Soil bacterium’s genome reveals how it unlocks phosphorus to boost maize growth

Phosphorus is one of the nutrients plants cannot live without, yet in most soils the overwhelming majority of it is locked away in insoluble mineral and organic compounds that roots simply cannot absorb. Farmers around the world compensate with phosphate fertilizers, but much of what is applied quickly binds to soil particles or runs off into waterways, driving both rising costs and environmental damage. A team of researchers in China has now taken a close genetic look at a soil bacterium that can free this trapped phosphorus, and their findings, published in BMC Genomics, suggest that a single strain of Enterobacter ludwigii could become a serious candidate for the next generation of sustainable biofertilizers.

The study, led by Dongying Zhao and colleagues at Dezhou University together with Chengqiang Wang of Shandong Agricultural University, focused on a strain designated I42. This bacterium belongs to a broader class of soil dwellers known as phosphate-solubilizing bacteria, or PSB, microorganisms capable of converting insoluble inorganic and organic phosphorus into soluble forms that plant roots can take up. What makes the new work stand out is the combination of classical microbiology, greenhouse experimentation and whole-genome sequencing, allowing the team to connect what the bacterium actually does in the soil with the specific genes that make it possible.

In laboratory assays, strain I42 displayed an impressive portfolio of plant growth-promoting traits. Beyond its core ability to solubilize phosphorus, the bacterium also mobilized potassium, another essential macronutrient that is frequently abundant in soil minerals but poorly available to plants. It produced indole-3-acetic acid, the best-known natural auxin, a phytohormone that stimulates root elongation and branching, and it secreted siderophores, small iron-chelating molecules that deprive pathogenic microbes of this vital metal while simultaneously improving iron nutrition for the plant. Together, these traits place I42 firmly within the category of plant growth-promoting rhizobacteria, the beneficial root-colonizing microbes that have attracted intense agricultural interest in recent years.

The real test, however, takes place in living soil, and here the researchers turned to pot experiments with maize seedlings. When the seeds or seedlings were treated with strain I42, the plants grew measurably better than untreated controls. The treated maize developed larger maximum leaf areas, greater fresh and dry weights, and thicker stems. Critically, the improvements were matched by changes in the soil itself: the rhizosphere, the narrow zone of soil surrounding the roots, contained significantly higher levels of available phosphorus and potassium in the inoculated pots. That pattern is exactly what one would expect if the bacterium were actively mining insoluble nutrients and handing them to the plant, rather than simply stimulating growth through some other route.

To understand how I42 reshapes the root environment at the community level, the team analyzed the rhizosphere microbiome. The results showed that inoculation with I42 did not merely add one more species to the mix; it restructured the bacterial community in a meaningful way. Among the genera enriched in the treated rhizosphere were Bacillus and Arthrobacter, two groups widely recognized as beneficial soil bacteria associated with nutrient cycling, disease suppression and stress tolerance. This suggests that a single inoculant can act as a kind of ecological organizer, recruiting or amplifying other helpful microbes and potentially compounding the growth benefits over time.

The genomic half of the study provides the molecular explanation for these observations. Whole-genome sequencing revealed that E. ludwigii I42 carries a single circular chromosome of 4,719,369 base pairs with an average GC content of 54.5 percent, a size and composition typical of members of the Enterobacteriaceae family. Scanning the annotated genome, the researchers confirmed the presence of genes directly tied to each of the observed phenotypes: genes implicated in phosphate solubilization, genes involved in the biosynthesis of indole-3-acetic acid, and genes encoding the machinery for siderophore production. In other words, the genome contains a coherent toolkit for the very traits the bacterium displays in culture and in pots.

Perhaps the most intriguing result came from comparative genomics. When the researchers compared I42 against related genomes, they identified 133 unique genes that are absent from the comparison strains and that may underpin its particularly strong plant growth-promoting properties. While the precise functions of many of these genes remain to be experimentally verified, their existence hints that the ability to promote plant growth is not a single-trait affair but a layered system, in which accessory genes fine-tune nutrient mobilization, hormone output and interactions with the surrounding microbial community. Dissecting that accessory genome could become a roadmap for engineering or selecting even more effective biofertilizer strains in the future.

The agricultural significance of the work is hard to overstate. Phosphorus fertilizer is produced from finite phosphate rock reserves, and its inefficient use is a chronic problem: crops typically take up only a fraction of applied phosphorus in the season it is applied, while the remainder accumulates in soil or is lost to waterways, contributing to eutrophication. Microbial inoculants that unlock the vast reservoir of phosphorus already present in agricultural soils could reduce fertilizer demand, lower input costs for farmers and shrink the environmental footprint of crop production. Because strain I42 also mobilizes potassium and produces auxin, a single inoculation could address several yield-limiting factors at once, which is precisely the kind of multifunctionality that makes a biofertilizer commercially attractive.

The authors conclude that E. ludwigii I42 demonstrates strong potential as a plant growth-promoting bacterium, enhancing maize growth through phosphorus solubilization, phytohormone production and modification of the rhizosphere bacterial community, and they position the strain as a promising biofertilizer candidate for sustainable agriculture. The research was supported by the National Natural Science Foundation of China and the Natural Science Foundation of Shandong Province, among other funders, and the paper is published open access, making the genomic data and methods available to other groups working on root microbiomes and microbial fertilizers.

There are, of course, familiar caveats on the road from pot experiment to field. Performance in sterilized or controlled potting soil does not always translate to open fields, where climate, soil chemistry, native microbial competitors and crop management all exert pressure on an introduced strain. The authors’ own genomic framework, however, gives researchers a concrete starting point: with the chromosome assembled, the phosphate-solubilizing, IAA and siderophore genes identified, and the 133 unique genes flagged for follow-up, future studies can test which functions matter most under real field conditions. If those trials succeed, the humble soil bacterium sequenced in this study could move from the pages of a genomics journal into the seed coatings and soil inoculants of maize fields, turning an invisible genetic toolkit into visible harvests.

Subject of Research: Genomic mechanisms of phosphate-solubilizing bacterium Enterobacter ludwigii I42 and its plant growth-promoting effects on maize

Article Title: Genomic analysis of phosphate-solubilizing bacteria Enterobacter ludwigii I42 and its impact on maize growth

Article References: Zhao, D., Liu, S., Zheng, R., Ren, M., Liu, L., Xiao, L., Wen, C., Qiu, L., Sun, P., Li, C., Gao, J., Liu, F., Li, Z., & Wang, C. (2026). Genomic analysis of phosphate-solubilizing bacteria Enterobacter ludwigii I42 and its impact on maize growth. BMC Genomics. https://doi.org/10.1186/s12864-026-13420-4

Image Credits: AI Generated

DOI: 10.1186/s12864-026-13420-4

Keywords: Enterobacter ludwigii, phosphate-solubilizing bacteria, plant growth-promoting rhizobacteria, maize, phosphorus solubilization, indole-3-acetic acid, siderophores, rhizosphere microbiome, whole-genome sequencing, biofertilizer, sustainable agriculture, Bacillus