The dgc2 gene encoding di-guanylate cyclase suppresses both motility and biofilm formation in the filamentous cyanobacterium Leptolyngbya boryana.

Colony pattern formations of bacteria with motility manifest complicated morphological self-organization phenomena. Leptolyngbya boryana is the filamentous cyanobacterial species, which has been used as a genetic model organism for studying metabolism including photosynthesis and nitrogen-fixation. Although a widely used type strain (wild type) of this species has not been reported to show any motile activity, we isolated a spontaneous mutant strain which shows active motility (gliding activity) to give rise to complicated colony patters, including comet-like wandering clusters and disk-like rotating vortices on solid media. Whole-genome resequencing identified multiple mutations on the genome in the mutant strain. We confirmed that inactivation of a candidate gene, dgc2 (LBDG_02920), in the wild type background was sufficient to give rise to motility and the morphological colony patterns. This gene encodes a protein, containing the GGDEF motif, which is conserved at the catalytic domain of diguanylate cyclase (DGC). Although DGC has been reported to be involved in biofilm formation, the mutant strain lacking dgc2 significantly facilitated biofilm formation, suggesting a role of DGC for suppressing both gliding motility and biofilm formation. Thus, L. boryana provides an excellent genetic model to study dynamic colony pattern formation, and novel insight on a role of c-di-GMP for biofilm formation.

Flv3A facilitates O2 photoreduction and affects H2 photoproduction independently of Flv1A in diazotrophic Anabaena filaments

The model heterocyst-forming filamentous cyanobacterium, Anabaena sp. PCC 7120 (Anabaena) represents multicellular organisms capable of simultaneously performing oxygenic photosynthesis in vegetative cells and the O2-sensitive N2-fixation inside the heterocysts. The flavodiiron proteins (FDPs) have been shown to participate in photoprotection of photosynthesis by driving excess electrons to O2 (Mehler-like reaction). Here, we addressed the physiological relevance of the vegetative cell-specific Flv1A and Flv3A on the bioenergetic processes occurring in the diazotrophic Anabaena under variable CO2. We demonstrate that both Flv1A and Flv3A are required for proper induction of the Mehler-like reaction upon a sudden change in light intensity, which is likely important for the activation of carbon-concentrating mechanisms (CCM) and CO2 fixation. Nevertheless, Flv3A showed a more important role in photoprotection than Flv1A. Under low CO2 diazotrophic conditions, Flv3A is capable of mediating moderate O2 photoreduction, independently of Flv1A, but in coordination with Flv2 and Flv4. Strikingly, the lack of Flv3A resulted in strong downregulation of the heterocyst-specific uptake hydrogenase, which led to enhanced H2 photoproduction under both oxic and micro-oxic conditions. These results reveal a novel regulatory network between the Mehler-like reaction and the H2 metabolism, which is of great interest for future photobiological production of H2 in Anabaena.

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.

Complete Genome Sequence of a Thin-Sheath Mutant of the Phototropic Cyanobacterium Calothrix sp. Strain PCC 7716

Calothrix sp. strain PCC 7716 is a filamentous cyanobacterium whose morphology is tapered, with basal-apical polarity. The apical filament shows positive phototropism toward white light or blue light. To elucidate the molecular basis of the phototropism, we determined the complete genome sequence of a spontaneous mutant of this strain that has a thin sheath and is suitable for genomic DNA extraction.

Phytoplankton settling quality has a subtle but significant effect on sediment microeukaryotic and bacterial communities

In coastal aphotic sediments, organic matter (OM) input from phytoplankton is the primary food resource for benthic organisms. Current observations from temperate ecosystems like the Baltic Sea report a decline in spring bloom diatoms, while summer cyanobacteria blooms are becoming more frequent and intense. These climate-driven changes in phytoplankton communities may in turn have important consequences for benthic biodiversity and ecosystem functions, but such questions are not yet sufficiently explored experimentally. Here, in a 4-week experiment, we investigated the response of microeukaryotic and bacterial communities to different types of OM inputs comprising five ratios of two common phytoplankton species in the Baltic Sea, the diatom Skeletonema marinoi and filamentous cyanobacterium Nodularia spumigena. Metabarcoding analyses on 16S and 18S ribosomal RNA (rRNA) at the experiment termination revealed subtle but significant changes in diversity and community composition of microeukaryotes in response to settling OM quality. Sediment bacteria were less affected, although we observed a clear effect on denitrification gene expression (nirS and nosZ), which was positively correlated with increasing proportions of cyanobacteria. Altogether, these results suggest that future changes in OM input to the seafloor may have important effects on both the composition and function of microbenthic communities.

