Amino Acids Are an Ineffective Fertilizer for Dunaliella spp. Growth

Comparative transcriptomic analysis of Stenotrophomonas sp. MNB17 revealed mechanisms of manganese tolerance at different concentrations and the role of histidine biosynthesis in manganese removal

Bacteria possess protective mechanisms against excess Mn(Ⅱ) to reduce its toxicity. Stenotrophomonas sp. MNB17 showed high Mn(Ⅱ) removal capacity (92.24-99.16 %) by forming Mn-precipitates (MnCO₃ and Mn-oxides), whose Mn-oxides content increased with increasing Mn(Ⅱ) concentrations (10-50 mM). Compared with 0 mM Mn(Ⅱ)-stressed cells, transcriptomic analysis identified genes with the same transcriptional trends in 10 mM and 50 mM Mn(Ⅱ)-stressed cells, including genes involved in metal transport, cell envelope homeostasis, and histidine biosynthesis, as well as genes with different transcriptional trends, such as those involved in oxidative stress response, glyoxylate cycle, electron transport, and protein metabolism. The upregulation of histidine biosynthesis and oxidative stress responses were the most prominent features of these metabolisms under Mn(Ⅱ) stress. We confirmed that the increased level of reactive oxygen species was one of the reasons for the increased Mn-oxides formation at high Mn(Ⅱ) concentrations. Metabolite analysis indicated that the enhanced histidine biosynthesis rather than the tricarboxylic acid cycle resulted in an elevated level of α-ketoglutarate, which helped eliminate reactive oxygen species. Consistent with these results, the exogenous addition of histidine significantly reduced the production of reactive oxygen species and Mn-oxides and enhanced the removal of Mn(Ⅱ) as MnCO₃. This study is the first to correlate histidine biosynthesis, reactive oxygen species, and Mn-oxides formation at high Mn(Ⅱ) concentrations, providing novel insights into the molecular regulatory mechanisms associated with Mn(Ⅱ) removal in bacteria.

Waste Gastro-intestinal Wall of Sheep as an Alternative Nutrition Source for Cultivation of Dunaliella salina

In the production of natural sausage casings, three layers of serosa, muscular, and mucosa are removed from gastro-intestinal wall of sheep as waste materials. The submocusa layer is taken for further processing. There is no report about generating added value out of these wastes. In this study, a novel approach was introduced for bioconversion of waste gastro-intestinal wall (WGW) to a value-added product. Alkaline hydrolysis of WGW was investigated and the hydrolysate was utilized for cultivation of Dunaliella salina, a value-added biomass. The hydrolysate that contained the highest total soluble protein was used for three sets of cultivations on different medium compositions, i.e., (1) cultivations on the modified Johnson's medium enriched with different percentage of hydrolysate (0.5, 1, 2.5, 5, and 10 (%v/v)), (2) cultivations on modified Johnson's medium which was free of nitrogen and carbon sources and enriched with different percentage of hydrolysate (0.5, 1, 2.5, 5, and 10 (%v/v), and (3) cultivation on modified Johnson's medium which was free of nitrogen source and enriched with 2.5% hydrolysate. The results showed that WGW contained 60.7, 8.4, 15.8, and 15.2% protein, lipid, moisture, and ash, respectively and the enrichment of the medium with the hydrolysate (2.5%) increased biomass productivity by 20%. Additionally, substitution of 2.5% hydrolysate for nitrogen source (KNO3) resulted in the same biomass productivity. The results of this study revealed the potential of the hydrolysate as an alternative for KNO3 in cultivation of D. salina. Overall, this work proposed a novel approach for converting waste gastro-intestinal wall to value.

Resource recovery from wastewaters using microalgae-based approaches: A circular bioeconomy perspective

The basic concepts of circular bioeconomy are reduce, reuse and recycle. Recovery of recyclable nutrients from secondary sources could play a key role in meeting the increased demands of the growing population. Wastewaters of different origin are rich in energy and nutrients sources that can be recovered and reused in a circular bioeconomy perspective. Microalgae can effectively utilize wastewater nutrients for growth and biomass production. Integration of wastewater treatment and microalgal cultivation improves the environmental impacts of the currently used wastewater treatment methods. This review provides comprehensive information on the potential of using microalgae for the recovery of carbon, nitrogen, phosphorus and other micronutrients from wastewaters. Major factors influencing large scale microalgal wastewater treatment are discussed and future research perspectives are proposed to foster the future development in this area.