Studies have shown that the microbiome of saline‐tolerant plants plays a significant role in promoting salt stress in non‐saline‐tolerant plants, but the microorganisms are still unclear. In the present study, the microbial diversity changes in Suaeda salsa (L.) Pall . in the Yellow River Delta region were investigated. In the bacterial community, the dominant bacteria in the rhizosphere soil of the low‐saline soil (YDL), moderate‐saline soil (YDM), and high‐saline soil (YDH) groups were Proteobacteria , Chloroflexi , Bacteroidota , and Actinobacteriota (at the phylum level), while Ascomycota and Basidiomycota were the dominant fungi in the fungal community. At the family level, with the increase of salinity, the relative abundance of Rhodobacteraceae (bacterial community), Thermoascaceae , and Phaffomycetaceae (fungal community) gradually increased; and to the best of our knowledge, there are no reports on the relationship between Thermoascaceae and Phaffomycetaceae families with salt stress. At the genus level, Salinimicrobium (bacterial community) was the dominant bacterium in the rhizosphere soil of the YDL, YDM, and YDH groups, while with the increase of salinity, the relative abundance of Byssochlamys and Wickerhamomyces (fungal community) gradually increased, and to the best of our knowledge there are no reports on the relationship between Byssochlamys and salt stress. Salinity mainly affected the bacterial community abundance, but it had little effect on the fungi community abundance. The bacterial community of the YDH group was dominated by bacteria of unknown origin (52.76%), while bacteria of unknown origin accounted for 26.46% and 20.78% of the bacterial communities in the YDM and YDL groups, respectively. The fungi community of the YDH group was dominated by YDL group fungi (relative abundance of 44.44%), followed by YDM group fungi (29.42%) and fungi of unknown origin (26.14%). These results provide a better understanding of the rhizosphere microbial diversity of saline–alkali‐tolerant plants, laying a foundation for developing a saline–alkali‐tolerant plant microbiome.

Oenococcus oeni is a commercial wine-fermenting bacterial strain, owing to its high efficiency of malolactic fermentation and stress tolerance. The present study explored the function of key genes in O. oeni to enhance stress resistance by heterologous expression of these genes in another species. The orf00404 gene that encodes a two-component signal transduction response regulator in O. oeni was heterologously expressed in Lactiplantibacillus plantarum WCFS1. The expression of orf00404 significantly enhanced the growth rate of the recombinant strain under acid stress. At 60 h, 72 h, and 108 h of culture at pH 4.0, the recombinant strain had 1562, 641, and 748 differentially expressed genes compared to the control strain, respectively. At all three time points, 20 genes were upregulated in the recombinant strain, including the lamA-D operon-coding genes of the quorum-sensing two component signal transduction system and the spx5 RNA polymerase-binding protein coding gene, which may help adaptation to acid stress. In addition, 47 genes were downregulated in the recombinant strain at all three time points, including the hsp1 heat shock protein-coding gene, the trxA1 thioredoxin-coding gene, and the dinP, mutY, umuC, and uvrB DNA damage repair-related protein-coding genes, potentially indicating that the recombinant strain was less susceptible to stress and had less DNA damage than the control strain in acid stress conditions. The recombinant strain had higher membrane fluidity, permeability, and integrity at an early stage of logarithmic growth (72 h), suggesting that it had a more complete and active cell membrane state at this stage. The intracellular ATP content was significantly reduced in the recombinant strain at the beginning of logarithmic growth (60 h), implying that the recombinant strain consumed more energy at this stage to resist acid stress and growth. These results indicated that the recombinant strain enhances acid stress tolerance by regulating a gene expression pattern, increasing ATP consumption, and enhancing cell membrane fluidity, membrane permeability, and membrane integrity at specific growth stages. Thus, the recombinant strain may have potential application in the microbial biotechnology industry.

Oenococcus oeni is the main microorganism that undergoes malolactic fermentation (MLF) in the winemaking industry due to its excellent adaptability to harsh wine environments. The start of MLF is often delayed or even fails, and low pH appears to be a crucial parameter. To study the function of the trxA gene in acid stress, a plasmid containing the trxA gene of O. oeni SD-2a was heterologously expressed in Lactiplantibacillus plantarum WCFS1. The recombinant strain (WCFS1-trxA) grew better than the control strain (WCFS1-Vector) under acid stress. The expression of thioredoxin system genes was much higher in the recombinant strain compared with the control strain under acid stress. In addition, a series of physiological and biochemical assays were conducted. The ATP content was lower in the recombinant strain, while the cell membrane fluidity and integrity improved in the recombinant strain. Moreover, reactive oxygen species (ROS) accumulation, intracellular GSH level, and superoxide dismutase (SOD) activity assays showed that the recombinant strain decreased the intracellular reactive oxygen species (ROS) accumulation by improving the SOD activity. In conclusion, heterologous expression of trxA improves the SOD activity of L. plantarum WCFS1, reducing bacterial ROS and increasing cell membrane fluidity and integrity, enhancing the tolerance of Lactiplantibacillus plantarum WCFS1 under acid stress.

