Purification and partial characterisation of a fish lethal extracellular protease from Vibrio pelagius

A putative cytotoxic serine protease from Salmonella typhimurium UcB5 recovered from undercooked burger

A putative virulence exoprotease designated as UcB5 was successfully purified from the bacterium Salmonella typhimurium to the electrophoretic homogeneity with 13.2-fold and 17.1% recovery by hydrophobic, ion-exchange, and gel permeation chromatography using Phenyl-Sepharose 6FF, DEAE-Sepharose CL-6B, and Sephadex G-75, respectively. By applying SDS-PAGE, the molecular weight was confirmed at 35 kDa. The optimal temperature, pH, and isoelectric point were 35 °C, 8.0, 5.6 ± 0.2, respectively. UcB5 was found to have a broad substrate specificity against almost all the tested chromogenic substrates with maximal affinity against N-Succ-Ala-Ala-Pro-Phe-pNA achieving K_m of 0.16 mM, K_cat/K_m of 3.01 × 10⁵ S^-1 M^-1, and amidolytic activity of 28.9 µmol min^-1 L^-1. It was drastically inhibited by TLCK, PMSF, SBTI, and aprotinin while, DTT, β-mercaptoethanol, 2,2'-bipyridine, o-phenanthroline, EDTA, and EGTA had no effect, which suggested a serine protease-type. Also, it has shown a broad substrate specificity against a broad range of natural proteins including serum proteins. A cytotoxicity and electron microscopy study revealed that UcB5 could cause subcellular proteolysis that finally led to liver necrosis. For this, future research should focus on using a combination of external antiproteases and antimicrobial agents for the treatment of microbial diseases instead of using drugs alone.

Analysis of immune response in the sea urchin larva

Sea urchin larvae deploy a complex immune system in the context of relatively simple morphology. Several types of phagocytic or granular immune cells respond rapidly to microbes and microbial components within the body cavity. Many of these cells also respond to microbial disturbances in the gut lumen. In the course of immune response, hundreds of genes are up- and downregulated, many of which have homologs involved in immunity in other species. Thus, the larval sea urchin provides an experimentally advantageous model for investigating the response to immune challenge at the level of cell behavior and gene regulatory networks. Importantly, the morphological simplicity and optical clarity of these larvae allow studies to be carried out within the intact animal. Here, we outline techniques to probe and visualize the immune system of the feeding sea urchin larva, particularly for quantifying gene expression and cell migration as the animal responds to both pathogens and symbionts. Techniques addressed in this chapter include (1) exposure of larvae to microbes and microbial products in sea water and by blastocoelar microinjection, (2) time-lapse imaging of immune response, (3) isolation of culturable bacteria associated with feeding larvae, (4) quantification of larval associations with isolated bacterial strains and (5) preparation of secreted products from isolated bacteria for testing in larval culture.

Bacteriophage Interactions with Marine Pathogenic Vibrios: Implications for Phage Therapy

A global distribution in marine, brackish, and freshwater ecosystems, in combination with high abundances and biomass, make vibrios key players in aquatic environments, as well as important pathogens for humans and marine animals. Incidents of Vibrio-associated diseases (vibriosis) in marine aquaculture are being increasingly reported on a global scale, due to the fast growth of the industry over the past few decades years. The administration of antibiotics has been the most commonly applied therapy used to control vibriosis outbreaks, giving rise to concerns about development and spreading of antibiotic-resistant bacteria in the environment. Hence, the idea of using lytic bacteriophages as therapeutic agents against bacterial diseases has been revived during the last years. Bacteriophage therapy constitutes a promising alternative not only for treatment, but also for prevention of vibriosis in aquaculture. However, several scientific and technological challenges still need further investigation before reliable, reproducible treatments with commercial potential are available for the aquaculture industry. The potential and the challenges of phage-based alternatives to antibiotic treatment of vibriosis are addressed in this review.

