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Microalgae exhibit extensive potential for counteracting imminent challenges in the nutraceutical, pharmaceutical, and biomaterial sectors, but lack economic viability. Biotechnological systems for contamination control could advance the economic viability of microalgal feedstock, but the selection of suitable strains that sustainably promote microalgal productivity remains challenging. In this study, total diversity in phototrophic Chlorella vulgaris cultures was assessed by amplicon sequencing comparing cultures subjected to five different cultivation conditions. Overall, 12 eukaryotic and 53 prokaryotic taxa were identified; Alphaproteobacteria (36.7%) dominated the prokaryotic and C. vulgaris (97.2%) the eukaryotic community. Despite altering cultivation conditions, 2 eukaryotic and 40 prokaryotic taxa remained stably associated with C. vulgaris; diversity between systems did not significantly differ (P > 0.05). Among those, 20 cultivable taxa were isolated and identified by 16S rDNA sequencing. Subsequently, controlled co-cultures were investigated showing stable associations of C. vulgaris with Sphingopyxis sp. and Pseudomonas sp.. Out-competition of C. vulgaris due to ammonium or phosphate limitation was not observed, despite significantly elevated growth of Sphingopyxis sp. and Tistrella sp.. (P < 0.05). Nevertheless, C. vulgaris growth was impaired by Tistrella sp.. Hence, the study provides a selection of stable indigenous prokaryotes and eukaryotes for artificially tailoring microbial biocenoses. Following a bottom-up approach, it provides a base for controlled co-cultures and thus the establishment of even more complex biocenoses using interkingdom assemblages. Such assemblages can benefit from functional richness for improved nutrient utilization, as well as bacterial load control, which can enhance microalgal feedstock production through improved culture stability and productivity.

Nanosecond pulsed electric field (nsPEF) processing is gaining momentum as a physical means for single-cell bioconversion efficiency enhancement. The technology allows biomass yields per substrate (YX/S) to be leveraged and poses a viable option for stimulating intracellular compound production. NsPEF processing thus resonates with myriad domains spanning the pharmaceutical and medical sectors, as well as food and feed production. The exact working mechanisms underlying nsPEF-based enhancement of bioconversion efficiency, however, remain elusive, and a better understanding would be pivotal for leveraging process control to broaden the application of nsPEF and scale-up industrial implementation. To bridge this gap, the study provides the electrotechnological and metabolic fundamentals of nsPEF processing in the bio-based domain to enable a critical evaluation of pathways underlying the enhancement of single-cell bioconversion efficiency. Evidence suggests that treating cells during the rapid proliferating and thus the early to mid-exponential state of cellular growth is critical to promoting bioconversion efficiency. A combined effect of transient intracellular and sublethal stress induction and effects caused on the plasma membrane level result in an enhancement of cellular bioconversion efficiency. Congruency exists regarding the involvement of transient cytosolic Ca2+ hubs in nsPEF treatment responses, as well as that of reactive oxygen species formation culminating in the onset of cellular response pathways. A distinct assignment of single effects and their contributions to enhancing bioconversion efficiency, however, remains challenging. Current applications of nsPEF processing comprise microalgae, bacteria, and yeast biorefineries, but these endeavors are in their infancies with limitations associated with a lack of understanding of the underlying treatment mechanisms, an incomplete reporting, insufficient characterization, and control of processing parameters. The study aids in fostering the upsurge of nsPEF applications in the bio-based domain by providing a basis to gain a better understanding of cellular mechanisms underlying an nsPEF-based enhancement of cellular bioconversion efficiency and suggests best practice guidelines for nsPEF documentation for improved knowledge transfer. Better understanding and reporting of processes parameters and consequently improved process control could foster industrial-scale nsPEF realization and ultimately aid in perpetuating nsPEF applicability within the bio-based domain., Biotechnology Advances, 53, ISSN:0734-9750, ISSN:1873-1899

Microalgae exhibit extensive potential for counteracting imminent challenges in the nutraceutical, pharmaceutical, and biomaterial sectors, but lack economic viability. Biotechnological systems for contamination control could advance the economic viability of microalgal feedstock, but the selection of suitable strains that sustainably promote microalgal productivity remains challenging. In this study, total diversity in phototrophic Chlorella vulgaris cultures was assessed by amplicon sequencing comparing cultures subjected to five different cultivation conditions. Overall, 12 eukaryotic and 53 prokaryotic taxa were identified; Alphaproteobacteria (36.7%) dominated the prokaryotic and C. vulgaris (97.2%) the eukaryotic community. Despite altering cultivation conditions, 2 eukaryotic and 40 prokaryotic taxa remained stably associated with C. vulgaris; diversity between systems did not significantly differ (P > 0.05). Among those, 20 cultivable taxa were isolated and identified by 16S rDNA sequencing. Subsequently, controlled co‐cultures were investigated showing stable associations of C. vulgaris with Sphingopyxis sp. and Pseudomonas sp.. Out‐competition of C. vulgaris due to ammonium or phosphate limitation was not observed, despite significantly elevated growth of Sphingopyxis sp. and Tistrella sp.. (P

Microalgae can be incorporated in different bio-based products; however, the green colour is a barrier for a successful integration. This study aims to overcome this barrier by growing microalgae in different cultivation modes. Mixotrophic cultivation of Chlorella protothecoides resulted in the highest biomass production after 5 days (5.56 ± 0.09 g/L), followed by heterotrophic and photoautotrophic cultivation (4.33 ± 0.15 and 1.80 ± 0.05 g/L, respectively). Mixotrophically and heterotrophically produced biomass presented a reduced greenish colouration compared to photoautotrophically produced biomass. Chlorophyll content resulted in 1.46 ± 0.21 and 0.95 ± 0.28 mg/g dry weight (DW) in mixotrophic and heterotrophic cultures, respectively, and 25.98 ± 1.28 mg/g DW in photoautotrophic cultures. In contrast, the fraction of carotenoids in the total pigments was much higher. With the whole microalgae fractions after cell disruption as ingredients, stable emulsions containing 50% oil could be produced. No syneresis with serum separation was observed 24 h after preparation.

