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Microalgae are photosynthetic organisms with potentials in sustainable production of valuable metabolites such as polyunsaturated oil. Low nitrogen cultivation is widely used for induction of microalgal oil production. Previously we found that low inorganic nitrogen (low N, 4.5 mM NaNO3) favored oil production in a dryland-isolated eustigmatophyte microalga Vischeria sp. WL1, relative to the usually used nitrogen level (18 mM NaNO3), while low organic nitrogen (low pepN, 4.5 mM peptone) led to both rapider growth and higher oil yield than low N. Here we analyzed the lipidome profiles of Vischeria sp. WL1 under low N and low pepN conditions. Our results revealed that the lipidome profiles induced by both conditions were apparently different. Overall, low N had a much weaker impact on the lipidome profile than low pepN. Notably, low N uniquely induced a significant increase of phosphatidylinositol (PI), phosphatidylinositol phosphate (PIP), phosphatidylinositol bisphosphate (PIP2) and phosphatidylinositol trisphosphate (PIP3), whereas low pepN induced a significant increase of phosphatidylcholine (PC) and phosphatidylethanolamine (PE). In addition, low pepN induced a significant increase of neutral glycerolipids. This research deepens our understanding on the lipid metabolism of Vischeria sp. WL1 under different nitrogen conditions and could also guide oil production strategy in microalgae by adopting suitable nitrogen resources. [ABSTRACT FROM AUTHOR]

Halophilic Archaea are widely distributed globally in hypersaline environments. However, little is known of how dominant halophilic archaeal genera are distributed across environments and how they may co-associate across ecosystems. Here, the archaeal community composition and diversity from hypersaline environments (> 300 g/L salinity; total of 33 samples) in the Qaidam Basin of China were investigated using high-throughput Illumina sequencing of 16S rRNA genes. The archaeal communities (total of 3,419 OTUs) were dominated by the class Halobacteria (31.7–99.6% relative abundances) within the phylum Euryarchaeota (90.8–99.9%). Five predominant taxa, including Halorubrum, Halobacterium, Halopenitus, Methanothrix, and Halomicrobium, were observed across most samples. However, several distinct genera were associated with individual samples and were inconsistently distributed across samples, which contrast with previous studies of hypersaline archaeal communities. Additionally, co-occurrence network analysis indicated that five network clusters were present and potentially reflective of interspecies interactions among the environments, including three clusters (clusters II, III, and IV) comprising halophilic archaeal taxa within the Halobacteriaceae and Haloferacaceae families. In addition, two other clusters (clusters I and V) were identified that comprised methanogens. Finally, salinity comprising ionic concentrations (in the order of Na+ > Ca2+ > Mg2+) and pH were most correlated with taxonomic distributions across sample sites. [ABSTRACT FROM AUTHOR]

Ectoine has gained considerable attention as a high-value chemical with significant application potential and market demand. This study aimed to increase ectoine yields by blocking the metabolic shunt pathway of l-aspartate-4-semialdehyde, the precursor substrate in ectoine synthesis. The homoserine dehydrogenase encoded by hom in H. campaniensis strain XH26 is responsible for the metabolic shunt of l-aspartate-4-semialdehyde to glycine. CRISPR/Cas9 technology was used to seamlessly knockout hom, blocking the metabolic shunt pathway to increase ectoine yields. The ectoine yield of XH26/Δhom was 351.13 mg (g CDW)−1 after 48 h of incubation in 500 mL shake flasks using optimal medium with 1.5 mol L−1 NaCl, which was significantly higher than the 239.18 mg (g CDW)−1 of the wild-type strain. Additionally, the absence of the ectoine metabolic shunt pathway affects betaine synthesis, and thus the betaine yields of XH26/Δhom was 19.98 mg (g CDW)−1, considerably lower than the 69.58 mg (g CDW)−1 of the wild-type strain. Batch fermentation parameters were optimized, and the wild-type strain and XH26/Δhom were fermented in 3 L fermenters, resulting in a high ectoine yield of 587.09 mg (g CDW)−1 for the defective strain, which was significantly greater than the ectoine yield of 385.03 mg (g CDW)−1 of the wild-type strain. This study showed that blocking the metabolic shunt of synthetic substrates effectively increases ectoine production, and a reduction in the competitively compatible solute betaine appears to promote increased ectoine synthesis. [ABSTRACT FROM AUTHOR]

A new strain of Eustigmatophyceae, Vischeria sp. WL1, which accumulates oil droplets in the cells, was isolated from a large biological soil crust in the arid steppes of north-western China. Its growth and oil productivity were explored using nitrate–N and peptone-N sources, as well as salt stress treatment. Compared to the commonly used ~ 18.0 mM nitrate–N, 4.5 mM nitrate–N was found to be relatively cost-effective for oil production, and 4.5 mM peptone-N was much more effective. After 24 days of cultivation, the biomass increased up to 7.5 times the initial biomass and the oil yield reached 1.13 g L−1 for the 4.5 mM peptone-N condition. In addition, supplementation of 0.3 M NaCl in the medium was found to enhance the oil productivity, while 3.0 M NaCl treatment facilitated the obtaining of relatively pure oil, removing more than 95% of the cellular pigments prior to oil extraction. The oils produced are characterized by high contents of C16:1 (~ 50%) and C20:5 (~ 10%) fatty acids, implying that they may serve as ideal biodiesel feedstocks or nutritional supplements. In general, this study reported a new dryland microalgal strain and its biotechnological potential in the production of oils with biofuel or edible value. [ABSTRACT FROM AUTHOR]

Halophilic bacteria such as the genus Halomonas are promising candidates in diverse industrial, agricultural and biomedical applications. Here, we successfully isolated a halophilic Halomonas alkaliphila strain XH26 from Xiaochaidan Salt Lake, and studied its osmoadaptation strategies using transcriptome and ectoine analysis. Divergent mechanisms were involved in osmoadaptation at different salinities in H. alkaliphila XH26. At moderate salinity (6% NaCl), increased transcriptions of ABC transporters related to iron (III), phosphate, phosphonate, monosaccharide and oligosaccharide import were observed. At high salinity (15% NaCl), transcriptions of flagellum assembly and cell motility were significantly inhibited. The transcriptional levels of ABC transporter genes related to iron (III) and iron3+-hydroxamate import, glycine betaine and putrescine uptake, and cytochrome biogenesis and assembly were significantly up-regulated. Ectoine synthesis and accumulation was significantly increased under salt stress, and the increased transcriptional expressions of ectoine synthesis genes ectB and ectC may play a key role in high salinity induced osmoadaptation. At extreme high salinity (18% NaCl), 5-hydroxyectoine and ectoine worked together to maintain cell survival. Together these results give valuable insights into the osmoadaptation mechanisms of H. alkaliphila XH26, and provide useful information for further engineering this specific strain for increased ectoine synthesis and related applications. [ABSTRACT FROM AUTHOR]