Outer membrane protein A (OmpA) is a potential virulence factor of Vibrio alginolyticus strains isolated from diseased fish

DUF1127-containing protein and ProQ had opposite effects on biofilm formation in Vibrio alginolyticus

The RNA binding protein is crucial for gene regulation at the post transcription level. In this study, functions of the DUF1127-containing protein and ProQ, which are RNA-binding proteins, were revealed in Vibrio alginolyticus. DUF1127 deletion increased the ability of biofilm formation, whereas ProQ deletion reduced the amount of biofilm. Moreover, extracellular proteinase secretion was significantly reduced in the DUF1127 deletion strain. ProQ, not DUF1127-containing protein, can help the cell to defense oxidative stress. Deletion of DUF1127 resulted in a higher ROS level in the cell, however, ProQ deletion showed no difference. RNA-seq unveiled the expression of genes involved in extracellular protease secretion were significantly downregulated and biofilm synthesis-related genes, such as rbsB and alsS, were differentially expressed in the DUF1127 deletion strain. ProQ affected the expression of genes involved in biofilm synthesis (flgC and flgE), virulence (betB and hutG), and oxidative stress. Moreover, the DUF1127-containing and ProQ affected the mRNA levels of various regulators, such as LysR and BetI. Overall, our study revealed that the DUF1127-containing protein and ProQ have crucial functions on biofilm formation in V. alginolyticus.

Comparative Genomic Analysis of Shrimp-Pathogenic Vibrio parahaemolyticus LC and Intraspecific Strains with Emphasis on Virulent Factors of Mobile Genetic Elements

Vibrio parahaemolyticus exhibits severe pathogenicity in humans and animals worldwide. In this study, genome sequencing and comparative analyses were conducted for in-depth characterization of the virulence factor (VF) repertoire of V. parahaemolyticus strain LC, which presented significant virulence to shrimp Litopenaeus vannamei. Strain LC, harboring two circular chromosomes and three linear plasmids, demonstrated ≥98.14% average nucleotide identities with 31 publicly available V. parahaemolyticus genomes, including 13, 11, and 7 shrimp-, human-, and non-pathogenic strains, respectively. Phylogeny analysis based on dispensable genes of pan-genome clustered 11 out of 14 shrimp-pathogenic strains and 7 out of 11 clinical strains into two distinct clades, indicating the close association between host-specific pathogenicity and accessory genes. The VFDB database revealed that 150 VFs of LC were mainly associated with the secretion system, adherence, antiphagocytosis, chemotaxis, motility, and iron uptake, whereas no homologs of the typical pathogenic genes pirA, pirB, tdh, and trh were detected. Four genes, mshB, wbfT, wbfU, and wbtI, were identified in both types of pathogenic strains but were absent in non-pathogens. Notably, a unique cluster similar to Yen-Tc, which encodes an insecticidal toxin complex, and diverse toxin-antitoxin (TA) systems, were identified on the mobile genetic elements (MGEs) of LC. Conclusively, in addition to the common VFs, various unique MGE-borne VFs, including the Yen-Tc cluster, TA components, and multiple chromosome-encoded chitinase genes, may contribute to the full spectrum of LC virulence. Moreover, V. parahaemolyticus demonstrates host-specific virulence, which potentially drives the origin and spread of pathogenic factors.

Molecular characterization of a cation-dependent mannose-6-phosphate receptor gene in Crassostrea hongkongensis and its responsiveness in Vibrio alginolyticus infection

