c-di-GMP Homeostasis Is Critical for Heterocyst Development in Anabaena sp. PCC 7120

c-di-GMP is a ubiquitous bacterial signal regulating various physiological process. Anabaena PCC 7120 (Anabaena) is a filamentous cyanobacterium able to form regularly-spaced heterocysts for nitrogen fixation, in response to combined-nitrogen deprivation in 24h. Anabaena possesses 16 genes encoding proteins for c-di-GMP metabolism, and their functions are poorly characterized, except all2874 (cdgS) whose deletion causes a decrease in heterocyst frequency 48h after nitrogen starvation. We demonstrated here that c-di-GMP levels increased significantly in Anabaena after combined-nitrogen starvation. By inactivating each of the 16 genes, we found that the deletion of all1175 (cdgSH) led to an increase of heterocyst frequency 24h after nitrogen stepdown. A double mutant ΔcdgSHΔcdgS had an additive effect over the single mutants in regulating heterocyst frequency, indicating that the two genes acted at different time points for heterocyst spacing. Biochemical and genetic data further showed that the functions of CdgSH and CdgS in the setup or maintenance of heterocyst frequency depended on their opposing effects on the intracellular levels of c-di-GMP. Finally, we demonstrated that heterocyst differentiation was completely inhibited when c-di-GMP levels became too high or too low. Together, these results indicate that the homeostasis of c-di-GMP level is important for heterocyst differentiation in Anabaena.

Functional Diversity of TonB-Like Proteins in the Heterocyst-Forming Cyanobacterium Anabaena sp. PCC 7120

The genomes of many organisms encode more than one TonB protein, and their number does not necessarily correlate with that of TonB-dependent outer membrane transporters. Consequently, specific as well as redundant functions of the different TonB proteins have been identified.

Structure Insight into Photosystem I Octamer from Cyanobacteria

Diversity of photosystem oligomers is essential to understand how photosynthetic organisms adopted to light conditions. Given by the structural and physiological significance, the assemblies of PSI supercomplex is of great interest in both chloroplast and cyanobacteria recently. In this study, two novel photosystem I supercomplexes were isolated for the first time from the low light incubated culture of filamentous cyanobacterium Anabaena sp. PCC 7120. These complexes were defined as PSI hexamers and octamers through biochemical and biophysical characterization. Their 77K emission spectra indicated that the red forms of chlorophylls seemed not to be affected during oligomerization. By cryo-EM single particle analysis, a near-atomic (7.0 Å) resolution structure of PSI octamer was resolved, and the molecular assemblies of stable PSI octamer was revealed.

Evaluation of inducible promoter–riboswitch constructs for heterologous protein expression in the cyanobacterial species Anabaena sp. PCC 7120

Cyanobacteria are promising chassis for synthetic biology applications due to the fact that they are photosynthetic organisms capable of growing in simple, inexpensive media. Given their slower growth rate than other model organisms such as Escherichia coli and Saccharomyces cerevisiae, there are fewer synthetic biology tools and promoters available for use in model cyanobacteria. Here, we compared a small library of promoter–riboswitch constructs for synthetic biology applications in Anabaena sp. PCC 7120, a model filamentous cyanobacterium. These constructs were designed from six cyanobacterial promoters of various strengths, each paired with one of two theophylline-responsive riboswitches. The promoter–riboswitch pairs were cloned upstream of a chloramphenicol acetyltransferase (cat) gene, and CAT activity was quantified using an in vitro assay. Addition of theophylline to cultures increased the CAT activity in almost all cases, allowing inducible protein production with natively constitutive promoters. We found that riboswitch F tended to have a lower induced and uninduced production compared to riboswitch E for the weak and medium promoters, although the difference was larger for the uninduced production, in accord with previous research. The strong promoters yielded a higher baseline CAT activity than medium strength and weak promoters. In addition, we observed no appreciable difference between CAT activity measured from strong promoters cultured in uninduced and induced conditions. The results of this study add to the genetic toolbox for cyanobacteria and allow future natural product and synthetic biology researchers to choose a construct that fits their needs.

Comparative Growth Rate of Cyanobacteria from “Usar” Soil (saline/alkaline soils) with Respect to Pigments

The pigment content in Blue-green algae is a specific feature of each species. The pigment variation is specific features among microalgae. The paper aim to analyze cyanobacterial extracts of different Usar soil of Azamgarh and Varanasi, Uttar Pradesh. The main object here is the importance of the blue green algae especially because of the pigments present in this class of algae. Pigments from natural sources are gaining more importance mainly due to health and environmental issues. Algae contain a wide range of pigments. Three major classes of pigments are chlorophylls, carotenoids (carotenes and xanthophylls) and phycobilins (Phycocyanin and phycoerythrin). Our present study investigates the efficiency for phycobiliprotein pigment production from four different cyanobacteria Hapalosiphon sp., Phormidium sp., Anabaena sp. and Nostoc sp. The harvested and dried biomass was subjected to extract pigments using different solvents. Thin Layer Chromatography was performed from extracted pigments using Acetone as extraction solvents. And running solvent especially for phycocyanin pigment was optimized and concluded that Petroleum ether and Acetone in the ratio of 7:3. This paper presents the information about the natural pigments of cyanobacteria and how they can be extracted and identified using different procedures and spectrophotometry. It emphasizes that the principal algal pigments are Phycobilins, Chlorophylls and Carotenoids.