Abstract
Microalgae of the Chlorella clade are extensively investigated as an environmentally friendly source of renewable biofuels and high-value nutrients. In addition, essentially unprocessed Chlorella serves as wholesome food additive. A recent study on 80 commercial Chlorella preparations revealed an unexpected variety of protein-linked N-glycan patterns with unprecedented structural features, such as the occurrence of arabinose. Two groups of products exhibited a characteristic major N-glycan isobaric to the Man2GlcNAc2XylFuc N-glycan known from pineapple stem bromelain, but tandem mass spectrometry (MS/MS) analysis pointed at two types of N-glycan different from the bromelain structure, as well as from each other. Here we report the exact structures of these two novel N-glycan structures, elucidated by nuclear magnetic resonance spectroscopy and MS/MS, as well as on their phylogenetic context. Despite their humble size, these two N-glycans exhibited a very different design with structural features unrelated to those recently described for other Chlorella-clade strains. The major glycans of this study presented several novel structural features such as substitution by arabinose or xylose of the internal N-acetylglucosamine, as well as methylated sugars. ITS1-5.8S-ITS2 rDNA barcode analyses revealed that the xylose-containing structure derived from a product primarily comprising Scenedesmus species, and the arabinose-containing glycan type related to Chlorella species (SAG211-34 and FACHB-31) and to Auxenochlorella. This is another example where characteristic N-glycan structures distinguish phylogenetically different groups of microalgae.
Highlights
Microalgae of the genus Chlorella find a plethora of current and potential uses
An example is posed by the strain FACHB-31 that originally was seen as Scenedesmus obliquus (Xu et al, 2015) and as such as a member of the class of Chlorellaceae, which against cursory impression does not comprise the family of the Chlorellales, which is home to Chlorella
We examined the N-glycan structures of the dominating os2221 glycan in the “Raa” and “” glyco groups by various techniques including two-dimensional (2D) nuclear magnetic resonance (NMR) spectroscopy
Summary
Microalgae of the genus Chlorella find a plethora of current and potential uses. Many hopes are lain in their ability to convert sewage into useful materials (Liu and Chen, 2016; Markou et al, 2018), to constitute a source of renewable fuel (Wang et al, 2020) or—at lower volumes but higher value—of a nonsynthetic source of chemicals, not at least food or feed additives such as polyunsaturated fatty acids (Haslam et al, 2020; Madhubalaji et al, 2020), carotenoids (Sun et al, 2019; Zhang et al, 2020), or many other pharmaceutically valuable compounds (Rosales-Mendoza et al, 2020).Structural Difference of Microalgae N-GlycansChlorella is regarded as a potential future source of protein for direct consumption, as well as use in livestock farming (Amorim et al, 2020). Microalgae of the genus Chlorella find a plethora of current and potential uses. Chlorella is regarded as a potential future source of protein for direct consumption, as well as use in livestock farming (Amorim et al, 2020). A multitude of Chlorella tablets and powders are offered for human consumption as something between healthy food and food supplement, where the protein and/or vitamin content or other health benefits are emphasized. An example is posed by the strain FACHB-31 that originally was seen as Scenedesmus obliquus (Xu et al, 2015) and as such as a member of the class of Chlorellaceae, which against cursory impression does not comprise the family of the Chlorellales, which is home to Chlorella. An example of two different classes in the animal area is the classes of birds and mammals, where misclassifications are hard to imagine
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