The cation-dependent mannose-6-phosphate receptor (CD-M6PR) is a P-type lectin that plays a crucial role in lysosomal enzyme transport, bacterial resistance, and viral entry. In this study, we cloned and analyzed the ORF of the CD-M6PR gene from Crassostrea hongkongensis and named it ChCD-M6PR. We analyzed the nucleotide and amino acid sequence of ChCD-M6PR, its tissue expression pattern and immune response to Vibrio alginolyticus. Our results showed that the ORF of ChCD-M6PR was 801 bp long and encoded a protein of 266 amino acids with a signal peptide at the N-terminus, as well as Man-6-P_recep, ATG27 and transmembrane structural domains. Phylogenetic analysis indicated that Crassostrea hongkongensis shared the highest similarity with Crassostrea gigas in the terms of CD-M6PR. The ChCD-M6PR gene was found to be expressed in various tissues, with the highest expression observed in the hepatopancreas and the lowest in the hemocytes by the fluorescence quantitative PCR. Furthermore, the expression of ChCD-M6PR gene was significantly up-regulated for a short time in response to Vibrio alginolyticus infection in the gill and hemocytes, while it was down-regulated in the gonads. The expression patterns of ChCD-M6PR also varied in the other tissues. The 96 h cumulative mortality rate of Crassostrea hongkongensis infected with Vibrio alginolyticus after knockdown the ChCD-M6PR gene was significantly higher. Overall, our findings suggests that ChCD-M6PR plays a crucial role in the immune response of Crassostrea hongkongensis to Vibrio alginolyticus infection, and its tissue-specific expression patterns may be indicatitive of varied immune responses across tissues.

Andrographolide promote the growth and immunity of Litopenaeus vannamei, and protects shrimps against Vibrio alginolyticus by regulating inflammation and apoptosis via a ROS-JNK dependent pathway

Vibrio alginolyticus (V. alginolyticus) is one of the major pathogens causing mass mortality of shrimps worldwide, affecting energy metabolism, immune response and development of shrimps. In the context of the prohibition of antibiotics, it is necessary to develop a drug that can protect shrimp from V. alginolyticus. Andrographolide (hereinafter called Andr), a traditional drug used in Chinese medicine, which possesses diverse biological effects including anti-bacteria, antioxidant, immune regulation. In this study, we investigated the effect of Andr on growth, immunity, and resistance to V. alginolyticus infection of Litopenaeus vannamei (L. vannamei) and elucidate the underlying molecular mechanisms. Four diets were formulated by adding Andr at the dosage of 0 g/kg (Control), 0.5 g/kg, 1 g/kg, and 2 g/kg in the basal diet, respectively. Each diet was randomly fed to one group with three replicates of shrimps in a 4-week feeding trial. The results showed that dietary Andr improved the growth performance and non-specific immune function of shrimps. L. vannamei fed with Andr diets showed lower mortality after being challenged by V. alginolyticus. After 6 h of V. alginolyticus infection, reactive oxygen species (ROS) production, tissue injury, apoptosis, expression of inflammatory factors (IL-1 β and TNFα) and apoptosis-related genes (Bax, caspase3 and p53) were increased in hemocytes and hepatopancreas, while feeding diet with 0.5 g/kg Andr could inhibit the increase. Considering that JNK are important mediators of apoptosis, we examined the influence of Andr on JNK activity during V. alginolyticus infection. We found that Andr inhibited JNK activation induced by V. alginolyticus infection on L. vannamei. The ROS scavenger N-acetyl-l-cysteine (NAC) suppressed V. alginolyticus-induced inflammation and apoptosis, suggesting that ROS play an important role in V. alginolyticus-induced inflammation and apoptosis. Treated cells with JNK specific activator anisomycin, the inflammation and apoptosis inhibited by Andr were counteracted. Collectively, Andr promote the growth and immunity of L. vannamei, and protects shrimps against V. alginolyticus by regulating inflammation and apoptosis via a ROS-JNK dependent pathway. These results improve the understanding of the pathogenesis of V. alginolyticus infection and provide clues to the development of effective drugs against V. alginolyticus.

