Simultaneous production of algal biomass and lipid by heterotrophic cultivation of linoleic acid-rich oleaginous microalga Chlorella sorokiniana using high acetate dosage

The low-cost carbon source, acetate, was utilized to feed a linoleic acid-rich Chlorella sorokiniana for microalgal biomass and lipid accumulation. Remarkably high tolerance capability to high acetate dosage up to 30 g/L was observed, with heterotrophy being the preferred trophic mode for algal growth and lipogenesis when supplemented 20 g/L acetate. Transcriptome analysis revealed a marked activation of pathways involved in acetate bioconversion and lipogenesis upon exposure to high-level of acetate. However, the enhancement of photorespiration inhibited photosynthesis, which ultimately led to a decrease in biomass and lipid under mixotrophy. Heterotrophic acetate-feeding generated more superior amino acid profiling of algal biomass and a predominant linoleic acid content (50 %). Heterotrophic repeat fed-batch strategy in 5 L fermenter significantly increased the growth performance and lipid titer, with the highest levels achieved being 23.4 g/L and 7.0 g/L, respectively. This work provides a viable approach for bio-products production through acetate-based heterotrophic algal cultivation.

Photoheterotroph improved the growth and nutrient levels of Chlorella vulgaris and the related molecular mechanism

Microalgae are rich in fatty acids, proteins, and other nutrients, which have gained the general attention of researchers all over the world. For the development of Chlorella vulgaris in food and feed industry, this study was conducted to investigate the differences in C. vulgaris' growth and nutritional components under different culture conditions (autotrophic, heterotrophic, photoheterotrophic) and the internal factors through cell counting in combination with transcriptome and nutrient analyses. The results showed that, under the photoheterotrophic condition, Chlorella's growth and the contents of lipid and protein were significantly higher than that under the heterotrophic condition, and the moisture content was lower than that under the heterotrophic condition. The saturated fatty acid content under the photoheterotrophic condition was the lowest, while the polyunsaturated fatty acid content was significantly higher than those under the other two conditions. There were 46,583 differentially expressed genes (DEGs), including 33,039 up-regulated DEGs (70.93%) and 13,544 down-regulated DEGs (29.07%), under the photoheterotrophic condition in comparison with the autotrophic condition. The fold change between the two conditions of samples of up-regulated genes was higher than that of the down-regulated genes. The KEGG enrichment showed that the up-regulated DEGs in the photoheterotrophic condition were significantly enriched in 5 pathways, including protein processing in endoplasmic reticulum pathway, photosynthesis pathway, photosynthesis-antenna protein pathway, endocytosis pathway, and phosphonate and phosphinate metabolism pathway. DEGs related to fatty acid metabolic pathways were significantly enriched in the fatty acid biosynthesis pathway and the biosynthesis of unsaturated fatty acid pathway. The qPCR analysis showed that the expression pattern of the selected genes was consistent with that of transcriptome analysis. The results of this study lay a theoretical foundation for the large-scale production of Chlorella and its application in food, feed, and biodiesel. KEY POINTS: • Nutrient levels under photoheterotrophic condition were higher than other conditions. • Six important pathways were discovered that affect changes in nutritional composition. • Explored genes encode important enzymes in the differential metabolic pathways.

Composted biochar affects structural dynamics, function and co-occurrence network patterns of fungi community

A few researchers have reported enhancing soil physicochemical properties and reducing greenhouse gas emission using biochar-compost mixture as an alternative method to address soil fertility, soil degradation and climate change. However, information about its effects on soil microbiome has rarely been studied. This investigation was on the impact of a combined biochar-compost application on soil physicochemical variables, fungal community composition, function and network patterns in maize at seedling stage (SS), reproductive stage (RS), and maturity stage (MS). The experimental design consists of five treatments: control (CNT), compost (CMP), composted biochar (CMB), compost fortified with biochar (CFWB), biochar (BCH). The results showed that CFWB, CMB, and CMP increased fungal diversity indices (Shannon, Sobs, and Chao) at the RS and MS stages respectively, compared to BCH and CNT. Distance-based redundancy analysis (db-RDA) at genus level indicated that the pH, available nitrogen, and soil organic matter at SS; available phosphorus at RS; Mg, Mn, Fe, and Zn at MS significantly and positively affected the fungi community. Based on the Linear discriminant analysis (LDA) and effect size (LEfSe) analysis, the results revealed that only Cystofilobasidiaceae and Guehomyces were the MS biomarkers; and significantly enriched in CFWB. FUNGuild analysis indicated that organic amendments (CFWB, CMB, CMP, and BCH) suppressed the abundance of plant pathogenic fungi (Edenia and Waitea) compared to CNT. Network analysis showed that CFWB and CMB had a high niche overlap and cross-feeding in their networks compared to other treatments. However, CMP network had more positive links with Saprotroph, Pathotroph-Saprotroph-Symbiotroph, Pathotroph and Pathotroph-Symbiotroph compared with other treatments. This study showed that applying biochar, compost and a mixture of both, positively affected soil fungal communities plus co-occurrence network pattern in a single cropping season. Thus, their application as soil amendments may improve the soil fungi ecosystem, soil health and quality and mitigate climate change.

