Acute inflammation is frequently triggered by pathogen infections and contributes to host mortality. In this study, a new exopolysaccharide (ObEPS) was isolated from the moss endophyte Ovatospora brasiliensis and characterized for its structure and biological activity. Monosaccharide composition analysis revealed that ObEPS was mainly composed of galactose, glucose, mannose, and glucuronic acid. Multi-angle light scattering and conformation analysis showed a molar mass of 10⁵–10⁶ Da and a compact chain conformation. In vitro experiments showed that ObEPS markedly inhibited nitric oxide production and reduced pro-inflammatory cytokine expression in lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages. In a systemic Candida albicans infection model, ObEPS combined with fluconazole significantly reduced fungal colony-forming units (CFUs)/g kidney from 3.8 × 10⁵ to 0.1 × 10⁵, with the reduction of pro-inflammatory cytokine levels and tissue damage compared with the EPS-free groups suffering from C. albicans infection. Overall, these findings indicate that ObEPS has potent anti-inflammatory activity and may serve as a promising natural adjunct for mitigating infection-associated inflammatory damage.

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.

Intestinal drug-resistant pathogens, e.g., Salmonella enterica subsp. enterica serovar Typhimurium (S. Tm) and enteropathogenic Escherichia coli (E. coli), frequently cause life-threatening infectious enteritis. Probiotic-based therapy is a promising way to eliminate drug-resistant pathogens for treatment of infectious enteritis, but its colonizing and therapeutic efficacy after oral administration are limited. Here, we developed a facile therapeutic agent to treat infectious enteritis by co-assembly of the peptide nanodrug melittin-loaded MSN grafted by polysaccharide-binding protein (MMPB) with the famous probiotic bacteria Lactobacillus plantarum (Lac) and Bifidobacterium animalis subsp. lactis (Bif). The nanodrug was composed of the antimicrobial peptide melittin and mesoporous silica nanoparticles exposing the artificial polysaccharide-binding protein. Owing to presence of the artificial protein on the MMPB surface, the nanodrug strongly bound and cross-linked the probiotic cells, forming the Lac+Bif+MMPB co-assembly. During co-incubation with the kanamycin-resistant E. coli strain (Ecka), the co-assembly strongly reduced the viability of Ecka, leading to the increase in the ratio of probiotic to Ecka from 1.6 to 9.2. After oral administration of the co-assembly to the mice pre-colonized by Ecka, Lac+Bif+MMPB almost eliminated the kanamycin-resistant gene in the intestine, and led to 2–3-fold higher levels of the probiotic cells than the nanodrug MMPB or the combined probiotics Lac+Bif. More importantly, in the mice suffering from enteritis caused by drug-resistant S. Tm, the co-assembly remarkably recovered the mouse body weight, reduced intestine colonization of S. Tm cells, and decreased the levels of pro-inflammatory cytokines in both serum and colons. This study realized the synthetic biology technique-mediated abiotic/biotic co-assembly for efficient treating infectious enteritis induced by drug-resistant pathogens.