Eliminating the ecological hazards of Heterosigma akashiwo bloom by a microbial algicide: removal of nitrite contamination, redirection of carbon flow and restoration of metabolic generalists.

Abstract

Harmful algal blooms (HABs) attracted much attention due to their extensive ecological hazards and the increasing influences on global biogeochemical cycles with the intensification of human impact and global warming. Lysing algal cells with species-specific microbial algicide seemed to be promising to eliminate HABs, but the potential ecotoxicity was rarely studied. In this study, microcosms simulating Heterosigma akashiwo blooms were established to reveal the influences of a microbial algicide from Streptomyces sp. U3 on the biological, physicochemical parameters and bacterial community. The results showed that H. akashiwo bloom accumulated nitrite to a lethal dose, produced bio-labile DOM with widespread influences and enriched pathogenic Coxiella to a high abundance. Lysing H. akashiwo cells by microbial algicide induced a bacterial bloom, eliminated nitrite contamination, enhanced the recalcitrance of DOM, and restored bacterial population from a Gammaproteobacteria-dominant community during bloom back to an Alphaproteobacteria-dominant community similar to the non-bloom seawater. Succession of bacterial genera further suggested that the variation from algal exudates to lysates promoted the restoration of metabolic generalists, which redirected the carbon flow to a less ecologically impactive path. This study revealed the benefits of using microbial algicide to remediate the ecological hazards of HABs, which provided references for future application.