Fungal Community Composition and Potential Depth-Related Driving Factors Impacting Distribution Pattern and Trophic Modes from Epi- to Abyssopelagic Zones of the Western Pacific Ocean

Fungi play an important role in cycling organic matter and nutrients in marine ecosystems. However, the distribution of fungal communities in the ocean, especially the vertical distribution along depth in the water column, remained poorly understood. Here, we assess the depth-related distribution pattern of fungal communities along the water column from epi- to abyssopelagic zones of the Western Pacific Ocean using internal transcribed spacer 2 (ITS2) metabarcoding. Majority of the assigned OTUs were affiliated to Ascomycota, followed by three other minor phyla (Basidiomycota, Chytridiomycota, and Mucoromycota). The epipelagic zone harbored a higher OTU richness with distinct fungal communities as compared with meso-, bathy-, and abyssopelagic zones. Across the whole water column, depth appears as a key parameter for both fungal α- and β-diversity. However, when the dataset was split into the upper (5-500 m) and deeper (below 500 m) layers, no significant correlation was observed between depth and community compositions. In the upper layer, temperature and dissolved oxygen were recognized as the primary environmental factors shaping fungal α- and β- diversity. By parsing fungal OTUs into ecological categories, multi-trophic mode of nutrition was found to be more prevalent with increasing depth, suggesting a potential adaptation to the extreme conditions of the deep sea. This study provides new and meaningful information on the depth-stratified fungal diversity, community structure, and putative ecological roles in the open sea.

The algal trophic mode affects the interaction and oil production of a synergistic microalga-yeast consortium

The use of non-food feedstocks to produce renewable microbial resources can limit our dependence on fossil fuels and lower CO₂ emissions. Since microalgae display a virtuous CO₂ and O₂ exchange with heterotrophs, the microalga Chlamydomonas reinhardtii was combined with the oleaginous yeast Lipomyces starkeyi, known for their production of oil, base material for biodiesel. The coupled growth was shown to be synergistic for biomass and lipid production. The species were truly symbiotic since synergistic growth occurred even when the alga cannot use the organic carbon in the feedstock and in absence of air, thus depending entirely on CO₂-O₂ exchange. Since addition of acetate as the algal carbon source lowered the performance of the consortium, the microbial system design should take into account algal mixotrophy. The mixed biomass was found be suitable for biodiesel production, and whereas lipid production increased in the consortium, yields should be improved in future studies.

Changes in structure and function of fungal community in cow manure composting

In this study, dynamic changes in fungal communities, trophic modes and effect factors in 60 days composting of cow manure were analyzed by using high throughput sequencing, FUNGuild and Biolog FF MicroPlate, respectively. Orpinomyces (relative abundance >10.85%) predominated in feedstock, and Mycothermus became the dominating genus (relative abundance >75%) during the active phase. Aerobic composting treatment had a significant effect on fungal trophic modes with pathogenic fungi fading away and wood saprotrophs increasing over composting time. Fungal communities had the higher carbon sources utilization capabilities at the thermophilic phase and mature phase than those in the other periods. Oxidation reduction potential (ORP) significantly increased from -180 to 180 mV during the treatment. Redundancy analysis showed that the succession of fungal community during composting had a significant association with ORP (p < .05). This indicated that aerobic composting treatment not only influenced fungal community structure, but also changed fungal trophic modes and metabolic characteristics.