Cyanobacterial Strains Research Articles

Trichocoleus desertorum isolated from Negev desert petroglyphs: Characterization, adaptation and bioerosion potential

The Negev petroglyphs are considered valuable cultural heritage sites, but unfortunately, they are exposed to deterioration processes caused by anthropogenic and natural forces. Despite the many studies that have already pointed to the role of cyanobacteria in biogenic rock weathering, the knowledge involved in the process is still lacking. In this study, a cyanobacterial strain was isolated from the Negev Desert petroglyphs aiming to reveal its involvement in geochemical cycles and in the weathering processes of the rock substrate. The strain was characterized using morphological, molecular, and microscopic studies. The morphological research revealed a green-bluish, bundle-forming filamentous strain characterized by trichomes embedded in a common sheath. A combination of Nanopore and Illumina sequencing technologies facilitated the assembly of a near-complete genome containing 5,458,034 base pairs. A total of 5027 coding sequences were revealed by implementing PROKKA software. Annotation of five replicas of the 16S ribosomal RNA genes revealed that the Negev cyanobacteria isolate is closely (99.73 %) related to Trichocoleus desertorum LSB90_MW403957 isolated from the Sahara Desert, Algeria. The local strain was thus named Trichocoleus desertorum NBK24 CP116619. Several gene sequences that code for possible environmental adaptation mechanisms were found. Our study also identified genes for membrane transporters involved in the exchange of chemical elements, suggesting a possible interaction with rock minerals. Microscopic observations of T. desertorum NBK24 CP116619 infected onto calcareous stone slabs under laboratory conditions demonstrated the effect of the isolated cyanobacteria on stone surface degradation. In conclusion, the findings of this study further our understanding of terrestrial cyanobacterial genomes and functions and highlight the role of T. desertorum NBK24 CP116619 in stone weathering processes. This information may contribute to the creation of efficient restoration strategies for stone monuments affected by cyanobacteria.

Heterotrophy among Cyanobacteria.

Cyanobacteria have been studied in recent decades to investigate the principle mechanisms of plant-type oxygenic photosynthesis, as they are the inventors of this process, and their cultivation and research is much easier compared to land plants. Nevertheless, many cyanobacterial strains possess the capacity for at least some forms of heterotrophic growth. This review demonstrates that cyanobacteria are much more than simple photoautotrophs, and their flexibility toward different environmental conditions has been underestimated in the past. It summarizes the strains capable of heterotrophy known by date structured by their phylogeny and lists the possible substrates for heterotrophy for each of them in a table in the Supporting Information. The conditions are discussed in detail that cause heterotrophic growth for each strain in order to allow for reproduction of the results. The review explains the importance of this knowledge for the use of new methods of cyanobacterial cultivation, which may be advantageous under certain conditions. It seeks to stimulate other researchers to identify new strains capable of heterotrophy that have not been known so far.

New terrestrial cyanobacteria from the Azores Islands: description of Venetifunis gen. nov. and new species of Albertania, Kovacikia and Pegethrix

ABSTRACT The taxonomy of cyanobacteria has advanced quickly with the use of molecular methods in combination with well-defined morphological and ecological characters. Using this approach, many taxonomical changes have occurred in the Synechococcales and Oscillatoriales, with the description of new families, genera and species. Here we present the study of four cyanobacterial strains from the Bank of Algae and Cyanobacteria of the Azores (BACA) culture collection, all isolated from the Azores Archipelago. The strains were genetically characterized through the amplification of the 16S rRNA gene and 16S-23S rRNA internal transcribed spacer (ITS) region, as well as morphologically by light and transmission electron microscopy. One of the strains presented a high genetic divergence from known genera of Synechococcales and was described as Venetifunis florensis gen. & sp. nov. (Trichocoleusaceae, Cyanobacteria). The remaining three strains were found to be new species of the genera Albertania, Kovacikia and Pegethrix. Venetifunis florensis was isolated from the shores of Lake Rasa in Flores Island, Kovacikia atmophytica sp. nov. is a new species mainly distinguished genetically from other Kovacikia species from Terceira Island. Albertania obscura sp. nov. was isolated from inside a volcanic cave in Terceira Island and is distinct both morphologically and genetically from the already described species. Pegethrix atlantica sp. nov. is a new morphologically and genetically different species isolated from São Miguel Island. The description of these new taxa increases the biogeographic knowledge of the four mentioned cyanobacterial genera to remote oceanic islands and new terrestrial habitats.

