Mehdi Soltani

Bacillus spp. produce various types of bacteriocins with different molecular weights from 800 Dalton to 950 kilo Dalton. Several Bacillus bacteriocins belong to the lantibiotics that are the best-described antimicrobial peptides with regard to biosynthesis mechanisms, genetic determinants, and peptide structure. Some Bacillus species produce unmodified bacteriocins including pediocin-like bacteriocins and the two-peptide bacteriocins, while others show completely novel peptide sequences. Some of the well-described bacteriocins produced by Bacillus spp. are subtilin, cerein, bacillocin 490, haloduracin, thuricin, subtilosin, and megacin, all of which are mostly active against Gram-positive bacteria such as Streptococcus, Staphylococcus, Leuconostoc, Listeria, and Gardnerella. This chapter addressed an overview of the diverse classes of bacteriocins produced by bacilli, an update on the efficiency of fish gut-associated Bacillus spp. toward bacterial fish pathogens, and their prospective future applications in aquaculture sector.

In shrimp aquaculture, manipulation of microbiota using probiotics has been shown to control or inhibit pathogenic agents, can enhance digestive enzyme activity and growth performance, and enhance immune responses of the host toward the pathogenic infections or physical stress. Among the several probiotic candidates in shrimp aquaculture, species of Bacillus have brought well-encouraging results. Studies have documented that Bacillus species are able to secrete a wide range of extracellular substances and antimicrobial peptides, which improve feed digestion and absorption, boost shrimp health and immunity, promote shrimp growth and reproduction, and enhance survival against pathogenic microorganisms. This chapter addressed the efficacy and potency of bacilli probiotics on the growth performance, immunity, and disease resistance in shrimp aquaculture and discussed the present gaps and future studies needed.

Bacillus are Gram-positive, rod-shaped, aerobic or facultative anaerobic spore-forming bacteria with most species being saprophytes. In the form of endospore, they are resistant to some aggressive physical and chemical conditions with various species existing unusual physiological characters, enabling them to survive in different environments including fresh and marine waters, sediments, desert sands, hot springs, and Arctic soils. The genus of Bacillus includes thermophilic, psychrophilic, acidophilic, alkaliphilic, halotolerant, and halophilic representatives, which are capable of growing at wide ranges of environmental conditions such as temperature, pH, and salinity. The physiological life habitat of Bacillus bacteria is remarkable. They are able to degrade many substrates derived from animal and plant sources including cellulose, starch, proteins, agar, and hydrocarbons. These spore-forming bacteria are antibiotic producers, heterotrophic nitrifiers, denitrifiers, nitrogen fixers, iron precipitators, selenium oxidizers, oxidizers, manganese reducers, facultative chemolithotrophs, and acidophilic and alkalophilic bacteria, as well as having psychrophilic and thermophilic features. A better understanding of the cellular structure and life cycle biology of these spore-forming bacteria definitely results in a better understanding of the biological and physiological functions of these microorganisms, especially when they are used in the form of probiotics. This is very important due to an increased application of these spore-forming microorganisms as probiotics in different animals including cultured aquatic animal species. This chapter deals with the biology and life cycle of Bacillus spp. as nowadays some of them are widely used in aquaculture sector either in the feed or in the rearing water. Therefore, study of the biology of these bacteria will assist us in a better understanding of their mode of action and the mechanisms when are used as the probiotics in aquaculture sector.

Bioremediation of aquaculture rearing water quality means degradation and reduction of unsafe waste substances such as toxic gases in a contaminated fish/shellfish farm by living organisms such as probiotics Bacillus spp. and Lactobacillus spp. Obviously, the biological treatment systems can have different requests including clean-up of contaminated rearing water of fish/shellfish farm, pond soil, sludge, and streams. The intensive aquaculture farming plus other human activities such as industrialization and urbanization all have increased the adverse effects such as environmental pollution and land degradation with a consequence in the reduction of productivity in aquaculture activity. Thus, bioremediation as an emerging, effective, and attractive management tool can treat and recover the environment, e.g. rearing water quality. This ecofriendly way of bioremediation has been applied worldwide, but with varying degrees of achievement. Application of Bacillus probiotics as bioremediatory tools in the rearing water of aquaculture species and soil of ponds, both in situ and ex situ, has been demonstrated as a strong manner of improving water quality and improving the growth performance and health status of the cultured fish/shellfish species. Therefore, bioremediation technology as a tool to degrade the pollutants is a profitable and environmentally friendly alternative, particularly where the removing of toxic gases such ammonia, nitrite, nitrate, and carbon dioxide are crucially harmful for the aquatic animal species. The available information concerning the application of Bacillus probiotics such B. subtilis and B. licheniformis in rearing water of fish and shrimp is attractive and promising due to the removal of unsafe toxic gases. Further, it has been shown that the application of Bacillus probiotics in the rearing water of aquatic animals can make a balance between the microorganisms in the water column or in the pond soil via a bacterial competition with a consequence in reducing the load of secondary pathogens. This chapter discusses the role of Bacillus probiotics as bioremediatory tools of rearing water of aquatic animal species.

