Menaquinone (MKs) are a group of naphthoquinone derivatives that play important roles in various aspects of human health. This study aimed to investigate the congener profiles and yields of MKs produced by Elizabethkingia meningoseptica strain Fm, F41, and Fmlv under different cultivation conditions. Notably, the total MK production (three congeners: MK-4, MK-5, and MK-6) by Fm and F41 initially peaked at pH 6. In contrast, Fmlv achieved its maximum MK yield at pH 8 and exclusively produced MK-6. An agitation speed of 140 rpm was found to be optimal for MK production; Fm produced MK-5 and MK-6, whereas F41 produced all three congeners. In contrast, Fmlv showed peak MK production at 160 rpm. Temperature optimization revealed maximal total MK yields for Fm, F41, and Fmlv at 32 °C, with Fmlv demonstrating broader biosynthetic capacity by producing four MK congeners simultaneously. The newly identified MK-7 was further characterized. This is the first study reporting a single E. meningoseptica strain capable of synthesizing four different MKs within one fermentation cycle. Altogether, the findings suggest that elevated pH, dissolved oxygen concentration, and temperature during E. meningoseptica fermentation selectively enhance the biosynthesis of long-chain MKs, whereas reduced levels of these parameters favor the accumulation of short-chain MK.

Introduction: The conjugative transfer of antibiotic resistance genes (ARGs) mediated by plasmids occurred in different intestinal segments of mice was explored.Methods: The location of ARG donor bacteria and ARGs was investigated by qPCR, flow cytometry, and small animal imaging. The resistant microbiota was analyzed by 16S rRNA gene amplification sequencing.Results: The small intestine was the main site for the location of ARG donor bacteria and ARGs. The intestinal microbiota richness of the small intestine (duodenum and jejunum) and the large intestine (cecum, colon, and rectum) increased, and the ileum microbiota richness decreased under the action of donor bacteria. The differences in the number of bacteria in the small intestine and the large intestine, as well as the relative richness of Firmicutes from the small intestine to the large intestine, decreased. By contrast, the relative abundance of Proteobacteria increased. The intake of resistant plasmids alleviated the impact of antibiotics on intestinal microbiota, particularly increasing the proportion of Proteobacteria and Bacteroides, which were presumed to be susceptible to ARGs.Discussion: The acquisition of ARGs by intestinal microbes is an important reason why infectious diseases are difficult to cure, which brings risks to human health and intestinal microecology.