The enhancement of the oxidative pentose phosphate pathway maybe involved in resolving imbalance between photosystem I and II in Dunaliella salina

Preharvest spraying of phenylalanine activates the sucrose and respiratory metabolism in muskmelon wounds during healing

Phenylalanine (Phe) accelerates fruit wound healing by activating phenylpropanoid metabolism. However, whether Phe affects sucrose and respiratory metabolism in fruit during wound healing remains unknown. In this research, we found that preharvest Phe spray promoted sucrose degradation and increased glucose and fructose levels by activating acid invertase (AI), neutral invertase (NI), sucrose synthase (SS) and sucrose phosphate synthase (SPS) on harvested muskmelons. The spray also activated hexokinase (HK), phosphofructokinase (PFK), pyruvate kinase (PK), malate dehydrogenase (MDH), succinate dehydrogenase (SDH) and glucose-6-phosphate dehydrogenase (G6PDH). In addition, the spray improved energy and reducing power levels in the fruit. Taken together, preharvest Phe spray can provide carbon skeleton, energy and reducing power for wound healing by activating the sucrose metabolism, Embden-Meyerhof-Parnas (EMP) pathway, tricarboxylic acid (TCA) cycle and pentose phosphate (PPP) pathway in muskmelon wounds during healing, which is expected to be developed as a new strategy to accelerate fruit wound healing.

The Time-Resolved Salt Stress Response of Dunaliella tertiolecta-A Comprehensive System Biology Perspective

Algae-driven processes, such as direct CO2 fixation into glycerol, provide new routes for sustainable chemical production in synergy with greenhouse gas mitigation. The marine microalgae Dunaliella tertiolecta is reported to accumulate high amounts of intracellular glycerol upon exposure to high salt concentrations. We have conducted a comprehensive, time-resolved systems biology study to decipher the metabolic response of D. tertiolecta up to 24 h under continuous light conditions. Initially, due to a lack of reference sequences required for MS/MS-based protein identification, a high-quality draft genome of D. tertiolecta was generated. Subsequently, a database was designed by combining the genome with transcriptome data obtained before and after salt stress. This database allowed for detection of differentially expressed proteins and identification of phosphorylated proteins, which are involved in the short- and long-term adaptation to salt stress, respectively. Specifically, in the rapid salt adaptation response, proteins linked to the Ca2+ signaling pathway and ion channel proteins were significantly increased. While phosphorylation is key in maintaining ion homeostasis during the rapid adaptation to salt stress, phosphofructokinase is required for long-term adaption. Lacking β-carotene, synthesis under salt stress conditions might be substituted by the redox-sensitive protein CP12. Furthermore, salt stress induces upregulation of Calvin-Benson cycle-related proteins.

Bioaccumulation and toxicity of perfluorooctanoic acid and perfluorooctane sulfonate in marine algae Chlorella sp

The ocean is an important sink for perfluorinated alkyl acids (PFAAs), but the toxic mechanisms of PFAAs to marine organisms have not been clearly studied. In this study, the growth rate, photosynthetic activity, oxidative stress and bioaccumulation were investigated using marine algae Chlorella sp. after the exposure of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate acid (PFOS). The results showed that PFOA of <40 mg/L and PFOS of <20 mg/L stimulated algal reproduction, and high doses inhibited the algal growth. The absorbed PFOA and PFOS by algal cells damaged cell membrane and caused metabolic disorder. The photosynthesis activity was inhibited, which was revealed by the significantly reduced maximal quantum yield (Fv/Fm), relative electron transfer rate (rETR) and carbohydrate synthesis. However, the chlorophyll a content increased along with the up-regulation of its encoding genes (psbB and chlB), probably due to an overcompensation effect. The increase of ROS and antioxidant substances (SOD, CAT and GSH) indicated that PFOA and PFOS caused oxidative stress. The BCF of marine algae Chlorella sp. to PFOA and PFOS was calculated to be between 82 and 200, confirming the bioaccumulation of PFOA and PFOS in marine algae. In summary, PFOA and PFOS can accumulate in Chlorella sp. cells, disrupt photosynthesis, trigger oxidative stress and inhibit algal growth. PFOS shows higher toxicity and bioaccumulation than PFOA. The information is important to evaluate the environmental risks of PFAAs.