Bacillus species are highly regarded as probiotics in aquaculture due to their positive impact on host health and disease prevention. This chapter provides a comprehensive overview of the physiological aspects and optimization strategies involved in the production of Bacillus spp. probiotics for aquaculture that contributes to the development of efficient and sustainable aquaculture practices. It highlights the significance of Bacillus spp. as probiotic, their potential in enhancing aquaculture productivity, and the importance of understanding the physiological characteristics of Bacillus spp. to optimize their growth and spore production. The chapter discusses several key factors that influence Bacillus spp. spore production and growth. It explores the effects of carbon sources, lignocellulosic growth substrates, nitrogen sources, medium pH, agitation and aeration, and microelements on the physiology and productivity of Bacillus species. Additionally, the chapter emphasizes the importance of selecting the appropriate cultivation method for scaled-up Bacillus spp. probiotic production in aquaculture. Different cultivation methods, such as batch, continuous, and fed-batch cultures, are evaluated, taking into account their impact on growth, spore formation, and overall probiotic yield. It enables the cultivation of high-quality probiotics with enhanced benefits, including disease prevention, improved nutrient utilization, and growth promotion, thereby enhancing the health and productivity of aquaculture organisms.

This book provides a comprehensive examination of the role of Bacillus bacteria in aquaculture, particularly focusing on finfish and shellfish. It begins with foundational chapters on the anatomy and physiology of these aquatic species, their immune systems, and the biology of Bacillus bacteria. The book discusses the specific interactions between Bacillus and the gastrointestinal tracts of fish and shellfish, examining the production and effects of Bacillus-derived exoenzymes and bacteriocins and their role in enhancing aquatic health and water quality. Additionally, the book covers the role of Bacillus in bioremediation, particularly in improving water quality, which is a significant concern in aquaculture. The latter sections delve into the application of Bacillus as probiotics and paraprobiotics in fish and shellfish culture, their integration in feed biotechnology, and a critical evaluation of their safety. The book concludes with a critical discussion on the safety and regulatory aspects of using Bacillus in aquaculture. This book is intended for professionals and practitioners in the aquaculture industry and researchers, academicians, and students in the fields of microbiology, marine biology, and aquaculture

Fish are intriguing subjects for genomic and immune system studies due to their unique phylogenetic placement within vertebrate animals. The immune response serves as the body's defense mechanism against harmful pathogens. Across both fish and mammals, there exists a resemblance in fundamental immune molecules. Examining these molecules and the functioning of the immune system aids in uncovering the foundational elements shared by all vertebrate animals, including fish, in their defense against pathogens and provides valuable insights into the evolutionary aspects of the immune system. Fish possess a complex biological system that elicits diverse reactions to eliminate harmful pathogens. Like mammalian animals, the immune system in fish is divided into innate and adaptive components, and molecular interactions between the host and the invader determine the response to pathogens. This interaction involves the activation of receptors and the production of immune signals. The immune responses in fish encompass various elements, such as physical barriers like scale, skin, mucous secretions, and the gut environment. Additionally, antimicrobial peptides, complement proteins, and cytotoxic cells play crucial roles, primarily targeting antigens and functioning as part of the innate immune response. The initial and effective immunity is established through diverse innate immune responses, followed by the activation of adaptive immunity. Fish possess vital immune organs like the kidney, thymus, spleen, and mucosa-associated lymphoid tissues, which are crucial in generating immunomodulating molecules such as immunoglobulin IgM, IgD, and IgT, along with B and T lymphocytes. This chapter delves into host-pathogen interactions, immune response patterns in fish, and the evolving trends in fish immunogenomics. Understanding immune response pathways is essential for the long-term sustainability of aquaculture, especially in disease control. Exploring fish immune systems in depth provides valuable insights for developing better strategies to prevent and manage diseases in aquaculture sector. By uncovering how hosts and pathogens interact and the patterns of immune responses, we can create targeted and innovative approaches, like designing vaccines customized for specific pathogens.

