Kobresia humilis via root-released flavonoids recruit Bacillus for promoted growth.

Alpine meadows, which are critical for biodiversity and ecosystem services, are increasingly degrading, necessitating effective restoration strategies. This study explored the mechanism by which Kobresia humilis, an alpine meadow-constructive species, modulates the rhizosphere microbiome via root exudates to enhance growth. Field investigations revealed that the plant height of K. humilis in a severely degraded (SD) alpine meadow was significantly higher than that in other K. humilis populations. Consequently, we analysed the differences between this plot and other K. humilis samples with different degrees of degradation to explore the reasons underlying the phenotypic differences in K. humilis. 16 S rRNA amplicon sequencing results showed that the SD plots were significantly enriched with more Bacillus, altering the composition of the rhizosphere microbial community of K. humilis. The collection and analysis of root exudates from various K. humilis locations revealed distinct differences. Procrustes analysis indicated a strong correlation between the root exudates and the rhizosphere microbiome composition of K. humilis. Model-based integration of metabolite observations, species abundance 2 (MIMOSA2), and Spearman's rank correlation coefficient analysis were used to identify the root exudates potentially related to the enrichment and recruitment of Bacillus. Bacillus from SD samples was isolated and screened, and the representative strain D334 was found to be differentially enriched compared to other samples. A series of in vitro experiments with the screened root exudates and strain D334 demonstrated that K. humilis could recruit Bacillus and promote its colonisation by releasing flavonoids, particularly baicalin. Additionally, K. humilis can release sucrose and riboflavin, which promote strain growth. Finally, soil microbiome transplantation experiments confirmed that different K. humilis phenotypes were closely related to the functions of the rhizosphere microbiome, especially in root morphological shaping. Moreover, the effects of Bacillus inoculation and the microbiome on the plant phenotypes were consistent. In summary, this study revealed a new mechanism by which K. humilis recruits rhizosphere growth-promoting bacteria and enhances soil nutrient utilisation, thereby promoting plant growth. These findings provide a theoretical basis for ecological restoration using soil microbial communities and clarify the relationship between plant metabolites and microbial community assembly.

Effect of TBC of raw milk and thermal treatment intensity on endotoxin contents of milk products.

Endotoxin in dairy products may pose risks to consumers' health, but the effects of raw-milk total bacterial count (TBC) and thermal treatment temperature on endotoxin content of dairy products are not clear. In this study, TBC of raw milk and processed milk with different thermal treatment temperatures were detected by pilot processing experiment. We then verified it by detecting the endotoxin content of commercial dairy products. TBC was determined by conventional culture method, and the changes in alkaline phosphatase (ALP) and lactoperoxidase (LPO) activities in bovine milk before and after heat treatment were determined. The levels of fatty acids in bovine milk were detected by gas chromatography using a flame ionization detector (GC-FID). In the pilot experiment, raw milk was treated at 72, 75, 80, 85, 90, 95, 100, 105, 110, 115, and 120 °C for 15 s. After that, the raw milk was stored at 20 °C for 24 h and 48 h to greatly increase the TBC, and treated at 75 °C for 15 s and 90 °C for 15 s. The results show that the endotoxin content of sterilized milk increased with the increase in TBC and thermal treatment temperature. With the increase in thermal treatment temperature, the activities of ALP and LPO with endotoxin inhibition decreased. In addition, a total of 226 dairy samples were tested. The endotoxin content of 37 commercial PM milk samples were 6 EU/ml to 231 EU/ml, with 31 EU/ml to 1437 EU/ml for 40 commercial UHT milk samples, and 6 EU/ml to 9080 EU/ml for 149 reconstituted IFM samples. There was a significant difference in the endotoxin content of different dairy products (P < 0.05), and there was no significant difference between domestic and imported IFM (P > 0.05). This study found that TBC and thermal treatment temperature of raw milk could affect the endotoxin content of dairy products.