RESUMEN
Previous studies revealed that the type VI secretion system (T6SS) has an essential role in bacterial competition and virulence in many gram-negative bacteria. However, the role of T6SS in virulence in Pectobacterium atrosepticum remains controversial. We examined a closely related strain, PccS1, and discovered that its T6SS comprises a single-copy cluster of 17 core genes with a higher identity to homologs from P. atrosepticum. Through extensive phenotypic and functional analyses of over 220 derivatives of PccS1, we found that three of the five VgrGs could be classified into group I VgrGs. These VgrGs interacted with corresponding DUF4123 domain proteins, which were secreted outside of the membrane and were dependent on either the T6SS or type IV secretion system (T4SS). This interaction directly governed virulence and competition. Meanwhile, supernatant proteomic analyses with strains defective in the T6SS and/or T4SS confirmed that effectors, such as FhaB, were secreted redundantly to control the virulence and suppress host callose deposition in the course of infection. Notably, this redundant secretion mechanism between the T6SS and T4SS is believed to be the first of its kind in bacteria.
Asunto(s)
Proteínas Bacterianas , Pectobacterium , Enfermedades de las Plantas , Sistemas de Secreción Tipo VI , Pectobacterium/patogenicidad , Pectobacterium/genética , Virulencia , Sistemas de Secreción Tipo VI/genética , Sistemas de Secreción Tipo VI/metabolismo , Enfermedades de las Plantas/microbiología , Proteínas Bacterianas/genética , Proteínas Bacterianas/metabolismo , Sistemas de Secreción Tipo IV/genética , Sistemas de Secreción Tipo IV/metabolismo , Factores de Virulencia/genética , Factores de Virulencia/metabolismo , Glucanos/metabolismoRESUMEN
The decomposition and oxidation of fat is essential for the formation and quality of the unique flavor of sausage. To explore the effect of lactic acid bacteria on fat decomposition and oxidation in fermented sausage, free fatty acids and volatile flavor compounds were determined by gas chromatography (GC) and headspace solid-phase microextraction (HS-SPME)-GC-MS, respectively. The results showed that the addition of Lactobacillus helveticus IMAUJBH1 inhibited fat peroxidation and relatively increased the proportion of monounsaturated fatty acids. A total of 47 volatile flavor compounds were detected, including aldehydes, esters, alcohols, and ketones. The content of substances such as hexanal, heptanal, nonanal and 1-octene-3-ol related to lipid oxidation was significantly reduced. The results obtained in this study show that the strain can further affect the flavor of the product by inhibiting the formation of lipid oxidation or peroxide flavor substances to a certain extent.
