Population genetic structure of Semisulcospira gottschei: simultaneous examination of mtDNA and microsatellite markers.

Semisulcospira gottschei is an Asian endemic species inhabiting Korea and China. However, genetic structure analysis of the resource management of this species has not been performed. To investigate the genetic diversity among populations, microsatellites can be used to determine the geographic origins of marine and freshwater species. This study investigated the genetic structures of the Korean and Chinese populations of S. gottschei based on mitochondrial DNA (mtDNA) Cytochrome oxidase subunit I (COI) and polymorphic microsatellite loci developed from Semisulcospira coreana. Analysis of the mtDNA COI sequence revealed 43 haplotypes, which indicated no gene flow between the Korean and Chinese populations. To further elucidate the genetic structures of the Korean and Chinese populations, the population genetics of S. gottschei were analyzed using nine microsatellite markers. The genetic diversity analysis showed an average of 5.25 alleles per locus, with an average allelic richness of 4.02. Excessive homozygosity was found at all loci, which was expected to be due to the presence of null alleles at all loci. Populations of S. gottschei formed two separate clusters according to pairwise FST and AMOVA. Also, the UPGMA tree, PCA, STRUCTURE, and GeneClass indicated separation of the 11 populations into two clusters: Korea and China. These results have potential use in the management, restoration, and distinction of the origin country of populations.

Potential use of newly isolated bacteriophage as a biocontrol against Acidovorax citrulli.

Acidovorax citrulli, the gram-negative bacteria that causes bacterial fruit blotch (BFB), has been responsible for huge worldwide economic losses in watermelon and melon production since 1980. No commercial cultivar resistant to BFB has been reported. Of the two reported genotypes of A. citrulli, genotype I is the main causal agent of BFB in melon and genotype II causes disease in watermelon. After the isolation of the first bacteriophage against A. citrulli (ACP17), efforts have been made to isolate bacteriophages with wider host ranges by collecting samples from watermelon, pumpkin, and cucumber. The newly isolated phage ACPWH, belonging to the Siphoviridae family, has a head size of 60 ± 5 nm and tail size of 180 ± 5 nm, and can infect 39 out of 42 A. citrulli strains. ACPWH has genome size of 42,499 and GC content of 64.44%. Coating watermelon seeds with bacteriophage ACPWH before soil inoculation with A. citrulli resulted in 96% germination and survival, compared to 13% germination of uncoated control seeds. These results suggest that phage ACPWH may be an effective and low-cost biocontrol agent against BFB.

Effect of CXCL12-expressing viral hemorrhagic septicemia virus replicon particles on leukocytes migration and vaccine efficacy in olive flounder (Paralichthys olivaceus).

Viral replicon particles are single-cycle viruses defective for function(s) needed for viral replication, which allow them to be recognized as a safer form for the vaccination of animals compared to attenuated live viruses. However, deletion of genes that are critical for the induction of protective immunity can diminish the vaccine potential of viral replicon particles. Therefore, the manipulation of viral replicon particles to produce a molecular adjuvant can be a way to increase immunogenicity of vaccines based on viral replicon particles. Chemokines are a class of chemotactic cytokines that control the migration of diverse cells of vertebrates. CXC chemokine ligand 12 (CXCL12) binds to a receptor CXCR4, and CXCL12-CXCR4 signaling plays an important role in the migration of hematopoietic cells during embryogenesis and the attraction of leukocytes. In the present study, to evaluate the possible use of CXCL12 as a molecular adjuvant for an rVHSV-ΔG vaccine and to know differences between CXCL12a and CXCL12b in the adjuvant ability, we rescued VHSV replicon particles that are expressing olive flounder CXCL12a, CXCL12b, or eGFP (rVHSV-ΔG-CXCL12a, rVHSV-ΔG-CXCL12b, or rVHSV-ΔG-eGFP), and compared the ability to attract olive flounder leucocytes and to induce protection against a VHSV challenge. In the leukocytes migration assay, supernatants collected from cells infected with rVHSV-ΔG-CXCL12a and rVHSV-ΔG-CXCL12b showed significantly higher ability to attract olive flounder leukocytes than the supernatant of cells infected with rVHSV-ΔG-eGFP. Moreover, the significantly higher number of leukocytes were attracted to rVHSV-CXCL12a supernatant compared to rVHSV-CXCL12b supernatant, suggesting that CXCL12a would be more appropriate for the induction of immunity than CXCL12b in olive flounder. In the immunization experiment, olive flounder immunized with rVHSV-ΔG-CXCL12a showed significantly higher survival rate than fish immunized with rVHSV-ΔG-CXCL12b or rVHSV-ΔG-eGFP. In addition, fish immunized with rVHSV-ΔG-CXCL12a showed the highest serum neutralization activity. These results suggest the availability of CXCL12a for a molecular adjuvant of vaccines based on VHSV replicon particles.

