Probiotics are live microorganisms that confer health benefits to the host when consumed in adequate amount [1]. They improve resistance against infectious diseases by regulating gut eubiosis, suppressing pathogenic bacteria, and enhancing the natural defense system of host [2,3,4]. Probiotics provide protection against virulent pathogens through the secretion of short-chain fatty acids, extracellular polymeric substances, bacteriocins, siderophores, enzymes and antimicrobial peptides [5]. They are also able to provide protection against deadliest viruses [6]. The antimicrobial compounds they produce in the host gut act as a robust barrier against pathogen growth. Lactic acid, acetic acid, propionic acid, butyric acid, and volatile fatty acids play a role in regulating intestinal pH and contribute positively to the host's health [7]. Furthermore, they have the potential to enhance the immune responses of the host [8, 9]. Probiotics provide a sustainable alternative to traditional antimicrobial compounds and chemotherapeutic agents, alleviating concerns related to antibiotic resistance and the potential adverse impacts on food safety and human health [10].

A probiotic must maintain viability without genetic alteration during extended storage and under field conditions [11]. Its capacity to withstand bile and acids is essential for colonizing the digestive tract of the host. Additionally, probiotics need high cell-surface hydrophobicity to adhere effectively to the intestinal wall [12]. It is also essential that probiotics are specific to their intended target and capable of reaching the desired location within the host [13]. Probiotics must be non-pathogenic, non-toxic to the host, and free from virulent or antibiotic-resistant genes [14]. The most crucial prerequisites of a putative probiotic include sensitivity to antibiotics, hydrophobic cell surfaces, tolerance to bile salts, cholesterol-lowering ability and the ability to break down bile salts [9, 15]. Probiotic often posses genetic markers including bsh (bile salt hydrolase), uvr (UV resistance), and slpA (S-layer protein A), aggregation promoting factors (e.g., Apf), FbpA proteins, or adh genes to effectively colonize the host and produce immune-modulatory substances [16, 17]. These characteristics collectively ensure the optimal efficacy of probiotic applications, supporting their role in promoting health and well-being.

Lactobacillus plantarum strains play a significant role in food processing due to their ability to convert polyunsaturated fatty acids, such as linoleic acid (LA), into bioactive metabolites. Aziz et al. [18] examined the ability of L. plantarum 13–3 to transform LA in media supplemented with 1 to 10% LA. GC–MS analysis identified five fatty acid metabolites: (Z)-Ethyl heptadec-9-enoate, 9,12-Octadecadienoic acid (Z,Z), methyl ester, Octadec-9-enoic acid, cis-11,14-Eicosadienoic acid, methyl ester, and (Z)-18-Octadec-9-enolide. Notably, Octadec-9-enoic Acid, a long-chain fatty acid, was reported for the first time in media supplemented with 4 to 10% LA. In silico analysis suggested that enzymes such as linoleate isomerase, acetoacetate decarboxylase, and oxidoreductase facilitated these conversions.

Aziz et al. [19] assessed L. plantarum YW11, which exhibited a dose-dependent transformation of LA into conjugated linoleic acid (CLA) and other metabolites. Identified metabolites included 9-cis,11-trans-octadecadienoic acid (rumenic acid), linoelaidic acid, (E)-9-octadecenoic acid ethyl ester, trans, trans-9,12-octadecadienoic acid, propyl ester, and stearic acid. CLA was detected only at 10% LA. Four enzymes—10-linoleic acid hydratase, linoleate isomerase, acetoacetate decarboxylase, and dehydrogenase—were implicated in this transformation.

Further investigated L. plantarum K25, which produced nine fatty acid analogues from 1 to 10% LA. Linolenic acid was detected at 9% LA for the first time. Enzymes, including linoleate isomerase and dehydrogenase, were identified as key contributors to the biotransformation process. These studies highlight the potential of L. plantarum strains in biotechnological applications.

In agriculture and food industries, probiotics serve as potential alternative of biocontrol agents, addressing limitations of conventional antimicrobial methods [20]. They enhance nutrient availability, support sustainable field management practices, and mitigate the adverse effects of pesticides and fertilizers on water, soil, and environmental health [21]. Plant probiotic microorganisms (PPM) play crucial roles in agriculture by promoting soil health, stimulating plant growth, controlling pathogens, and enhancing plant stress tolerance [21]. PPM, encompassing bacteria and fungi, serve as bioprotectants, biocontrollers, biofertilizers, or biostimulants, offering a sustainable approach to agriculture.

