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

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

A closer look into the microbiome of microalgal cultures

“…In their study, they used P. tricornutum strain CCAP 1052/1B, which is a deposition of strain U640, and interestingly the bacterial community composition was very different to the ones observed in our study. In a study of Lian et al (2022) the bacterial community composition in different pilot-scale photobioreactors producing Nannochloropsis sp. was shown to correlate significantly with the nitrate concentration, and Tait et al (2019) observed a shift in the bacterial community composition associated with a freshwater Chlorella sp .…”

Large-Scale Integration of Amplicon Data Reveals Massive Diversity within Saprospirales, Mostly Originating from Saline Environments

“…Saprospirales can indeed be found in various environments, such as saline water, freshwater, soil, bioreactors, and wastewater treatment plants, as has been already mentioned in various studies [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ]. In addition, air, plants, as well as terrestrial and saline water hosts are also potential environments for Saprospirales.…”

“…In the last two decades, numerous studies have reported the presence of bacteria belonging to the order of Saprospirales in various artificial and natural ecosystems. Bacteria belonging to Saprospirales can be found in natural ecosystems such as marine and freshwater environments, and soils [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ]. Furthermore, several studies have reported that Saprospirales members can be found in wastewater treatment plants, and especially in activated sludge and anaerobic ammonium oxidation reactors [ 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ].…”

The Impact of Nutrient Limitation and Harvest Method on the Wet Preservation of Chlorella vulgaris Biomass

“…The nitrate concentration, for instance, was suggested to be a primary driver in the bacterial community composition of outdoor Nannochloropsis sp. cultures [18]. Finally, several studies indicated that nutrient depletion may also increase the algal production of extracellular polymeric substances (EPS), another possible fermentation substrate.…”