Transcriptome analysis of gene expression in Chlorella vulgaris under salt stress.

Chlorella vulgaris is an important freshwater alga that is widely used as a food source for humans and animals. High-salinity environments can cause accumulation of lipids and proteins in this species, but the mechanism of this accumulation and the salt response remain unclear. In this work, transcriptome analysis was performed for the C. vulgaris response to salt stress (1% and 3% NaCl) applied for different times (2 h and 4 h). In total, 5232 and 9196 were differentially expressed after 1% NaCl for 2 and 4 h, and 3968 and 9035 unigenes were differentially expressed after 3% NaCl for 2 and 4 h, respectively. The number of upregulated genes after 4 h of salinity stress was greater than the number of downregulated genes, suggesting that the alteration of gene expression may be related to a mechanism of adaptation to a high-salinity environment. Furthermore, gene ontology and KEGG pathway analyses revealed that numerous biological pathways are affected by salt stress. Among the upregulated pathways, the cytoplasmic calcium signaling pathway, which is involved in the regulation of homeostasis, was highly upregulated. Genes involved in the photosystem I light-harvesting pathway were downregulated under salt stress. These results provide foundational information on the effects of salt stress on C. vulgaris metabolism and its possible mechanism of surviving high concentrations of NaCl.

Antiviral effects of extracts from Celosia cristata and Raphanus sativus roots against viral hemorrhagic septicemia virus.

The antiviral activity of an extract mixture from Celosia cristata and Raphanus sativus was tested against viral hemorrhagic septicemia virus (VHSV). Pretreatment of EPC cells with this extract up to 72 h before VHSV infection markedly reduced the virus titer, but it had no effect when added after virus inoculation. In olive flounder that received 5 µg of extract per fish, Mx expression peaked at 48 h after treatment. In contrast, ISG15 and TLR2 expression peaked at 72 h, and that of TLR7 peaked at 48 h, followed by a slight decrease at 72 h, indicating that the antiviral activity was mediated by induction of gene expression involved in the innate immune response.

Fusion of flagellin 2 with bivalent white spot syndrome virus vaccine increases survival in freshwater shrimp.

Despite large economic losses attributable to white spot syndrome virus (WSSV), an infectious pathogen of penaeid shrimp and other crustaceans worldwide, no efficient vaccines or antiviral agents to control the virus are available at present. Here, we designed and constructed baculovirus-based vaccines delivering genes encoding the WSSV envelope proteins, VP28 and VP19. To enhance the immunogenicity of the baculovirus-based vaccine, we fused a Salmonella typhimurium flagellin 2 (FL2) gene with VP28 or VP19 gene. Both vaccine constructs elicited similar high titlers of anti-WSSV IgG after oral immunization in mice. The protective effect of oral vaccines upon WSSV challenge was observed in Macrobrachium nipponense. Bivalent vaccine displaying WSSV envelope proteins, VP19 and VP28, led to enhanced more than 10% survival protection against WSSV infection, compared to monovalent vaccine containing WSSV envelope protein, VP19 or VP28. Furthermore, a baculovirus-based WSSV vaccine fused with FL2 gene, Ac-VP28-ie1VP19FL2, efficiently protected mice against WSSV challenge (89.5% survival rate). In support of the efficacy of FL2 in our vaccine, we verified FL2 enhanced survival rate and induced the NF-κB gene in Palaemon paucidens. The collective results strongly suggest that our recombinant baculoviral system displaying WSSV envelope protein and delivering FL2-fused WSSV envelope gene effectively induced protective responses, supporting the utility of a potential new oral DNA vaccine against WSSV.

Purification and characterization of a carboxymethyl cellulase from Artemia salina.

