Adapting from Low to High: An Update to CO2-Concentrating Mechanisms of Cyanobacteria and Microalgae

The intracellular accumulation of inorganic carbon (C_i) by microalgae and cyanobacteria under ambient atmospheric CO₂ levels was first documented in the 80s of the 20th Century. Hence, a third variety of the CO₂-concentrating mechanism (CCM), acting in aquatic photoautotrophs with the C₃ photosynthetic pathway, was revealed in addition to the then-known schemes of CCM, functioning in CAM and C₄ higher plants. Despite the low affinity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) of microalgae and cyanobacteria for the CO₂ substrate and low CO₂/O₂ specificity, CCM allows them to perform efficient CO₂ fixation in the reductive pentose phosphate (RPP) cycle. CCM is based on the coordinated operation of strategically located carbonic anhydrases and CO₂/HCO₃^- uptake systems. This cooperation enables the intracellular accumulation of HCO₃^-, which is then employed to generate a high concentration of CO₂ molecules in the vicinity of Rubisco's active centers compensating up for the shortcomings of enzyme features. CCM functions as an add-on to the RPP cycle while also acting as an important regulatory link in the interaction of dark and light reactions of photosynthesis. This review summarizes recent advances in the study of CCM molecular and cellular organization in microalgae and cyanobacteria, as well as the fundamental principles of its functioning and regulation.

[Treatment of laryngeal pathology associated with gastroesophageal reflux disease]

OBJECTIVE

To increase the effectiveness of the treatment of laryngeal pathology associated with gastroesophageal reflux disease (GERD), to determine the indications for the appointment of anti-inflammatory therapy to these patients.

MATERIAL AND METHODS

120 patients were examined and treated, 58 of them men and 62 women, aged 30 to 82 years with GERD-associated laryngeal pathology. Three groups of patients were formed, comparable in age and gender, in accordance with the type of pachydermia in interarytenoid region; type 1 (40 patients) - pachydermia did not go beyond the middle of the interarytenoid cartilage (according to G.F. Ivanchenko), less than 3 mm, without signs of perifocal inflammation; type 2 (40 patients) - pachydermia of large size, extending beyond the middle of the interarytenoid cartilage with a spread to the entire interarytenoid region (according to G.F. Ivanchenko), often in combination with hyperkeratosis or epithelial dysplasia; type 3 (30 patients) - pachydermia of large size in combination with severe perifocal inflammation. All patients received antireflux therapy. Each group is divided into two subgroups: patients who did not receive anti-inflammatory therapy, and patients who received anti-inflammatory therapy, the basis of which was inhalation with degassed alkaline mineral water, as well as according to indications acetylcysteine, benzyldimethylammonium chloride 0.01% or hydroxymethylquinoxalindioxide, with severe swelling of the mucous membrane - budesonide. All patients completed the questionnaire "Reflux Symptoms Scale" before and after treatment.

RESULTS

In group 2 patients (with type 2 pachydermia), the effectiveness of anti-inflammatory therapy was 75%. Of the 20 patients in this group, after inhaled therapy, 4 patients had pachydermia in interarytenoid region disappeared, 11 patients had type 1 pachydermia visualized, 5 (25%) patients had no pronounced dynamics. In group 3 patients (with type 3 pachydermia), the effectiveness of inhaled treatment was 100%, out of 15 patients after inhaled therapy, type 2 pachydermia was diagnosed in 8 patients, type 1 pachydermia - in 7 patients. In 4 patients, complex therapy led to the complete disappearance of reflux-associated laryngeal granulomas without surgical treatment. The effectiveness of inhaled therapy in relation to patient complaints after a month was 87%, while the effectiveness of treatment of patients without inhalation was 45%.

CONCLUSIONS

Indications for the appointment of inhaled anti-inflammatory therapy in patients with reflux-associated pathology of the larynx are the presence of complaints of hoarseness, dryness, tickling, lump in the throat and chronic cough, endolaryngoscopic signs of exacerbation of chronic inflammation of the mucous membrane of the posterior larynx.

[Screening for laryngeal disease in patients with gastroesophageal reflux disease]

OBJECTIVE

To improve the diagnosis of laryngeal disease in patients with gastroesophageal reflux disease (GERD).

MATERIAL AND METHODS

171 patients (89 (52%) men, 82 (48%) women) with non-erosive (39 (23%) people) and erosive (132 (77%) people) forms of GERD were examined. None of the patients made active complaints about the condition of the larynx and pharynx. The examination included a questionnaire, examination by an otorhinolaryngologist, and videoendolaryngoscopy.

