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Guardians of green gold: exploring microalgal cell walls and their significance in industrial processing
Umeå University, Faculty of Science and Technology, Department of Chemistry.
2024 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Väktare av grönt guld : utforskning av mikroalgers cellväggar och deras betydelse i industriell bearbetning (Swedish)
Abstract [en]

Microalgae are a remarkable source of high-value compounds. They can rapidly and efficiently produce proteins, lipids, antioxidants, omega-3s, pigments and many other compounds that are of great interest to pharmaceutical, cosmetic, food, feed, and fuel industries. Their fast growth rate, lack of need for fertile land, and their ability to capture carbon more efficiently than higher plants, further highlights their immense potential.

However, microalgal cells are surrounded by a thick and robust cell wall that hampers the extraction of compounds of interest. Furthermore, the interaction of the cell wall with its environment greatly impacts algal harvesting. Despite their significant role in downstream processing, there is a lack of knowledge about algal cell walls, and specifically about their structure and composition. This thesis aimed to address this knowledge gap by studying the cell walls of various Nordic microalgal strains and their involvement in harvesting (paper II), extraction (paper I), and nutrient removal processes (paper IV). This research aims to mitigate the monetary and energetic costs that are currently hindering the microalgal industry from reaching its full potential.

This thesis shows that cell walls vary not only with the algal strain (paper I) but also with growth phases (paper I) and growth conditions (paper III). The plasticity of the cell wall means that its composition cannot be defined per se. However, this thesis describes methodologies and techniques that can be used for cell wall characterization and visualization for future researchers that would like to investigate the cell walls of their own algal strains under varying conditions. Characterization techniques used in this thesis include Fourier Transform Infrared Spectroscopy (FTIR), Cryogenic-X-ray photoelectron spectroscopy (Cryo-XPS), Transmission electron microscopy (TEM), Scanning electron microscopy (SEM) and Gas Chromatography- Mass spectrometry (GC-MS).

Place, publisher, year, edition, pages
Umeå: Umeå University, 2024. , p. 79
Keywords [en]
Microalgae, cell wall, algal harvesting, compound extraction, cell wall composition, biotechnology, biochemistry
National Category
Biochemistry and Molecular Biology Chemical Sciences
Identifiers
URN: urn:nbn:se:umu:diva-224011ISBN: 978-91-8070-358-1 (print)ISBN: 978-91-8070-359-8 (electronic)OAI: oai:DiVA.org:umu-224011DiVA, id: diva2:1856261
Public defence
2024-05-30, Stora Hörsalen, KBC, 10:00 (English)
Opponent
Supervisors
Available from: 2024-05-08 Created: 2024-05-06 Last updated: 2024-05-06Bibliographically approved
List of papers
1. Detailed Characterization of the Cell Wall Structure and Composition of Nordic Green Microalgae
Open this publication in new window or tab >>Detailed Characterization of the Cell Wall Structure and Composition of Nordic Green Microalgae
2022 (English)In: Journal of Agricultural and Food Chemistry, ISSN 0021-8561, E-ISSN 1520-5118, Vol. 70, no 31, p. 9711-9721Article in journal (Refereed) Published
Abstract [en]

Green microalgae are attractive to food, pharmaceutical, and biofuel industries due to the promising and diverse properties of their intracellular components. In current biotechnological applications, however, clear bottlenecks are the cell disruption and cell harvesting steps. Challenges in both of these processes are directly linked to the properties of the microalgal cell wall. The aim of this study was to explore the cell wall compositions and morphologies of four Nordic microalgal strains (Chlorella vulgaris (13-1), Scenedesmus sp. (B2-2), Haematococcus pluvialis, and Coelastrella sp. (3-4)) and their changes in relation to logarithmic and stationary growth phases. Transmission electron microscopy imaging enabled us to visualize the cell walls and to observe structural elements such as spines, microfibrillar hairs, or layers. Using cryogenic X-ray photoelectron spectroscopy, we quantified lipid, protein, and polysaccharide content of the outer surface of the microalgal cell wall in cultures. Fourier transform infrared spectroscopy highlighted changes between growth phases within the polysaccharide and protein fractions of the cell wall. Very prominent differences were observed in sugar and protein composition of the Scenedesmus sp. (B2-2) cell wall compared to the cell walls of the other three Nordic strains using trimethylsilyl derivatization.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2022
Keywords
cell wall, cryo-XPS, FTIR, imaging, microalgae
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:umu:diva-198732 (URN)10.1021/acs.jafc.2c02783 (DOI)000834288300001 ()35894177 (PubMedID)2-s2.0-85135768057 (Scopus ID)
Funder
NordForsk, 82845Swedish Research Council Formas, 2019-00492Bio4Energy, B4E3-TM-2-03
Available from: 2022-08-22 Created: 2022-08-22 Last updated: 2024-05-06Bibliographically approved
2. A step towards more eco-friendly and efficient microalgal harvesting: Inducing flocculation in the non-naturally flocculating strain chlorella vulgaris (13-1) without chemical additives
Open this publication in new window or tab >>A step towards more eco-friendly and efficient microalgal harvesting: Inducing flocculation in the non-naturally flocculating strain chlorella vulgaris (13-1) without chemical additives
2024 (English)In: Algal Research, ISSN 2211-9264, Vol. 79, article id 103450Article in journal (Refereed) Published
Abstract [en]

