Enhancement of catabolite regulatory genes in Saccharomyces cerevisiae to increase ethanol production using hydrolysate from red seaweed Gloiopeltis furcata

Metabonomics analysis of microalga Scenedesmus obliquus under ciprofloxacin stress

The wide use of antibiotics in aquaculture has triggered global ecological security issue. Microalgal bioremediation is a promising strategy for antibiotics elimination due to carbon recovery, detoxification and various ecological advantages. However, a lack of understanding with respect to the corresponding regulation mechanism towards antibiotic stress may limit its practical applicability. The microalga Scenedesmus obliquus was shown to be capable of effectively eliminating ciprofloxacin (CIP), which is a common antibiotic used in aquaculture. However, the corresponding transcriptional alterations require further investigation and verification at the metabolomic level. Thus, this study uncovered the metabolomic profiles and detailed toxic and defense mechanisms towards CIP in S. obliquus using untargeted metabolomics. The enhanced oligosaccharide/polyol/lipid transport, up-regulation of carbohydrate and arachidonic acid metabolic pathways and increased energy production via EMP metabolism were observed as defense mechanisms of microalgal cells to xenobiotic CIP. The toxic metabolic responses included: (1) down-regulation of parts of mineral and organic transporters; (2) electrons competition between antibiotic and NAD during intracellular CIP degradation; and (3) suppressed expression of the hem gene in chlorophyll biosynthesis. This study describes the metabolic profile of microalgae during CIP elimination and reveals the key pathways from the perspective of metabolism, thereby providing information on the precise regulation of antibiotic bioremediation via microalgae.

Hydrothermal Processing of Agar Waste to Levulinic acid and Fermentation of Hydrolysate to Bioethanol

Increasing global energy consumption and depleting fossil-fuel supplies prompted the search for green-alternatives. This study focuses on conversion of waste agar using different acids/alkalis (0.5% and 1%) as catalysts under varied temperature and time towards galactose (Gal), 5-hydroxymethylfurfural (HMF) and levulinic acid (LA) production in a sequential reaction. The optimized process for agar depolymerisation was achieved using 1 % acid (H₂SO₄/HCl) catalysed conditions with a maximum of 11 g/L Gal yield (121 °C; 15 min). Increase in temperature (150 °C) and time (180 min) with 1% HCl/H₂SO₄ catalyst resulted in improved LA production along with Gal and HMF. The hydrolysis process was optimised for the selective production of LA (10 g/L) at 175 °C; 180 min. Further, galactose-rich hydrolysates were assessed for bioethanol fermentation using Saccharomyces cerevisiae and resulted 3 g/L ethanol. Thus, the study comprehensively demonstrates waste agar utilization to yield biochemicals/fuels in a circular bio-based economy approach.