Brine shrimp (Artemia salina) belong to a group of crustaceans that feed on microalgae and require a cellulase enzyme that can be used in ethanol production from marine algae. Protein with potential cellulase activity was purified and the activity analyzed under different conditions. After initial identification of cellulase activity by CMC cellulase, surface sterilization and PCR using 16s rRNA primers was conducted to confirm that the cellulase activity was not produced from contaminating bacteria. The enzyme was purified by ammonium sulfate fractionation, gel filtration, and ion exchange chromatography. After the final purification, a 70-fold increase in specific enzyme activity was observed. SDS-PAGE results revealed that the cellulase enzyme had a molecular mass of 96 kDa. Temperature, pH, and salinity values were found to be optimal at 55 °C, pH 8.0, and 600 mM NaCl, respectively. Specifically, the enzyme showed a fivefold increase in enzyme activity in seawater compared to 600 mM NaCl in phosphate buffer. Further analysis of the purified enzyme by molecular spectrometry showed no match to known cellulases, indicating this enzyme could be a novel halophilic cellulase that can be used for the production of bioethanol from marine macroalgae.

Isolation and Characterization of a Salt Inducible Promoter from Chlorella vulgaris PKVL7422.

Chlorella is a eukaryotic organism that can be used as an industrial host to produce recombinant proteins. In this study, a salt-inducible promoter (SIP) was isolated from the freshwater species Chlorella vulgaris PKVL7422 from the screening of genes that were upregulated after salt treatment. Several cis-acting elements, including stress response elements, were identified in the isolated SIP. Moreover, the Gaussia luciferase gene was cloned after the SIP and transformed into C. vulgaris to test the inducibility of this promoter. Reexamination of transcriptome of C. vulgaris revealed that genes involved in the synthesis of methyl jasmonic acid (MeJA), gibberellin (GA), and abscisic acid (ABA) were upregulated when C. vulgaris was treated with salt. Furthermore, the expression level of recombinant luciferase increased when the transformed C. vulgaris was treated with salt and MeJA, GA, and ABA. This study represents the first report of the C. vulgaris SIP and highlights how transformed microalgae could be used for robust expression of recombinant proteins.

Efficacy of White Spot Syndrome Virus Protein VP28-Expressing Chlorella vulgaris as an Oral Vaccine for Shrimp.

The white spot syndrome virus (WSSV) is the causative agent of white spot disease, which kills shrimp within a few days of infection. Although WSSV has a mortality rate of almost 100% and poses a serious threat to the shrimp farming industry, strategies for its prevention and treatment are extremely limited. In this study, we examined the efficacy of VP28, a recombinant WSSV protein expressed in Chlorella vulgaris (C. vulgaris), as an oral shrimp vaccine. When compared with the control group, in which WSSV had a cumulative mortality of 100%, shrimp treated with 5% VP28-expressing C. vulgaris in their feed only had a 20% cumulative mortality rate 12 days after the WSSV challenge. When compared with the nonvaccinated group, the transcription of anti-lipopolysaccharide factor, C-type lectin, and prophenoloxidase genes, which are involved in shrimp defense against WSSV infection, was upregulated 29.6 fold, 15.4 fold, and 11.5 fold, respectively. These findings highlight C. vulgaris as a potential host for industrial shrimp vaccine production.

High-Level Expression of Recombinant VHSV Glycoprotein Using Transformed C. vulgaris and Verification of Vaccine Efficacy.

The demand for aquaculture is increasing, but production is declining due to high feed costs and disease outbreaks. Viral hemorrhagic septicemia (VHS) is a viral disease that seriously affects seawater and freshwater fish in aquaculture, including the olive flounder (Paralichthys olivaceus), a major aquaculture fish in Korea. However, very few vaccines are currently available for viral hemorrhagic septicemia virus (VHSV). The nutrient-rich microalga Chlorella vulgaris has been used as a feed additive in aquaculture and as a host for the industrial production of recombinant VHSV glycoprotein as an oral vaccine. In this study, VHSV glycoprotein was cloned with a salt-inducible promoter, and high levels of expression up to 41.1 mg/g wet C. vulgaris, representing 27.4% of total extracted soluble protein, were achieved by growing the transformed C. vulgaris for 5 days in the presence of 250 mM NaCl. The production of a neutralizing antibody was detected in the serum of fish given feed containing 9% VHSV glycoprotein-expressing C. vulgaris. Furthermore, relative survival rates of 100% and 81.9% were achieved following challenges of these fish with VHSV at 106 and 107 pfu/fish, respectively, indicating that C. vulgaris could be used as a platform for the production of recombinant proteins for use as oral vaccines in the control of viral diseases in aquaculture.

Isolation and characterization of a bacteriophage F20 virulent to Enterobacter aerogenes.

