Potassium-solubilizing bacteria are an important microbial group that play a critical role in releasing mineral potassium from potassium-containing minerals, e.g., potassium feldspar. Their application may reduce eutrophication caused by overused potassium fertilizers and facilitate plants to utilize environmental potassium. In this study, a high-efficiency potassium-solubilizing bacterium, named NK851, was isolated from the Astragalus sinicus rhizosphere soil. This bacterium can grow in the medium with potassium feldspar as the sole potassium source, releasing 157 mg/L and 222 mg/L potassium after 3 days and 5 days of incubation, respectively. 16S rDNA sequencing and cluster analysis showed that this strain belongs to Priestia megaterium. Genome sequencing further revealed that this strain has a genome length of 5,305,142 bp, encoding 5473 genes. Among them, abundant genes are related to potassium decomposition and utilization, e.g., the genes involved in adherence to mineral potassium, potassium release, and intracellular trafficking. Moreover, the strong potassium-releasing capacity of NK851 is not attributed to the acidic pH but is attributed to the extracellular potassium feldspar-binding proteins, such as the elongation factor TU and the enolase that contains potassium feldspar-binding cavities. This study provides new information for exploration of the bacterium-mediated potassium solubilization mechanisms.

Soil saline–alkali stress is a major problem faced by global agriculture, and there is an urgent need to develop efficient amelioration strategies. While both probiotics and plant stress-resistant molecules play critical roles in the alleviation of crop stress, their efficient retention in crop rhizosphere regions remains a great challenge. In this study, the nanocarrier ZIF-8@SPBP@betaine (ZSBet) was constructed by introduction of the synthesized polysaccharide-binding protein (SPBP) and the stress-resistant molecule betaine to the metal–organic framework ZIF-8. During co-incubation, the probiotic Novosphingobium capsulatum and ZSBet efficiently bound together to form ZSBet + Novo co-assemblies, i.e., the integrated protein-ZIF-8-probiotic complexes mediated by polysaccharide-receptor recognition, which exhibited strong root-binding abilities. Microbiome analysis revealed that ZSBet + Novo reduced the α-diversity of rhizosphere bacteria and increased the absolute abundance of biofilm formation-related bacteria, e.g., Novosphingobium, Sphingobium, and Lactococcus. During wheat cultivation in saline–alkali soil, ZSBet + Novo reduced soil pH by 0.63 units, decreased soil salt content by 0.11 g/kg, and increased soil nutrient levels. Furthermore, the co-assembly enhanced the wheat grain number by 145.05% and reduced root malondialdehyde and proline contents by 42.00% and 39.13%, respectively. This study provides a new strategy for improving crop resistance under saline–alkali stress in combination with nanotechnology and synthetic biology.

The utilization of the widely distributed saline–alkali lands by planting forage grasses is a hot topic. However, the promotion of plant growth remains a great challenge during the exploration of this stressful soil. While halotolerant bacteria are beneficial for plants against saline–alkali stress, their stable colonization on plant roots should be further strengthened. In this study, we investigated the effect of moss biochar on the root colonization of the exogenous halotolerant Halomonas salifodinae isolated from saline lake sediments. During the incubation with the bacteria, the biochar strongly bound the bacterium and induced biofilm formation on the biochar surface. When the biochar and the bacterium were added into the culturing soil of the forage grass Medicago sativa, the biochar remarkably assisted the root binding and biofilm formation of this bacterium on the plant roots. Under the biochar–bacterium combined treatment, the numbers of total bacteria, halotolerant bacteria, and nitrogen-fixing bacteria increased from 10^5.5 CFU/g soil to 10^7.2 CFU/g soil, from 10^4.5 CFU/g soil to 10^6.1 CFU/g soil, and from 10^4.7 CFU/g soil to 10^6.3 CFU/g soil, respectively. After 30 days of culturing, the biochar and the bacterium in combination increased the plant height from 10.3 cm to 36 cm, and enhanced the accumulation of chlorophyll a, reducing sugars, soluble proteins, and superoxide dismutase in the leaves. Moreover, the combined treatment increased the activity of soil enzymes, including peroxidase, alkaline phosphatase, and urease. Meanwhile, the levels of various cations in the rhizosphere soil were reduced by the combined treatment, e.g., Na⁺, Cu²⁺, Fe²⁺, Mg²⁺, Mn²⁺, etc., indicating an improvement in the soil quality. This study developed the biochar–halotolerant bacterium joint strategy to improve the yield of forage grasses in saline–alkali soil.

The development of efficient fungal vaccines is urgent for preventing life-threatening systemic fungal infections. In this study, we prepared a synthetic, cell-based fungal vaccine for preventing systemic fungal infections using synthetic biology techniques. The synthetic cell EmEAP1 was constructed by transforming the Escherichia coli chassis using a de novo synthetic fragment encoding the protein mChEap1 that was composed of the E. coli OmpA peptide, the fluorescence protein mCherry, the Candida albicans adhesin Eap1, and the C-terminally transmembrane region. The EmEAP1 cells highly exposed the mChEap1 on the cell surface under IPTG induction. The fungal vaccine was then prepared by mixing the EmEAP1 cells with aluminum hydroxide gel and CpG. Fluorescence quantification revealed that the fungal vaccine was stable even after 112 days of storage. After immunization in mice, the vaccine resided in the lymph nodes, inducing the recruitment of CD11c⁺ dendritic cells. Moreover, the vaccine strongly activated the CD4⁺ T splenocytes and elicited high levels of anti-Eap1 IgG. By the prime-boost immunization, the vaccine prolonged the survival time of the mice infected by the C. albicans cells and attenuated fungal colonization together with inflammation in the kidneys. This study sheds light on the development of synthetic biology-based fungal vaccines for the prevention of life-threatening fungal infections.

Soil saline–alkali stress has become a great risk, leading to significant decline in crop yields, especially in protected agriculture that is frequently threatened by excessive chemical fertilization. There is an urgent need to develop friendly strategies for improving the quality of saline–alkali soil. Microbial inoculants are promising agents in attenuating soil stress, but their colonization ability in the crop rhizosphere is often limited. To improve the efficiency of microbial inoculants, this study constructed the assembly of a salt-tolerant bacterium Halomonas (Homs) and a hydrogel composed of sodium alginate, chitosan and xanthine with the assistance of artificial Homs-binding protein (Schx). The effect of this Homs + Schx assembly on the growth of crops and the rhizosphere microecology under saline–alkali stress was systematically evaluated by pot experiments. The results indicate that the application of Homs + Schx enhanced the Shannon index of the rhizosphere bacterial community and increased the relative abundance of key bacterial genera related to biofilm formation and nitrogen cycling (e.g., Curvibacter and Nitrospira). Furthermore, Homs + Schx enhanced the activity of soil urease, peroxidase, and sucrase, reducing the sodium ion content, increasing the potassium ion content, and effectively lowering the soil pH and salt contents. Physiologically, this treatment induced a root osmotic regulatory response, resulting in an increase in the proline contents and a decrease in malondialdehyde contents. Consequently, Homs-Schx promoted the growth of tomatoes and wheat in saline–alkali soil. This study provides new ideas for enhancing the rhizosphere colonization of plant growth-promoting bacteria, regulating the structure of microbial communities, and enhancing crop stress tolerance with the aid of green material strategies.