Deletion of speA and aroC genes impacts the pathogenicity of Vibrio anguillarum in spotted sea bass.

Vibrio anguillarum is one of the major pathogens responsible for bacterial infections in marine environments, causing significant impacts on the aquaculture industry. The misuse of antibiotics leads to bacteria developing multiple drug resistances, which is detrimental to the development of the fisheries industry. In contrast, live attenuated vaccines are gradually gaining acceptance and widespread recognition. In this study, we constructed a double-knockout attenuated strain, V. anguillarum ΔspeA-aroC, to assess its potential for preparing a live attenuated vaccine. The research results indicate a significant downregulation of virulence-related genes, including Type VI secretion system, Type II secretion system, biofilm synthesis, iron uptake system, and other related genes, in the mutant strain. Furthermore, the strain lacking the genes exhibited a 67.47% reduction in biofilm formation ability and increased sensitivity to antibiotics. The mutant strain exhibited significantly reduced capability in evading host immune system defenses and causing in vivo infections in spotted sea bass (Lateolabrax maculatus), with an LD50 that was 13.93 times higher than that of the wild-type V. anguillarum. Additionally, RT-qPCR analysis of immune-related gene expression in spotted sea bass head kidney and spleen showed a weakened immune response triggered by the knockout strain. Compared to the wild-type V. anguillarum, the mutant strain caused reduced levels of tissue damage. The results demonstrate that the deletion of speA and aroC significantly reduces the biosynthesis of biofilms in V. anguillarum, leading to a decrease in its pathogenicity. This suggests a crucial role of biofilms in the survival and invasive capabilities of V. anguillarum.

Pseudomonas piscis sp. nov., isolated from the profound head ulcers of farmed Murray cod (Maccullochella peelii peelii).

A Gram-stain-negative, strictly aerobic, motile, rod-shaped bacterium with monopolar flagella, designated as MC042T, was isolated from the profound head ulcers of farmed Murray cod sampled from Zhejiang Province, China. Analysis of its 16S rRNA gene sequence and multilocus sequence analysis phylogeny showed that strain MC042T belonged to the genus Pseudomonas, showing the highest 16S rRNA gene sequence similarity to Pseudomonas juntendi BML3T (98.9 %), and less than 98.8 % similarity to other Pseudomonas species with validly published names. Whole-genome sequencing and phylogenetic reconstruction based on a core set of 1563 Pseudomonas genes further indicated that strain MC042T was most closely related to the clade formed by Pseudomonas protegens CHA0T and Pseudomonas saponiphila DSM 975T and distantly related to any of the validly published species of the genus Pseudomonas. Furthermore, strain MC042T could be distinguished from its closely related species of the genus Pseudomonas by its ability to assimilate maltose, d-xylose and melibiose, but not d-mannitol. The principal fatty acids were C16 : 0, summed feature 3 (iso-C15 : 0 2-OH and/or C16 : 1ω7c) and summed feature 8 (C18 : 1 ω7c and/or C18 : 1 ω6c). The respiratory quinone was Q-9. Polar lipids of strain MC042T comprised diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, unidentified glycolipids, an unidentified lipid, an unknown glycolipid and aminolipid. Based on its phenotypic, chemotaxonomic and phylogenetic features, strain MC042T is considered to represent a novel species, for which the name Pseudomonas piscis sp. nov. is proposed. The type strain is MC042T (=KCTC 72033T=MCCC 1K03575T).

Pseudomonas ovata sp. nov., Isolated from the Skin of the Tail of Farmed Murray cod (Maccullochella peelii peelii) with a Profound Ulceration.

A Gram-negative, strictly aerobic, motile, rod-shaped bacterium with monopolar flagellum, designated as F51T, was isolated from the skin ulcer of farmed Murray cod sampled from Zhejiang Province, China. Strain F51T grew at 4-37 °C (optimal temperature, 28 °C), pH 5.0-8.5 (optimal pH, 7.5) and NaCl concentration of 0-6.0% (w/v) (optimal concentration, 2.0%). Phylogenetic analysis based on average nucleotide identity (76.2-78.4%) and in silico DNA-DNA hybridization (22.3-23.2%) values revealed that strain F51T forms a distinct lineage in the clade of genus Pseudomonas with less than 98.9% 16S rRNA gene sequence similarity to type strains of the genus and represents a novel species related most closely to Pseudomonas floridensis LMG 30013T. Three housekeeping genes (rpoB, rpoD and gyrB) of strain F51T were analysed to further confirm that the isolate is distinctly delineated from related Pseudomonas species. Chemotaxonomic analysis indicated that the sole respiratory quinone of strain F51T is Q-9; its predominant cellular fatty acids are C16:0, summed feature 3 (iso-C15:0 2-OH and/or C16:1ω7c), summed feature 8 (C18:1ω7c and/or C18:1ω6c) and C10:0 3-OH; and its major polar lipids consist of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, two unidentified glycolipids, three unidentified phospholipids and an unidentified aminophosphoglycolipid. This composition is typical of the chemotaxonomic attributes of Pseudomonas. Based on its phenotypic, chemotaxonomic and phylogenetic features, strain F51T is considered to represent a novel species for which the name Pseudomonas ovata sp. nov. is proposed. The type strain is F51T (= KCTC 62133T = MCCC 1K03458T).

Draft Genome Sequence of Thiobacimonas sp. Strain D13, a Phthalate Ester-Degrading Bacterium Isolated from Deep-Sea Sediments.

