Abstract
Contamination by the predatory zooplankton Poterioochromonas malhamensis is one of the major threats that causes catastrophic damage to commercial-scale microalgal cultivation. However, knowledge of how to manage predator contamination is limited. Previously, we established a phosphite (Pt)-based culture system by engineering Synechococcus elongatus, which exerted a competitive growth advantage against microbial contaminants that compete with phosphate source. Here, we examined whether Pt is effective in suppressing predator-type contamination. Co-culture experiment of Synechococcus with isolated P. malhamensis revealed that, although an addition of Pt at low concentrations up to 2.0 mM was not effective, increased dosage of Pt (~20 mM) resulted in the reduced grazing impact of P. malhamensis. By using unsterilized raw environmental water collected from rivers or ponds, we found that the suppression effect of Pt was dependent on the type of environmental water used. Eukaryotic microbial community analysis of the cultures using environmental water samples revealed that Paraphysomonas, a colorless Chrysophyceae, emerged and dominated under high-Pt conditions, suggesting that Paraphysomonas is insensitive to Pt compared to P. malhamensis. These findings may provide a clue for developing a strategy to reduce the impact of grazer contamination in commercial-scale microalgal cultivation.
Highlights
Photosynthetic microalgae have drawn great attention due to their ability to produce lipids, proteins, and other value-added chemicals from CO2 [1]
We investigated the effect of Pt on predation of P. malhamensis and showed that the increased dose of Pt in Syn 7942 culture could mitigate the predation impact of P. malhamensis
To check whether predatory protists inhabiting environmental sample affect growth performance of cyanobacteria when they were co-cultured, 25 environmental water samples were collected from 10 different locations in the local rivers and ponds at HigashiHiroshima, Hiroshima, Japan
Summary
Photosynthetic microalgae have drawn great attention due to their ability to produce lipids, proteins, and other value-added chemicals from CO2 [1]. Their commercial application is expected to sequester 513 t of atmospheric CO2 and to produce more than 120 t of dry biomass per hectare annually [2]. The predator-type contamination often results in catastrophic damages called “pond crush”, in which predator zooplanktons quickly outcompete microalgae-preyed cells [5,6,7]. Only limited microalgae strains that can grow under harsh conditions, such as high salinity (Dunaliella) and high pH conditions (Spirulina), have been demonstrated as monocultures in an open-pond culture system [3,5]
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