Response of Key Metabolites during a UV-A Exposure Time-Series in the Cyanobacterium Chlorogloeopsis fritschii PCC 6912

Ultraviolet A (UV-A) is the major component of UV radiation reaching the Earth’s surface, causing indirect damage to photosynthetic organisms via the production of reactive oxygen species (ROS). In comparison, UV-B causes both direct damage to biomolecules and indirect damage. UV-B is well studied in cyanobacterial research due to their long evolutionary history and adaptation to high levels of UV, with less work on the effects of UV-A. In this study, the response of key metabolites in Chlorogloeopsis fritschii (C. fritschii) during 48 h of photosynthetically active radiation (PAR, 15 µmol·m−2·s−1) supplemented with UV-A (11 µmol·m−2·s−1) was investigated using gas chromatography- mass spectrometry (GC-MS). Results showed an overall significant increase in metabolite levels up to 24 h of UV-A exposure. Compared with previously reported UV-B (PAR + UV-B) and PAR only results, UV-A showed more similarity compared to PAR only exposure as opposed to supplemented UV-B. The amino acids glutamate, phenylalanine and leucine showed differences in levels between UV (both supplemented UV-A and supplemented UV-B) and PAR only (non-supplemented PAR), hinting to their relevance in UV stress response. The fatty acids, palmitic and stearic acid, showed positive log2 fold-change (FC) in supplemented UV-A and PAR only experiments but negative log2 FC in UV-B, indicating the more harmful effect of UV-B on primary metabolism. Less research has been conducted on UV-A exposure and cyanobacteria, a potential environmental stimuli for the optimisation of metabolites for industrial biotechnology. This study will add to the literature and knowledge on UV-A stress response at the metabolite level in cyanobacteria, especially within the less well-known species C. fritschii.

Mycosporine-like amino acid and aromatic amino acid transcriptome response to UV and far-red light in the cyanobacterium Chlorogloeopsis fritschii PCC 6912

The “UV sunscreen” compounds, the mycosporine-like amino acids (MAAs) are widely reported in cyanobacteria and are known to be induced under ultra-violet (UV) light. However, the impact of far red (FR) light on MAA biosynthesis has not been studied. We report results from two experiments measuring transcriptional regulation of MAA and aromatic amino acid pathways in the filamentous cyanobacterium Chlorogloeopsis fritschii PCC 6912. The first experiment, comparing UV with white light, shows the expected upregulation of the characteristic MAA mys gene cluster. The second experiment, comparing FR with white light, shows that three genes of the four mys gene cluster encoding up to mycosporine-glycine are also upregulated under FR light. This is a new discovery. We observed corresponding increases in MAAs under FR light using HPLC analysis. The tryptophan pathway was upregulated under UV, with no change under FR. The tyrosine and phenylalanine pathways were unaltered under both conditions. However, nitrate ABC transporter genes were upregulated under UV and FR light indicating increased nitrogen requirement under both light conditions. The discovery that MAAs are upregulated under FR light supports MAAs playing a role in photon dissipation and thermoregulation with a possible role in contributing to Earth surface temperature regulation.

Natural competence in Chlorogloeopsis fritschii PCC 6912 and other ramified cyanobacteria

Lateral DNA transfer plays an important role in the evolution of genetic diversity in prokaryotes. DNA acquisition via transformation involves the uptake of DNA from the environment. The ability of recipient cells to actively transport DNA into the cytoplasm – termed natural competence – depends on the presence of type IV pili and competence proteins. Natural competence has been described in cyanobacteria for several organisms including unicellular and filamentous species. However, the presence of natural competence in ramified cyanobacteria, which are considered the peak of cyanobacterial morphological complexity, remains unknown. Here we show that ramified cyanobacteria harbour the genes essential for natural competence and experimentally demonstrate natural competence in the ramified cyanobacterium Chlorogloeopsis fritschii PCC 6912 (hereafter Chlorogloeopsis). Searching for homologs to known natural competence genes in ramified cyanobacteria showed that these genes are conserved in the majority of tested isolates. Experimental validation of natural competence using several alternative protocols demonstrates that Chlorogloeopsis could be naturally transformed with a replicative plasmid. Our results show that natural competence is a common trait in ramified cyanobacteria and that natural transformation is likely to play an important role in cyanobacteria evolution.ImportanceCyanobacteria are crucial players in the global biogeochemical cycles where they contribute to CO2- and N2-fixation. Their main ecological significance is the oxygen-producing photosynthetic apparatus that contributes to contemporary food chains. Ramified cyanobacteria form true-branching and multiseriate cell filament structures that represent a peak of prokaryotic multicellularity. Species in that group inhabit fresh and marine water habitats, thermal springs, arid environments, as well as endolithic and epiphytic habitats. Here we show that ramified cyanobacteria harbor the mechanisms required for DNA acquisition via natural transformation. The prevalence of mechanisms for natural uptake of DNA has implications for the role of DNA acquisition in the evolution of cyanobacteria. Furthermore, presence of mechanisms for natural transformation in ramified cyanobacteria opens up new possibilities for genetic modification of ramified cyanobacteria.