Pigment assemblages in subtropical bloom-forming cyanobacteria strains

Abstract Pigments are powerful indicators for chemotaxonomy and remote sensing studies, which are the approaches used for cyanobacterial bloom monitoring. Cyanobacterial pigments include high concentrations of phycobilins and diverse carotenoids. Filamentous nitrogen-fixing species (Nostocales) are frequent in cyanobacterial blooms of warm climate lakes, and more information about pigments can be useful for improving management. We analyzed the carotenoid ratios to chlorophyll a of nine subtropical cyanobacterial strains (orders: Synechococcales, Chroococcales, Oscillatoriales and Nostocales), for some of which we also characterized the in vivo absorption spectra (aph). The main carotenoids were β,β-carotene, echinenone, hydroxy-echinenone-like, zeaxanthin and myxoxanthophyll (including aphanizophyll and unknown myxoxanthophyll-like myxol-glycoside carotenoids); however, proportions diverged greatly between orders, a trend also observed for the aph. Zeaxanthin ratios were highest in the picocyanobacterium. Nostocales species were rich in myxoxanthophyll and echinenone, with low zeaxanthin signals. We identified four pigment assemblages differentiating the strains according to their phylogenetic orders, information that needs to be considered for tracking cyanobacterial groups, particularly Nostocales.

Initial type and abundance of cyanobacteria determine morphotype development of phototrophic ecosystems.

Phototrophic aggregates containing filamentous cyanobacteria occur naturally, for example, as cryoconite on glaciers and microbialites in fresh or marine waters, but their formation is not fully understood. Laboratory models are now available to reproduce aggregation, that is, the formation of different morphotypes like hemispheroids, microbial mats or sphere-like aggregates we call photogranules. In the model, activated sludge as starting matrix is transformed into aggregates enclosed by a phototrophic layer of growing cyanobacteria. These cyanobacteria were either enriched from the matrix or we added them intentionally. We hypothesize that the resulting morphotype depends on the type and concentration of the added cyanobacteria. When cyanobacteria from mature photogranules were added to activated sludge, photogranulation was not observed, but microbial mats were formed. Photogranulation of sludge could be promoted when adding sufficient quantities of cyanobacterial strains that form clumps when grown as isolates. The cyanobacteria putatively responsible for photogranulation were undetectable or only present in low abundance in the final communities of photogranules, which were always dominated by mat-forming cyanobacteria. We suggest that, in a temporal succession, the ecosystem engineer initiating photogranulation eventually disappears, leaving behind its structural legacy. We conclude that understanding phototrophic aggregate formation requires considering the initial succession stages of the ecosystem development.

Bioprospecting for industrially relevant exopolysaccharide-producing cyanobacteria under Portuguese simulated climate

Cyanobacterial exopolysaccharides (EPS) are potential candidates for the production of sustainable biopolymers. Although the bioactive and physicochemical properties of cyanobacterial-based EPS are attractive, their commercial exploitation is limited by the high production costs. Bioprospecting and characterizing novel EPS-producing strains for industrially relevant conditions is key to facilitate their implementation in various biotechnological applications and fields. In the present work, we selected twenty-five Portuguese cyanobacterial strains from a diverse taxonomic range (including some genera studied for the first time) to be grown in diel light and temperature, simulating the Portuguese climate conditions, and evaluated their growth performance and proximal composition of macronutrients. Synechocystis and Cyanobium genera, from marine and freshwater origin, were highlighted as fast-growing (0.1–0.2 g L−1 day−1) with distinct biomass composition. Synechocystis sp. LEGE 07367 and Chroococcales cyanobacterium LEGE 19970, showed a production of 0.3 and 0.4 g L−1 of released polysaccharides (RPS). These were found to be glucan-based polymers with high molecular weight and a low number of monosaccharides than usually reported for cyanobacterial EPS. In addition, the absence of known cyanotoxins in these two RPS producers was also confirmed. This work provides the initial steps for the development of cyanobacterial EPS bioprocesses under the Portuguese climate.

