Effect of nutrient limitation and light in the production of polyhydroxybutyrates and glycogen by cyanobacteria cultivated in wastewater

Non-degradable plastics are a serious environmental problem. The use of living resources to produce biodegradable plastics could be a possible solution. Polyhydroxybutyrates (PHB), which are polymers with similar properties to polypropylene, and glycogen, which can be converted into bioethanol, are produced by cyanobacteria and other microorganisms. Cyanobacteria have the advantage of accumulating these substances using only CO2 and solar energy. Wastewater treatment could be used as a culture medium for cyanobacteria to reduce the bioplastics production costs. The main objectives of this work are to study the use of cyanobacteria as tertiary wastewater treatment, the effect of nutrient limitations and light hours on the accumulation of PHB and glycogen, and the best way to operate a reactor to select cyanobacteria against green algae. It has been possible to eliminate 64,8% of the nitrogen and 70,5% of the phosphorus coming from the secondary treatment and the digestate. Proving the ability of cyanobacteria to remove contaminants. A maximum glycogen concentration of 838 mg / L was obtained under nitrogen limitation and 12 h light conditions and a PHB of 104,2 mg / L under phosphorus limitation and 24 h light conditions. Therefore, it can be deduced that nitrogen limitation has more effect on glycogen accumulation, and phosphor on PHB. However, according to the defined economical Key performance indicator (KPI) the product benefits do not justify the lighting expenses. Finally, it can be said that the optimal cultivation conditions are limitation of phosphor and 12h light per day

Selection of cyanobacteria over green algae in a photo-sequencing batch bioreactor fed with wastewater

In this work, a strategy based on photo-sequencing batch operationwas used to select cyanobacteria over unsettled green algae in awastewater treatment system, evaluating for the first time the effect of hydraulic regimes on nutritional dynamics and microorganisms' competition. During 30 days of operation, an initial microalgae mixed consortia dominated by the green microalgae Scenedesmus sp. was cultivated in two different photo-sequencing batch reactors operated at hydraulic retention time (HRT) of 6 days (PSBR6) and 4 days (PSBR4) at a theoretical solids retention time (SRT) of 10 d. Both reactorswere compared with a semi-continuous reactor (SC10) operated at 10 d of HRT and 10 days of SRT (used as a control). The results indicated that PSBR6 and PSBR4 decreased Scenedesmus sp. population by 88% and 48%, respectively. However, only PSBR6 provided suitable conditions to select cyanobacteria from an initial green algae dominated culture. These conditions included volumetric loads of 11.72 mg TN L-1 d-1, 2.04mg TP L-1 d-1 and 53.31 mg TOC L-1 d-1. The remaining nutrients in the culture led also to a phosphorus limiting N:P ratio (34:1) that improved the increase of cyanobacteria from an initial 2% until 70% of the total population. In addition, PSBR6 reached a biomass production of 0.12 g L-1 d-1,while removing TN, TP and TOC by 58%, 83% and 85%, respectively. Conversely, the application of higher nutrients loads caused by lowerHRT (PSBR4) led to an increase of only 13% of cyanobacteriawhile SC10 remainedwith the same biomass composition during all the experimental time. Thus, this study showed that the dominance of cyanobacteria in microalgal-based wastewater treatment systems can be controlled by the operational and nutritional conditionsPeer ReviewedPostprint (author's final draft

Inorganic carbon stimulates the metabolic routes related to the polyhydroxybutyrate production in a Synechocystis sp. strain (cyanobacteria) isolated from wastewater

Cyanobacteria are capable of transforming CO2 into polyhydroxybutyrate (PHB). In this study, different inorganic carbon concentrations (0–2 gC L−1) were evaluated for a Synechocystis sp. strain isolated from wastewater. Quantitative RT-qPCR was also performed to decipher the links between inorganic carbon and PHB and glycogen metabolism. 2 gC L−1 of bicarbonate stimulated cell growth, nutrients consumption and production of PHB. Using this concentration, a 14%dcw of PHB and an average productivity of 2.45 mgPHB L−1 d−1 were obtained. Gene expression analysis revelated that these conditions caused the overexpression of genes related to glycogen and PHB synthesis. Moreover, a positive correlation between the genes codifying for the glycogen phosphorylase, the acetyl-CoA reductase and the poly(3-hydroxyalkanoate) polymerase was found, meaning that PHB synthesis and glycogen catabolism are strongly related. These results provide an exhaustive evaluation of the effect of carbon on the PHB production and cyanobacterial metabolism