Nanosecond pulsed electric field treatment (nsPEF) is a technology-driven, resource-efficient approach fostering microalgae biorefineries for transforming them into economically viable scenarios. A processing window of 100 ns, 7 Hz, and 10 kV cm−1 significantly leveraged phototrophic Chlorella vulgaris and bacterial counts up to + 50.1 ± 12.2% and + 77.0 ± 37.4%, respectively (n = 4; p < 0.05) in non-axenic cultures. Applying the same processing window decreased C. vulgaris (−17.1 ± 13.8%) and prokaryotic (−82.7 ± 14.6%) counts owing to alterations in the prokaryotic community diversity. Principle coordinate analysis of prokaryotic phenotypic fingerprints indicated that phenotype or metabolism related diversity changes in the prokaryotic community affected the treatment outcome. The study fosters the upsurge of industrial-scale nsPEF realization and the economic viability of microalgae biorefineries through improved process understanding and thus control. It perpetuates nsPEF applicability for microalgae feedstock production and several other applications within single-cell biorefineries in the bio-based domain., Bioresource Technology, 319, ISSN:1873-2976, ISSN:0960-8524

Nanosecond pulsed electric field treatment (nsPEF) is an innovative, technology-driven, and resource-efficient approach to foster the upstream performance of microalgae-based biorefinery concepts to transform microalgae into economic more viable raw materials for the biobased industry. A processing window applying three treatments of 100 ns, 5 Hz, and 10 kV cm−1 to industrially relevant phototrophic Chlorella vulgaris in the early exponential growth phase significantly increased biomass yields by up to 17.53 ± 10.46% (p = 3.18 × 10−5). Treatments had limited effects on the carbon and pigment contents, but the protein content was decreased. The longest possible pulse width (100 ns) resulted in the highest biomass yield indicating underlying working mechanisms of enhanced cell proliferation based on intracellular and plasma membrane-related effects. The applicability to eukaryotes and prokaryotes, such as C. vulgaris and cyanobacteria highlights the possible impacts of nsPEF across multiple domains of the biobased industry relying on single-cell-based value-chains., Bioresource Technology, 293, ISSN:1873-2976, ISSN:0960-8524

Alternatives to animal proteins with similar texture, appearance and taste are demanded by an increasing group of consumers. Plant-based meat analogues produced by high moisture extrusion cooking can provide relevant solutions. Here, microalgae combined to soy concentrates were shown to create fibrillary textured extrudates. The incorporation of spray-dried microalgae biomass in up to 50% affected the formation of fibers, which could be balanced by reducing moisture levels. The elevated fat content of microalgae biomass led to lubrication effects, while probably undisrupted microalgae cells acted as passive fillers and limited the access of intracellular proteins. Both effects may have reduced texturing but increased tenderness in comparison to pure soy based extrudates. By using heterotrophically cultivated Auxenochlorella protothecoides with a light-yellow coloration, a consumer-adverse visual appearance could be omitted. Microalgae integration improved the extrudate's nutritional profile by incorporating vitamins B and E, where over 95% was retained in the final product. Industrial relevance The meat analogue industry strives to be more than an alternative for vegetarian and vegan customers. Large initial public offerings of relevant players underline the current economic and industrial interest. Besides animal wellbeing, meat analogues are praised mainly for their reduced ecological and environmental impact. Yet, most of the products on the market are based on environmentally questionable resources, such as soy. Hence, this study with focus on microalgae as a protein alternative to the ubiquitously applied soy protein concentrate is relevant to the evolving industry and research. In this manuscript, a fibrillary textured plant-based product using microalgae is shown without an adverse color., Innovative Food Science & Emerging Technologies, 59, ISSN:1466-8564

Microalgae-based biorefinery concepts can contribute to providing sufficient resources for a growing world population. However, the performance needs to be improved, which requires innovative technologies and processes. Continuous extraction from Chlorella vulgaris cultures via pulsed electric field (PEF) processing might be a viable process to increase the performance of microalgae-based biorefinery concepts. In this study, increasing protein extraction rates were observed with increasing electric field strength, up to 96.6 ± 4.8% of the free protein in the microalgae. However, increased extraction rates negatively influenced microalgae growth after PEF treatment. A free protein extraction rate up to 29.1 ± 1.1% without a significant influence on microalgal growth after 168 h was achieved (p = 0.788). Within the scope of this work, a protocol for continuous protein extraction during microalgae cultivation by PEF processing was developed. The incorporation of innovative downstream into upstream processing could be a viable future concept., Bioresource Technology, 291, ISSN:1873-2976, ISSN:0960-8524