Interaction of Liberibacter Solanacearum with Host Psyllid Vitellogenin and Its Association with Autophagy

Candidatus Liberibacter solanacearum (CLso) haplotype D, transmitted by the carrot psyllid Bactericera trigonica, is a major constraint for carrot production in Israel. Unveiling the molecular interactions between the psyllid vector and CLso can facilitate the development of nonchemical approaches for controlling the disease caused by CLso. Bacterial surface proteins are often known to be involved in adhesion and virulence; however, interactions of CLso with carrot psyllid proteins that have a role in the transmission process has remained unexplored. In this study, we used CLso outer membrane protein (OmpA) and flagellin as baits to screen for psyllid interacting proteins in a yeast two-hybrid system assay. We identified psyllid vitellogenin (Vg) to interact with both OmpA and flagellin of CLso. As Vg and autophagy are often tightly linked, we also studied the expression of autophagy-related genes to further elucidate this interaction. We used the juvenile hormone (JH-III) to induce the expression of Vg, thapsigargin for suppressing autophagy, and rapamycin for inducing autophagy. The results revealed that Vg negatively regulates autophagy. Induced Vg expression significantly suppressed autophagy-related gene expression and the levels of CLso significantly increased, resulting in a significant mortality of the insect. Although the specific role of Vg remains obscure, the findings presented here identify Vg as an important component in the insect immune responses against CLso and may help in understanding the initial molecular response in the vector against Liberibacter. IMPORTANCE Pathogen transmission by vectors involves multiple levels of interactions, and for the transmission of liberibacter species by psyllid vectors, much of these interactions are yet to be explored. Candidatus Liberibacter solanacearum (CLso) haplotype D inflicts severe economic losses to the carrot industry. Understanding the specific interactions at different stages of infection is hence fundamental and could lead to the development of better management strategies to disrupt the transmission of the bacteria to new host plants. Here, we show that two liberibacter membrane proteins interact with psyllid vitellogenin and also induce autophagy. Altering vitellogenin expression directly influences autophagy and CLso abundance in the psyllid vector. Although the exact mechanism underlying this interaction remains unclear, this study highlights the importance of immune responses in the transmission of this disease agent.

In vivo test of Vibrio alginolyticus and Vibrio harveyi infection in the humpback grouper (Cromileptes altivelis) from East Java Indonesia

Background and Aim:

The need for fish seeds resistant to bacterial and viral infections has encouraged studies on the molecular pathogenesis mechanism of Vibrio bacteria, such as Vibrio alginolyticus and Vibrio harveyi, regarding the receptor organs, protein adhesion mechanisms, and antibody responses of the humpback grouper. This study aims to confirm the characteristics of the specific proteins expressed in the receptor organ of the humpback grouper (Cromileptes altivelis) using the expression of V. alginolyticus and V. harveyi bacteria.

Materials and Methods:

The study was conducted by isolating crude protein and whole cells from both the Vibrio bacteria. In addition, serum and organ tissue were also isolated from fish samples. Then, hemagglutination and dot blot tests with polyacrylamide gel electrophoresis analysis were performed to determine the highest expression of receptor from the whole bacterial cells and crude protein from both healthy and infected (V. alginolyticus and V. harveyi) fishes. Scanning electron microscope results showed that V. alginolyticus and V. harveyi could express bundle-forming pili, which is involved in bacterial autoaggregation and the mediation of the initial attachment of bacteria to their host cells.

Results:

These results indicated that all the specific receptors for protein in fish organs recognized vibriosis antigens. The specificity test showed that the brain, eye, and kidney organs’ receptors provided a quality and quantity level of responses at 22.63, 53.95, and 43.15 kDa, respectively. The polyclonal anti-V. alginolyticus immunoglobulin M (IgM) antibodies were more cross-reactive than the anti-V. harveyi IgM. Hence, this shows that V. alginolyticus bacteria are more pathogenic than V. harveyi.

Conclusion:

In the future, the molecular characteristics of V. alginolyticus and V. harveyi antigens and the specific receptor organ proteins in the humpback grouper can be developed as the basis for constructing molecular peptide-based vaccine materials.