Energy transfer and trapping in photosystem I with and without chlorophyll-f

We establish a general kinetic scheme for energy transfer and trapping in the photosystem I (PSI) of cyanobacteria grown under white light (WL) or far-red light (FRL) conditions. With the help of simultaneous target analysis of all emission and transient absorption datasets measured in five cyanobacterial strains, we resolved the spectral and kinetic properties of the different species present in PSI. WL-PSI can be described by Bulk Chl a, two Red Chl a, and a reaction center compartment (WL-RC). The FRL-PSI contains two additional Chl f compartments. The lowest excited state of the FRL-RC is downshifted by≈ 29nm. The rate of charge separation drops from≈900ns-1 in WL-RC to≈300ns-1 in FRL-RC. The delayed trapping in the FRL-PSI (≈130 ps) is explained by uphill energy transfer from the Chl f compartments with Gibbs free energies of≈kBT below that of the FRL-RC.

Impact of the carbon flux regulator protein pirC on ethanol production in engineered cyanobacteria.

Future sustainable energy production can be achieved using mass cultures of photoautotrophic microorganisms such as cyanobacteria, which are engineered to synthesize valuable products directly from CO2 and sunlight. For example, strains of the model organism Synechocystis sp. PCC 6803 have been generated to produce ethanol. Here, we performed a study to prove the hypothesis that carbon flux in the direction of pyruvate is one bottleneck to achieve high ethanol titers in cyanobacteria. Ethanol-producing strains of the cyanobacterium Synechocystis sp. PCC 6803 were generated that bear mutation in the gene pirC aiming to increase carbon flux towards pyruvate. The strains were cultivated at different nitrogen or carbon conditions and the ethanol production was analysed. Generally, a clear correlation between growth rate and ethanol production was found. The mutation of pirC, however, had only a positive impact on ethanol titers under nitrogen depletion. The increase in ethanol was accompanied by elevated pyruvate and lowered glycogen levels indicating that the absence of pirC indeed increased carbon partitioning towards lower glycolysis. Metabolome analysis revealed that this change in carbon flow had also a marked impact on the overall primary metabolism in Synechocystis sp. PCC 6803. Deletion of pirC improved ethanol production under specific conditions supporting the notion that a better understanding of regulatory mechanisms involved in cyanobacterial carbon partitioning is needed to engineer more productive cyanobacterial strains.

Saxitoxin-Producing Raphidiopsis raciborskii (Cyanobacteria) Constrains Daphnia Fitness and Feeding Rate despite High Nutritious Food Availability.

Changes in food quality can dramatically impair zooplankton fitness, especially in eutrophic water bodies where cyanobacteria are usually predominant. Cyanobacteria are considered a food with low nutritional value, and some species can produce bioactive secondary metabolites reported as toxic to zooplankton. Considering that cyanobacteria can limit the survival, growth and reproduction of zooplankton, we hypothesized that the dietary exposure of neotropical Daphnia species (D. laevis and D. gessneri) to saxitoxin-producing cyanobacteria impairs Daphnia feeding rates and fitness regardless of a high availability of nutritious algae. Life table and grazing assays were conducted with different diets: (1) without nutritional restriction, where neonates were fed with diets at a constant green algae biomass (as a nutritious food source), and an increasing cyanobacterial concentration (toxic and poor food source), and (2) with diets consisting of different proportions of green algae (nutritious) and cyanobacteria (poor food) at a total biomass 1.0 mg C L-1. In general, the presence of high proportions of cyanobacteria promoted a decrease in Daphnia somatic growth, reproduction and the intrinsic rate of population increase (r) in both diets with more pronounced effects in the nutritionally restricted diet (90% R. raciborskii). A two-way ANOVA revealed the significant effects of species/clone and treatments in both assays, with significant interaction between those factors only in the second assay. Regarding the grazing assay, only D. laevis was negatively affected by increased cyanobacterial proportions in the diet. In the life table assay with constant nutritious food, a reduction in the reproduction and the intrinsic rate of the population increase (r) of all species were observed. In conclusion, we found adverse effects of the toxic cyanobacterial strain R. raciborskii on Daphnia fitness, regardless of the constant amount of nutritious food available, proving the toxic effect of R. raciborskii and that the nutritional quality of the food has a greater influence on the fitness of these animals.

