Hepatic encephalopathy (HE) is a neurological disorder that occurs in patients with liver insufficiency. However, its pathogenesis has not been fully elucidated. Pharmacotherapy is the main therapeutic option for HE. It targets the pathogenesis of HE by reducing ammonia levels, improving neurotransmitter signal transduction, and modulating intestinal microbiota. Compared to healthy individuals, the intestinal microbiota of patients with liver disease is significantly different and is associated with the occurrence of HE. Moreover, intestinal microbiota is closely associated with multiple links in the pathogenesis of HE, including the theory of ammonia intoxication, bile acid circulation, GABA-ergic tone hypothesis, and neuroinflammation, which contribute to cognitive and motor disorders in patients. Restoring the homeostasis of intestinal bacteria or providing specific probiotics has significant effects on neurological disorders in HE. Therefore, this review aims at elucidating the potential microbial mechanisms and metabolic effects in the progression of HE through the gut–brain axis and its potential role as a therapeutic target in HE.

Ochrobactrum intermedium strain SCUEC4 is a newly isolated nicotine-degrading bacterium and can use the nicotine as the sole carbon source via a series of enzymatic catalytic processes. Mechanisms underlying nicotine degradation in this bacterium and the corresponding functional genes remain unclear. Here, we analyzed the function and biological properties of the ocnE gene involved in nicotine degradation pathways in strain SCUEC4. The ocnE gene was cloned by PCR with total DNA of strain SCUEC4, and used to construct the recombinant plasmid pET28a-ocnE. The overexpression of OcnE protein was detected by SDS-PAGE analysis, and functional insight of this protein was spectrophotometrically carried out with monitoring the changes of 2, 5-dihydroxypyridine. Moreover, effects of temperature, pH and metal ions on the biological activities of OcnE protein were analyzed. The results demonstrated that optimal conditions for the biological activities of OcnE, approximate 37.6 kDa, was determined as 25°C, pH 7.0 and 25 μM Fe2+, and the suitable storage conditions for OcnE protein was determined as 0°C and pH 7.0. Conclusively, the ocnE gene owns the ability of 2, 5-dihydroxypyridine dioxygenase. These findings will be beneficial in clarifying the mechanisms of nicotine degradation in Ochrobactrum intermedium strain SCUEC4.

Agrobacterium tumefaciens strain SCUEC1 is a nicotine-degrading bacterium, which has been recently isolated from the tobacco waste-contaminated field soil. However, the mechanism for nicotine degradation in this strain remains unclear. Here, we analyze the function and biological properties of the agnH gene in the strain SCUEC1. The overexpression of the AgnH protein was detected by SDS-PAGE analysis, and functional insight of the AgnH protein was carried out with monitoring the changes of maleic acid into fumaric acid by high performance liquid chromatography (HPLC). Moreover, the effects of temperature, pH and metal ions on the enzymatic activities of the AgnH protein were also analyzed. The results demonstrated that the agnH gene was successfully ligated to the plasmid pET28a. The optimal condition for the enzymatic activities for the AgnH, approximately 28.0 kDa, was determined as 37 °C, pH 8.0 and 25 µM Mg2+. Conclusively, the agnH gene fulfils an important role in the conversion of maleic acid into fumaric acid involved in nicotine-degradation pathways in Agrobacterium tumefaciens strain SCUEC1.

Panax notoginseng is a traditional Chinese medicine. The roots of P. notoginseng can be used for treatment of diseases and raw materials in Chinese medicinal products. High yield and quality roots require cultivation in shade and humid conditions for 3 years. The long period cultivation makes P. notoginseng vulnerable to infect by pathogens. So control diseases are vital for the high yield and quality of P. notoginseng. The seed is the carrier systems of many probiotics and pathogens. To explore the indigenous bacterial community diversity, the endophytic bacteria from the seeds of the medicinal plant P. notoginseng were isolated and identified using traditional cultivation methods in combination with molecular technique. A total of 137 endophytic bacteria strains were isolated. The 16S rDNA of these strains was amplified and subjected to amplified ribosomal DNA restriction analysis (ARDRA) with restriction enzyme HaeIII. All the isolated strains were grouped into 9 OTUs (Operational Taxonomic Units) on the basis of the similarity of the ARDRA band profiles. Each representative strain of 9 OTUs was selected for sequencing. r-proteobacteria was the most dominant group among the isolates (98.5%), containing eight genera. Pseudomonas was the most dominant genus (58 of 135 isolates), whose isolates occurred in the seeds collected from all three places. The second dominant genus was Enterobacter (20.7%), followed by uncultured bacterium (14.8%) and Stenotrophomonas (10.4%). Among the six areas sampled, endophytic bacteria in the seeds collected from Panlong of Yanshan exhibited species diversity and contained the most isolates. These results suggest an abundant diversity of bacterial community within the seeds of P. notoginseng. These data provide insights into monitoring the seed health and disease outbreak during seeding.