The role of dctP gene in regulating colonization, adhesion and pathogenicity of Vibrio alginolyticus strain HY9901

Vibriosis caused by Vibrio alginolyticus has severely affected the development of mariculture industry in recent decades. DctP, a tripartite ATP-independent periplasmic transporter solute-binding subunit, is thought to be one of the virulence factors in Vibrio. In this study, the results displayed no difference in morphological characteristics and growth between ΔdctP (dctP mutant strain) and WT (wild-type strain). Nevertheless, the ability of swarming motility, biofilm formation, ECPase formation, cell adhesion and colonized ability of ΔdctP significantly decreased compared to those of WT. The LD₅₀ of ΔdctP significantly increased by 40-fold compared to that of WT. The transcriptome analysis demonstrated the deletion mutation of dctP could regulate the expression levels of 22 genes related to colonization, adhesion and pathogenicity in V. alginolyticus. The analysis of qRT-PCR showed the transcriptome data were reliable. These results reveal the effect of attenuated function of DctP on colonization, adherence and pathogenicity by controlling the expression of related gene.

Strategies for Rapid Identification of Acinetobacter baumannii Membrane Proteins and Polymyxin B's Effects

Acinetobacter baumannii, especially multidrug resistant Acinetobacter baumannii, is a notable source of pressure in the areas of public health and antibiotic development. To overcome this problem, attention has been focused on membrane proteins. Different digestion methods and extraction detergents were examined for membrane proteome sample preparation, and label-free quantitative and targeted proteome analyses of the polymyxin B-induced Acinetobacter baumannii ATCC 19606 membrane proteome were performed based on nano LC-MS/MS. Ultracentrifugation of proteins at a speed of 150,000×g, digestion by trypsin, filter-aided sample preparation, and detergents such as lauryldimethylamine-N-oxide were proved as a fast and effective way for identification of membrane proteome by nano LC-MS/MS. Upon treatment with polymyxin B, expression levels of 15 proteins related to membrane structure, transporters, cell surface, and periplasmic space were found to be significantly changed. Furthermore, targeted proteome was also used to confirm these changes. A relatively rapid membrane proteome preparation method was developed, and a more comprehensive view of changes in the Acinetobacter baumannii membrane proteome under polymyxin B pressure was obtained.

Roles of ompA of Citrobacter werkmanii in bacterial growth, biocide resistance, biofilm formation and swimming motility

The genus Citrobacter is commonly found in environmental and industrial settings, some members of which have been used for bioremediation of heavy metals owing to the absorption ability of their biofilms. Although our previous studies have found that the outer membrane protein A (OmpA) contributes to the process of Citrobacter werkmanii biofilm formation, the underlying mechanisms remain elusive. Therefore, we deleted ompA from the genome of C. werkmanii and investigated its phenotypes in comparison to the wild type strain (WT) and the complementary strain using biochemical and molecular techniques including RNA-Seq. Our results demonstrated that the deletion of ompA led to an increase in biofilm formation on both polystyrene and glass surfaces due to upregulation of some biofilm formation related genes. Meanwhile, swimming ability, which is mediated by activation of flagellar assembly genes, was increased on semi-solid plates in the ∆ompA strain when compared with WT. Additionally, inactivation of ompA also caused increased 1,2-benzisothiazolin-3-one (BIT) resistance, differential responses to Ca²⁺ stress, curli protein expression and cellulose production. Finally, ∆ompA caused differential expression of a total of 1470 genes when compared with WT, of which 146 were upregulated and 1324 were downregulated. These genes were classified into different Gene Ontology (GO) and KEGG pathways. In summary, ompA in C. werkmanii contributes to a variety of biological functions and may act as a target site to modulate biofilm formation. KEY POINTS: • ompA is a negative regulator for biofilm formation by C. werkmanii. • ompA inhibits swimming motility of C. werkmanii. • ompA deletion causes different expression profiles in C. werkmanii.

