## 1 Introduction  
Ulcerative colitis (UC) is an inflammatory bowel disease (IBD) characterized by symptoms such as abdominal pain, diarrhea, rectal bleeding, and weight loss, with an increased risk of colorectal cancer [1]. Although the exact cause of UC remains unclear, it is generally considered a multifactorial condition triggered by genetic, environmental, and microbial factors, resulting in inflammation of the colonic mucosa, disruption of tight junctions, heightened production of pro-inflammatory cytokines, and induction of dysbiosis in the gut microbiota [2, 3]. Cytokines act as signaling molecules in the inflammatory process and play a significant role in the onset and progression of inflammation and UC by activating inflammatory pathways and mediating the generation of inflammatory mediators [4]. Recognized as a global public health challenge by the World Health Organization, the incidence of UC is surging, owing to shifts in dietary habits and heightened stress [5]. The existing medications for UC, including 5-aminosalicylates, systemic and local corticosteroids, and immunomododulators, may cause severe side effects [6]. Therefore, there is an urgent need for more effective natural preventive and therapeutic approaches to alleviate the clinical course of this disease. _Eisenia bicyclis (E.bicyclis)_, a brown marine algae, is rich in the polyphenol phlorotannin, consisting of phloroglucinol. Phlorotannins isolated from _E. bicyclis_ include eckol, phlorofrototoevocol-A, dieckol, and phloroglucional-A [7; 8]. Extensive research has illuminated the diverse physiological activities of phlorotannins, including their antioxidant, anti-inflammatory, anti-allergic, neuroprotective, and memory-enhancing effects [9; 10]. Furthermore, phlorotannins from _E. bicyclis_ have demonstrated positive effects on tight junction cells, affecting the integrity of the intestinal mucosal barrier and contributing to the regulation of gut microbiota, thereby preventing and inhibiting the onset of UC [11]. In addition, phlorotannins, which are categorized as plant polymeric polyphenols, are considered prebiotic candidates because of their potential to interact with and stimulate the growth and metabolite production of the gut microbiota [12; 13]. Probiotics, particularly various strains of Lactobacillus, such as _Lactobacillus casei_ and _Lactobacillus reuteri_, have been reported to alleviate colitis in animal models by modulating the gut bacterial composition, decreasing inflammation-related cytokine production, and improving intestinal membrane function [14; 15]. In addition, probiotics demonstrate synergistic effects when combined with polysaccharides or polymeric polyphenols, contributing to improved metabolic rates through digestion and improved gut microbiota composition [16]. The coexistence of specific bacteria with prebiotics, offering greater health benefits to the host than individual substances and producing synergistic effects via the production of bacterial metabolites, is referred to as symbiotics [17; 18]. For example, the synergistic effects of _Ligilactobacillus salivarius_ and the plant-derived prebiotic resveratrol have demonstrated efficacy in ameliorating colitis in mice through a reduction in inflammatory cytokine (IL-1\(\beta\) and IL-6) levels [19]. Previous findings have indicated that probiotic Lactobacillus can metabolize phlorotannins, producing beneficial metabolites [15; 20]. However, limited research exists on whether synbiotics formed through the interaction of phlorotannins and probiotics have preventive and therapeutic effects on UC and their underlying mechanisms. The aryl hydrocarbon receptor (AhR) is a transcription factor that is increasingly recognized for its pivotal role in intestinal immune regulation and tight junction modulation in UC [21; 22]. Upon binding to diverse ligands, including xenobiotics, natural products, and microbiome metabolites, AhR undergoes cytoplasmic-to-nuclear translocation.