Pilot-Scale Fermentation of Pseudoalteromonas sp. Strain FDHY-MZ2: An Effective Strategy for Increasing Algicidal Activity

SIMPLE SUMMARY: Recently, the occurrence of harmful algal blooms (HABs) in coastal areas has increased rapidly, negatively impacting fishing resources, public health, and marine ecosystems. Certain microorganisms play a significant role in the termination of HABs. To exploit these algicidal bacteria effectively, it is imperative to amplify their algicidal ratio and devise efficient large-scale cultivation methods; however, research in these areas is underdeveloped. We previously identified Pseudoalteromonas sp. strain FDHY-MZ2, which exhibited significant algicidal activity against Karenia mikimotoi, a species globally acknowledged for forming HAB. To improve the algicidal efficacy of FDHY-MZ2, cultures were progressed from shaking flask conditions to small-scale (5 L) and pilot-scale fermentation (50 L). The optimal fermentation medium and conditions at a pilot-scale level were established, resulting in a substantial improvement in algicidal properties. This enhancement might be due to a rise in algal H(2)O(2) production accompanied by increased cell membrane disintegration, pronounced damage to cell chlorophyll and algal photosynthesis, and severe protein degradation. These findings provide new insights into the previously unknown potential of systematically applied microbial agents for the treatment of HABs. ABSTRACT: The role of microorganisms in effectively terminating harmful algal blooms (HABs) is crucial for maintaining environmental stability. Recent studies have placed increased emphasis on bio-agents capable of inhibiting HABs. The bacterium Pseudoalteromonas sp. strain FDHY-MZ2 has exhibited impressive algicidal abilities against Karenia mikimotoi, a notorious global HAB-forming species. To augment this capability, cultures were progressively scaled from shake flask conditions to small-scale (5 L) and pilot-scale (50 L) fermentation. By employing a specifically tailored culture medium (2216E basal medium with 1.5% soluble starch and 0.5% peptone), under precise conditions (66 h, 20 °C, 450 rpm, 30 L/min ventilation, 3% seeding, and constant starch flow), a notable increase in algicidal bacterial biomass was observed; the bacterial dosage required to entirely wipe out K. mikimotoi within a day decreased from 1% to 0.025%. Compared to an unoptimized shake flask group, the optimized fermentation culture caused significant reductions in algal chlorophyll and protein levels (21.85% and 78.3%, respectively). Co-culturing induced increases in algal malondialdehyde and H(2)O(2) by 5.98 and 5.38 times, respectively, leading to further disruption of algal photosynthesis. This study underscores the unexplored potential of systematically utilized microbial agents in mitigating HABs, providing a pathway for their wider application.