Effect of removal of bacteria on the biomass and extracellular carbohydrate productivity of Botryococcus braunii

Joao D Gouveia,Lolke Sijtsma,Detmer Sipkema,Yvonne Griekspoor,Antoine Moers,Rene H Wijffels,Jan Springer,Maria J Barbosa,Lambertus A M Van Den Broek

doi:10.1007/s10811-019-01847-0

Abstract

Botryococcus braunii CCALA778 is a green microalga that can produce large amounts of extracellular carbohydrates and therefore is a potential host for industrial applications such as materials, food and pharmaceutical products. The downside of B. braunii is its slow growth and therefore, improvements on the biomass productivity or carbohydrate production will make this microalga more attractive for industrial exploitation. Microalgae grow naturally in the presence of bacteria and these can be beneficial or antagonistic. In outdoor cultivation systems, contamination by bacteria is common. The role or effects of bacteria present in B. braunii CCALA778 are not yet fully elucidated. We used UV-C treatment to reduce bacterial abundance in B. braunii CCALA778 cultures and 16S rRNA gene amplicon MiSeq sequencing for bacterial community analysis. The effect of the reduced amount of bacteria on biomass growth and production of extracellular carbohydrates was analysed. It is shown that UV-C treatment can reduce the bacterial population substantially without harming B. braunii. Bacteria removed by UV-C were antagonistic to B. braunii CCALA778 as in their absence production of biomass and extracellular carbohydrates was enhanced significantly. CCALA778 treated with UV-C accumulated 826 ± 61 mg L−1 of extracellular carbohydrates by day 15 compared with 422 ± 135 mg L−1 accumulated extracellular carbohydrates in the untreated culture.

Highlights

Botryococcus braunii is a green microalga that can produce long-chain hydrocarbons and high amounts of extracellularElectronic supplementary material The online version of this article contains supplementary material, which is available to authorized users.Botryococcus braunii is a colony-forming microalga found in fresh and brackish water across the world
In both untreated and UV-C treated (UV)+Bac treated CCALA778 at days 0 and 15, the dominant phylum was Proteobacteria followed by Bacteroidetes, with the exception of one replicate of UV treated with added bacteria (UV+Bac) treated CCALA778 at day 0 in which the abundance of Bacteroidetes was higher than Proteobacteria
For the UV treated CCALA778, we observed the disappearance of 3 bacteria species detected at day 0 and the appearance of 3 new ones in lower relative abundance compared with the 3 species found at day 0

Summary

Introduction

Botryococcus braunii is a green microalga that can produce long-chain hydrocarbons and high amounts of extracellular. Botryococcus braunii is a colony-forming microalga found in fresh and brackish water across the world. Depending on what type of hydrocarbons are produced, B. braunii is subclassified into four chemical races, designated A, B, L and S (Kawachi et al 2012). Some strains of B. braunii can produce up to 86% hydrocarbons on biomass dry weight basis (Brown et al 1969), whereas the carbohydrate producing strains can produce up to 4.5 g L−1 of exopolysaccharides (EPS) into the medium. The EPS from B. braunii is mainly composed of galactose and minor quantities of other sugars as fucose, rhamnose, glucose and uronic acid residues The drawback of B. braunii is that it is a slowgrowing microorganism and it is not currently attractive for industrial applications

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