Flocculation is often regarded as a cost-effective and reliable method for microalgal harvesting. However, the traditional method often requires the addition of chemical agents to induce flocculation. This carries certain disadvantages including the chemical contamination of the biomass and the subsequent need to remove the flocculants from the medium. To address these issues, this study aimed to induce flocculation in a naturally non-flocculating strain (Chlorella vulgaris 13-1) without resorting to chemical additives, with the ultimate goal of increasing harvesting efficiency. Scanning electron microscopy showed that Scotelliopsis reticulata UFA-2, a naturally flocculating strain, produces extracellular polymeric substances (EPS) whereas 13-1 does not. As a result, two methods were used to induce flocculation in 13-1: co-cultivation of UFA-2 and 13-1, and insertion of EPS produced by UFA-2 into the growth medium of 13-1. The co-cultivation of 13-1 with UFA-2 significantly increased the flocculation efficiency compared to that of 13-1 alone (30 % higher flocculation efficiency after one hour of settling and 52 % higher after three hours of settling). Alternatively, the insertion of dry tightly-bound (TB) UFA-2 EPS into 13-1 cultures also improved flocculation efficiency (by 19 % compared to the control), while addition of soluble or loosely-bound (LB) EPS was less efficient (less than 1 % and 10 %, respectively). FTIR results showed that the composition of TB-EPS was different to that of LB and soluble EPS. TB-EPS contained higher proportions of proteins and different types of carbohydrates, potentially contributing to its increased efficacy in inducing flocculation in microalgae.

Place, publisher, year, edition, pages
Elsevier, 2024
Keywords
Cell wall, Extracellular polymeric substances, Flocculation, Harvesting, Microalgae
National Category
Microbiology
Identifiers
urn:nbn:se:umu:diva-222219 (URN)10.1016/j.algal.2024.103450 (DOI)2-s2.0-85186696607 (Scopus ID)
Available from: 2024-03-14 Created: 2024-03-14 Last updated: 2024-05-06Bibliographically approved
3. Transcriptomic analysis of a cold-resistant Nordic microalga: unravelling the mechanisms underlying adaptation to low temperatures
Open this publication in new window or tab >>Transcriptomic analysis of a cold-resistant Nordic microalga: unravelling the mechanisms underlying adaptation to low temperatures
Show others...
2024 (English)In: Physiologia Plantarum, ISSN 0031-9317, E-ISSN 1399-3054Article in journal (Refereed) Accepted
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:umu:diva-224010 (URN)
Available from: 2024-05-06 Created: 2024-05-06 Last updated: 2024-05-06
4. The cell wall of green microalgae and its role in heavy metal removal
Open this publication in new window or tab >>The cell wall of green microalgae and its role in heavy metal removal
2021 (English)In: Physiologia Plantarum, ISSN 0031-9317, E-ISSN 1399-3054, Vol. 173, no 2, p. 526-535Article in journal (Refereed) Published
Abstract [en]

Heavy metals in industrial wastewaters are posing a serious threat to the environment and to human health. Microalgae are increasingly being seen as potential solutions to this problem as they can remove pollutants through biosorption. This process offers certain advantages over other more traditional metal removal techniques as it is simple, inexpensive, eco-friendly, and can be performed over a wide range of experimental conditions. Biosorption is possible due to the unique and complex structure of the microalgal cell wall. The variety of functional groups on the surface of the cell wall (such as carboxyl or amino groups) can act as binding sites for the heavy metals, thus removing them from the environment. This review focuses on the cell wall composition and structure of the most commonly used microalgae in heavy metal removal and shows the role of their cell wall in the biosorption process. This review also aims to report the most commonly used models to predict the velocity of microalgal biosorption and the removal capacities.

Place, publisher, year, edition, pages
John Wiley & Sons, 2021
National Category
Water Engineering Environmental Sciences
Identifiers
urn:nbn:se:umu:diva-182101 (URN)10.1111/ppl.13405 (DOI)000636551100001 ()33764544 (PubMedID)2-s2.0-85103418778 (Scopus ID)
Funder
NordForsk, 82845Swedish Energy Agency, 2018-017772Vinnova, 2017-03301Swedish Research Council Formas, 2019-00492
Available from: 2021-04-13 Created: 2021-04-13 Last updated: 2024-05-06Bibliographically approved

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5678910118 of 18
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