Expression of Collagenase is Regulated by the VarS/VarA Two-Component Regulatory System in Vibrio alginolyticus

The CpxA-CpxR two-component system regulates stress tolerance and virulence of Vibrio alginolyticus

The two-component systems (TCSs) play vital roles in the regulation of a series of biological processes in bacteria, and the CpxA-CpxR is considered as a kind of classical TCSs involved in bacterial envelope stress responses. However, the roles of the CpxA-CpxR are not sufficiently understood in Vibrio alginolyticus, a serious pathogen causing the outbreak of pathogenic diseases vibriosis in marine fishes. In this study, we examined the effect of cpxA and cpxR deletion on typical phenotypes of V. alginolyticus HY9901, and the result showed that deletion of cpxA and cpxR and increased the susceptibility to high salinity, iron limitation, certain antibiotics (kanamycin and midecamycin), but had no effects on growth curve and swarming motility of V. alginolyticus. Besides, deletion of cpxA (not cpxR) decreased biofilm formation of V. alginolyticus. In addition, the stimulation of ΔcpxA and ΔcpxR significantly up-regulated the expression of immune-related genes in grouper spleen (GS) cells compared to WT, and deletion of cpxA and cpxR decreased the bacterial adhesion and intracellular ferrous iron concentration in GS cells, and increased the viability of infected-GS cells. Consistently, deletion of cpxA and cpxR decreased bacterial invasion and intracellular replication in grouper primary macrophages. The present study thus improves the understanding of the functions of the CpxA-CpxR system in gamma proteobacteria, and also provides new insight into the molecular pathogenesis of vibriosis in marine fishes.

Discovery of a temperature-dependent protease spoiling meat from Pseudomonas fragi: Target to myofibrillar and sarcoplasmic proteins rather than collagen

Chilled meat frequently suffered microbial spoilage because bacteria can secrete various proteases that break down the proteins. In this study, Pseudomonas fragi NMC 206 exhibited a temperature-dependent secretion pattern, with the ability to release the specific protease only below 25 °C. It was identified as alkaline protease AprA by LC-MS/MS, with the molecular weight of 50.4 kDa, belonging to the Serralysin family metalloprotease. Its significant potential for meat spoilage in situ resulted in alterations in meat color and sensory evaluation, as well as elevated pH, total volatile basic nitrogen (TVB-N) and the formation of volatile organic compounds (VOCs). The hydrolysis of meat proteins in vitro showed that AprA possessed a considerable proteolysis activity and degradation preferences on meat proteins, especially its ability to degrade myofibrillar and sarcoplasmic proteins, rather than collagen. These observations demonstrated temperatures regulated the secretion of AprA, which was closely related to chilled chicken spoilage caused by bacteria. These will provide a new basis for the preservation of meat products at low temperatures.

The Vibriolysin-Like Protease VnpA and the Collagenase ColA Are Required for Full Virulence of the Bivalve Mollusks Pathogen Vibrio neptunius

Vibrio neptunius is an important pathogen of bivalve mollusks worldwide. Several metalloproteases have been described as virulence factors in species of Vibrio that are pathogenic to bivalves, but little is known about the contribution of these potential virulence factors to Vibrio neptunius pathogenesis. In silico analysis of the genome of V. neptunius strain PP-145.98 led to the identification of two hitherto uncharacterized chromosomal loci encoding a probable vibriolysin-like metalloprotease and a putative collagenase, which were designated VnpA and ColA, respectively. Single defective mutants of each gene were obtained in V. neptunius PP-145.98, and the phospholipase, esterase and collagenase activities were studied and compared with those of the wild-type strain. The results showed that the single inactivation of vnpA resulted in a 3-fold reduction in phospholipase/esterase activity. Inactivation of colA reduced the collagenase activity by 50%. Finally, infection challenges performed in oyster larvae showed that ΔvnpA and ΔcolA—single mutant strains of V. neptunius—are between 2–3-fold less virulent than the wild-type strain. Thus, the present work demonstrates that the production of both VnpA and ColA is required for the full virulence of the bivalve pathogen V. neptunius.

Vibrio Proteases for Biomedical Applications: Modulating the Proteolytic Secretome of V. alginolyticus and V. parahaemolyticus for Improved Enzymes Production

Proteolytic enzymes are of great interest for biotechnological purposes, and their large-scale production, as well as the discovery of strains producing new molecules, is a relevant issue. Collagenases are employed for biomedical and pharmaceutical purposes. The high specificity of collagenase-based preparations toward the substrate strongly relies on the enzyme purity. However, the overall activity may depend on the cooperation with other proteases, the presence of which may be essential for the overall enzymatic activity, but potentially harmful for cells and tissues. Vibrios produce some of the most promising bacterial proteases (including collagenases), and their exo-proteome includes several enzymes with different substrate specificities, the production and relative abundances of which strongly depend on growth conditions. We evaluated the effects of different media compositions on the proteolytic exo-proteome of Vibrio alginolyticus and its closely relative Vibrio parahaemolyticus, in order to improve the overall proteases production, as well as the yield of the desired enzymes subset. Substantial biological responses were achieved with all media, which allowed defining culture conditions for targeted improvement of selected enzyme classes, besides giving insights in possible regulatory mechanisms. In particular, we focused our efforts on collagenases production, because of the growing biotechnological interest due to their pharmaceutical/biomedical applications.