Polyhydroxybutyrate and glycogen production in photobioreactors inoculated with wastewater borne cyanobacteria monocultures

The aim of this study was to investigate the PHB and glycogen accumulation dynamics in two photobioreactors inoculated with different monocultures of wastewater-borne cyanobacteria, using a three-stage feeding strategy (growth phase, feast-famine phase and feast phase). Two cyanobacterial monocultures containing members of Synechocystis sp. or Synechococcus sp. were collected from treated wastewater and inoculated in lab-scale photobioreactors to evaluate the PHB and glycogen accumulation. A third photobioreactor with a complex microbial community grown in real wastewater was also set up. During each experimental phase different concentrations of inorganic carbon were applied to the cultures, these shifts allowed to discern the accumulation mechanism of carbon storage polymers (PHB and glycogen) in cyanobacteria. Conversion of one into the other was directly related to the carbon content. The highest PHB and glycogen contents (5.04%dcw and 69%dcw, respectively) were achieved for Synechocystis sp

Inorganic carbon stimulates the metabolic routes related to the polyhdroxybutyrate production in a Synechocystis sp. strain (cyanobacteria) isolated from wastewater

Cyanobacteria are capable of transforming CO2 into polyhydroxybutyrate (PHB). In this study, different inorganic carbon concentrations (0–2 gC L-1) were evaluated for a Synechocystis sp. strain isolated from wastewater. Quantitative RT-qPCR was also performed to decipher the links between inorganic carbon and PHB and glycogen metabolism. 2 gC L-1 of bicarbonate stimulated cell growth, nutrients consumption and production of PHB. Using this concentration, a 14%dcw of PHB and an average productivity of 2.45 mgPHB L-1 d-1 were obtained. Gene expression analysis revelated that these conditions caused the overexpression of genes related to glycogen and PHB synthesis. Moreover, a positive correlation between the genes codifying for the glycogen phosphorylase, the acetyl-CoA reductase and the poly(3-hydroxyalkanoate) polymerase was found, meaning that PHB synthesis and glycogen catabolism are strongly related. These results provide an exhaustive evaluation of the effect of carbon on the PHB production and cyanobacterial metabolism.Authors want to acknowledge the support received by the Spanish Ministry of Science, Innovation and Universities (MCIU), the Research National Agency (AEI), and the European Regional Development Fund (FEDER) [AL4BIO, RTI2018-099495-B-C21]. Estel Rueda thanks the Spanish Ministry of Education, Culture and Sport [FPU18/04941] for her grant. Joaquim Vila is a Serra Húnter Fellow (Generalitat de Catalunya). Rubén Díez-Montero would also like to thank the Spanish Ministry of Industry and Economy for his research grants [IJC2019-042069-I].Peer ReviewedPostprint (published version

Production of phycobiliproteins, bioplastics and lipids by the cyanobacteria Synechocystis sp. treating secondary effluent in a biorefinery approach