The primary transcriptome of hormogonia from a filamentous cyanobacterium defined by cappable-seq

Hormogonia are motile filaments produced by many filamentous cyanobacteria that function in dispersal, phototaxis and the establishment of nitrogen-fixing symbioses. The gene regulatory network promoting hormogonium development is initiated by the hybrid histidine kinase HrmK, which in turn activates a sigma factor cascade consisting of SigJ, SigC and SigF. In this study, cappable-seq was employed to define the primary transcriptome of developing hormogonia in the model filamentous cyanobacterium Nostoc punctiforme ATCC 29133 in both the wild-type, and sigJ, sigC and sigF mutant strains 6 h post-hormogonium induction. A total of 1544 transcriptional start sites (TSSs) were identified that are associated with protein-coding genes and are expressed at levels likely to lead to biologically relevant transcripts in developing hormogonia. TSS expression among the sigma-factor deletion strains was highly consistent with previously reported gene expression levels from RNAseq experiments, and support the current working model for the role of these genes in hormogonium development. Analysis of SigJ-dependent TSSs corroborated the presence of the previously identified J-Box in the −10 region of SigJ-dependent promoters. Additionally, the data presented provides new insights on sequence conservation within the −10 regions of both SigC- and SigF-dependent promoters, and demonstrates that SigJ and SigC coordinate complex co-regulation not only of hormogonium-specific genes at different loci, but within an individual operon. As progress continues on defining the hormogonium gene regulatory network, this data set will serve as a valuable resource.

A novel filamentous cyanobacterium Microseira minor sp. nov. (Oscillatoriaceae, Cyanobacteria) from the Ganfu Channel, Jiangxi, China

Two filamentous cyanobacterial strains were isolated from the mats attached to rock surfaces in the Ganfu Channel, Jiangxi Province, China. A polyphasic approach based on the combination of morphological and molecular features was used to characterize the two strains. Both strains showed the Lyngbya-like morphology under the light microscopy, and had the highest similarity range of 16S rRNA gene sequences as 95.00-96.01% to clones of Microseira wollei, exceeding the cutoff for species delimitation in cyanobacteria. Phylogenetic analyses based on both 16S rRNA and nifH genes and smaller sizes of trichomes in the two Lyngbya-like strains supported them to be proposed as a new species in the genus Microseira as Microseira minor, which is the second species of the genus Microseira. The difference of the 16S-23S ITS region between the two Microseira minor strains and its implication for the evaluation on cyanobacterial diversity and species differentiation were also discussed.

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.

Harnessing Nutritional Benefits of Spirulina platensis: Standardization of Cultivating Conditions of Spirulina in Kilimanjaro

Malnutrition remains a challenge in Tanzania, notwithstanding government initiatives and health education geared towards assuaging the problem. According to the World Health Organization (WHO), there will be more than 600,000 severely malnourished children in Tanzania by the year 2030. In particular, protein based malnutrition remains the greatest challenge due to the irreplaceable nature of its essential amino acids. Macronutrients and micronutrients which are found in Spirulina platensis have been recommended by WHO to address malnutrition in developing countries. Spirulina platensis is a filamentous Cyanobacterium microalgae with the highest recorded protein content of plant origin with several immune boosting nutrients. Spirulina cultivation requires sufficient aeration, proper light intensity and salinity for maximum biomass yield, cell productivity, specific growth rate, and protein content. This paper presents the findings of a study carried out in Kilimanjaro on the optimized conditions, locally and economically tailored approach system required to grow spirulina in the region. The study established the use of food grade organic media with low-cost urea as nitrogen source, a greenhouse average temperature of 30–32 °C in the months between December to March, alkalinity of 5 g/L, mixing frequency of 3 times per day/100 L and partial shading, as the optimum conditions for outdoor cultivation of spirulina. Keywords: Malnutrition, Spirulina, Protein, growth condition

Functions of the Essential Gene mraY in Cellular Morphogenesis and Development of the Filamentous Cyanobacterium Anabaena PCC 7120

Bacterial cell shape is determined by the peptidoglycan (PG) layer. The cyanobacterium Anabaena sp. PCC 7120 (Anabaena) is a filamentous strain with ovoid-shaped cells connected together with incomplete cell constriction. When deprived of combined nitrogen in the growth medium, about 5–10% of the cells differentiate into heterocysts, cells devoted to nitrogen fixation. It has been shown that PG synthesis is modulated during heterocyst development and some penicillin-binding proteins (PBPs) participating in PG synthesis are required for heterocyst morphogenesis or functioning. Anabaena has multiple PBPs with functional redundancy. In this study, in order to examine the function of PG synthesis and its relationship with heterocyst development, we created a conditional mutant of mraY, a gene necessary for the synthesis of the PG precursor, lipid I. We show that mraY is required for cell and filament integrity. Furthermore, when mraY expression was being limited, persistent septal PG synthetic activity was observed, resulting in increase in cell width. Under non-permissive conditions, filaments and cells were rapidly lysed, and no sign of heterocyst development within the time window allowed was detected after nitrogen starvation. When mraY expression was being limited, a high percentage of heterocyst doublets were found. These doublets are formed likely as a consequence of delayed cell division and persistent septal PG synthesis. MraY interacts with components of both the elongasome and the divisome, in particular those directly involved in PG synthesis, including HetF, which is required for both cell division and heterocyst formation.