Potential influence of jaggery-based biofloc technology at different C:N ratios on water quality, growth performance, innate immunity, immune-related genes expression profiles, and disease resistance against Aeromonas hydrophila in Nile tilapia (Oreochromis niloticus)

Elevated proton motive force is a tetracycline resistance mechanism that leads to the sensitivity to gentamicin in Edwardsiella tarda

Tetracycline is a commonly used human and veterinary antibiotic that is mostly discharged into environment and thereby tetracycline-resistant bacteria are widely isolated. To combat these resistant bacteria, further understanding for tetracycline resistance mechanisms is needed. Here, GC-MS based untargeted metabolomics with biochemistry and molecular biology techniques was used to explore tetracycline resistance mechanisms of Edwardsiella tarda. Tetracycline-resistant E. tarda (LTB4-RTET ) exhibited a globally repressed metabolism against elevated proton motive force (PMF) as the most characteristic feature. The elevated PMF contributed to the resistance, which was supported by the three results: (i) viability was decreased with increasing PMF inhibitor carbonylcyanide-3-chlorophenylhydrazone; (ii) survival is related to PMF regulated by pH; (iii) LTB4-RTET were sensitive to gentamicin, an antibiotic that is dependent upon PMF to kill bacteria. Meanwhile, gentamicin-resistant E. tarda with low PMF are sensitive to tetracycline is also demonstrated. These results together indicate that the combination of tetracycline with gentamycin will effectively kill both gentamycin and tetracycline resistant bacteria. Therefore, the present study reveals a PMF-enhanced tetracycline resistance mechanism in LTB4-RTET and provides an effective approach to combat resistant bacteria.

A detailed look at the impacts of biofloc on immunological and hematological parameters and improving resistance to diseases

The innate immunity of invertebrates serves as a critical trait that provides a valuable foundation for studying the common biological responses to environmental changes. With the exponential growth of the human population, the demand for protein has soared, leading to the intensification of aquaculture. Regrettably, this intensification has resulted in the overuse of antibiotics and chemotherapeutics, which have led to the emergence of resistant microbes or superbugs. In this regard, biofloc technology (BFT) emerges as a promising strategy for disease management in aquaculture. By harnessing the power of antibiotics, probiotics, and prebiotics, BFT offers a sustainable and eco-friendly approach that can help mitigate the negative impacts of harmful chemicals. By adopting this innovative technology, we can enhance the immunity and promote the health of aquatic organisms, thereby ensuring the long-term viability of the aquaculture industry. Using a proper carbon to nitrogen ratio, normally adding an external carbon source, BFT recycles waste in culture system with no water exchange. Heterotrophic bacteria grow along with other key microbes in the culture water. Heterotrophs play a major role in assimilating ammonia from feed and fecal waste, crucial pathway to form suspended microbial aggregates (known as 'biofloc'); while chemoautotrophs (e.g. nitrifying bacteria) oxidize ammonia into nitrite, and nitrite into nitrate promoting a healthy farming conditions. By using a highly aerated media and an organic substrates that contain carbon and nitrogen, protein-rich microbes are able to flocculate in culture water. Several types of microorganisms and their cell components have been studied and applied to aquatic animals as probiotics or immunostimulants (lipopolysaccharide, peptidoglycan, and 1-glucans) to enhance their innate immunity and antioxidant status, thereby enhancing their resistance to disease. In recent years, many studies have been conducted on the application of BFT for different farmed aquatic species and it has been observed as a promising method for the development of sustainable aquaculture, especially due to less use of water, increased productivity and biosecurity, but also an enhancement of the health status of several aquaculture species. This review analyses the immune status, antioxidant activity, blood and biochemical parameters, and level of resistance against pathogenic agents of aquatic animals farmed in BFT systems. This manuscript aims to gather and showcase the scientific evidences related to biofloc as a 'health promoter' in a unique document for the industry and academia.

Biofloc Technology in Fish Aquaculture: A Review

The application of biofloc to fish species has several advantages, including the enhancement of production by increasing growth performance and survival rate and the improvement of fish aquaculture physiological activity. There has been a recent increase in biofloc addition to fish culture, and this review examines changes this causes to the survival and growth rate of fish and its economic feasibility. Physiological activity and disease resistance of biofloc-fed fish is being extensively studied. The hematological parameters and antioxidant and immune responses of fish fed biofloc were reviewed in this study, as well as their disease resistance by testing them for major specific diseases. Standards for effectively applying biofloc to fish aquaculture are also suggested.