High-level biocidal products effectively eradicate pathogenic γ-proteobacteria biofilms from aquaculture facilities

The use of effective biocides as disinfectants is essential in aquaculture facilities. However, while most biocides act effectively on free-living planktonic pathogens, they are seldom useful against biofilms. In this study, we evaluate the biocidal efficacy and antimicrobial specific contact time of three disinfectants, Virkon™Aquatic (VirA), peracetic acid (PerA) and hydrogen peroxide (HydP), on Vibrio anguillarum, V. harveyi, V. alginolyticus, and Photobacterium damselae subspecies piscicida against their both life phases. By using the minimum inhibitory, bactericidal, and eradication concentrations of disinfectants acting on the free-living planktonic state (MIC; MBC) and biofilms (MBIC; MBEC), we determined the in vitro susceptibility of each bacterial strain against three different individual concentrations of VirA, PerA, and HydP added at 1, 5, and 10 min intervals. PerA and VirA had the highest bactericidal efficacies against the free-living planktonic state and biofilm of all bacteria. Kinetically, PerA gave a positive result more quickly in both cases regardless of the strain in question, while the weakest HydP required longer than 10 min to act effectively. Moreover, we conducted a short in vivo safety trial by pouring the suggested MIC of each disinfectant into tanks containing juvenile Gilthead seabream (Sparus aurata). A significant mortality after 24 h was observed pointing to the potential risk a mishap of these chemicals might cause to fish. Nevertheless, collectively, our results support the inclusion of biocides within biosecurity protocols in aquaculture facilities and highlight PerA as the most effective disinfectant for fighting against biofilms produced by V. anguillarum, V. harveyi, V. alginolyticus or P. damselae subsp. piscicida.

Complete genome analysis of an active prophage of Vibrio alginolyticus

An active prophage, Vibrio phage ValM-yong1, was isolated from pathogenic Vibrio alginolyticus by mitomycin C induction. This phage is a member of the family Myoviridae and contains a head approximately 90 nm in diameter and a retractable tail approximately 250 nm in length. The genome of the phage is 33,851 bp in length with a G+C content of 45.6%. The noteworthy features of Vibrio phage ValM-yong1 are its flower-like head and genomic mosaicism. Here, we focus on presenting the genomic characterization of the virus.

Virulence of Vibrio alginolyticus Accentuates Apoptosis and Immune Rigor in the Oyster Crassostrea hongkongensis

Vibrio species are ubiquitously distributed in marine environments, with important implications for emerging infectious diseases. However, relatively little is known about defensive strategies deployed by hosts against Vibrio pathogens of distinct virulence traits. Being an ecologically relevant host, the oyster Crassostrea hongkongensis can serve as an excellent model for elucidating mechanisms underlying host-Vibrio interactions. We generated a Vibrio alginolyticus mutant strain (V. alginolyticus^△vscC ) with attenuated virulence by knocking out the vscC encoding gene, a core component of type III secretion system (T3SS), which led to starkly reduced apoptotic rates in hemocyte hosts compared to the V. alginolyticus^WT control. In comparative proteomics, it was revealed that distinct immune responses arose upon encounter with V. alginolyticus strains of different virulence. Quite strikingly, the peroxisomal and apoptotic pathways are activated by V. alginolyticus^WT infection, whereas phagocytosis and cell adhesion were enhanced in V. alginolyticus^△vscC infection. Results for functional studies further show that V. alginolyticus^WT strain stimulated respiratory bursts to produce excess superoxide (O2^•-) and hydrogen peroxide (H₂O₂) in oysters, which induced apoptosis regulated by p53 target protein (p53tp). Simultaneously, a drop in sGC content balanced off cGMP accumulation in hemocytes and repressed the occurrence of apoptosis to a certain extent during V. alginolyticus^△vscC infection. We have thus provided the first direct evidence for a mechanistic link between virulence of Vibrio spp. and its immunomodulation effects on apoptosis in the oyster. Collectively, we conclude that adaptive responses in host defenses are partially determined by pathogen virulence, in order to safeguard efficiency and timeliness in bacterial clearance.