Comparative Genome Analysis of a Novel Alkaliphilic Actinobacterial Species Nesterenkonia haasae

In the present study, a comparative genome analysis of the novel alkaliphilic actinobacterial Nesterenkonia haasae with other members of the genus Nesterenkonia was performed. The genome size of Nesterenkonia members ranged from 2,188,008 to 3,676,111 bp. N. haasae and Nesterenkonia members of the present study encode the essential glycolysis and pentose phosphate pathway genes. In addition, some Nesterenkonia members encode the crucial genes for Entner-Doudoroff pathways. Some Nesterenkonia members possess the genes responsible for sulfate/thiosulfate transport system permease protein/ ATP-binding protein and conversion of sulfate to sulfite. Nesterenkonia members also encode the genes for assimilatory nitrate reduction, nitrite reductase, and the urea cycle. All Nesterenkonia members have the genes to overcome environmental stress and produce secondary metabolites. The present study helps to understand N. haasae and Nesterenkonia members' environmental adaptation and niches specificity based on their specific metabolic properties. Further, based on genome analysis, we propose reclassifying Nesterenkonia jeotgali as a later heterotypic synonym of Nesterenkonia sandarakina.

Could co-substrate sodium acetate simultaneously promote Chlorella to degrade amoxicillin and produce bioresources?

Integrating microalgae culture and wastewater purification is a promising technology for sustainable bioresource production. However, the challenge is that toxins in wastewater usually limit risk elimination and cause poor bioresource production. Easy-to-biodegrade substrates could alleviate the resistant stress on a bacterial community but we know little about how they function with microalgae. In this study, we tested if Easy-to-biodegrade substrates could simultaneously promote Chlorella to degrade antibiotic amoxicillin (AMO) and produce bioresources. Sodium acetate (NaAC) was used as the representative co-substrate. The results showed NaAC could enhance AMO removal by 76%. The β-lactam structure was destroyed and detoxified to small molecules, due to the up-regulation of hydrolase, oxidoreductase, reductase, and transferase. Chlorella biomass production increased by 36%. The genes encoding the glutathione metabolism and peroxisome pathways were significantly up-regulated to alleviate the antibiotic stress, and the DNA replication pathway was activated. As a result, the production of lipid, carbohydrate, and protein was enhanced by 61%, 122%, and 34%, respectively. This study provides new insights for using microalgae to recover bioresources from toxic wastewater and reveals the critical underlying mechanisms.

Carbon dots enhance the recovery of microalgae bioresources from wastewater containing amoxicillin

The cultivation of microalgae using wastewater could bring some major economic benefits; however, the toxics in wastewater typically lead to a reduction in bioresource production. In this study, carbon dots (CDs) could enhance the photosynthetic activity of Chlorella under antibiotic stress because they might optimize photoluminescence by red-shifting incident light. Adding of 1 mg/L CDs increased the specific growth rate of Chlorella by 36.0% (day 8-13) and 52.7% (day 14-18) and significantly increased photosystems II activity. This treatment also increased amoxicillin removal by 18.6%. Thus, the toxicity of residuals was significantly eliminated (P < 0.05). The removal of nitrogen and phosphorous was increased by 14.6% and 9.9%, respectively. The production of pigments, lipids and proteins was increased by 16.6%, 19.5% and 24.8%, respectively. This work provided a new strategy of using CDs to mediate the coupling of microalgal bioresources production and toxic wastewater purification.

Trophic Transition Enhanced Biomass and Lipid Production of the Unicellular Green Alga Scenedesmus acuminatus

Microalgal heterotrophic cultivation is an emerging technology that can enable producing high cell-density algal cell cultures, which can be coupled with photoautotrophic cultivation for valuable chemicals such as lipids manufacturing. However, how the heterotrophically grown algal cells respond to the lipid-inducing conditions has not been fully elucidated so far. In this study, when the heterotrophically grown Scenedesmus acuminatus cells were subjected to the high light (HL) and nitrogen-limited (NL) conditions, both the biomass and lipid productivity were enhanced as compared to that of the photoautotrophically grown counterparts. The chlorophyll a fluorometry analysis showed that the Fv/Fm and Y(II) of the heterotrophically grown cells subjected to the HL and NL conditions was recovered to the maximum value of 0.75 and 0.43, respectively, much higher than those of the photoautotrophically grown cells under the same stress conditions. Transcriptomic analysis revealed that heterotrophically grown cells fully expressed the genes coding for the photosystems proteins, including the key photoprotective proteins D1, PsbS, light-harvesting-complex (LHC) I and LHC II. Meanwhile, downregulation of the carotenoid biosynthesis and upregulation of the glycolysis/gluconeogenesis, tricarboxylic acid (TCA) cycle and oxidative phosphorylation pathways were observed when the heterotrophically grown cells were subjected to the HL and N-limited conditions for lipid production. It was deduced that regulation of these pathways not only enhanced the light utilization but also provided the reducing power and ATP by which the biomass accumulation was significantly elevated. Besides, upregulation of the acetyl-CoA carboxylase/biotin carboxylase, digalactosyl diacylglycerol synthase and diacylglycerol acyltransferase 2 encoding genes may be attributable to the enhanced lipid production. Understanding the cellular responses during the trophic transition process could guide improvement of the strength of trophic transition enhancing microalgal biomass and lipid production.