Investigation on cyanobacterial production of the proposed neurotoxin β-N-methylamino-L-alanine (BMAA)

β-N-methylamino-L-alanine (BMAA) is an environmental neurotoxin thought to be produced by cyanobacteria. However, the cyanobacterial origin of BMAA remains controversial. The detection method and culture conditions of cyanobacteria are often cited as factors behind the discrepancy of published results. We showed previously that BMAA was highly toxic to the cyanobacterium Nostoc PCC 7120, and it is taken up via an amino acid transport system. Using a mutant ΔnatAΔbgtA deficient in amino acid transport as a genetic control, we show here that BMAA taken up from the medium can be detected quantitatively at a threshold similar to, or below those reported, but was undetectable in the mutant. The BMAA isomer, 2,4-diaminobutanoic acids (DAB), but not BMAA, could be detected in cell free extracts of Nostoc PCC 7120. Long-term (20 ​days) diazotrophic growth or non-limiting supply of phosphate, conditions reported to enhance BMAA synthesis, did not lead to the detection of BMAA. An UPLC-MS/MS signal with a similar retention time to BMAA was found after prolonged diazotrophic incubation, but did not have fragment ions of BMAA after further analysis. When extended to 29 different cyanobacterial strains and 6 natural cyanobacterial bloom samples, none of them was found to produce BMAA. The cytotoxicity of BMAA to cyanobacteria, and the lack of a cellular protective mechanism against such toxicity, contradict the presence of a BMAA synthesis pathway in these organisms. More specific methods for BMAA detection in vivo need to be developed to clarify the cyanobacterial origin of BMAA.

Cyanobacterial Biofuel: A Platform for Green Energy

Cyanobacteria have great potential as a platform for biofuel production because of their fast growth, ability to fix CO<sub>2 </sub>gas, and genetic tractability. They also preserve the sustainability of an ecosystem without harming the environment. High-performance biofuels made from cyanobacteria can be utilized as a base for the production of green energy. Although a lot of studies have been conducted where plants and crops are used as the source of energy, cyanobacteria have been reported to have a more efficient photosynthetic process strongly responsible for increased production with limited land input along with affordable cost. The production of cyanobacteria-based biofuels can be accelerated through genetic engineering or genomics research, which may help to meet the global demand for these fuels on a large scale. Cyanobacterial strains that have undergone genetic modifications have been developed as part of a green recovery approach to transform membrane lipids into fatty acids to produce cheap and eco-friendly green energy. Cyanobacteria also produce different biofuels such as butanol, ethanol and isoprene. The four different generations of biofuel production to meet the energy requirement have been discussed in this review. This review presents a comprehensive strategy for the commercial viability of green energy production utilizing cyanobacteria to achieve a price for biofuels that can compete with the present or future market.

Morphological and Molecular Evaluation of Pseudanabaena epilithica sp. nov. and P. suomiensis sp. nov. (Pseudanabaenaceae, Cyanobacteria) from Finland

Cyanobacteria represent a cosmopolitan group of oxyphototrophic bacteria. Although free-living cyanobacteria thriving in aquatic habitats as well as cyanobacteria in terrestrial symbiotic systems (lichens) have been extensively studied in Finland, the diversity of terrestrial rock-inhabiting cyanobacteria is overlooked. As part of an ongoing effort to study terrestrial epilithic cyanobacteria from Finland, we isolated two Pseudanabaena-like cyanobacterial strains and characterized them using a polyphasic approach. Although the two strains were firmly placed within the Pseudanabaena clade in the 16S rRNA phylogenetic analyses, relationships among species were better resolved when phylogenetic analyses were based on a concatenate alignment of 16S rRNA gene and 16S–23S Internal Transcribed Spacer (ITS) region. In addition, 16S–23S ITS percent dissimilarity proved to be more useful for species discrimination in Pseudanabaena compared to secondary structures of conserved 16S–23S ITS domains (D1–D1′, box B, V2 and V3 helices). Considering morphological, molecular and ecological information, we describe P. epilithica sp. nov. and P. suomiensis sp. nov. under the provisions of the International Code of Nomenclature for Algae, Fungi and Plants. Neither toxins nor antimicrobial metabolites were detected during LC-MS analysis or antimicrobial susceptibility testing, respectively. Lastly, our phylogenetic analyses revealed that many Pseudanabaena strains are misidentified and highlight the need for taxonomic revision in this poorly studied cyanobacterial genus.