Novacetimonas cocois WE7 (formally named Komagataeibacter cocois WE7) is a strain isolated from contaminated coconut milk, capable of producing bacterial cellulose (BC). We sequenced its genome to investigate why WE7 cannot synthesize BC from glucose efficiently. It contains about 3.5 Mb and six plasmid DNAs. N. cocois WE7 contains two bcs operons (bacterial cellulose operon, bcs I and bcs II); the absence of bcs III operons may lead to reduced BC production. From genome predictions, glucose, sucrose, fructose, maltose, and glycerol can be utilized to generate BC, with WE7 unable to metabolize carbohydrate carbon sources through the Embden–Meyerhof–Parnas (EMP) pathway, but rather through the Hexose Monophosphate Pathway (HMP) and tricarboxylic acid (TCA) pathways. It has a complete gluconic acid production pathway, suggesting that BC yield might be very low when glucose, maltose, and trehalose are used as carbon sources. This study represents the first genome analysis of N. cocois. This information is crucial for understanding BC production and regulation mechanisms in N. cocois and lays a foundation for constructing engineered strains tailored for diverse BC application purposes.

Pseudomonas aeruginosa can efficiently degrades petroleum hydrocarbons, but its degradation rate is affected by hydrocarbon pollutant concentrations, which must be neither too high nor too low. To quantitatively analyze P. aeruginosa’s gene expression and assess factors affecting it, reference genes stably expressed under varying concentrations of n-hexadecane stress need to be identified. In this study, we used P. aeruginosa L10 as the test strain and identified eight candidate reference genes: rpsL, nadB, clpX, anr, rpoS, gyrA, tipA, and recA. The cultures were cultured under different concentrations of n-hexadecane (the concentrations were 0%, 0.1%, 0.5%, 1.0%, 1.5%, 2.0%,), and then the gene expression was detected by quantitative Real-time PCR, that is, the changes of Ct values. Using geNorm, Normfinder, BestKeeper and RefFinder to conduct analysis. Among, geNorm measures the expression stability of a candidate gene by calculating the stability value of gene expression. Normfinder calculates gene stability values taking into account within- and between-group variation in gene expression. BestKeeper evaluates the stability of individual genes through correlation analysis. RefFinder provides a comprehensive assessment of reference gene stability by integrating four methods. The results indicated that among the reference genes of P. aeruginosa L10 cultured under various concentrations of n-hexadecane stress, anr had the highest Ct value and expression abundance, while tipA had the lowest. GeNorm analysis showed that nadB, anr and rpsL were more stable, while tipA and gyrA were less stable. Normfinder analysis showed that nadB, anr, gyrA and rpsL were more stable, while tipA was less stable. The analysis results of BestKeeper were different from the previous two analysis tools. Further comprehensive analysis using RefFinder showed that nadB and anr were the most stable parameters, and tipA was the most unstable. In different treatments, the most stable internal parameters are not same. After verification and analysis, nadB and anr were the two most stable internal reference gene, and tipA was the least stable. The excavation of stable internal reference can help the application of qPCR in the determination of gene expression of P. aeruginosa L10, and thus lay a foundation for the study of related genes or metabolic pathways.

Petroleum hydrocarbons (PHC) are organic pollutants that pose serious health risks to humans and the environment. Treating soils contaminated with these persistent pollutants is a global concern that is challenging to implement effectively. Synergistic remediation strategies, particularly those involving plants and functional endophytic bacteria, offer ecologically sustainable approaches for remediating PHC-contaminated soil and thus hold broad application prospects. This review collected the literature from databases including Elsevier, Web of Science, PubMed, and CNKI, using keywords such as endophytic bacteria, petroleum hydrocarbons, plants, microorganisms, polycyclic aromatic hydrocarbons, and alkanes. After screening the titles, abstracts, and secondary headings, 123 articles were selected for narrative synthesis. It systematically elaborates on the types, functions, sources, and distribution characteristics within plants of hydrocarbon-degrading endophytic bacteria. It comprehensively summarizes the key molecular pathways involved in the bacterial degradation of alkanes and polycyclic aromatic hydrocarbons (PAHs). Furthermore, from four dimensions—PHC metabolism modes, plant growth promotion (PGP), production of biosurfactants (PBS), and horizontal gene transfer—this article innovatively analyzes the mechanisms underlying the synergistic remediation of petroleum hydrocarbon-contaminated soil through functional bacterium–plant interactions. Finally, the review outlines future research directions in the field, providing a theoretical foundation and practical pathways for advancing green remediation strategies for PHC-polluted soil.