Cyanobacteria have been identified as promising organisms to reuse nutrients from waste effluents and produce valuable compounds such as lipids, polyhydroxyalkanoates (PHAs), and pigments. However, almost all studies on cyanobacterial biorefineries have been performed under lab scale and short cultivation periods. The present study evaluates the cultivation of the cyanobacterium Synechocystis sp. in a pilot scale 30 L semi-continuous photobioreactor fed with secondary effluent for a period of 120 days to produce phycobiliproteins, polyhydroxybutyrate (PHB) and lipids. To this end, the harvested biomass from the semi-continuous photobioreactor was transferred into 5 L vertical column batch photobioreactors to perform PHB and lipid accumulation under nutrient starvation. Three hydraulic retention times (HRT) (6, 8 and 10 days) were tested in the semi-continuous photobioreactor to evaluate its influence on biomass growth and microbial community. A maximum biomass concentration of 1.413 g L-1 and maximum productivity of 173 mg L-1 d-1 was reached under HRT of 8 days. Microscopy analysis revealed a shift from Synechocystis sp. to Leptolyngbya sp. and green algae when HRT of 6 days was used. Continuous, stable production of phycobiliproteins in the semi-continuous photobioreactor was obtained, reaching a maximum content of 7.4%dcw in the biomass. In the batch photobioreactors a PHB content of 4.8%dcw was reached under 7 days of nitrogen and phosphorus starvation, while a lipids content of 44.7%dcw was achieved under 30 days of nitrogen starvation. PHB and lipids production was strongly dependent on the amount of nutrients withdrawn from the grow phase. In the case of lipids, their production was stimulated when there was only phosphorus depletion. While Nitrogen and phosphorus limitation was needed to enhance the PHB production. In conclusion, this study demonstrates the feasibility of cultivating cyanobacteria in treated wastewater to produce bio-based valuable compounds within a circular bioeconomy approach.This research was funded by the Spanish Ministry of Science, Innovation and Universities (MCIU), the Research National Agency (AEI), and the European Regional Development Fund (FEDER) [AL4BIO, RTI2018-099495-B-C21]. Estel Rueda is grateful to the Spanish Ministry of Education, Culture and Sport (FPU18/04941), Marta Bellver is grateful to the Spanish Ministry of Science and Innovation (PRE2019-091552) and Rubén Díez-Montero is grateful to the Spanish Ministry of Industry and Economy (IJC2019-042069-I) for their research grants.Peer ReviewedPostprint (published version

Photosynthetic production of polyhydroxybutyrates (PHB) by cyanobacteria isolated from wastewater treatment processes

Polyhydroxybutirates (PHB) are a promising alternative to conventional plastics as they can be biodegraded and they have similar properties to ordinary plastics. PHB production by cyanobacteria can reduce the production costs of this bioplastics whereas a carbon neutral production process is achieved. The main objectives of this work were to isolate cyanobacterial from a system fed with wastewater and to study the PHB accumulation using a three-stage feeding strategy (growth phase, feast-famine phase and feast phase). Synechocystis sp, Synechococcus sp, Leptolyngbya sp, and Microcoleus sp, were isolated and a 5.04 %dcw of PHB and a 69%dcw of glycogen were reachedEls polihidroxibutirats (PHB) són una alternativa prometedora als plàstics convencionals perquè tenen propietats similars i poden ser biodegradats. Produir PHB amb cianobacteris redueix els costos de producció, a la vegada que aconsegueix un procés neutral en carboni. Els objectius d'aquest treball van ser aïllar cianobacteris a partir d'un sistema alimentat amb aigües residuals i estudiar l'acumulació de PHB mitjançant una estratègia en tres etapes (fase de creixement, fase de festa-fam, i fase de festa). Es van aïllar Synechocystis sp, Synechococcus sp, Leptolyngbya sp, i Microcoleus sp, i es va aconseguir un 5.04 %dcw de PHB i un 69%dcw de glucoge

Photosynthetic production of polyhydroxybutyrates (PHB) by cyanobacteria isolated from wastewater treatment processes

Polyhydroxybutirates (PHB) are a promising alternative to conventional plastics as they can be biodegraded and they have similar properties to ordinary plastics. PHB production by cyanobacteria can reduce the production costs of this bioplastics whereas a carbon neutral production process is achieved. The main objectives of this work were to isolate cyanobacterial from a system fed with wastewater and to study the PHB accumulation using a three-stage feeding strategy (growth phase, feast-famine phase and feast phase). Synechocystis sp, Synechococcus sp, Leptolyngbya sp, and Microcoleus sp, were isolated and a 5.04 %dcw of PHB and a 69%dcw of glycogen were reachedEls polihidroxibutirats (PHB) són una alternativa prometedora als plàstics convencionals perquè tenen propietats similars i poden ser biodegradats. Produir PHB amb cianobacteris redueix els costos de producció, a la vegada que aconsegueix un procés neutral en carboni. Els objectius d'aquest treball van ser aïllar cianobacteris a partir d'un sistema alimentat amb aigües residuals i estudiar l'acumulació de PHB mitjançant una estratègia en tres etapes (fase de creixement, fase de festa-fam, i fase de festa). Es van aïllar Synechocystis sp, Synechococcus sp, Leptolyngbya sp, i Microcoleus sp, i es va aconseguir un 5.04 %dcw de PHB i un 69%dcw de glucoge