Application of Microalgal Stress Responses in Industrial Microalgal Production Systems.

Adaptive laboratory evolution (ALE) has been widely utilized as a tool for developing new biological and phenotypic functions to explore strain improvement for microalgal production. Specifically, ALE has been utilized to evolve strains to better adapt to defined conditions. It has become a new solution to improve the performance of strains in microalgae biotechnology. This review mainly summarizes the key results from recent microalgal ALE studies in industrial production. ALE designed for improving cell growth rate, product yield, environmental tolerance and wastewater treatment is discussed to exploit microalgae in various applications. Further development of ALE is proposed, to provide theoretical support for producing the high value-added products from microalgal production.

Creation of an Industrial Bacillus thuringiensis Strain With High Melanin Production and UV Tolerance by Gene Editing.

Bacillus thuringiensis produces insecticidal crystal proteins (ICPs) which exhibit strong insecticidal toxicity. But when used in the field, ICPs would be destroyed by ultraviolet (UV) radiation in sunlight, thus decreasing the insecticidal activity and shortening the persistence. To improve the duration of B. thuringiensis preparations, we endowed a highly toxic industrial B. thuringiensis HD-1 with UV tolerance by making it produce melanin, a pigment that absorbs UV radiation. In B. thuringiensis, melanin is derived from homogentisate (HGA), an intermediate in the tyrosine pathway. And the absence of homogentisate-1,2-dioxygenase (HmgA) will lead to the formation of melanin. In this study, we used the CRISPR/Cas9 system to knock out the hmgA gene and obtained a melanin-producing mutant HD-1-ΔhmgA from strain HD-1. The melanin yield by mutant HD-1-ΔhmgA reached 3.60 mg/mL. And the anti-UV test showed that melanin serves as a protection to both the organism and the ICPs. After UV irradiation for 3 h, mutant HD-1-ΔhmgA still had an 80% insecticidal activity against the cotton bollworm, Helicoverpa armigera, while the control line only had about 20%. This study creates a light-stable biopesticide prototype based on a classic industrial strain that can be applied directly and takes the melanin-producing strain as a concept to improve the preparation validity.

Integrated metabolic tools reveal carbon alternative in Isochrysis zhangjiangensis for fucoxanthin improvement.

This study explored the regulation of photosystem and central carbon metabolism in cell growth and fucoxanthin accumulation of Isochrysis zhangjiangensis via transcriptome analysis, targeted metabolite measurements, and flux balance analysis. High light promoted biomass accumulation but dramatically decreased fucoxanthin productivity. It suppressed the active photosystem and reduced chlorophyll content, but improved metabolic flux of Calvin-Benson-Bassham and tricarboxylic acid cycle for massive biomass accumulation. The CO2 fixation was largely dependent on mitochondrial energy illustrated by the integrated metabolic tools. At a molecular level, glyceraldehyde-3-phosphate, acetyl-CoA, and pyruvate contents increased at exponential phase under high light, which tended to participate into fatty acid biosynthesis by the up-regulated ACCase. However, high light inhibited most genes involved in fucoxanthin biosynthesis and induced diadinoxanthin cycle to diatoxanthin form. Therefore, constant light at 100 µmol m-2 s-1 balancing biomass concentration and fucoxanthin content provided the highest fucoxanthin productivity at 3.06 mg L-1 d-1.