Diversity, metabolome profiling and bioactivities of benthic filamentous cyanobacteria isolated from coastal mangroves of Mayotte

IntroductionCyanobacteria are important members of the dense biofilms that colonize available substrates in mangrove habitats worldwide. However, their taxonomic diversity and biological activities have received little attention.MethodsThe occurrence of cyanobacteria is evaluated in 27 biofilms collected from mangroves in Mayotte. Filamentous cyanobacterial strains were isolated and characterized using 16S rRNA comparative gene sequence analysis. LC-MS/MS experiments were performed on the crude extracts of the faster-growing strains, and construction of their molecular network showed a conspectus of their chemical diversity. Biological activities of the strain extracts were then evaluated using standard assays.Results and discussionIsolation procedures yielded 43 strains representing 22 species-level taxa, of which only three could be assigned to existing species. Some of these strains were among the most abundant cyanobacteria present in biofilms. PCR assays did not support the production of the major cyanotoxins. Analysis of metabolites from 23 strains using both in silico tools ISDB- DNP (In silico Data Base–Dictionary of Natural Products) and MolDiscovery, revealed occurrence of godavarin K, a limonoid natural product previously isolated from the seeds of an Indian mangrove tree. This annotation was further confirmed by the marine database MarinLit, suggesting that cyanobacteria might be an alternative source of godavarin K and its four isomers. While no significant antimicrobial and cytotoxic activities were observed, some strains exhibited anthelmintic and antibiofilm activities that warrant further investigation and may be relevant to biofilm ecology. Mangrove biofilms thus appear to be an untapped reservoir of novel culturable cyanobacterial lineages, with bioactivities relevant to their biofilm lifestyle, which may be of interest for bioinspiration.

Bio-Characterization and Liquid Chromatography-Mass Spectrometry Analysis of Exopolysaccharides in Biofilm-Producing Cyanobacteria Isolated from Soil Crust: Exploring the Potential of Microalgal Biomolecules.

Exopolysaccharide-producing cyanobacterial strains in biological soil crusts are described, in addition to their chemical properties and antioxidant and flocculation activities. The EPSs from Pudukkottai blackish biological soil crusts (PBBSCs) showed significant amounts of total soluble proteins (0.1687 mg/mL) and carbohydrates (0.8056 mg/mL) compared with the Ariyalur blackish biological soil crusts (ABBSCs). LC-MS analysis of the cyanobacterial polysaccharides revealed the presence of natural sugars such as ribose and glucose/mannose, and uronic acids. The FTIR spectrum showed specific peak for OH and -NH stretching, C-H stretching, and carboxylic acids as the dominant groups in EPS. The in vitro DPPH assay of EPSs from PBBSCs showed 74.3% scavenging activity. Furthermore, the reducing power was determined to be 0.59 ata 500 mg/mL concentration, respectively. The extracted EPSs from the biological soil crust flocculated Kaolin clay suspension maximum at 500 mg/mL. Consequently, the cyanobacterial strain and exopolysaccharide characterization from the sacred forest's biological soil crust were analyzed for their bioactive potential, bio-crust diversity, and distribution.

Phosphorus storage and utilization strategies of two bloom-forming freshwater cyanobacteria.

The inter-relationships between cellular phosphorus (P) storage, dissolved inorganic P (DIP) uptake affinity, alkaline phosphatase activity (APA) and dissolved inorganic nitrogen (DIN) concentrations were studied in two ubiquitous diazotrophic freshwater cyanobacteria, Raphidiopsis raciborskii (six strains) and Chrysosporum ovalisporum (two strains). DIP uptake kinetics were measured using rates of incorporation of the radio-isotope, 33P and APA as a proxy for DOP-ester utilization. The study showed that DIP uptake of individual strains followed Michaelis-Menten kinetics (modified in our study to incorporate cellular P quotas), but differed with DIN and P availability, and between growth stages. High-affinity DIP uptake and APA were activated below a P quota threshold of approximately 0.01 µg P µg-1 C across the species and strains. C. ovalisporum had significantly higher APA and P quotas (per unit C and cell) but lower uptake affinity than R. raciborskii. Demand for DIP by C. ovalisporum increased when N fixation occurred, but typically not for R. raciborskii. Our results indicate that cyanobacterial species and strains differ in their strategies to P limiting conditions, and highlight the interplay between N and P. Physiological adaptations like APA and diazotrophy of cyanobacteria adapting to low DIP and/or DIN conditions may occur simultaneously and drive species dominance in oligotrophic environments.