Probiotics, being eco-friendly and biocompatible substances, have increasingly been employed in recent decades to prevent and manage aquatic diseases. They are often added as functional feed supplement to improve feed digestibility and fecundity [11]. Probiotics can enhance the environmental quality of sediment and culture water in closed recirculation systems. They provide protection by competitively excluding pathogens from adhesion sites and by producing antimicrobial substances [5]. Furthermore, probiotics modulate physiological and immunological responses in fish. Ganguly et al. [22] demonstrated that introducing Lysinibacillus sphaericus PKA17 into fish feed effectively inhibited Vibrio harveyi infection in Clarias batrachus. Sarwar et al. [23] reported that functional yogurt samples containing Saccharomyces boulardii and inulin in varying concentrations demonstrated an increase in antioxidant potential during the storage period, with the potential remaining stable over an extended period. Lactobacillus plantarum has made significant contributions to genome analysis, genetic diversity research, and food safety applications [24]. These findings emphasize the multifaceted benefits of probiotics in promoting sustainable aquaculture practices while minimizing reliance on conventional treatments. Probiotics increase the digestibility of indigestible compounds and enhance the nutritional value of feed in fish, leading to improved fish nutrition and overall health [9]. They also stimulate the production of antibodies, enzymes (such as acid phosphatase and lysozymes), complement pathways, cytokines (including IL-1, IL-6, IL-10, IL-12, TNF-α, IFN-γ, and TGF-β), and antiviral peptides. Lactobacillus plantarum has been found to induce significant levels of IgM in cyprinid fish. Bacillus subtilis VSG1, Pseudomonas aeruginosa VSG2, and Lactobacillus plantarum VSG3 significantly increased lysozyme activity in Labeo rohita [25]. Ganguly et al. [26] incorporated three probiotic Bacillus strains (Lysinibacillus sphaericus PKA17, Bacillus cereus PKA18, and Bacillus thuringiensis PKA19) as feed supplement and observed enhanced growth, and nutritional status of C. magur in captivity.

The study of probiotics has a rich history spanning over a century, beginning with the Nobel laureate Elie Metchnikoff who theorized that human health could be aided through the ingestion of fermented milk products [27]. However, the term probiotic was not introduced until 1965 by Lilly and Stillwell [28] as a modification of the original word “probiotika.” Parker [29] defined it as “organisms and substances that contribute to intestinal microbial balance” and described it as a microbial feed/food supplement. In 1989, Fuller expanded the definition to “live microbial food supplement that benefits the host (human or animal) by improving the microbial balance of the body” and remarked that it would be effective in a range of extreme temperatures and salinity variations. Research on probiotics surged in the 1980s, focusing initially on their impact on gut health and immunity [30]. Subsequent decades witnessed an expansion of this research to investigate their potential contributions in managing allergies, autoimmune diseases, and neurological conditions [31]. The initiation of the Human Microbiome Project in the 2010 further accelerated research, deepening our understanding of probiotic mechanisms and their interactions with the human microbiome [32]. Recent advances have highlighted role of probiotics in enhancing gut barrier function, modulating immune responses, and producing antimicrobial substances [26].

Indian microbiologists have made significant contributions to probiotic research, particularly in exploring traditional fermented foods as rich sources of lactic acid bacteria (LAB) with potential probiotic properties [33]. Nithya and Halami [34] conducted an evaluation of the probiotic potential of Bacillus species isolated from various food sources. Dr. J.P. Tamang integrated ethno-microbiology with metataxonomics and metagenomics to study fermented foods and beverages among various ethnic groups in the Himalayan regions of Bhutan, India, and Nepal [35]. Dahiya et al. [36] extensively investigated the modulation of gut microbiota and its association with obesity using probiotics and prebiotic fibers. Indian scientists have recently identified a next-generation probiotic bacterium, named Lactobacillus plantarum JBC5, from a dairy product. This strain has shown significant promise in promoting healthy aging [37, 38]. These contributions have not only advanced our understanding of probiotics but also paved the way for the development of innovative probiotic-based products and therapies in India, showcasing the country's growing expertise in this field.

Probiotics contribute to the United Nations Sustainable Development Goals (SDGs) by improving nutrient absorption, increasing food security, and promoting sustainable agriculture (SDG 2). They also support sustainable aquaculture, marine ecosystem conservation, and sustainable seafood production, helping to conserve ocean resources (SDG 14). By enhancing food security, nutrition, and sustainable resource use, probiotics play a valuable role in achieving a more sustainable future. Aquaculture-derived fish products contribute to global food security while also supporting SDG 3 (Good Health and Well-being) by providing essential nutrients and omega-3 fatty acids, promoting healthy diets and improved well-being [39].

The study of probiotics thus requires a profound level of research and analysis to uncover the intricacies of their mechanisms, potential benefits, and effects on human health. This endeavour involves identifying and characterizing new strains, conducting rigorous clinical trials, and exploiting advanced genomics and metabolomics technologies [40]. Most existing probiotic studies have focused on mode of actions, efficacy and application of probiotics. The global trends, geographical disparities and regional-specific research were unexplored. These hinder a comprehensive understanding of probiotic research. Addressing these gaps will provide valuable insights into the dynamics of probiotic research and its applications. The current study seeks to compile and analyze India's significant influence on the progress of Microbiology. It aims to highlight the substantial contributions of Indian scientists, groundbreaking discoveries, and notable advancements that have shaped the landscape of microbiology over the past few decades.