Bacterial diversity in different outdoor pilot plant photobioreactor types during production of the microalga Nannochloropsis sp. CCAP211/78

Jie Lian,Detmer Sipkema,Jeroen De Vree,Sven Meijer,Georg Steinert,Christa Heryanto,René H Wijffels,Hauke Smidt,Rouke Bosma,Maria J Barbosa

doi:10.1007/s00253-022-11815-3

Jie Lian, Detmer Sipkema + Show 8 more

Open Access

https://doi.org/10.1007/s00253-022-11815-3

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Abstract

As large-scale outdoor production cannot be done in complete containment, cultures are (more) open for bacteria, which may affect the productivity and stability of the algae production process. We investigated the bacterial diversity in two indoor reactors and four pilot-scale outdoor reactors for the production of Nannochloropsis sp. CCAP211/78 spanning four months of operation from July to October. Illumina sequencing of 16S rRNA gene amplicons demonstrated that a wide variety of bacteria were present in all reactor types, with predominance of Bacteroidetes and Alphaproteobacteria. Bacterial communities were significantly different between all reactor types (except between the horizontal tubular reactor and the vertical tubular reactor) and also between runs in each reactor. Bacteria common to the majority of samples included one member of the Saprospiraceae family and one of the NS11-12_marine group (both Bacteroidetes). Hierarchical clustering analysis revealed two phases during the cultivation period separated by a major shift in bacterial community composition in the horizontal tubular reactor, the vertical tubular reactor and the raceway pond with a strong decrease of the Saprospiraceae and NS11-12_marine group that initially dominated the bacterial communities. Furthermore, we observed a less consistent pattern of bacterial taxa appearing in different reactors and runs, most of which belonging to the classes Deltaproteobacteria and Flavobacteriia. In addition, canonical correspondence analysis showed that the bacterial community composition was significantly correlated with the nitrate concentration. This study contributes to our understanding of bacterial diversity and composition in different types of outdoor reactors exposed to a range of dynamic biotic and abiotic factors.Key points• Reactor types had significantly different bacterial communities except HT and VT• The inoculum source and physiochemical factors together affect bacterial community• The bacterial family Saprospiraceae is positively correlated to microalgal growth

Highlights

Microalgae are one of the most promising feedstocks for production of food, feed, biofuels and other valuable chemicals (Stephens et al 2010; Wijffels and Barbosa 2010)
After removal of chloroplast Operational Taxonomic Unit (OTU) from the dataset, 980 bacterial OTUs were used for bacterial diversity analyses
The other eight phyla together only contributed to a minor part of total bacterial reads in all reactors, which was approximately 1.2% in the vertical tubular reactor (VT) and less than 1% in other reactors

Summary

Introduction

Microalgae are one of the most promising feedstocks for production of food, feed, biofuels and other valuable chemicals (Stephens et al 2010; Wijffels and Barbosa 2010). The high performance of algal strains in the laboratory can hardly be accomplished in large-scale outdoor cultivation systems because of varying ambient conditions, including physicochemical and biological factors (Wen et al 2016). Both open and closed outdoor algae production systems cannot be operated strictly axenically and are prone to microbial contamination. This is a substantial discrepancy compared to laboratory-based studies where whole reactors can be autoclaved. Relatively little attention is paid to the bacteria present in algal photobioreactors and to their effects on algal cultivation (Lian et al 2018)

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