Multi-Strain Tropical Bacillus spp. as a Potential Probiotic Biocontrol Agent for Large-Scale Enhancement of Mariculture Water Quality

Wei Ren; Haiwu Wu; Cong Guo; Bingqing Xue; Hao Long; Xiang Zhang; Xiaoni Cai; Aiyou Huang; Zhenyu Xie

doi:10.3389/fmicb.2021.699378

Multi-Strain Tropical Bacillus spp. as a Potential Probiotic Biocontrol Agent for Large-Scale Enhancement of Mariculture Water Quality

Front Microbiol. 2021 Aug 11:12:699378. doi: 10.3389/fmicb.2021.699378. eCollection 2021.

Authors

Wei Ren^{1

2

3

4}, Haiwu Wu^{2

3}, Cong Guo^{2

3}, Bingqing Xue^{2

3}, Hao Long^{1

2

3

4}, Xiang Zhang^{1

2

3

4}, Xiaoni Cai^{1

2

3

4}, Aiyou Huang^{1

2

3

4}, Zhenyu Xie^{1

2

3

4}

Affiliations

¹ State Key Laboratory of Marine Resource Utilization in the South China Sea, Hainan University, Haikou, China.
² Hainan Provincial Key Laboratory for Tropical Hydrobiology and Biotechnology, Hainan University, Haikou, China.
³ College of Marine Sciences, Hainan University, Haikou, China.
⁴ Laboratory of Development and Utilization of Marine Microbial Resource, Hainan University, Haikou, China.

Abstract

Aquaculture is suffering from long-term water eutrophication in intensive models, whereas the knowledge of multi-strain/specie for improving water quality is extremely limited. Herein, we aimed to develop multi-strain tropical Bacillus spp. as a potential probiotic biocontrol agent for large-scale enhancement of mariculture water quality. Given the practical application, the optimum multi-strain tropical Bacillus spp. (B. flexus QG-3, B. flexus NS-4, and B. licheniformis XCG-6 with the proportion 5: 5: 4) as a probiotic biocontrol agent was screened and obtained, which effectively improved water quality by removing chemical oxygen demand (COD), ammonia-nitrogen, and nitrate and significantly inhibited Vibrio spp. even at relatively low bacterial concentrations (10⁴ CFU/ml) in artificial feed wastewater and large-scale shrimp aquaculture ponds. More importantly, we found that the initial proportion of these three Bacillus sp. strains of multi-strain tropical Bacillus spp. markedly affected the final purification effects, whereas the initial concentration of that only influenced the purification rates at the early stage (0-48 h) instead of final purification effects. We reason that this multi-strain tropical Bacillus spp. as a good probiotic biocontrol agent could perform multiple actions, such as COD-degrading, nitrifying, denitrifying, and antagonistic actions, for large-scale enhancement of tropical aquaculture water. Additionally, the multi-strain tropical Bacillus spp. was safe for shrimp and could be stored for at least 240 days in spore form at room temperature. This multi-strain probiotic biocontrol agent may facilitate its adoption for further marine recirculating aquaculture system development and large-scale commercial application.

Keywords: aquaculture wastewater; mariculture water quality; marine recirculating aquaculture system; multi-strain tropical Bacillus spp.; probiotic biocontrol agent.