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

Design and validation of universal and taxon-specific 16S rRNA qPCR primers for detection of freshwater harmful algal bloom-forming cyanobacteria

Freshwater harmful algal bloom-forming cyanobacteria have become an increasingly prominent global concern from both environmental and human health perspectives. To enable and facilitate timely decision making in taking preventative and mitigative measures, rapid, accurate, sensitive and quantitative tools are needed for the detection and monitoring of toxin-producing cyanobacteria. Here we report the development of taxon-specific quantitative polymerase chain reaction (qPCR) primers capable of distinguishing 10 cyanobacterial genera or clade from non-target groups as well as a new set of universal primers capable of amplifying all cyanobacteria species. When evaluated by 4 stringent metrics and primer-template mismatches, these de novo designed qPCR primers outperformed published primers in amplifying the 16S rRNA gene of their target strains among the collection of 16 in-house cyanobacterial strains belonging to 10 genera. The 10 best-performing designed primers were validated using field samples from three field locations with historically documented HAB events. The field validation results corroborated with both microscopic observations and Nanopore sequencing of full-length 16S amplicons. Our study demonstrated the effectiveness of our design-screen-evaluation-validation pipeline in developing taxon-specific qPCR primers for detecting and quantifying group-specific target populations and their promising application to field HABs samples. With the advancement of massive parallel sequencing technologies and bioinformatic tools, a community-wide 16S full-length sequencing run can provide a panoramic view of the genetic diversity and site-specific variant info about the target taxa of interest, enabling the fast development of new taxon-specific qPCR assays and their refinement or modification to adapt to site-specific genetic variations in field samples.

Cyanobacteria microbiomes for bioplastic production: Critical review of key factors and challenges in scaling from laboratory to industry set-ups

Cyanobacteria are photoautotrophic microorganisms capable of accumulating polyhydroxybutyrate (PHB). A novel approach for PHB production involves the exploration of cyanobacterial microbiomes, potentially reducing costs through non-sterile cultivation with non-pure substrates. Although still in its early stages, this approach shows promise for high yields and sustained synthesis. However, managing microbiome population dynamics in non-sterile environments requires effective monitoring and control. This review covers PHB production by cyanobacteria microbiomes, from sample procurement to laboratory-scale production. It highlights recent insights into optimizing cultivation parameters for enhanced biopolymer yield. Strategies to overcome challenges in PHB production are evaluated, emphasizing integrated molecular biology techniques with quantitative and qualitative PHB analysis. Finally, key challenges in scaling up production to industrial-scale scenarios are discussed, along with potential solutions to support the development of sustainable industrial processes. Cyanobacteria microbiomes show promise PHB production but challenges like managing non-sterile conditions and scaling up require optimized strategies and integrated approaches.

Bioplastic production by harnessing cyanobacteria-rich microbiomes for long-term synthesis

Departing from the conventional axenic and heterotrophic cultures, our research ventures into unexplored territory by investigating the potential of photosynthetic microbiomes for polyhydroxybutyrate (PHB) synthesis, a biodegradable polyester that presents a sustainable alternative to conventional plastics. Our investigation focused on a cyanobacteria-enriched microbiome, dominated by Synechocystis sp. and Synechococcus sp., cultivated in a 3 L photobioreactor under non-sterile conditions, achieving significant PHB production-up to 28 % dry cell weight (dcw) over a span of 108 days through alternating cycles of biomass growth and PHB accumulation. Nile Blue staining and Transmission Electron Microscope visualization allowed to successfully confirm the presence of PHB granules within cyanobacteria cells. Furthermore, the overexpression of PHA synthase during the accumulation phase directly correlated with the increased PHB production. Also, gene expression changes revealed glycogen as the primary storage compound, but under prolonged macronutrient stress, there was a shift of the carbon flux towards favoring PHB synthesis. Finally, analysis through Raman, Fourier- transform infrared spectroscopy and proton Nuclear Magnetic Resonance further validated the extracted polymer as PHB. Overall, it was demonstrated for the first time the feasibility of using phototrophic microbiomes to continuous production of PHB in a non-sterile system. This study also offers valuable insights into the metabolic pathways involved.

New strategy for bioplastic and exopolysaccharides production: Enrichment of field microbiomes with cyanobacteria

Seven photosynthethic microbiomes were collected from field environmental samples to test their potential in polyhydroxybutyrate (PHB) and exopolysaccharides (EPS) production, both alternatives to chemical-based polymers. Microscope observations together with microbial sequence analysis revealed the microbiome enrichment in cyanobacteria after culture growth under phosphorus limitation. PHB and EPS production were studied under three culture factors (phototrophy, mixotrophy and heterotrophy) by evaluating and optimizing the effect of three parameters (organic and inorganic carbon and days under light:dark cycles) by Box-Behnken design. Results showed that optimal conditions for both biopolymers synthesis were microbiome-dependent; however, the addition of organic carbon boosted PHB production in all the tested microbiomes, producing up to 14 %dcw PHB with the addition of 1.2 g acetate·L-1 and seven days under light:dark photoperiods. The highest EPS production was 59 mg·L-1 with the addition of 1.2 g acetate·L-1 and four days under light:dark photoperiods. The methodology used is suitable for enriching microbiomes in cyanobacteria, and for testing the best conditions for bioproduct synthesis for further scale up.

Phycobiliprotein recovery coupled to the tertiary treatment of wastewater in semi-continuous photobioreactors. Tracking contaminants of emerging concern

This study evaluated a tertiary wastewater treatment technology using cyanobacteria to recover value-added phycobiliproteins. The presence of contaminants of emerging concern (CECs) in wastewater, cyanobacteria biomass and pigments recovered were also analyzed. For this, a wastewater-borne cyanobacterium (Synechocystis sp. R2020) was used to treat secondary effluent from a municipal wastewater treatment plant, with and without nutrients supplementation. Then, the stability of phycobiliprotein production was assessed by operating the photobioreactor in semi-continuous mode. Results showed similar biomass productivity with and without nutrients supplementation (153.5 and 146.7 mg L^-1 d^-1, respectively). Upon semi-continuous operation, the phycobiliprotein content was stable and reached up to 74.7 mg gDW^-1. The phycocyanin purity ratio ranged from 0.5 to 0.8, corresponding to food grade (> 0.7). Out of 22 CECs detected in secondary effluent, only 3 were present in the phycobiliprotein extract. In order to identify applications, prospective research should focus on CECs removal during pigment purification.

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.