Far-Red Light Acclimation for Improved Mass Cultivation of Cyanobacteria

Improving mass cultivation of cyanobacteria is a goal for industrial biotechnology. In this study, the mass cultivation of the thermophilic cyanobacterium Chlorogloeopsis fritschii was assessed for biomass production under light-emitting diode white light (LEDWL), far-red light (FRL), and combined white light and far-red light (WLFRL) adaptation. The induction of chl f was confirmed at 24 h after the transfer of culture from LEDWL to FRL. Using combined light (WLFRL), chl f, a, and d, maintained the same level of concentration in comparison to FRL conditions. However, phycocyanin and xanthophylls (echinone, caloxanthin, myxoxanthin, nostoxanthin) concentration increased 2.7–4.7 times compared to LEDWL conditions. The productivity of culture was double under WLFRL compared with LEDWL conditions. No significant changes in lipid, protein, and carbohydrate concentrations were found in the two different light conditions. The results are important for informing on optimum biomass cultivation of this species for biomass production and bioactive product development.

Intracellular and Extracellular Metabolites from the Cyanobacterium Chlorogloeopsis fritschii, PCC 6912, During 48 Hours of UV-B Exposure

Cyanobacteria have many defence strategies to overcome harmful ultraviolet (UV) stress including the production of secondary metabolites. Metabolomics can be used to investigate this altered metabolism via targeted and untargeted techniques. In this study we assessed the changes in the intra- and extracellular low molecular weight metabolite levels of Chlorogloeopsis fritschii (C. fritschii) during 48 h of photosynthetically active radiation (PAR) supplemented with UV-B (15 µmol m−2 s−1 of PAR plus 3 µmol m−2 s−1 of UV-B) and intracellular levels during 48 h of PAR only (15 µmol m−2 s−1) with sampling points at 0, 2, 6, 12, 24 and 48 h. Gas chromatography–mass spectrometry (GC–MS) was used as a metabolite profiling tool to investigate the global changes in metabolite levels. The UV-B time series experiment showed an overall significant reduction in intracellular metabolites involved with carbon and nitrogen metabolism such as the amino acids tyrosine and phenylalanine which have a role in secondary metabolite production. Significant accumulation of proline was observed with a potential role in stress mitigation as seen in other photosynthetic organisms. 12 commonly identified metabolites were measured in both UV-B exposed (PAR + UV-B) and PAR only experiments with differences in significance observed. Extracellular metabolites (PAR + UV-B) showed accumulation of sugars as seen in other cyanobacterial species as a stress response to UV-B. In conclusion, a snapshot of the metabolome of C. fritschii was measured. Little work has been undertaken on C. fritschii, a novel candidate for use in industrial biotechnology, with, to our knowledge, no previous literature on combined intra- and extracellular analysis during a UV-B treatment time-series. This study is important to build on experimental data already available for cyanobacteria and other photosynthetic organisms exposed to UV-B.

Note on taxonomy of Chlorogloeopsis fritschii (Mitra) Mitra et Pandey with soil analysis, collected from a rice field in West Bengal, India

While studying on paddy field blue green algae, author for the first time recorded a blue green algal species Chlorogloeopsis fritschii (Mitra) Mitra et Pandey from rice field soil in summer during 2013 in Hooghly, West Bengal, India. In the present paper, taxonomical description with microphotographs of the species has been provided. In addition to that, soil which was collected from the algal occurrence site has been analyzed. The different physico-chemical parameters of soil were as followed: pH: 7.1; EC: 0.142 dSm-1; OC: 6.6 mgkg-1; Ca2+: 4.6 cmol+kg-1; Na+: 0.71 cmol+kg-1; K+: 0.15 cmol+kg-1; CEC: 12.6 cmol+kg-1; WHC: 45%. Soil textures were as: sand: 36.2%, slit: 28.1% and clay: 35.7%. This study of soil showed its nature and present nutrient content. As the alga contains heterocyst and can fix atmospheric nitrogen to soil so, it can apply in rice fields as biofertilizer to enhance the yield of rice and increase of soil fertility. This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.