Molecular cloning and characteristic analysis of polymeric immunoglobulin receptor-like (plgRL) in large yellow croaker (Larimichthys crocea)

In the present study, the polyimmunoglobulin receptor-like (pIgRL) of large yellow croaker (Larimichthys crocea) was first cloned and characterized. LcpIgRL's full-length cDNA was 1610 bp, encoding 377 amino acids, and the protein's predicted molecular weight was 41.9 kDa, containing two immunoglobulin-like structural domains. The transcript levels of LcpIgRL in different tissues of healthy large yellow croaker were examined by real-time fluorescence quantitative PCR, and the results showed that the gills and head kidney had the highest levels. Within 36 h of the large yellow croaker being infected with Vibrio harveyi, pIgRL mRNA first increased and then decreased in all determined tissues, with the highest expression in the skin and hindgut. Furthermore, a recombinant protein of the extracellular region of LcpIgRL was expressed in E. coli BL21, and a murine rLcpIgRL polyclonal antibody was prepared, which could react specifically with the natural LcpIgRL in skin mucus, but no natural LcpIgRL was detected in serum. Meanwhile, it was found that the rLcpIgRL could bind to the recombinant IgM and the natural IgM, indicating that LcpIgRL could mediate the transport of IgM in mucus. In addition, rLcpIgRL binds to Aeromonas hydrophila and V. harveyi, as well as lipopolysaccharide (LPS) and various saccharides, and reduced binding to bacteria was observed under LPS treatment, suggesting that LcpIgRL can bind to bacteria to prevent infection and that saccharide binding is an important mechanism of interaction between pIgRL and bacteria.

Biofloc Microbiome With Bioremediation and Health Benefits

The biofloc system has recently attracted great attention as a cost-effective, sustainable, and environmentally friendly technology and expected to contribute toward human food security (Zero Hunger SDG 2). It is also expected that this endeavor can be adopted widely because of its characteristics of zero water exchange and reduced artificial feeding features. In the biofloc system, the flocs which are generally formed by aggregation of heterotrophic microorganisms, serve as natural bioremediation candidates. These microbes effectively maintain water quality by utilizing the nutrient wastes, mostly originated from digested, unconsumed, and metabolic processes of feed. Additionally, the flocs are important sources of nutrients, mainly a protein source, and when these are consumed by aquaculture animals they improve the growth performance, immunity, and disease tolerance of host against pathogenic microbial infection. Here in this review, we focus on recent advances that could provide a mechanistic insight on how the microbial community developed in the biofloc system helps in the bioremediation process and enhances the overall health of the host. We have also tried to address the possible role of these microbial communities against growth and virulence of pathogenic microbes.

Applications of Lysozyme, an Innate Immune Defense Factor, as an Alternative Antibiotic

Lysozyme is a ~14 kDa protein present in many mucosal secretions (tears, saliva, and mucus) and tissues of animals and plants, and plays an important role in the innate immunity, providing protection against bacteria, viruses, and fungi. Three main different types of lysozymes are known: the c-type (chicken or conventional type), the g-type (goose type), and the i-type (invertebrate type). It has long been the subject of several applications due to its antimicrobial properties. The problem of antibiotic resistance has stimulated the search for new molecules or new applications of known compounds. The use of lysozyme as an alternative antibiotic is the subject of this review, which covers the results published over the past two decades. This review is focused on the applications of lysozyme in medicine, (the treatment of infectious diseases, wound healing, and anti-biofilm), veterinary, feed, food preservation, and crop protection. It is available from a wide range of sources, in addition to the well-known chicken egg white, and its synergism with other compounds, endowed with antimicrobial activity, are also summarized. An overview of the modified lysozyme applications is provided in the form of tables.

Biofloc Technology: Emerging Microbial Biotechnology for the Improvement of Aquaculture Productivity

With the significant increases in the human population, global aquaculture has undergone a great increase during the last decade. The management of optimum conditions for fish production, which are entirely based on the physicochemical and biological qualities of water, plays a vital role in the prompt aquaculture growth. Therefore, focusing on research that highlights the understanding of water quality and breeding systems’ stability is very important. The biofloc technology (BFT) is a system that maximizes aquaculture productivity by using microbial biotechnology to increase the efficacy and utilization of fish feeds, where toxic materials such as nitrogen components are treated and converted to a useful product, like a protein for using as supplementary feeds to the fish and crustaceans. Thus, biofloc is an excellent technology used to develop the aquaculture system under limited or zero water exchange with high fish stocking density, strong aeration, and biota. This review is highlighted on biofloc composition and mechanism of system work, especially the optimization of water quality and treatment of ammonium wastes. In addition, the advantages and disadvantages of the BFT system have been explained. Finally, the importance of contemporary research on biofloc systems as a figure of microbial biotechnology has been emphasized with arguments for developing this system for better production of aquaculture with limited natural resources of water.