A bacteriophage-related chimeric marine virus infecting abalone

Symbiotic virus-bacteria interactions in biological treatment of coking wastewater manipulating bacterial physiological activities

Biological treatment is commonly used in coking wastewater (CWW) treatment. Prokaryotic microbial communities in CWW treatment have been comprehensively studied. However, viruses, as the critical microorganisms affecting microbial processes and thus engineering parameters, still remain poorly understood in CWW treatment context. Employing viromics sequencing, the composition and function of the viral community in CWW treatment were discovered, revealing novel viral communities and key auxiliary metabolic functions. Caudovirales appeared to be the predominant viral order in the oxic-hydrolytic-oxic (OHO) CWW treatment combination, showing relative abundances of 62.47 %, 56.64 % and 92.20 % in bioreactors O1, H and O2, respectively. At the family level, Myoviridae, Podoviridae and Siphoviridae mainly prevailed in bioreactors O1 and H while Phycodnaviridae dominated in O2. A total of 56.23-92.24% of novel viral contigs defied family-level characterization in this distinct CWW habitat. The virus-host prediction results revealed most viruses infecting the specific functional taxa Pseudomonas, Acidovorax and Thauera in the entire OHO combination, demonstrating the viruses affecting bacterial physiology and pollutants removal from CWW. Viral auxiliary metabolic genes (AMGs) were screened, revealing their involvement in the metabolism of contaminants and toxicity tolerance. In the bioreactor O1, AMGs were enriched in detoxification and phosphorus ingestion, where glutathione S-transferase (GSTs) and beta-ketoadipyl CoA thiolase (fadA) participated in biodegradation of polycyclic aromatic hydrocarbons and phenols, respectively. In the bioreactors H and O2, the AMGs focused on cell division and epicyte formation of the hosts, where GDPmannose 4,6-dehydratase (gmd) related to lipopolysaccharides biosynthesis was considered to play an important role in the growth of nitrifiers. The diversities of viruses and AMGs decreased along the CWW treatment process, pointing to a reinforced virus-host adaptive strategy in stressful operation environments. In this study, the symbiotic virus-bacteria interaction patterns were proposed with a theoretical basis for promoting CWW biological treatment efficiency. The findings filled the gaps in the virus-bacteria interactions at the full-scale CWW treatment and provided great value for understanding the mechanism of biological toxicity and sludge activity in industrial wastewater treatment.

Susceptibility of Four Abalone Species, Haliotis gigantea, Haliotis discus discus, Haliotis discus hannai and Haliotis diversicolor, to Abalone asfa-like Virus

Abalone amyotrophia is a viral disease that causes mass mortality of juvenile Haliotis discus and H. madaka. Although the cause of this disease has yet to be identified, we had previously postulated a novel virus with partial genome sequence similarity to that of African swine fever virus is the causative agent and proposed abalone asfa-like virus (AbALV) as a provisional name. In this study, three species of juvenile abalone (H. gigantea, H. discus discus, and H. diversicolor) and four species of adult abalone (the above three species plus H. discus hannai) were experimentally infected, and their susceptibility to AbALV was investigated by recording mortality, quantitatively determining viral load by PCR, and conducting immunohistological studies. In the infection test using 7-month-old animals, H. gigantea, which was previously reported to be insusceptible to the disease, showed multiplication of the virus to the same extent as in H. discus discus, resulting in mass mortality. H. discus discus at 7 months old showed abnormal cell masses, notches in the edge of the shell and brown pigmentation inside of the shell, which are histopathological and external features of this disease, while H. gigantea did not show any of these characteristics despite suffering high mortality. Adult abalones had low mortality and viral replication in all species; however, all three species, except H. diversicolor, became carriers of the virus. In immunohistological observations, cells positive for viral antigens were detected predominantly in the gills of juvenile H. discus discus and H. gigantea, and mass mortality was observed in these species. In H. diversicolor, neither juvenile nor adult mortality from infection occurred, and the AbALV genome was not increased by experimental infection through cohabitation or injection. Our results suggest that H. gigantea, H. discus discus and H. discus hannai are susceptible to AbALV, while H. diversicolor is not. These results confirmed that AbALV is the etiological agent of abalone amyotrophia.