Reactive oxygen species and their applications toward enhanced lipid accumulation in oleaginous microorganisms

Oleaginous microorganisms are among the most promising alternative sources of lipids for oleochemicals and biofuels. However, in the course of lipid production, reactive oxygen species (ROS) are generated inevitably as byproducts of aerobic metabolisms. Although excessive accumulation of ROS leads to lipid peroxidation, DNA damage, and protein denaturation, ROS accumulation has been suggested to enhance lipid synthesis in these microorganisms. There are many unresolved questions concerning this dichotomous view of ROS influence on lipid accumulation. These include what level of ROS triggers lipid overproduction, what mechanisms and targets are vital and whether ROS act as toxic byproducts or cellular messengers in these microorganisms? Here we review the current state of knowledge on ROS generation, antioxidative defense system, the dual effects of ROS on microbial lipid production, and ROS-induced lipid peroxidation and accumulation mechanisms. Toward the end, the review summarizes strategies that enhance lipid production based on ROS manipulation.

β-Carotene Production from Dunaliella salina Cultivated with Bicarbonate as Carbon Source

Bicarbonate has been considered as a better approach for supplying CO₂ to microalgae cells microenvironments than gas bubbling owing t°Cost-effectiveness and easy operation. However, the β-carotene production was too low in Dunaliella salina cultivated with bicarbonate in previous studies. Also, the difference in photosynthetic efficiency between these tw°Carbon sources (bicarbonate and CO₂) has seldom been discussed. In this study, the culture conditions, including NaHCO₃, Ca²⁺, Mg²⁺ and microelement concentrations, were optimized when bicarbonate was used as carbon source. Under optimized condition, a maximum biomass concentration of 0.71 g/l and corresponding β-carotene content of 4.76% were obtained, with β-carotene yield of 32.0 mg/l, much higher than previous studies with NaHCO₃. Finally, these optimized conditions with bicarbonate were compared with CO₂ bubbling by online monitoring. There was a notable difference in F_v/F_m value between cultivations with bicarbonate and CO₂, but there was no difference in the F_v/F_m periodic changing patterns. This indicates that the high concentration of NaHCO₃ used in this study served as a stress factor for β-carotene accumulation, although high productivity of biomass was still obtained.

Proteomic analysis of salicylic acid regulation of grain filling of two near-isogenic rice (Oryza sativa L.) varieties under soil drying condition

Grain filling is the final determinant of yield, and this process is susceptible to abiotic stresses. Salicylic acid (SA) regulates grain filling in rice plants. A comparative proteomic study was conducted to understand how SA mediates grain filling under soil drying (SD) condition. Zhefu802 and its near-isogenic line (NIL) were planted in pots in an artificial chamber. SA (100 mg L^-1) was applied, followed by SD treatment (with a water potential of -30 to -35 kPa) at anthesis. The results showed that the grain yield and grain weight significantly decreased under SD in Zhefu802, but not in its NIL variety. SD also decreased expression of photosynthesis-related proteins in grains of Zhefu802, which resulted in its poorer drought resistance. Furthermore, the decreased grain filling rate rather than the grain size explained the observed decreased grain weight and grain yield under SD. Interestingly, these reductions were reversed by SA. Expression of proteins involved in glycolysis/TCA circle, starch and sucrose metabolism, antioxidation and detoxication, oxidative phosphorylation, transcription, translation, and signal transduction, were significantly down-regulated under SD and were significantly up-regulated in response to SA. The expression of these proteins was examined at transcriptional level and similar results were obtained. Inhibited expression of these proteins and related pathways contributed to the observed decrease in the grain filling rate of Zhefu802, and application of SA up-regulated expression of these proteins to improve grain weight. The findings of this study provide new insights into grain filling regulation by SA, and offer the scientific foundation for cultivation practice.

Biochemical response of indigenous microalgal consortia to variations in nitrogen concentration of treated effluent

Cultivation conditions influence microalgal cellular components, such as lipid accumulation under nutrient depletion, high light irradiation and salinity stress. In this study, indigenous microalgal consortia were cultivated in batch mode using an actual treated effluent. The temporal response of cellular components to the variations in nitrogen concentration and influence of light irradiation on the response were investigated. Prolonged exposure of indigenous microalgal consortia to nitrogen exhaustion had minor effects on total lipid accumulation and enhancement of energy content. Nitrogen replenishment was followed by immediate crude protein accumulation for growth recovery. Total lipid reduction was observed under light and dark conditions after nitrogen replenishment. A one-day lag after nitrogen replenishment in the total lipid reduction was revealed under nitrogen depletion; meanwhile, under nitrogen exhaustion, lipids were utilised as the primary carbon and/or energy source after replenishment, as represented by the decrease from 10.8% to 9.04% within 6 h after the replenishment.