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Elucidating the symbiotic interactions between a locally isolated microalga Chlorella vulgaris and its co-occurring bacterium Rhizobium sp. in synthetic municipal wastewater
Umeå University, Faculty of Science and Technology, Department of Chemistry. Department of Chemical Engineering and Environmental Technology, School of Industrial Engineering, University of Valladolid, Valladolid, Spain.ORCID iD: 0000-0002-9481-8537
Umeå University, Faculty of Science and Technology, Department of Chemistry.
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2019 (English)In: Journal of Applied Phycology, ISSN 0921-8971, E-ISSN 1573-5176, Vol. 31, no 4, p. 2299-2310Article in journal (Refereed) Published
Abstract [en]

Co-cultivation of microalgae and bacteria during municipal wastewater treatment can boost carbon and nutrient recovery as a result of their synergistic interactions. The symbiotic relationships between the locally isolated microalga Chlorella vulgaris and the bacterium Rhizobium sp., co-isolated from municipal wastewater, were investigated batchwise under photoautotrophic, heterotrophic, and mixotrophic conditions in a synthetic municipal wastewater medium. During photoautotrophic growth in BG11 medium, photosynthetic algal oxygenation and organic carbon production supported bacterial activity but no significant beneficial effects on microalgal growth were observed. In synthetic wastewater, a twofold higher biomass concentration was achieved in the axenic algal culture compared with the co-culture under heterotrophic conditions, suggesting a competition for nutrients. A comparable carbon removal was observed in all cultures (83–79% TOC), but a faster nitrogen consumption (59% TN) and complete phosphate assimilation (100% TP) was only achieved in the co-culture. A positive synergistic relationship was found under mixotrophic conditions, clearly supported by an in situ O2/CO2 exchange between the microorganisms. This mutualism led to a threefold higher biomass production with a 13-fold higher fatty acid content compared with the axenic algal culture, as well as a superior wastewater treatment performance (+ 58% TOC, + 41% TN and + 44% TP). The co-cultivation of C. vulgaris and Rhizobium is therefore suggested as a potential microbial consortium for a cost-efficient biomass generation during municipal wastewater reclamation, especially under mixotrophic conditions.

Place, publisher, year, edition, pages
Springer, 2019. Vol. 31, no 4, p. 2299-2310
Keywords [en]
Chlorella vulgaris, Rhizobium, Symbiosis, Mixotrophy, Heterotrophy, Wastewater treatment
National Category
Microbiology Oceanography, Hydrology and Water Resources
Identifiers
URN: urn:nbn:se:umu:diva-156463DOI: 10.1007/s10811-019-1741-1ISI: 000479057200012OAI: oai:DiVA.org:umu-156463DiVA, id: diva2:1289185
Funder
Swedish Energy Agency, 476 38239-1Swedish Research Council Formas, 942-2015-92Available from: 2019-02-15 Created: 2019-02-15 Last updated: 2019-08-30Bibliographically approved
In thesis
1. Wastewater treatment and biomass generation by Nordic microalgae: growth in subarctic climate and microbial interactions
Open this publication in new window or tab >>Wastewater treatment and biomass generation by Nordic microalgae: growth in subarctic climate and microbial interactions
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nordic native microalgal strains were isolated, genetically classified and tested for their ability to grow in municipal wastewater. Eight of the isolated strains could efficiently remove nitrogen and phosphate in less than two weeks. Two of these strains, Coelastrella sp. and Chlorella vulgaris, were found to have high biomass concentration and total lipid content; also two Desmodesmus sp. strains showed desirable traits for biofuel-feedstock, due to their fast growth rates and high oil content.

The adaptation to subarctic climate was comparatively evaluated in three Nordic strains (C. vulgaris, Scenedesmus sp. and Desmodesmus sp.) and a collection strain (S. obliquus). Their growth performance, biomass composition and nutrients removal was investigated at standard (25°C) or low temperature (5°C), under continuous light at short photoperiod (3 h light, 25°C) or moderate winter conditions (6 h light, 15°C). Only the Nordic strains could grow and produce biomass at low temperature, and efficiently removed nitrogen and phosphate during both cold- and dark-stress. Phenotypic plasticity was observed in Scenedesmus and Desmodesmus under different growth conditions, adaptation to low temperature increased their carbohydrate content. Short photoperiod strongly reduced growth rates, biomass and storage compounds in all strains and induced flocculation in C. vulgaris, which, however, performed best under moderate winter conditions.

The symbiotic relationships between the Nordic microalga C. vulgaris and the naturally co-occurring bacterium Rhizobium sp. were investigated batchwise under photoautotrophic, heterotrophic and mixotrophic conditions, comparing the co-culture to the axenic cultures. The photoautotrophic algal growth in BG11 medium mainly supported Rhizobium activity in the co-culture, with no significant effects on C. vulgaris. In synthetic wastewater, a synergistic interaction only occurred under mixotrophic conditions, supported by CO2/O2 exchange and a lower pH in the culture, resulting in higher biomass and fatty acids content and more efficient wastewater treatment in the co-culture. Under heterotrophic conditions, the lower biomass production in the co-culture suggested a competition for nutrients, although nutrients removal remained efficient.

A pilot-scale high rate algal pond (HRAP) located in Northern Sweden was inoculated with the collection strain Scenedesmus dimorphus UTEX 417 and operated from spring to autumn. Using metabarcoding of 18S and 16S rRNA genes, the microbial diversity of eukaryotic and prokaryotic communities was revealed. S. dimorphus was initially stable in the culture, but other microalgal species later colonized the system, mainly due to parasitic infections and predation by zooplankton in summer. The main competitor algal species were Desmodesmus, Pseudocharaciopsis, Chlorella, Characium and Oocystis. Proteobacteria, Firmicutes, Bacteroidetes and Actinobacteria were the most abundant bacterial phyla in the HRAP. The structure of the microbial communities followed a seasonal variation and partially correlated to environmental factors such as light, temperature and nutrients concentrations.

Overall, these results contribute with new knowledge on the establishment and optimization of microalgal-based wastewater treatment systems coupled with biomass generation in Nordic areas. The use of native microalgal species is proposed as a potential strategy to overcome the limitations posed to algal cultivation in subarctic regions.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2019. p. 75
Keywords
Microalgae, Wastewater, Nitrogen, Phosphate, Biomass, Lipids, Subarctic Climate, Light, Temperature, Bacteria, Photoautotrophy, Heterotrophy, Mixotrophy, HRAP, Metabarcoding, Microbial Communities, Alpha-diversity, Environmental Factors
National Category
Microbiology Other Biological Topics Biochemistry and Molecular Biology Chemical Sciences
Research subject
Biochemistry; Microbiology
Identifiers
urn:nbn:se:umu:diva-156470 (URN)978-91-7855-014-2 (ISBN)
Public defence
2019-03-15, Carl Kempe salen (KB.E3.03), KBC-huset, Umeå, 10:00 (English)
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Supervisors
Available from: 2019-02-22 Created: 2019-02-15 Last updated: 2019-02-21Bibliographically approved

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Ferro, LorenzaFunk, Christiane

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