Thiobacimonas sp. strain D13, newly isolated from the sediments of the southeastern Pacific, can effectively degrade phthalate ester. Here, we report the 5.22-Mbp draft genome sequence of this strain, which will provide insights into the molecular mechanisms underlying its degradation ability.

Chryseobacterium aurantiacum sp. nov., isolated from a freshwater pond used for Murray cod (Maccullochella peelii peelii) culture.

A yellow-pigmented, Gram-staining-negative, aerobic, non-motile and rod-shaped bacterium, designated strain F30T, was isolated from fresh water of a diseased farmed Murray cod with a profound ulceration pond in Zhejiang province, PR China. Growth was observed at NaCl concentrations of 0.5-3.5 % (w/v) (optimum, 1.5-2.0 %), temperatures of 10-35 °C (optimum, 28 °C) and pH 5.0-9.0 (optimum, 6.5). Phylogenetic analysis based on 16S rRNA gene sequences indicated that F30T represented a member of the genus Chryseobacterium, showing the highest similarity to Chryseobacterium jejuense DSM 19299T (99.0 %) and Chryseobacterium nakagawai NCTC 13529T (99.0 %), and less than 98.7 % similarity to other species of the genus Chryseobacterium with validly published names. The average nucleotide identity and in silico DNA-DNA hybridization values between F30T and the reference strains were 78.4-90.5 % and 2.6-42.5 %, respectively. The results of chemotaxonomic analysis indicated that the fatty acids, as well as the polar lipid profiles of F30T were similar to those of species of the genus Chryseobacterium, and the sole respiratory quinone was MK-6. On the basis of its phylogenetic, chemotaxonomic and phenotypic data, strain F30T represents a novel species, for which the name Chryseobacteriumaurantiacum sp. nov. is proposed. The type strain is F30T (=KCTC 62135T=MCCC 1K03457T).

Acinetobacter piscicola sp. nov., isolated from diseased farmed Murray cod (Maccullochella peelii peelii).

A taxonomic study was carried out on strain LW15T, which was isolated from the external lesions of diseased farmed Murray cod (Maccullochella peelii peelii) from an intensive culture pond. Cells of strain LW15T were Gram-negative, facultative-anaerobic, non-motile, and both coccobacillus- and bacillus-shaped. Growth was observed at NaCl concentrations of 0-2 % (w/v) (optimum, 0 %), 4-32 °C (optimum, 25-28 °C) and pH 5.0-9.0 (optimum, 7.0). Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain LW15T was affiliated to the genus Acinetobacter, showing the highest similarity to Acinetobacter guillouiae CIP 63.46T (97.7 %) and other Acinetobacter species with validly published names (93.5-97.6 %). Whole-genome sequencing and phylogeny reconstruction based on a core set of 1061 Acinetobacter genes indicated that strain LW15T was most closely related to the clade formed by A. guillouiae CIP 63.46T and Acinetobacter bereziniae CIP 70.12T and distantly related to any of the described species of genus Acinetobacter. Furthermore, strain LW15T could be distinguished from all known Acinetobacter species by its ability to assimilate ß-alanine and l-arginine, but not d-glucose. The principal fatty acids were C18 : 1ω9c, C16 : 0 and C16 : 1ω7c/C16 : 1ω6c. The major respiratory quinone was Q-9. Polar lipids of strain LW15T comprised diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine, four phospholipids, aminolipid and two unknown lipids. Based on its phenotypic and genotypic data, strain LW15T represents a novel species of the genus Acinetobacter, for which the name Acinetobacterpiscicola sp. nov. is proposed. The type strain is LW15T (=MCCC 1K03337T=CICC 24241T=KCTC 62134T=JCM 32101T).

Draft Genome Sequence of Streptococcus sp. X13SY08, Isolated from Murray Cod (Maccullochella peelii peelii).

Streptococcus sp. X13SY08, isolated from freshwater Murray cod fish, likely presents a novel species of Streptococcus. Here, we present an annotated draft genome sequence of this species, which will improve our understanding of its physiology and pathogenesis.

Ultrastructural changes in the pulmonary mechanical barriers in a rat model of severe acute pancreatitis-associated acute lung injury.

This study examined the ultrastructural changes in the pulmonary mechanical barriers in a rat model of severe acute pancreatitis (SAP)-associated acute lung injury (ALI). Animals were randomized into the SAP group (n = 60) and the control group (n = 60). SAP was induced by retrograde injection of 5% taurocholic acid into the biliopancreatic duct. The morphological abnormalities assessed by histology and the lung wet/dry weight ratio and the ultrastructural abnormalities assessed by transmission electron microscope and scanning electron microscope examinations plus lanthanum nitrate tracing were compared between the two groups at 6, 12, and 24 h post-SAP induction (n = 10/group/time point). The SAP group had significantly greater extravascular effusion than the control group at each time point as assessed by the lung wet/dry weight ratio (p < .001). The severity of the tissue damage increased in the lung and pancreas over time in the SAP group (all p < .001). In the SAP group, ultrastructural damages to the endothelial, epithelial, and pleural barriers were apparent and the damages to the endothelial barrier were detected earlier than the other two barriers, suggesting its fundamental role in preventing the further development of SAP-associated ALI. Moreover, the ultrastructural abnormalities were detected earlier than symptoms and morphological changes. The ultrastructural damages in the endothelial, epithelial, and pleural barriers occurred in the early stage of SAP. The endothelial barrier is likely to be the first line to prevent the further development in this rat model of SAP-associated ALI.