Abstract
Open algal cultivation platforms often suffer crop losses to herbivorous grazers that have potential to devastate biomass production within a few days. While a number of studies suggest synthetic chemicals as control agents for voracious algal grazers, environmental and safety concerns associated with the use of these chemicals encourage the exploration of alternative biological control agents. We hereby propose the application of a biosurfactant produced by Bacillus subtilis C9 (referred to as C9-biosurfactant) for controlling cladoceran grazers commonly found in algal cultivation systems. The results indicated that C9-biosurfactant completely eradicated Daphnia pulex and Moina macrocopa within 24 hours when concentrations were equal to or exceeded 6 mg/L. Moreover, supplying C9-biosurfactant into the cultures of selected algal species with and without cladoceran grazers indicated no adverse effect of C9-biosurfactant on the growth and lipid productivity of algal crops, while cladocerans were selectively controlled by C9-biosurfactant even under the presence of their prey. These results thus indicate that C9-biosurfactant could be an effective biocontrol agent for cladoceran grazers at industrial algal cultivation.
Highlights
Open algal cultivation platforms often suffer crop losses to herbivorous grazers that have potential to devastate biomass production within a few days
A one-year-long operation of wastewater-fed open algal ponds experienced repeated outbreaks of cladoceran Daphnia, and it was subsequently confirmed in laboratory that this cladoceran grazer imposed 12.5–87.87% reductions in the dry cell weight (DCW) of common microalgal strains found in outdoor open ponds[14]
Our subsequent mass spectrometry analysis of C9-biosurfactant exhibited the highest peak at m/z 1058.67, where the highest peak of HPLC-grade surfactin from B. subtilis was observed (Fig. S1)
Summary
Open algal cultivation platforms often suffer crop losses to herbivorous grazers that have potential to devastate biomass production within a few days. Supplying C9biosurfactant into the cultures of selected algal species with and without cladoceran grazers indicated no adverse effect of C9-biosurfactant on the growth and lipid productivity of algal crops, while cladocerans were selectively controlled by C9-biosurfactant even under the presence of their prey. These results indicate that C9-biosurfactant could be an effective biocontrol agent for cladoceran grazers at industrial algal cultivation. Sustainable cost-effective strategies that control growth and proliferation of grazing zooplanktons in algal cultivation platforms without the use of synthetic chemicals are needed[17,26,27,28,29,30]
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