RESULTS

The survey revealed the presence of symptoms of otorhinolaryngological pathology in 74% of patients. Videolaryngoscopy revealed no laryngeal pathology in 55 (32%) patients, and signs of GERD-associated laryngitis were detected in 116 (68%) patients. The most common pathology was pachydermia in interarytenoid region - in 89 people, laryngeal granuloma was detected in 7 patients, leukoplakia - in 2 patients, chronic edematous polypous laryngitis - in 2 patients, benign laryngeal formations - in 9 patients. In patients with GERD (erosive and non-erosive forms), an asymptomatic course of chronic laryngitis associated with this pathology was observed in 44% of cases. In 52% of patients, pachydermia in interarytenoid region was diagnosed, of which every second had pronounced hyperplasia and folding of the mucous membrane in interarytenoid region, which must be differentiated from laryngeal cancer (in this case, patients should be under the dynamic supervision of an otorhinolaryngologist). Other precancerous formations of the larynx (granulomas and leukoplakia) were found in 5% of patients. Benign neoplasms of the larynx (polyps and cysts) were also detected in 5% of cases.

CONCLUSIONS

Despite the high frequency of detection of otorhinolaryngological diseases in the examined patients with gastroesophageal reflux disease, none of the patients presented complaints related to the pathology of the larynx, which indicates the need for active detection of this pathology in this category of patients by questioning, questioning, as well as examination by an otorhinolaryngologist.

Putative extracellular α-class carbonic anhydrase, EcaA, of Synechococcus elongatus PCC 7942 is an active enzyme: a sequel to an old story

Carbonic anhydrase (CA) EcaA of Synechococcus elongatus PCC 7942 was previously characterized as a putative extracellular α-class CA, however, its activity was never verified. Here we show that EcaA possesses specific CA activity, which is inhibited by ethoxyzolamide. An active EcaA was expressed in heterologous bacterial system, which supports the formation of disulfide bonds, as a full-length protein (EcaA+L) and as a mature protein that lacks a leader peptide (EcaA-L). EcaA-L exhibited higher specific activity compared to EcaA+L. The recombinant EcaA, expressed in a bacterial system that does not support optimal disulfide bond formation, exhibited extremely low activity. This activity, however, could be enhanced by the thiol-oxidizing agent, diamide; while a disulfide bond-reducing agent, dithiothreitol, further inactivated the enzyme. Intact E. coli cells that overexpress EcaA+L possess a small amount of processed protein, EcaA-L, whereas the bulk of the full-length protein resides in the cytosol. This may indicate poor recognition of the EcaA leader peptide by protein export systems. S. elongatus possessed a relatively low level of ecaA mRNA, which varied insignificantly in response to changes in CO2 supply. However, the presence of protein in the cells is not obvious. This points to the physiological insignificance of EcaA in S. elongatus, at least under the applied experimental conditions.

The complete genome of a cyanobacterium from a soda lake reveals the presence of the components of CO2-concentrating mechanism

At present geological epoch, the carbon concentrating mechanism (CCM) of cyanobacteria represents the obligatory tool for adaptation to low content of CO₂ in the atmosphere and for the maintenance of sufficient photosynthetic activity. Functional CCM was found in modern cyanobacteria from different ecological niches. However, the presence of such mechanism in species that inhabit soda lakes is not obvious due to high content of inorganic carbon (C _i) in the environment. Here we analyze CCM components that have been identified by sequencing of the whole genome of the alkaliphilic cyanobacterium Microcoleus sp. IPPAS B-353. The composition of the CCM components of Microcoleus is similar to that of 'model' β-cyanobacteria, freshwater and marine Synechococcus or Synechocystis spp. However, CahB1 protein of Microcoleus, which is the homolog of CcaA, the carboxysomal β-type carbonic anhydrase (CA) of β-cyanobacteria, appeared to be the only active CA located in cell envelopes. The conservative regions of CcmM, CahG (a homolog of archeal γ-CAs, Cam/CamH), and ChpX of Microcoleus possess single amino acid substitutions that may cause a lack of CA activities. Unlike model cyanobacteria, Microcoleus induces only one BicA-type bicarbonate transporter in response to C _i limitation. The differences in the appearance of CCM components and in their characteristics between alkaliphilic Microcoleus and freshwater or marine cyanobacteria are described. The possible reasons for the maintenance of CCM components in cyanobacteria, which permanently live at high concentrations of C _i in soda lakes, are discussed.

