# Unlocking Wellness: Probiotics as Key Drivers in Functional Food Innovation and Health Promotion
## 2. Probiotic Strains, Sources, and Isolation Methods  
The human body hosts over 400 types of probiotics, which can mostly be categorized into five major genera: _Lactobacillus_, _Bifidobacterium_, _Bacillus_, _Streptococcus_, and others (Table 1). Systematic taxonomy reveals their taxonomic distribution: _Lactobacillus_, _Streptococcus_, and _Bacillus_ belong to the phylum Firmicutes; _Bifidobacterium_ belongs to the phylum Actinobacteria; and _Saccharomyces_ belongs to the phylum Ascomyca in the kingdom Fungi [14]. Currently, 56 species of _Lactobacillus_ (of which more than 10 are in everyday use), more than 32 species of _Bifidobacterium_ (14 of which are closely related to humans), more than 150 species of _Bacillus_ (with more than a dozen in common use), and more than 60 species of _Streptococcus_, including various strains and subspecies, have been reported and classified. Familiar sources of probiotics include the following: first, the human gut is the primary habitat for many probiotics, such as _Bifidobacterium_ and _Lactobacillus_[15]. These symbiotic microbial communities play a crucial role in maintaining host health. Fermented foods are an important dietary source of probiotics. During the fermentation process involving specific microorganisms, changes occur in the flavor and texture of the food matrix, and a large number of active probiotics are enriched. Typical fermented foods include yogurt and fermented dairy products. Consuming these foods is an effective way to obtain active probiotics. Certain probiotic strains can also be isolated from natural environments, such as soil and water bodies. These environmentally sourced probiotics play an indispensable role in maintaining biochemical cycles and balance in the microbial community in their native ecosystems [16]. However, environmental isolates must undergo rigorous assessment, screening, and safety validation to confirm their probiotic properties before they can be used in human or animal health applications. The development of probiotic isolation technology has progressed from traditional methods to modern multi-technology integration. The most basic and widely used method is the traditional plate isolation method, which involves diluting samples in a gradient and spreading them on selective culture media, followed by screening based on colony morphological characteristics. However, its significant limitations include low efficiency in isolating slow-growing strains and an inability to accurately reflect the true diversity of microbial communities. To address these shortcomings, optimized dilution plating and gradient dilution methods improved screening efficiency, but they still could not overcome the fundamental limitations of traditional culture techniques. To break through this bottleneck, molecular biology techniques have brought about a methodological revolution. Specifically, 16S rRNA gene sequencing directly analyzes the microbial composition of a sample [17], while metagenomics technology analyzes functional gene information to guide the targeted isolation of strains with specific functions [18]. Meanwhile, innovations in physical separation technologies have significantly enhanced single-cell manipulation capabilities. Microfluidic chips simulate the intestinal microenvironment to capture active bacterial cells [19], and flow cytometry combined with fluorescently labeled probes enables high-precision sorting at the single-cell level [20]. In recent years, the development of function-driven platforms has further driven technological innovation. High-throughput phenotypic screening systems can simultaneously assess the probiotic characteristics of thousands of strains, including acid tolerance and adhesion ability [21]. Notably, culturomics has successfully increased the cultivability rate of human gut microbiota to over 70% by optimizing combinations of cultivation conditions [22].