An aquatic phage, designated F20, was characterized and its physico-chemical characteristics studied. F20 was specifically virulent to only two strains of Enterobacter aerogenes (ATCC 13048 and the multi-drug-resistant strain K113) among other species tested (n = 15). It was classified in the family Siphoviridae of T1-like viruses and contained a linear dsDNA genome estimated to be 51.5 kbp enclosed by an isometric capsid of 50±2 nm in diameter and a tail of 150±3 nm in length. F20 was able to survive in a broad pH range between 4 and 11, showed potential for future animal trials using oral solution and resisted chloroform and ethanol. It exhibited remarkable stability between room temperature and 70 °C for up to 150 min, and even up to 6 months at room temperature. Knowledge of this phage belonging to the widespread T1-like viruses might be helpful for adopting therapeutic strategies against E. aerogenes.

Complete nucleotide sequence analysis of a Korean strain of hepatopancreatic parvovirus (HPV) from Fenneropenaeus chinensis.

Hepatopancreatic parvovirus (HPV) of shrimp is distributed worldwide and the entire genome of Thailand and Indian strains (PmDNV) and one Australian strain (PmergDNV) have now been reported. The complete nucleotide sequence of a HPV strain isolated from the fleshy prawn Fenneropenaeus chinensis in Korea (FcDNV) was determined and compared to previously reported sequences. The entire genome of FcDNV contains 6,336 nucleotides, with 40% G+C content, which is the biggest of the known HPV strains. The HPV genome has three open reading frames (ORFs) with a slight overlap between the first and second ORFs. The three ORFs encode the NS2 and NS1 proteins and VP that consist of 425, 578, and 820 amino acids, respectively. Among the three proteins, the NS1 protein shows the highest sequence similarity to the NS1 protein of other known HPV strains, followed by the NS2 protein and the VP protein. Phylogenetic analyses showed that HPV can be grouped into three genotypes, as previously reported, and FcDNV can be grouped as genotype I, with HPV strains isolated in Madagascar and Tanzania. The nucleotide sequences of the noncoding regions at the 5'- and 3'-ends of the plus-strand genome showed a Y-shaped hairpin structure and simple hairpin structure, respectively.

Antimicrobial Resistance Caused by KPC-2 Encoded by Promiscuous Plasmids of the Klebsiella pneumoniae ST307 Strain.

BACKGROUND: A lineage of Klebsiella pneumoniae that produces carbapenemase-2 (KPC-2), sequence type (ST) 307, emerged in 2017. We analyzed the complete sequences of plasmids from KPC-2-producing K. pneumoniae (KPC-Kp) ST307, investigated the antimicrobial resistance conferred by this strain, and confirmed the horizontal interspecies transmission of KPC-carbapenemase-producing Enterobacteriaceae (CPE) characteristics among Enterobacteriaceae. METHODS: We performed antimicrobial susceptibility testing, PCR analysis, multilocus sequence typing, curing tests, and whole-genome sequencing to characterize plasmid-derived KPC-2-producing Enterobacteriaceae clinical isolates. RESULTS: Sequence analysis of KPC-Kp strain ST307 revealed novel plasmid-located virulence factors, including a gene cluster for glycogen synthesis. Three Enterobacteriaceae strains were identified in one patient: K. pneumoniae (CPKp1825), Klebsiella aerogenes (CPEa1826), and Escherichia coli (CPEc1827). The bla KPC-2 gene from K. pneumoniae ST307 was horizontally transmitted between these strains. The plasmids could be transferred through conjugation, because all three strains of bacteria contained the type IV secretion system, pilus genes, and tra genes for conjugal transfer. The bla KPC-2 gene was located on a truncated Tn4401 transposon. Plasmids containing the bla KPC-2 gene could not be artificially removed; thus, the three strains could not be cured. CONCLUSIONS: The ease of horizontal transfer of KPC-Kp ST307 carbapenem resistance has serious public health and epidemiological implications. This study provides a better understanding of the genetic characteristics that can contribute to the growth and spread of KPC-Kp ST307, and their association with antimicrobial resistance genes.

Potential Solutions Using Bacteriophages against Antimicrobial Resistant Bacteria.