Characterization of a new phage, termed ϕA318, which is specific for Vibrio alginolyticus

Vibrio alginolyticus is an opportunistic pathogen of animals and humans; its related strains can also produce tetrodotoxin and hemolysins. A new phage, ϕA318, which lysed its host V. alginolyticus with high efficiency, was characterized. The burst size of ϕA318 in V. alginolyticus was 72 PFU/bacterium at an MOI of 1 at room temperature; the plaque size was as large as 5 mm in diameter. Electron microscopy (EM) of the phage particles revealed a 50- to 55-nm isomorphous icosahedral head with a 12-nm non-contractile tail, similar to the T7-like phages of the family Podoviridae. Phylogenetic analysis based on complete sequences of the DNA-directed RNA polymerase gene revealed that ϕA318 had 28-47% amino acid identity to enterobacteria phages T7 and SP6, and other Vibrio phages, and the phylogenetic distance suggested that ϕA318 could be classified as a new T7-like bacteriophage. Nevertheless, several motifs in the ϕA318 phage RNA polymerase were highly conserved, including DFRGR (T7-421 motif), DG (T7-537 motif), PSEKPQDIYGAVS (T7-563 motif), RSMTKKPVMTL PYGS (T7-627 motif), and HDS (T7-811 motif). Genetic analysis indicated that phage ϕA318 is not a thermostable direct hemolysin producer. The results suggest that the MOI should be higher than 0.1 to prevent the chance of hemolysin production by the bacteria before they are lysed by the phage.

Proteases produced by vibrios

Bacteria of the genus Vibrio are normal habitants of the aquatic environment but the some species are believed to be human pathogens. Pathogenic vibrios produce various pathogenic factors, and the proteases are also recognized to play pathogenic roles in the infection: the direct roles by digesting many kinds of host proteins or indirect roles by processing other pathogenic protein factors. Especially VVP from Vibrio vulnificus is thought to be a major pathogenic factor of the vibrio. Although HA/P, the V. cholerae hemagglutinin/protease, is not a direct toxic factor of cholera vibrio, its significance is an undeniable fact. Production of HA/P is regulated together with major pathogenic factors such as CT (cholera toxin) or TCP (toxin co-regulated pilus) by a quorum-sensing system. HA/P is necessary for full expression of pathogenicity of the vibrio by supporting growth and translocation in the digestive tract. Processing of protein toxins such as CT or El Tor hemolysin is also an important pathogenic role.

Extracellular proteases and possible disease related virulence mechanisms of two marine bacteria implicated in an opportunistic bacterial infection of Nephrops norvegicus

The extracellular products (ECP) secreted by two strains of gram-negative bacteria isolated from Nephrops norvegicus exhibiting signs of an opportunistic bacterial infection were investigated with the objective of understanding their role in the spoilage of host muscle tissue and identifying disease related virulence mechanisms. ECP from Vibrio sp. demonstrated no proteolytic activity. ECP from Pseudoalteromonas sp. (isolate N10) degraded several substrates, including azocasein and host muscle tissue. Proteolytic activity increased with temperature. Substrate-impregnated sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis of the effect of the isolates' ECP on the molecular weight of proteins derived from abdominal muscle tissue revealed that the ECP of Pseudoalteromonas sp. selectively degraded the myosin heavy chain, troponin-T, troponin-I, paramyosin and several unidentified muscle proteins approximately 110 kDa in size. Topomyosin was also reduced in quantity. Degradation of SDS-PAGE gels impregnated with host muscle proteins, by the ECP of Pseudoalteromonas sp. revealed 3 zones of proteolysis, with estimated molecular weights between 100 and 30 kDa, indicating multiple proteases in the ECP. Through the API ZYM system, both isolates demonstrated strong leucine arylamidase activity, with the Vibrio sp. showing strong acid phosphatase activity. These enzymes have been identified as disease related virulence mechanisms in other bacterial pathogens. There is likely a complex pathway to the final condition, involving virulence factors of other species and the stresses involved in capture and transport.

LuxO controls extracellular protease, haemolytic activities and siderophore production in fish pathogen Vibrio alginolyticus

AIMS

To characterize the luxO gene in fish pathogen Vibrio alginolyticus MVP01 and investigate its roles in regulation of extracellular products (ECP) and siderophore production.

