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Currently, it is widely accepted that the type III secretion system (T3SS) serves as the transport platform for bacterial virulence factors, while flagella act as propulsion motors. However, there remains a noticeable dearth of comparative studies elucidating the functional disparities between these two mechanisms. Entomopathogenic nematode symbiotic bacteria (ENS), including Xenorhabdus and Photorhabdus, are Gram-negative bacteria transported into insect hosts by Steinernema or Heterorhabdus. Flagella are conserved in ENS, but the T3SS is only encoded in Photorhabdus. There are few reports on the function of flagella and the T3SS in ENS, and it is not known what role they play in the infection of ENS. Here, we clarified the function of the T3SS and flagella in ENS infection based on flagellar inactivation in X. stockiae (flhDC deletion), T3SS inactivation in P. luminescens (sctV deletion), and the heterologous synthesis of the T3SS of P. luminescens in X. stockiae. Consistent with the previous results, the swarming movement of the ENS and the formation of biofilms are dominated by the flagella. Both the T3SS and flagella facilitate ENS invasion and colonization within host cells, with minimal impact on secondary metabolite formation and secretion. Unexpectedly, a proteomic analysis reveals a negative feedback loop between the flagella/T3SS assembly and the type VI secretion system (T6SS). RT-PCR testing demonstrates the T3SS's inhibition of flagellar assembly, while flagellin expression promotes T3SS assembly. Furthermore, T3SS expression stimulates ribosome-associated protein expression. [ABSTRACT FROM AUTHOR]

Aeromonas salmonicida is an important pathogen that causes furunculosis in trout and salmon with high morbidity and mortality, resulting in significant economic losses in aquaculture. Overuse of antibiotics has led to the continuous emergence of drug-resistant strains. Hence, there is an urgent need to find an alternative environmentally friendly antimicrobial agent. In this study, we isolated a virulent phage of A. salmonicida, named ASG01, which belongs to the Myoviridae family and maintains lytic activity at a pH value range from 4 to 12 and in the temperature range from 30 °C to 60 °C. The whole genomic sequence of ASG01 showed 82% similarity to Aeromonas phage pAh6-C. The cell wall hydrolase (Cwh)-encoding gene from the genome of ASG01 was predicted and heterologously expressed. Notably, in the absence of additional phage genes, endogenous expression of Cwh could lyse E. coli cells and greatly inhibit the growth of tested fish pathogenic bacteria. The lytic activity of Cwh was eliminated when the predicted active site was mutated. These results indicate that Cwh of ASG01 possessed excellent lytic activity and a wide antibacterial spectrum, suggesting its potential as an effective enzybiotic. [ABSTRACT FROM AUTHOR]

Bacterial diseases of fish pose a serious threat to the development of fish breeding industry, and the abuse of antibiotics and the emergence of drug resistance of pathogenic bacteria have a serious impact on the yield of fish breeding, the quality of aquatic products and the breeding environment. In order to promote the development of healthy fish breeding industry, it is urgent to innovate the green prevention and control technology of fish diseases. As a natural and non-residual bacterial killer, phage has the characteristics of strong specificity and high lysis efficiency. Using phage to treat bacterial diseases of fish will be an important technical approach. This paper reviews the important resource mining of phages, the mechanism of action in the prevention and control of bacterial diseases in fish and its application prospects, and puts forward measures to speed up the research of phage treatment technology in the field of healthy aquaculture of fish, which is of great significance for healthy aquaculture of fish. [ABSTRACT FROM AUTHOR]

ABSTRACT A 8.7 kDa lectin with high agglutin activity was isolated by affinity chromatography and cloned from Allium chinense in this study. For the MTT assay, approximately 60 µg/ml A. [...]

As a large class of secondary metabolites, PKs have important biological activity and economic value. Streptomyces has the potential to synthesize a variety of PKs, whereas the yield of PKs synthesized by wild-type strains is difficult to meet the needs of industrial production. The degradation of storage lipids can provide a large number of acyl-CoA precursors for the biosynthesis of PKs. Therefore, controlling the balance of the biosynthetic flux of fatty acids and PKs is conducive to improving the production of the target PKs. This paper briefly reviews on improving the production of PKs by strengthening the fatty acids β-oxidation pathway, and prospects prospective research ideas on improving the biosynthesis of PKs by engineering the β-oxidation pathway. [ABSTRACT FROM AUTHOR]

The Streptomyces lateritius Z1‐26 was isolated from soil samples which showed broad‐spectrum antibacterial activity against a broad range of fish pathogens. The In Vivo Imaging System (IVIS) monitored that strain Z1‐26 could survive and colonize in the gills and abdomen of crucian carp. The effects of dietary supplementation with strain Z1‐26 were evaluated with respect to the growth performance, antioxidant capacity, and immune response of crucian carp. The results showed that the Z1‐26‐fed fish had a significantly higher growth rate than the fish fed the control diet. The immune and antioxidant parameters revealed that the non‐specific immune indicators (AKP, SOD, and LZM) of the serum, the expression of immune‐related genes (IgM, C3, and LZM), and antioxidant‐related genes (Nrf2 and Keap1) of the immune organs were significantly increased, whereas the expression of pro‐inflammatory factors (IL‐1β, IL‐8, and TNF‐α) of the immune organs was significantly down‐regulated in crucian carp fed strain Z1‐26 compared with fish fed a control diet. Moreover, fish fed with Z1‐26 supplemented diets showed a significantly improved survival rate after Aeromonas hydrophila infection. In addition, the whole genome analysis showed that strain Z1‐26 possesses 28 gene clusters, including 6 polyketide synthetase (PKS), 4 non‐ribosomal peptide‐synthetase (NRPS), 1 bacteriocin, and 1 lantipeptide. In summary, these results indicated that strain Z1‐26 could improve the growth performance and disease resistance in crucian carp, and has the potential to be developed as a candidate probiotics for the control of bacterial diseases in aquaculture. [ABSTRACT FROM AUTHOR]