Assessment of taxonomically diverse Chlorococcum species and Chroococcus species for cell density, pigments, biochemical components, and fatty acid composition for fuel/food applications

In this study, a comparison of two microalgal and two cyanobacterial species for biomass yield, carbohydrate, protein, lipids, chlorophyll, and fatty acids was carried out to evaluate their potential for fuel/food/feed applications. Among the tested green algal strains, Chlorococcum sp. isolate 4, Chlorococcum sp. isolate 5, and cyanobacterial strains Chroococcus sp. isolate 1, Chroococcus sp. isolate 2, Chlorococcum sp. isolate 4 were found to yield higher biomass, i.e. about 1.33 g/L (under aeration), 1.21 g/L (no aeration condition) on the 24th day and it also showed higher chlorophyll content of 14.3 mg/g dry cell weight than other species. Besides, a maximal carbohydrate and protein content of 63.7 % and 27.3 %, respectively, were noticed in Chlorococcum sp. isolate 4. The lipid contents of Chlorococcum sp. isolate 4, Chlorococcum sp. isolate 5, Chroococcus sp. isolate 1 and Chroococcus sp. isolate 2 were 18.3, 16.7, 4.7, and 3.8 %, respectively. Eventually, the biodiesel production potential of Chlorococcum sp. isolate 4 showed 29.83, 9.11, 8.22, 19.42, 9.22 and 10.68 % of palmitic, palmitoleic, stearic, oleic, linoleic, and linolenic acid, respectively. Among the strains studied, Chlorococcum sp. isolate 4 can be proposed to be an ideal feedstock for the production of biodiesel and other high-value products due to its higher content of biomass, proteins, carbohydrates, total lipids, and desirable fatty acid composition.

Metabolic engineering of Synechococcus elongatus for photoautotrophic production of mannitol.

With multiple applications in food, pharmaceutical, and chemical industries as antioxidant or nonmetabolizable sweetener; the bioproduction of d-mannitol is gaining global attention, especially with photosynthetic organisms as hosts. Considering the sustainability prospects, the current work encompasses metabolic engineering of a widely used cyanobacterial strain, Synechococcus elongatus PCC 7942, and two newly isolated fast-growing cyanobacterial strains; S. elongatus PCC 11801 and S. elongatus PCC 11802, for mannitol production. We engineered these strains with a two-step pathway by cloning genes for mannitol-1-phosphate dehydrogenase (mtlD) and mannitol-1-phosphatase (mlp), where the mtlD expression was under the control of different promoters from PCC 7942, namely, Prbc225 , PcpcB300 , PcpcBm1 , PrbcLm17 , and PrbcLm15 . The strains were tested under the "switch conditions," where the growth conditions were switched after the first 3 days, thereby resulting in differential promoter activity. Among the engineered strains of PCC 11801 and PCC 11802, the strains possessing Prbc225 -mtlD module produced relatively high mannitol titers of 401 ± 18 mg/L and 537 ± 18 mg/L, respectively. The highest mannitol titer of 701 ± 15 mg/L (productivity 60 mg/L.d, yield 895 µM/OD730 ) was exhibited by the engineered strain of PCC 7942 expressing PcpcB300 -mtlD module. It is by far the highest obtained mannitol yield from the engineered cyanobacteria.

Laboratory evolution of Synechocystis sp. PCC 6803 for phenylpropanoid production

Cyanobacteria are promising as a biotechnological platform for production of various industrially relevant compounds, including aromatic amino acids and their derivatives, phenylpropanoids. In this study, we have generated phenylalanine resistant mutant strains (PRMs) of the unicellular cyanobacterium Synechocystis sp. PCC 6803, by laboratory evolution under the selective pressure of phenylalanine, which inhibits the growth of wild type Synechocystis. The new strains of Synechocystis were tested for their ability to secrete phenylalanine in the growth medium during cultivation in shake flasks as well as in a high-density cultivation (HDC) system. All PRM strains secreted phenylalanine into the culture medium, with one of the mutants, PRM8, demonstrating the highest specific production of 24.9 ± 7 mg L−1·OD750−1 or 610 ± 196 mg L−1 phenylalanine after four days of growth in HDC. We further overexpressed phenylalanine ammonia lyase (PAL) and tyrosine ammonia lyase (TAL) in the mutant strains in order to determine the potential of PRMs for production of trans-cinnamic acid (tCA) and para-coumaric acid (pCou), the first intermediates of the plant phenylpropanoid pathway. Productivities of these compounds were found to be lower in the PRMs compared to respective control strains, except for PRM8 under HDC conditions. The PRM8 background strain in combination with PAL or TAL expression demonstrated a specific production of 52.7 ± 15 mg L−1·OD750−1tCA and 47.1 ± 7 mg L−1·OD750−1pCou, respectively, with a volumetric titer reaching above 1 g L−1 for both products after four days of HDC cultivation. The genomes of PRMs were sequenced in order to identify which mutations caused the phenotype. Interestingly, all of the PRMs contained at least one mutation in their ccmA gene, which encodes DAHP synthase, the first enzyme of the pathway for aromatic amino acids biosynthesis. Altogether, we demonstrate that the combination of laboratory-evolved mutants and targeted metabolic engineering can be a powerful tool in cyanobacterial strain development.