A novel Asfarvirus-like virus identified as a potential cause of mass mortality of abalone

A novel Asfarvirus-like virus is proposed as the etiological agent responsible for mass mortality in abalone. The disease, called abalone amyotrophia, originally was recognized in the 1980s, but efforts to identify a causative agent were unsuccessful. We prepared a semi-purified fraction by nuclease treatment and ultracentrifugation of diseased abalone homogenate, and the existence of the etiological agent in the fraction was confirmed by a challenge test. Using next-generation sequencing and PCR-based epidemiological surveys, we obtained a partial sequence with similarity to a member of the family Asfarviridae. BLASTP analysis of the predicted proteins against a virus database resulted in 48 proteins encoded by the novel virus with top hits against proteins encoded by African swine fever virus (ASFV). Phylogenetic analyses of predicted proteins of the novel virus confirmed that ASFV represents the closest relative. Comparative genomic analysis revealed gene-order conservation between the novel virus and ASFV. In situ hybridization targeting the gene encoding the major capsid protein of the novel virus detected positive signals only in tissue from diseased abalone. The results of this study suggest that the putative causative agent should be considered a tentative new member of the family Asfarviridae, which we provisionally designate abalone asfa-like virus (AbALV).

Complete genome sequence of a phage hyperparasite of Candidatus Xenohaliotis californiensis (Rickettsiales) - a pathogen of Haliotis spp (Gasteropoda)

Bacteriophages are recognized as major mortality agents of microbes, among them intracellular marine rickettsiales-like bacteria. Recently, a phage hyperparasite of Candidatus Xenohaliotis californiensis (CXc) has been described. This bacterium is considered the causal agent of Withering Syndrome (WS) which is a chronic and potentially lethal disease of abalone species from California, USA and the peninsula of Baja California, Mexico. This hyperparasite which infects CXc could be used as a biocontrol agent for WS. Therefore, it is necessary to obtain genomic information to characterize this phage. In this study, the first complete genome sequence of a novel phage, Xenohaliotis phage (pCXc) was determined. The complete genome of pCXc from red abalone (Haliotis rufescens) is 35,728 bp, while the complete genome of pCXc from yellow abalone (Haliotis corrugata) is 35,736 bp. Both phage genomes consist of double-stranded DNA with a G + C content of 38.9%. In both genomes 33 open reading frames (ORFs) were predicted. Only 10 ORFs encode proteins that have identifiable functional homologues. These 10 ORFs were classified by function, including structural, DNA replication, DNA packaging, nucleotide transport and metabolism, life cycle regulation, recombination and repair, and additional functions. A PCR method for the specific detection of pCXc was developed. This information will help to understand a new group of phages that infect intracellular marine rickettsiales-like bacteria in mollusks.

Identification of candidate antimicrobial peptides derived from abalone hemocyanin

Hemocyanins present in invertebrate hemolymph are multifunctional proteins, responsible for oxygen transport and contributing to innate immunity through phenoloxidase-like activity. In arthropods, hemocyanin has been identified as a source of broad-spectrum antimicrobial peptides during infection. Conversely, no hemocyanin-derived antimicrobial peptides have been reported for molluscs. The present study describes a putative antimicrobial region, termed haliotisin, located within the linking sequence between the α-helical domain and β-sheet domain of abalone (Haliotis tuberculata) hemocyanin functional unit E. A series of synthetic peptides based on overlapping fragments of the haliotisin region were tested for their bactericidal potential. Incubating Gram-positive and Gram-negative bacteria in the presence of certain haliotisin peptides, notably peptides 3-4-5 (DTFDYKKFGYRYDSLELEGRSISRIDELIQQRQEKDRTFAGFLLKGFGTSAS) led to reductions in microbial growth. Furthermore, transmission electron micrographs of haliotisin-treated bacteria revealed damages to the microbial cell wall. Data discussed here provides the first evidence to suggest that molluscan hemocyanin may act as a source of anti-infective peptides.

