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Lactobacillus acidophilus is a probiotic commonly used in aquaculture to enhance the growth and immune system of aquatic species through the synthesis of various enzymes, and antimicrobial compounds like lactic acid. Traditional method of growing L. acidophilus involes using the De Man–Rogosa–Sharpe (MRS) medium. However, L. acidophilus belongs to a non-spore forming group, which make it vulnerable to stress conditions, especially during the usage process. Therefore, the present study aimed to improve the survival rate, antibacterial activity, and enrich the polyunsaturated fatty acids (PUFAs) content of L. acidophilus LB when cultured in an algae-supplemented medium, thus increasing its benefits in aquaculture applications. Using different algae biomass species as an alternative to MRS medium for the growth of L. acidophilus LB, the results showed that Spirulina platensis promoted the highest density of L. acidophilus LB. When grown in (S. platensis + glucose) medium, L. acidophilus LB produced the highest lactic acid concentration of 18.24 ± 2.43 mg/mL and survived in extreme conditions such as 4% NaCl, pH 1.0–2.0, and 50 ºC, and inhibited 99.82 ± 0.24% of Vibrio parahaemolyticus population after 2 days of treatment. Additionally, it was observed that the PUFAs content, specifically omega-6, and -7, also increased in the fermentation mixture as compared to the control sample. These findings highlighted the potential of utilizing the cyanobacteria S. platensis as an alternative, eco-friendly growth substance for L. acidophilus LB to enhance its bioactivity and viability under extreme conditions. [ABSTRACT FROM AUTHOR]

Ammonia and nitrite treatments are the critical steps that must be done to ensure the healthy growth of aquatic animals. The nitrification process is often used for nitrogen removal purposes due to its efficiency and environmentally friendly properties. However, the varied growth rate between ammonia and nitrite-oxidizing bacteria can cause nitrite accumulation, leading to the massive mortality of aquatic animals at high concentrations. Therefore, this study aimed to integrate the fast-growing heterotrophic nitrite-reducing bacteria with nitrifying bacteria to achieve a quicker nitrite removal activity. The two denitrifying Bacillus sp. ST20 and Bacillus sp. ST26 were screened from shrimp ponds in Bac Lieu province, Vietnam. Obtained results showed that under anoxic conditions, the nitrite removal efficiency of these two strains reached 68.5–82% at nitrite initial concentration of 20 mgN-NO2/L after 72 h. Higher efficiency of over 95% was gained under oxic conditions. Hence, it enabled the use of denitrifying and nitrifying bacteria-co-immobilized carriers for ammonia oxidation and nitrite reduction simultaneously in a single-aerated bioreactor. A total of over 96% nitrogen content was removed during the bioreactor operation, despite the increase of inputting nitrogen concentration from 40 to 200 mgN/L. Moreover, the suitable conditions for bacterial growth and nitrite conversion activity of the ST20 and ST26 were detected as 15‰ salinity and 35 °C. The isolates also utilized various C-sources for growth, hence widening their applicability. The present study suggested that the isolated aerobic denitrifying bacteria are potentially used for the complete removal of nitrogen compounds from aquaculture wastewater. [ABSTRACT FROM AUTHOR]