The rare and endangered plant species Abies fanjingshanensis, which has a limited habitat, a limited distribution area, and a small population, is under severe threat, particularly due to poor leaf health. The plant endophytic microbiome is an integral part of the host, and increasing evidence indicates that the interplay between plants and endophytic microbes is a key determinant for sustaining plant fitness. However, little attention has been given to the differences in the endophytic microbial community structure, network complexity, and assembly processes in leaves with different leaf health statuses. Here, we investigated the endophytic bacterial and fungal communities in healthy leaves (HLs) and non-healthy leaves (NLs) of A. fanjingshanensis using 16S rRNA gene and internal transcribed spacer sequencing and evaluated how leaf health status affects the co-occurrence patterns and assembly processes of leaf endophytic microbial communities based on the co-occurrence networks, the niche breadth index, a neutral community model, and C-score metrics. HLs had significantly greater endophytic bacterial and fungal abundance and diversity than NLs, and there were significant differences in the endophytic microbial communities between HLs and NLs. Leaf-health-sensitive endophytic microbes were taxonomically diverse and were mainly grouped into four ecological clusters according to leaf health status. Poor leaf health reduced the complexity of the endophytic bacterial and fungal community networks, as reflected by a decrease in network nodes and edges and an increase in degrees of betweenness and assortativity. The stochastic processes of endophytic bacterial and fungal community assembly were weakened, and the deterministic processes became more important with declining leaf health. These results have important implications for understanding the ecological patterns and interactions of endophytic microbial communities in response to changing leaf health status and provide opportunities for further studies on exploiting plant endophytic microbes to conserve this endangered Abies species.

2-Phenylethanol (2-PE) and indole-3-acetic acid (IAA) are important secondary metabolites produced by microorganisms, and their production are closely linked to the growth state of microorganisms and environmental factors. Enterobacter CGMCC 5087 can produce both 2-PE and IAA depending on α-ketoacid decarboxylase KDC4427. This study aimed to investigate the effects of different environment factors including osmotic pressure, temperature, and pH on the synthesis of 2-PE and IAA in Enterobacter sp. CGMCC 5087. The bacteria exhibited an enhanced capacity for 2-PE synthesis while not affecting IAA synthesis under 5% NaCl and pH 4.5 stress conditions. In an environment with pH 9.5, the synthesis capacity of 2-PE remained unchanged while the synthesis capacity of IAA decreased. The synthesis ability of 2-PE was enhanced with an increase in temperature within the range of 25 °C to 37 °C, while the synthesis capacity of IAA was not affected significantly. Additionally, the expression of KDC4427 varied under stress conditions. Under 5% NaCl stress and decreased temperature, expression of the KDC4427 gene was increased. However, altering pH did not result in significant differences in gene expression levels, while elevated temperature caused a decrease in gene expression. Furthermore, molecular docking and molecular dynamics simulations suggested that these conditions may induce fluctuation in the geometry shape of binding cavity, binding energy, and especially the d_αC-C- value, which played key roles in affecting the enzyme activity. These results provide insights and strategies for the synthesis of metabolic products 2-PE and IAA in bacterial fermentation, even under unfavorable conditions.

Dimethyl disulfide (DMDS) is an important volatile organic sulfur compound with diverse applications and substantial demand in the chemical, agricultural, and food industries. The challenges associated with their chemical synthesis have spurred exploration of biological synthesis as an alternative route. Nevertheless, there is limited research on the biosynthesis of DMDS, and the yield remains low. In this study, strain W2-3, exhibiting high DMDS production, was isolated from aged tobacco leaves collected in Hubei Province, China. Based on morphological characteristics, 16S rRNA gene sequencing and phylogenetic analysis, the strain was identified as Alcaligenes faecalis. Through single-factor experimental methods, an initial pH of 7 and temperature ranging from 19.5 to 30 °C were demonstrated to be the optimal fermentation conditions for DMDS production. Under these optimized conditions, the maximum yield of DMDS reached 213.49 mg/L, which was a 1.34-fold increase from the pre-optimization yield of 159.86 mg/L. Moreover, optimization of sulfur sources and concentrations showed that increasing methionine concentration led to higher DMDS production. Under sufficient Met conditions, W2-3 achieved a peak of 2440.71 mg/L DMDS, representing an increase of 11.43-fold compared to the control group without methionine supplementation. This yield significantly surpassed the highest yield reported in the literature (40.06 mg/L) by 60.93-fold, establishing a new record for the highest yield currently known. This study identifies A. faecalis W2-3 as a promising microbial chassis for the biosynthesis of DMDS, characterized by a high yield and strong temperature adaptability. It offers insights into the metabolic pathways and fermentation conditions for industrial-scale DMDS production. As the first systematic optimization research aimed at enhancing DMDS production, it fills a gap in the literature. Our findings pave the way for sustainable and efficient DMDS biosynthesis, with significant implications for promoting its application in agriculture, industry, and environmental management.