Impact of dehydration on the physiochemical properties of Nostoc calcicola BOT1 and its untargeted metabolic profiling through UHPLC-HRMS.

The global population growth has led to a higher demand for food production, necessitating improvements in agricultural productivity. However, abiotic and biotic stresses pose significant challenges, reducing crop yields and impacting economic and social welfare. Drought, in particular, severely constrains agriculture, resulting in unproductive soil, reduced farmland, and jeopardized food security. Recently, the role of cyanobacteria from soil biocrusts in rehabilitating degraded land has gained attention due to their ability to enhance soil fertility and prevent erosion. The present study focused on Nostoc calcicola BOT1, an aquatic, diazotrophic cyanobacterial strain collected from an agricultural field at Banaras Hindu University, Varanasi, India. The aim was to investigate the effects of different dehydration treatments, specifically air drying (AD) and desiccator drying (DD) at various time intervals, on the physicochemical properties of N. calcicola BOT1. The impact of dehydration was assessed by analyzing the photosynthetic efficiency, pigments, biomolecules (carbohydrates, lipids, proteins, osmoprotectants), stress biomarkers, and non-enzymatic antioxidants. Furthermore, an analysis of the metabolic profiles of 96-hour DD and control mats was conducted using UHPLC-HRMS. Notably, there was a significant decrease in amino acid levels, while phenolic content, fatty acids, and lipids increased. These changes in metabolic activity during dehydration highlighted the presence of metabolite pools that contribute to the physiological and biochemical adjustments of N. calcicola BOT1, mitigating the impact of dehydration to some extent. Overall, present study demonstrated the accumulation of biochemical and non-enzymatic antioxidants in dehydrated mats, which could be utilized to stabilize unfavorable environmental conditions. Additionally, the strain N. calcicola BOT1 holds promise as a biofertilizer for semi-arid regions.

Looking beyond Arthrospira: Comparison of antioxidant and anti-inflammatory properties of ten cyanobacteria strains

Cyanobacteria are a widely distributed group of photosynthetic prokaryotes with potential to produce biologically active compounds. Arthrospira is the most widespread grown cyanobacteria for commercial purposes; however, many other species could be used as sources of a wide variety of bio-products. The pigment phycocyanin explains part of the therapeutic properties attributed to Arthrospira (e.g. antioxidant and anti-inflammatory). Many chronic diseases include, on its etiology, oxidative stress and abnormalities in the inflammatory response; thus, there is great interest in finding new sources of natural antioxidants and anti-inflammatory compounds. The aim of this work was to evaluate growth attributes, chemical composition and antioxidant and anti-inflammatory properties of ten cyanobacteria isolates. After 15 days of culture, biomass production ranged between 0.06 g/L (Anabaena) and 0.27 g/L (Phormidium) in 20 L volume cultures. Protein content of dry biomass ranged between 28.86 % (Nodularia) and 56.39 % (Arthrospira) while phycocyanin content ranged between 0.86 % (Nodularia) and 6.66 % (Spirulina). Aqueous extracts were evaluated regarding total phenolic content (TPC), total flavonoids content (TFC) and antioxidant activities (DPPH, ABTS and FRAP). Spirulina and Desertifilum exhibited the highest phenols and flavonoids contents; as well as the highest ABTS and FRAP antioxidant activities. Five strains were selected for measuring anti-inflammatory activity by the human erythrocyte membrane stabilization assay. All the strains evaluated exhibited a remarkable anti-inflammatory capacity, being the highest value for Desertifilum. Strains of Spirulina and Desertifilum were also tested for their ability to scavenge reactive oxygen species (ROS) on Hek293 cells; both strains showed significant intracellular antioxidant capacity and were not cytotoxic. This research demonstrated that other cyanobacterial strains, besides the popular Arthrospira, might be new sources of antioxidant and anti-inflammatory compounds for biotechnological applications in functional food, nutraceutical or pharmaceutical industries.