Bacillus amyloliquefaciens-modified clay for controlling harmful algal blooms in eutrophic aquaculture ponds.Production of Bacillus amyloliquefaciens-modified clay for eutrophic aquaculture ponds and its removal effect on typical HAB organisms, toward a healthy aquaculture ecosystem

Zaixing Wu Zhiming Yu ^* Xiuxian Song Kaiqin Jiang Xihua Cao Yongquan Yuan

• Institute of Oceanology, Chinese Academy of Sciences (CAS), Qingdao, China

Bacillus amyloliquefaciens is a commonly used probiotic microecological regulator in aquaculture water with the ability to inhibit harmful algae blooms (HABs) and improve the health status of aquaculture ecosystem. Modified clay has been widely applied in the field for eliminating HABs. In this study, clay particles are used as carriers and to provide a microenvironment for microbial fermentation, yielding a microbial modified clay product with high efficiency for eliminating typical HAB organisms. Methods are developed for the fermentation of microorganisms and clay particles and also for subsequent preparation of a dry powder, which stably produce microbial modified clay in dry powder form for HAB elimination. The results showed that the obtained microbial modified clay has a stable bacterial content of more than 10 9 cfu/mL, and the removal rate of the HAB organism Heterosigma akashiwo equivalent to that obtained with other HAB removal materials at the same dosage, indicating good potential for HAB removal. The removal rate of Heterosigma akashiwo at a dosage of 0.1 g/L microbial modified clay exceeded 90%. By combining two natural and commonly used material, both the function of emergency flocculation disposal (when HAB outbreaks) and long-term ecological regulation (to maintain a healthier phytoplankton community structure through specific algicidal effect) were achieved, resulting in a 1+1>2 effect when applied in the eutrophic aquaculture environment. Also this exploratory study with the unique combination of microbial fermentation and clay modification preliminarily provides an important scientific basis for promoting the large-scale application of microbial modified clay in the field of HAB control, especially in the eutrophic aquaculture ecosystems., even though Also, extensive ecological assessment before filed application is still required, such like the scientific support of environmental criteria, the safety to other aquaculture organisms and the ecological effect of the whole aquaculture ecosystem.