Bacteriophages are viruses that specifically infect a bacterial host. They play a great role in the modern biotechnology and antibiotic-resistant microbe era. Since the discovery of phages, their application as a control agent has faced challenges that made antibiotics a better fit for combating pathogenic bacteria. Recently, with the novel sequencing technologies providing new insight into the nature of bacteriophages, their application has a second chance to be used. However, novel challenges need to be addressed to provide proper strategies for their practical application. This review focuses on addressing these challenges by initially introducing the nature of bacteriophages and describing the phage-host-dependent strategies for phage application. We also describe the effect of the long-term application of phages in natural environments and other bacterial communities. Overall, this review gathered crucial information for the future application of phages. We predict the use of phages will not be the only control strategy against pathogenic bacteria. Therefore, more studies must be done for low-risk control methods against antimicrobial-resistant bacteria.

Identification of a Cupin Protein Gene Responsible for Pathogenicity, Phage Susceptibility and LPS Synthesis of Acidovorax citrulli.

Bacteriophages infecting Acidovorax citrulli, the causal agent of bacterial fruit blotch, have been proven to be effective for the prevention and control of this disease. However, the occurrence of bacteriophage-resistant bacteria is one of hurdles in phage biocontrol and the understanding of phage resistance in this bacterium is an essential step. In this study, we aim to investigate possible phage resistance of A. citrulli and relationship between phage resistance and pathogenicity, and to isolate and characterize the genes involved in these phenomena. A phage-resistant and less-virulent mutant named as AC-17-G1 was isolated among 3,264 A. citrulli Tn5 mutants through serial spot assays and plaque assays followed by pathogenicity test using seed coating method. The mutant has the integrated Tn5 in the middle of a cupin protein gene. This mutant recovered its pathogenicity and phage sensitivity by complementation with corresponding wild-type gene. Site-directed mutation of this gene from wild-type by CRISPR/Cas9 system resulted in the loss of pathogenicity and acquisition of phage resistance. The growth of AC-17-G1 in King's B medium was much less than the wild-type, but the growth turned into normal in the medium supplemented with D-mannose 6-phosphate or D-fructose 6-phosphate indicating the cupin protein functions as a phosphomannos isomerase. Sodium dodecyl sulfa analysis of lipopolysaccharide (LPS) extracted from the mutant was smaller than that from wild-type. All these data suggest that the cupin protein is a phosphomannos isomerase involved in LPS synthesis, and LPS is an important determinant of pathogenicity and phage susceptibility of A. citrulli.

Biocontrol of Soft Rot Caused by Pectobacterium odoriferum with Bacteriophage phiPccP-1 in Kimchi Cabbage.

Pectobacterium odoriferum has recently emerged as a widely infective and destructive pathogen causing soft-rot disease in various vegetables. Bacteriophage phiPccP-1 isolated from Pyeongchang, South Korea, showed lytic activity against P. odoriferum Pco14 and two other Pectobacterium species. The transmission electron microscopy and genome phylograms revealed that phiPccP-1 belongs to the Unyawovirus genus, Studiervirinae subfamily of the Autographivirinae family. Genome comparison showed that its 40,487 bp double-stranded DNA genome shares significant similarity with Pectobacterium phage DU_PP_II with the identity reaching 98% of the genome. The phiPccP-1 application significantly inhibited the development of soft-rot disease in the mature leaves of the harvested Kimchi cabbage up to 48 h after Pco14 inoculation compared to the untreated leaves, suggesting that phiPccP-1 can protect Kimchi cabbage from soft-rot disease after harvest. Remarkably, bioassays with phiPccP-1 in Kimchi cabbage seedlings grown in the growth chamber successfully demonstrated its prophylactic and therapeutic potential in the control of bacterial soft-rot disease in Kimchi cabbage. These results indicate that bacteriophage phiPccP-1 can be used as a potential biological agent for controlling soft rot disease in Kimchi cabbage.

Sequence and expression analysis of extracellular signal-regulated kinase 1 from flounder (Paralichthys olivaceous).

Extracellular signal-regulated kinases (ERKs) are a subgroup of mitogen-activated protein kinases (MAPK) that function as important intermediates in signal transduction pathways initiated by several types of cell surface receptors. We cloned a transcript of ERK1 from a cDNA library of flounder leukocytes stimulated with bacterial lipopolysaccharide and hemagglutinin lectin. Flounder ERK1 consists of 1502 nucleotides and encodes a polypeptide of 393 amino acids. Flounder ERK1 showed 90 and 89% amino acid sequence identity to ERK1 of carp and zebrafish, respectively, and over 85% to that of mammals. Multiple bands were detected by Southern blot analysis of flounder genomic DNA after digestion with various restriction enzymes, implying the presence of additional MAPK genes in flounder. Real-time PCR revealed the ubiquitous expression of flounder MAPK in all tissues with high levels of transcription in brain, gill, and fin, but not in muscle or skin. Flounder MAPK was successfully expressed in mammalian COS1 cells and phosphorylated myelin basic protein (MBP) substrate when the cells were stimulated with PMA or EGF, indicating that flounder MAPK is functional in animal cells.