METHODS AND RESULTS

The luxO gene was cloned from V. alginolyticus MVP01. Genetic analysis revealed that it encoded a protein with high similarity to other LuxO homologues. The luxO in-frame deletion mutant and rpoN null mutant were constructed with suicide plasmids. We demonstrated that sole deletion in LuxO increased the secretion of extracellular protease and haemolytic products, but decreased siderophore production for V. alginolyticus MVP01. Mutants with null rpoN displayed significantly enhanced protease level and siderophore production while notable reduction in haemolytic activities of ECP.

CONCLUSIONS

Vibrio alginolyticus harbours functional luxO gene that regulates the secretion of extracellular protease and haemolytic materials as well as siderophore production in either sigma(54) dependent or independent manners.

SIGNIFICANCE AND IMPACT OF THE STUDY

The current study demonstrated that V. alginolyticus MVP01 produces extracellular protease and haemolytic activity material as well as siderophore, which may be characteristics of the virulence of the strain. Revelations that secretion of these products is under the regulation of LuxO and sigma(54) as well as the potential quorum sensing systems in V. alginolyticus MVP01 will expedite the understanding of vibriosis pathogenesis.

Presence of a lethal protease in the extracellular products of Vibrio splendidus-Vibrio lentus related strains

The presence of a lethal extracellular 39-kDa protease, a virulence determinant of a Listonella pelagia strain which produces vibriosis in turbot, was determined in the extracellular products (ECP) of 33 Vibrionaceae strains. Both immunological and enzymatic techniques distinguished this specific protease from other Vibrionaceae proteins. It was detected in 15% (5/33) of the ECPs assayed belonging to strains of the Vibrio splendidus-V. lentus related group isolated in Galician aquaculture systems (NW Spain). As these strains were associated with diseased octopus and cultured turbot, were able to colonize the internal organs of fish and produced a lethal ECP for fish, they are a potential risk for the health of reared aquatic organisms.

Complete genome sequence of phiHSIC, a pseudotemperate marine phage of Listonella pelagia

The genome for the marine pseudotemperate member of the Siphoviridae phiHSIC has been sequenced using a combination of linker amplification library construction, restriction digest library construction, and primer walking. phiHSIC enters into a pseudolysogenic relationship with its host, Listonella pelagia, characterized by sigmoidal growth curves producing >10(9) cells/ml and >10(11) phage/ml. The genome (37,966 bp; G+C content, 44%) contained 47 putative open reading frames (ORFs), 17 of which had significant BLASTP hits in GenBank, including a beta subunit of DNA polymerase III, a helicase, a helicase-like subunit of a resolvasome complex, a terminase, a tail tape measure protein, several phage-like structural proteins, and 1 ORF that may assist in host pathogenicity (an ADP ribosyltransferase). The genome was circularly permuted, with no physical ends detected by sequencing or restriction enzyme digestion analysis, and lacked a cos site. This evidence is consistent with a headful packaging mechanism similar to that of Salmonella phage P22 and Shigella phage Sf6. Because none of the phage-like ORFs were closely related to any existing phage sequences in GenBank (i.e., none more than 62% identical and most <25% identical at the amino acid level), phiHSIC is unique among phages that have been sequenced to date. These results further emphasize the need to sequence phages from the marine environment, perhaps the largest reservoir of untapped genetic information.

Marine phage genomics: what have we learned?

Marine phages are the most abundant and diverse form of life on the planet, and their genomes have been described as the largest untapped reservoir of genomic information. To date, however, the complete genome sequences of only 17 marine phage are known. Nevertheless, these genomes have revealed some interesting features, including the presence of photosynthetic genes in cyanophage and common patterns of genomic organization. Intriguing findings are also being made from studies of the uncultivated marine viral community genome ('metavirome'). The greatest challenge in interpreting the biology of these phages, and for making comparisons with their terrestrial counterparts, is the high proportion of unidentifiable open reading frames (approximately 60%). Future studies are likely to focus on sequencing more marine phage genomes from disparate hosts and diverse environments and on further basic studies of the biology of existing marine phages.