assembled genomes of T. brucei and T. cruzi. In order to achieve this level of assembly we employed multiple informatics pipelines, which are discussed here. Finally, as a preliminary view of the genome architecture, we discuss the tubulin and calmodulin genes, which highlight potential novel splicing mechanisms.

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