Mychonastes homosphaera (Chlorophyceae): A promising feedstock for high quality feed production in the arid environment

A rapid and multi-endpoint ecotoxicological test using Mychonastes afer for efficient screening of metals and herbicides

Microalgal growth-based tests are international standards for ecotoxicity assessment; however, their long exposure times, large sample volumes, and reliance on a single growth-endpoint make them inadequate for rapid toxicity screening. Here, we aimed to develop a rapid and simple ecotoxicological test using the fast-growing green alga Mychonastes afer, with multiple endpoints-growth, lipid content, and photosynthesis. We exposed M. afer to two metals-silver and copper-and two herbicides-atrazine and diuron-for 24 h and identified the most sensitive and reliable endpoints for each toxicant: the maximum electron transport rate (ETRmax) for Ag, Cu and atrazine, and the lipid content for diuron. Lipid content was found to be both a sensitive and reliable biomarker, meeting the effluent limit guidelines in both the Republic of Korea and the USA. The sensitivity of M. afer to Ag and atrazine also closely matched the HC5 values derived from the species sensitivity distribution approach, confirming its reliability for setting regulatory concentrations of these contaminants. Our calculated predicted no-effect concentration (PNEC) values were similar to established European Union PNECs for Ag, Cu, atrazine, and diuron, underlining the utility of these biological endpoints for ecological risk assessment and regulatory decision making. This method required lower sample volume (2 mL vs 100 mL) and exposure time (24 h vs 72-120 h) than conventional green algal tests, and eliminated the need for labour-intensive cell counting, expensive equipment, and chlorophyll fluorescence measurement expertise. Overall, this M. afer test can be a valuable tool for the rapid screening of wastewater for metals and herbicides, contributing to environmental protection and management practices.

Exploring the dynamics of algae-associated microbiome during the scale-up process of Tetraselmis sp. microalgae: A metagenomics approach

Microalgae have become a key source of valuable compounds, promoting commercial scale applications. However, biological contamination is one of the most critical problems associated with large scale algal production, especially in open systems such as raceway ponds. The current research is the first to assess the effectiveness of open raceway ponds in maintaining a pure culture of Tetraselmis sp., starting from 20 L culture up to 10,000 L culture. Microbial profiling of each successive stage revealed lower abundance of eukaryotic organisms, whereas bacterial abundance increased notably resulting in a significant decrease in Tetraselmis sp. abundance. Furthermore, several bacteria with algae growth-promoting properties were found throughout the various culture stages including Balneola, Roseovarius, and Marinobacter. However, some algae-suppressive bacteria were evidenced at later stages such as Ulvibacter, Aestuariicoccus, and Defluviimonas. Overall, due to the increasing bacterial concentration, considerations limiting bacterial contamination need to be taken.

Screening of microalgae species and evaluation of algal-lipid stimulation strategies for biodiesel production

Microalgae is considered an alternative source for biodiesel production producing renewable, sustainable and carbon-neutral energy. Microalgae property changes among species, which determines the efficiency of biodiesel production. Besides the lipid content evaluation, multi-principles (including high lipid productivity, high biomass yield, pollution resistance and desired fatty acid, etc.) for superior oil-producing species screening was proposed in this review and three microalgae species (Chlorella vulgaris, Scenedesmus obliquus and Mychonastes afer) with high bio-lipid producing prospect were screened out based on big data digging and analysis. The multilateral strategies for algal-lipid stimulating were also compared, among which, nutrient restriction, temperature control, heterotrophy and chemicals addition showed high potential in enhancing lipid accumulation; while electromagnetic field showed little effect. Interestingly, it was found that the lipid accumulation was more sensitive to nitrogen (N)-limitation other than phosphorus (P). Nutrient restriction, salinity stress etc. enhanced lipid accumulation by creating a stressed environment. Hence, optimum conditions (e.g. N:15-35 mg/L and P:4-16 mg/L) should be set to balance the lipid accumulation and biomass growth, and further guarantee the algal-lipid productivity. Otherwise, two-step cultivation could be applied during all the stressed stimulation. Different from lab study, effectiveness, operability and economy should be all considered for stimulation strategy selection. Nutrient restriction, temperature control and heterotrophy were highly feasible after the multidimensional evaluation.

A New Cryptic Species of the Genus Mychonastes (Chlorophyceae, Sphaeropleales)

A new species of green coccoid algae, Mychonastes hindakii sp. nov., was isolated from the River Moscow (Russia, Moscow). The taxon is described using morphological and molecular methods. Mychonastes hindakii sp. nov. belongs to the group of species of the genus Mychonastes with spherical single cells joined with mucilaginous, irregularly shaped stalks. A comparison of ITS2 rDNA sequences and its secondary structures combined with the compensatory base changes approach confirms the separation between Mychonastes hindakii and other species of the genus. Mychonastes hindakii sp. nov. represents a cryptic species that can only be reliably identified using molecular data.

Spatiotemporal changes of bacterial communities during a cyanobacterial bloom in a subtropical water source reservoir ecosystem in China

Cyanobacterial blooms, which not only threaten the health and stability of aquatic ecosystems but also influence the microbial community within, emerges as one of the most concerning problems in China. However, how cyanobacterial blooms affect the spatiotemporal variation of aquatic microbial communities remains relatively unclear. In this study, we used high-throughput sequencing to investigate how the cyanobacterial and bacterial community spatiotemporally vary along with main cyanobacterial bloom phases in upstream rivers of a eutrophicated water source reservoir. Both cyanobacterial and bacterial diversities in each river were significantly lower (P < 0.05) during the bloom outbreak phase, showing the apparent influence of cyanobacterial bloom. Dominant cyanobacterial taxa included Cyanobacteriales and Synechococcales, and dominant bacterial taxa comprised Acinetobacter, CL500-29, hgcI clade, Limnohabitans, Flavobacterium, Rhodoluna, Porphyrobacter, Rhodobacter, Pseudomonas, and Rhizobiales, whose changes of relative abundance along with the bloom indicated distinct community composition. Non-metric multidimensional scaling analysis proved that community composition had significant difference amongst bloom phases. Linear discriminant analysis (LDA) with LDA effect size analysis (LEfSe) identified unique dominant cyanobacterial and bacterial OTUs at different phases in each river, indicating spatiotemporal variations of communities. Canonical correlation analysis or redundancy analysis revealed that at different bloom phases communities of each river had distinct correlation patterns with the environmental parameters (temperature, ammonium, nitrate, and total phosphorus etc.), implying the spatial variations of microbial communities. Overall, these results expand current understanding on the spatiotemporal variations of microbial communities due to cyanobacterial blooms. Microbial interactions during the bloom may shed light on controlling cyanobacterial blooms in the similar aquatic ecosystems.

Microalgal lipids: biochemistry and biotechnology

Microalgae, including cyanobacteria, are a genetically diverse and biochemically diverse group of mostly photosynthetic organisms that can be found in nearly every ecosystem. They produce a broad range of compounds, including structural and bioactive lipids with various roles in the metabolism of the cell and potential applications in biotechnology. The majority of lipids are synthesized in the chloroplast using acetate to produce fatty acids and terpenoids via the acetate pathway and methylerythritol phosphate deoxy-xylulose phosphate pathway, respectively. This review will highlight the major groups of microalgal lipids as well as their applications in food, fuels, and specialty chemicals. Future directions include the development of microalgal chassis organisms and molecular tools to manipulate lipid synthesis for the enhanced production of target metabolites.