Today, a high global demand for food security and food safety has caused rapid development in the aquaculture industry. Research on the efficacy and potency of Bacillus in the form of probiotics on growth performance and immunity is inadequate. The diverse physiological characteristics of Bacillus bacteria can provide a suitable condition in fish gastrointestinal tract resulting in better digestion and absorption of feed nutrients by fish, with an ultimate improvement in the animal growth performance. The detailed mode of action by bacilli bacteria as the major producers of proteinaceous substances, however, required more investigations. The probiotic bacilli can change the ecology of the gut microbiota of recipient fish via bacterial competition that can result in the prevention of pathogen attachment to the intestinal mucosa, ultimately improving of growth and health status of the target fish. In addition, Bacillus probiotics can modulate innate immune responses including lysozyme and phagocytic activity, anti-protease, respiratory burst, and antioxidant enzymes such as peroxidase, superoxide dismutase, and myeloperoxidase through an enhancement in some fish immunocompetent cell populations, for example, leukocytes, lymphocytes, monocytes, goblet cells, and erythrocytes. In addition, Bacillus probiotics can elicit changes in animal cell physiology, for example, increasing neutrophil adherence capacity, neutrophil migration, and plasma bactericidal activity that ultimately can result in the enhancement of immune effector functions such as enhancement in complement activity, immunoglobulin production, and cell cytotoxicity. The studies of immune-stimulatory effects by Bacillus spp. take place in the gut-associated lymphoid tissue of fish. However, detailed mechanisms of such studies warranted future research works. This chapter addressed the efficacy and potency of bacilli probiotics on growth immunity and disease resistance of various fish species and discussed the present gaps.

The intestinal microbiota in finfish and shellfish is involved in a wide range of biological processes that benefit the host. In this respect, genus Bacillus is highly represented, and approximately 25 species have been detected in the digestive tract of numerous finfish and shellfish species. In the early studies of the gut microbiota of finfish and shellfish, cultured methods were used, for example, Bacillus, but due to limitations, culture-independent techniques have been used during the last decade. Studies conducted on the gut microbiome composition using amplicon sequencing have also confirmed the abundance of Firmicutes indicating bacilli as one of the major gut-associated bacteria in diverse fish species. Evaluation of Bacillus species as a part of the gut microbiota of finfish and shellfish species is of importance as they have great potential applications in aquaculture as they can form the spores that help them survive in the harsh environmental conditions. According to the available literature, Bacillus are one of the most studied probiotics in aquaculture, as they are non-pathogenic and non-toxic to aquacultural environments and animals. In this chapter, we present information on the presence of Bacillus in digestive tract of finfish and shellfish species and some general characteristic information on their ability of exo-enzyme production, production of antimicrobial substances to inhibit in vitro growth of pathogens, making them suitable candidates compared to other probiotics.

Contribution of the exogenous enzymes supplemented by the gut-associated endosymbionts has been realized of late. Autochthonous gut microbiota is now considered as an important secondary factor that positively influences digestion and nutrient utilization of the host. Being one of the major colonizers within the gut of the fish, bacilli are metabolically active and produce a wide array of enzymes that play a vital role in the digestive processes of the host. The enzymes of nutritional importance produced by the gut bacteria may be categorized as (1) digestive enzymes, e.g., protease, amylase, and lipase, and (2) degradation enzymes, e.g., non-starch polysaccharide (NSP) - degrading enzymes, phytase, tannase, and chitinase. The probiotic attributes of the bacilli often lie within their capacity to produce this extensive range of enzymes that could act on diverse biological substrates of nutritional importance. Diverse species of the gut-associated bacilli with different enzymatic potential have been detected in varied fish species. Among these, Bacillus subtilis, Bacillus licheniformis, B. amyloliquefaciens, B. methylotropicus, Bacillus pumilus, and B. cereus may be mentioned. The present chapter will critically evaluate the occurrence of exo-enzyme-producing and gut-associated bacilli in fish and their contribution to fish nutrition.