The application of probiotics in aquaculture has been proven to increase growth performance, food conversion and health status. It also increases disease resistance and decreases stress susceptibility.
Probiotics immobilized on oyster shell, vesuvianite and walnut shells have been shown to remediate nutrient-rich aquaculture water and sediment. They show improved effects on dissolved organic nitrogen and total nitrate in water and better effects on sediment parameters.
Remediation of Water and Sediment
Probiotics are live microorganisms that, when administered in adequate amounts, confer a health benefit on the host. As such, they have a wide range of applications in environmental remediation. By interfering with the development of pathogenic bacteria in your facility, they can help prevent and control contamination without the need for harsh chemicals.
Several studies have shown the effectiveness of dietary probiotics in the removal of heavy metals, such as mercury (Hg) and lead (Pb). They can significantly reduce Hg and Pb levels by promoting intestinal resorption, changing expression of metal transporter proteins, and increasing gut barrier function. They also enhance the resistance of aquatic organisms to challenge infections.
In addition, a number of probiotics have denitrification capabilities. They can increase the availability of nitrogen in the soil by converting ammonia-nitrogen (NH4-N) and nitrate-nitrogen (NO3-N) into nitrite-nitrogen (NO2-N). They can also lower the concentrations of phosphorus, chemical oxygen demand, total nitrogen and dissolved organic carbon.
The immobilization of probiotics is essential for achieving better results in environmental remediation. It increases the biodegradation rate, improves control of the biological process, and increases the stability of the immobilized microorganisms. Moreover, it allows the reuse of immobilized biomass in subsequent treatments. In this study, NY5 was immobilized on oyster shells, vesuvianite, and walnut shells. SEM observations were performed to visualize the carrier structure and immobilized bacteria.
Remediation of Sewage Sludge
Probiotics are effective microbial agents for bioremediation and have been demonstrated to improve the health and performance of aquatic organisms by altering their gut microbiota. A number of studies have also shown that probiotics can stimulate the synthesis of some major physiological processes. For instance, probiotics can stimulate growth in European seabass by enhancing insulin-like growth factor (IGF) I mRNA transcription and activating the expression of antioxidative enzymes such as superoxide dismutase, catalase, and glutathione peroxidase. Probiotics can also increase stress tolerance in corals by decreasing the concentration of the hormone cortisol and promoting the production of antioxidant proteins (Zolotukhin, Prazdnova, & Chistyakov, 2018).
The use of immobilized probiotics in aquaculture pond environments provides an eco-friendly and economically viable way to reduce organic wastes in the pond water and sediment and improve the water quality. However, it is challenging to immobilize probiotics in aqueous media because they are susceptible to being washed out of the system. In addition, the selection of the ideal immobilization carrier is also crucial to minimize washed-out probiotics and achieve a stable effect.
One of the best strategies to immobilize probiotics is to use low-cost and abundant agricultural byproducts as the immobilization carriers. For example, waste oyster shells can be used to immobilize probiotics because they are rich in humic acids and able to effectively degrade organic waste in aquaculture ponds (Banerjee et al. 2018). Similarly, walnut shells are an excellent adsorbent for Cr (Banerjee et. al. 2018) and Cd (Qiu et al. 2019).
Remediation of Food Waste
Probiotics can act as natural technology to detoxify environmental contaminants. This xenobiotic bioremediation capacity involves the natural metabolic pathways of these microorganisms to degrade and reduce heavy metals in the environment. These microorganisms can also remove organic contaminants by enzymatic reactions or physical sequestration. In addition, these microorganisms can produce a variety of compounds including propionate and acetic acid that have strong antimicrobial activity against pathogenic bacteria (Caulier et al., 2019).
These characteristics make them an attractive tool for the remediation of food waste. For example, probiotic bacteria can reduce the concentration of metabolites such as ammonia and nitrate in water and sediment through denitrification. These microorganisms can also produce bacteriocins and other antibiotics that inhibit the growth of certain pathogens. They can also synthesize fatty acids such as butyrate, which can enhance gut health and immune system function.
Probiotics can also enhance the performance of aquatic organisms, such as reducing stress and improving gonad development in European seabass. In addition, dietary probiotic supplementation of Lactobacillus rhamnosus improves gut microbiota and promotes growth and condition in Senegalese sole larviculture ponds.
Remediation of Waste Water
Probiotics can be an effective alternative to harsh chemicals in the cleaning of food processing facilities and aquaculture ponds. In addition to sanitizing and disinfecting, probiotics can also inhibit and remediate pathogen contamination within facilities by interfering with the development of biofilms.
A number of research studies have shown that dietary probiotics improve the growth performance and immune responses of fish. For example, the probiotic Shewanella putrefaciens Pdp11 enhances the growth of Nile tilapia (Oreochromis niloticus). In other experiments, a dietary supplementation with the probiotic Shewanella licheniformis improved intestinal morphology and resistance to challenge infections in a white shrimp (Litopenaeus vannamei) culture.
However, these results are limited as the microbial manipulating ability of commercial probiotics depends on external/environmental factors such as water quality, temperature and pH. Moreover, the efficacy of a probiotic can also depend on fish age, binding strength of the microbe to gut mucosal surface, and the duration of the probiotic dietary supplementation.
Therefore, it is necessary to develop a method for immobilizing probiotics to improve the environmental remediation efficiency of these bacteria. The aim of the present study was to use oyster shells, vesuvianite and walnut shells as immobilized carriers for probiotics and test their remediation effects on aquaculture water and sediment. High-throughput sequencing showed that the immobilized probiotics significantly enhanced the bacterial community composition in both water and sediment. The relative abundances of phyla detected by 16S rRNA analysis in the water and sediment samples treated with the immobilized probiotics were higher than those in the control sample.