Species Transferability of Klebsiella pneumoniae Carbapenemase-2 Isolated from a High-Risk Clone of Escherichia coli ST410.

Sequence type 410 (ST410) of Escherichia coli is an extraintestinal pathogen associated with multi drug resistance. In this study, we aimed to investigate the horizontal propagation pathway of a highrisk clone of E. coli ST410 that produces Klebsiella pneumoniae carbapenemase (KPC). blaKPCencoding E. coli and K. pneumoniae isolates were evaluated, and complete sequencing and comparative analysis of blaKPC-encoding plasmids from E. coli and K. pneumoniae, antimicrobial susceptibility tests, polymerase chain reaction, multilocus sequence typing, and conjugal transfer of plasmids were performed. Whole-genome sequencing was performed for plasmids mediating KPC-2 production in E. coli and K. pneumoniae clinical isolates. Strains E. coli CPEc171209 and K. pneumoniae CPKp171210 were identified as ST410 and ST307, respectively. CPEc171209 harbored five plasmids belonging to serotype O8:H21, which is in the antimicrobial-resistant clade C4/H24. The CPKp171210 isolate harbored three plasmids. Both strains harbored various additional antimicrobial resistance genes. The IncX3 plasmid pECBHS_9_5 harbored blaKPC-2 within a truncated Tn4401a transposon, which also contains blaSHV-182 with duplicated conjugative elements. This plasmid displayed 100% identity with the IncX3 plasmid pKPBHS_10_3 from the K. pneumoniae CPKp171210 ST307 strain. The genes responsible for the conjugal transfer of the IncX3 plasmid included tra/trb clusters and pil genes coding the type IV pilus. ST410 can be transmitted between patients, posing an elevated risk in clinical settings. The emergence of a KPC-producing E. coli strain (ST410) is concerning because the blaKPC-2-bearing plasmids may carry treatment resistance across species barriers. Transgenic translocation occurs among carbapenem-resistant bacteria, which may spread rapidly via horizontal migration.

Transport of Phage in Melon Plants and Inhibition of Progression of Bacterial Fruit Blotch.

Bacterial fruit blotch (BFB) is an economically important disease in melons and watermelons for which no effective control method is available. Application of phytobacterium-infecting phage has been evaluated as an alternative means of preventing bacterial diseases in plants. Coating of seeds with bacteriophages infecting Acidovorax citrulli, the causal agent of BFB, is effective for controlling the disease, as shown in our previous study. We evaluated the transport of bacteriophage ACPWH from soil to the leaves of melon plants, and we also evaluated its effect on BFB. Leaves of melon plants were spray-inoculated with A. citrulli, and bacteriophage ACPWH was added to soil after symptoms had developed. ACPWH was detected by PCR in foliar tissue 8 h after addition to soil. DAPI-stained ACPWH accumulated at the leaf tip after 24 h. Melon treated with ACPWH showed 27% disease severity, compared to 80% for the non-treated control, indicating that ACPWH can be used to control BFB.

Isolation, Characterization, and Application of a Bacteriophage Infecting the Fish Pathogen Aeromonas hydrophila.

Bacteriophages are increasingly being used as biological control agents against pathogenic bacteria. In the present study, we isolate and characterize bacteriophage Akh-2 from Geoje Island, South Korea, to evaluate its utility in controlling motile Aeromonas septicemia. Akh-2 lysed four of the seven Aeromonas hydrophila strains tested. Transmission electron microscopy analysis showed that Akh-2 belongs to the Siphoviridae family, with head and tail sizes of 50 ± 5 and 170 ± 5 nm, respectively. One-step growth curve analysis revealed that the phage has a latent period of 50 ± 5 min and a burst size of 139 ± 5 plaque-forming units per infected cell. The phage appeared stable in a pH range of 6-8 and a temperature range of -80 to 46 °C. Based on next-generation sequencing analysis, its genome is 114,901 bp in size, with a 44.22% G + C content and 254 open reading frames. During an artificial induction of the disease, loach (Misgurnus anguillicaudatus) treated with Akh-2 showed an increased survival rate and time compared with the non-treated control. Our results suggest that Akh-2 is a potential biological agent for the treatment of Aeromonas infections in fish.