Protection of algae grown for biofuel using a consortium of environmentally harvested bacteria
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Abstract
Crop loss due to infection by pests and pathogens is a major barrier to the large-scale production of algal biofuels. Test systems have seen loss of green algae crops due to infection by the fungus-like Amoeboaphelidium occidentale FD01. While current antifungal compounds are effective in inhibiting the infection, their application raises the overall cost of the crop and lowers its economic viability as a biofuel source. Here we show that co-culturing environmentally harvested bacteria alongside algae crops can drastically lower the rate of infection in two different green algae species of interest for biofuel production. These bacteria-algae consortia increase the mean time to crop failure (MTTF) by up to 350% when tested under environmentally relevant conditions. While there was an increase in diversity over time, there was no statistically significant correlation between an increase in diversity and a longer MTTF. Community composition analysis reveals similarities between the bacterial genera growing alongside both green algae species even as bacterial harvest locations differed, although there was not a single dominant genus responsible for the increase in crop protection. These results show a promising new method of anti-fungal crop protection that can be applied to algal biofuels with no increase in fuel cost.
Highlights
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Bacteria-algal cocultures protect against fungal pests without impact to productivity
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Bacterial community composition is variable over time even as protection persists
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Bacterial consortia can increase mean time to failure by 350%
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I'm curious whether you have any insight into where in the infection cycle the bacterial protection is actually acting? Since aphelids are obligate intracellular parasites that have to physically attach to and penetrate the algal cell wall, there are a few pretty distinct points where bacteria could be intervening, disrupting zoospore motility or chemotaxis, blocking cell wall attachment, or producing antifungal compounds that inhibit development post-penetration. These would have pretty different implications for how stable and generalizable the protection is.
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Conclusions
Great work! The core finding that environmental bacterial consortia can meaningfully delay pond crashes is really promising for large, outdoor cultivation. One thing I kept wondering about as I read through: have you looked at whether the bacterial co-culture (or the aphelid infection itself) affects lipid accumulation in the algae? Some of the Rhizobiaceae you're seeing enriched have been shown to boost fatty acid production, but high-stress conditions like infection are also known to push microalgae toward lipid accumulation, so bacterialized vs unbacterialized cultures might look similar by biomass but be pretty different in terms of actual fuel yield. A quick Nile Red screen across your conditions might be really informative. Have you thought about following up on this?
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