Cryo-EM structure of isomeric molluscan hemocyanin triggered by viral infection

Hemocyanins (Hcs) of arthropods and mollusks function not only as oxygen transporters, but also as phenoloxidases (POs). In invertebrates, PO is an important component in the innate immune cascade, where it functions as the initiator of melanin synthesis, a pigment involved in encapsulating and killing of pathogenic microbes. Although structures of Hc from several species of invertebrates have been reported, the structural basis for how PO activity is triggered by structural changes of Hc in vivo remains poorly understood. Here, we report a 6.8 Å cryo-electron microscopy (cryo-EM) structure of the isomeric form of hemocyanin, which was isolated from Abalone Shriveling syndrome-associated Virus (AbSV) infected abalone (Halitotis diversicolor), and build a pseudoatomic model of isomeric H. diversicolor hemocyanin 1 (HdH1). Our results show that, compared with native form of HdH1, the architecture of isomeric HdH1 turns into a more relaxed form. The interactions between certain functional units (FUs) present in the native form of Hc either decreased or were totally abolished in the isomeric form of Hc. As a result of that, native state Hc switches to its isomeric form, enabling it to play its role in innate immune responses against invading pathogens.

Effects of dietary supplementation of probiotic Shewanella colwelliana WA64, Shewanella olleyana WA65 on the innate immunity and disease resistance of abalone, Haliotis discus hannai Ino

The effects of dietary administration of two probiotics, Shewanella colwelliana WA64 and Shewanella olleyana WA65, on the innate immunity of abalone (Haliotis discus hannai Ino), and survival of juvenile abalone challenged with Vibrio harveyi have been studied. Two groups of abalone were fed with three different diets: one control, and two diets supplemented with 10(9) cell g(-1) of probiotic WA64 (WA64 diet) and WA65 (WA65 diet) for up to four weeks. Results showed that abalone fed diets containing S. colwelliana WA64 and S. olleyana WA65 had led to an enhanced cellular and humoral immune response, notably higher haemocytes, respiratory burst activity, serum lysozyme activity and total protein levels were recorded after one week of probiotic administration. On the other hand, mortality after the challenges with V. harveyi in the group fed with control diet ranged from 77 to 80%, while mortality rates observed in the groups fed with diets supplemented with WA64 and WA65 ranged from 27 to 50% and 30-43%, respectively. The results demonstrated potential for S. colwelliana WA64 and S. olleyana WA65 to improve innate immunity and disease resistance in H. discus hannai.

Nested PCR detection of abalone shriveling syndrome-associated virus in China

Haliotis diversicolor (small abalone) is an economic seafood found off the Southern coast of China. Since 1999, the cultured abalone yields in China have been affected severely by continual outbreaks of a fatal epidemic disease caused by abalone shriveling syndrome associated virus (AbSV), a double-stranded DNA virus. Although the pathogenicity and genome of AbSV have been ascertained, the epidemiology of AbSV infection remains to be investigated. In the present study, four pairs of AbSV-specific primers were designed on the basis of open reading frame (ORF)24 and ORF25 sequences in the AbSV genome. Two nested PCR detection methods were established by optimization of the annealing temperatures of primers. The results showed that the specificity of primers for AbSV detection could not be interfered with by the host genome and other aquaculture species or viruses. The detection limits of the two methods were about 10 copies of recombinant plasmid containing AbSV genes in 20μL reaction mixture. The results of detection of the AbSV epidemic showed that AbSV was still present in juvenile abalones in some farms along the Southern coast of China (Fujian and Guangdong).

Quantitative PCR detection for abalone shriveling syndrome-associated virus

Haliotis diversicolor (small abalone) is an important seafood found along the southern coast of China. Since 1999, the yields of cultured abalone in China have been severely affected by an epidemic of continuous outbreaks of a fatal disease. A novel double-stranded DNA virus, abalone shriveling syndrome-associated virus (AbSV), was proven to be one of the main causative agent. Although the pathogenicity and genome of AbSV has been ascertained, the epidemiology of AbSV remains to be investigated. In this study, four pairs of AbSV-specific primers were designed on the basis of the AbSV genome, and were tested for their specificities and sensitivities in quantitative real-time PCRs (qPCRs) after optimization of the annealing temperature. The 3F3/3B3 primer pair was finally chosen with a good specificity and high efficiency of amplification, with a detection limit of about 10 copies of recombinant plasmid containing AbSV genes in a 20-μL reaction mixture. In the detection of AbSV in abalone samples along the southern coast of China, most of the diseased samples had more than 80 virus copies in 1ng host genome DNA. AbSV was also demonstrated in mature hybrid (LY) and juvenile (JH) abalones from assays of healthy animals collected in recent years.