Novel biological method for controlling bacterial contaminants using the ciliate Colpoda sp. HSP-001 in open pond algal cultivation

Abstract

Outdoor algal cultivation is frequently limited by bacterial contaminants. The aim of this study was to develop a biological control technique for removing bacterial contaminants using a small-size ciliate. During the cultivation of Chlorella sp. HS2 in a designed raceway pond, the bacterial population was significantly reduced by the ciliate strain. 18S rDNA analysis identified the ciliate as Colpoda sp. HSP-001. To verify selective bacterial grazing by the ciliate, an isolated phycospheric bacterium Microbacterium sp. was co-cultivated with Chlorella sp. HS2 while varying the ciliate cell concentrations. Colpoda sp. efficiently eliminated bacterial cells, whereas no algal grazing was observed by fluorescence microscopy. Based on the results, the utilization of Colpoda sp. HSP- 001 in an outdoor algal cultivation system is a cost-effective strategy for controlling bacterial contamination without degrading the algal biomass.