T6SS and T4SS redundantly secret effectors to govern the virulence and bacterial competition in Pectobacterium PccS1.

The 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 T6SS or T4SS. This interaction directly governed virulence and competition. Meanwhile, supernatant proteomic analyses with stains defective in T6SS or/and T4SS confirm 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 T6SS and T4SS is believed to be the first of its kind in bacteria.

Effect of Lactobacillus helveticus IMAUJBH1 on fat and volatile flavor substances in fermented mutton sausages.

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.