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　degrees　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　H2O2　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.