Genomic Survey and Biochemical Analysis of Recombinant Candidate Cyanobacteriochromes Reveals Enrichment for Near UV/Violet Sensors in the Halotolerant and Alkaliphilic Cyanobacterium Microcoleus IPPAS B353

Cyanobacteriochromes (CBCRs), which are exclusive to and widespread among cyanobacteria, are photoproteins that sense the entire range of near-UV and visible light. CBCRs are related to the red/far-red phytochromes that utilize linear tetrapyrrole (bilin) chromophores. Best characterized from the unicellular cyanobacterium Synechocystis sp. PCC 6803 and the multicellular heterocyst forming filamentous cyanobacteria Nostoc punctiforme ATCC 29133 and Anabaena sp. PCC 7120, CBCRs have been poorly investigated in mat-forming, nonheterocystous cyanobacteria. In this study, we sequenced the genome of one of such species, Microcoleus IPPAS B353 (Microcoleus B353), and identified two phytochromes and seven CBCRs with one or more bilin-binding cGMP-specific phosphodiesterase, adenylyl cyclase and FhlA (GAF) domains. Biochemical and spectroscopic measurements of 23 purified GAF proteins from phycocyanobilin (PCB) producing recombinant Escherichia coli indicated that 13 of these proteins formed near-UV and visible light-absorbing covalent adducts: 10 GAFs contained PCB chromophores, whereas three contained the PCB isomer, phycoviolobilin (PVB). Furthermore, the complement of Microcoleus B353 CBCRs is enriched in near-UV and violet sensors, but lacks red/green and green/red CBCRs that are widely distributed in other cyanobacteria. We hypothesize that enrichment in short wavelength-absorbing CBCRs is critical for acclimation to high-light environments where this organism is found.

CO2-concentrating mechanism in cyanobacterial photosynthesis: organization, physiological role, and evolutionary origin

The cellular and molecular organization of the CO2-concentrating mechanism (CCM) of cyanobacteria is reviewed. The primary processes of uptake, translocation, and accumulation of inorganic carbon (Ci) near the active site of carbon assimilation by the enzyme ribulose-1,5-bisphosphate carboxylase in the C3 cycle in cyanobacteria are described as one of the specialized forms of CO2 concentration which occurs in some photoautotrophic cells. The existence of this form of CO2 concentration expands our understanding of photosynthetic Ci assimilation. The means of supplying Ci to the C3 cycle in cyanobacteria is not by simple diffusion into the cell, but it is the result of coordinated functions of high-affinity systems for the uptake of CO2 and bicarbonate, as well as intracellular CO2/HCO3 (-) interconversions by carbonic anhydrases. These biochemical events are under genetic control, and they serve to maintain cellular homeostasis and adaptation to CO2 limitation. Here we describe the organization of the CCM in cyanobacteria with a special focus on the CCM of relict halo- and alkaliphilic cyanobacteria of soda lakes. We also assess the role of the CCM at the levels of the organism, the biosphere, and evolution.

Identification and functional role of the carbonic anhydrase Cah3 in thylakoid membranes of pyrenoid of Chlamydomonas reinhardtii

The distribution of the luminal carbonic anhydrase Cah3 associated with thylakoid membranes in the chloroplast and pyrenoid was studied in wild-type cells of Chlamydomonas reinhardtii and in its cia3 mutant deficient in the activity of the Cah3 protein. In addition, the effect of CO(2) concentration on fatty acid composition of photosynthetic membranes was examined in wild-type cells and in the cia3 mutant. In the cia3 mutant, the rate of growth was lower as compared to wild-type, especially in the cells grown at 0.03% CO(2). This might indicate a participation of thylakoid Cah3 in the CO(2)-concentrating mechanism (CCM) of chloroplast and reflect the dysfunction of the CCM in the cia3 mutant. In both strains, a decrease in the CO(2) concentration from 2% to 0.03% caused an increase in the content of polyunsaturated fatty acids in membrane lipids. At the same time, in the cia3 mutant, the increase in the majority of polyunsaturated fatty acids was less pronounced as compared to wild-type cells, whereas the amount of 16:4ω3 did not increase at all. Immunoelectron microscopy demonstrated that luminal Cah3 is mostly located in the thylakoid membranes that pass through the pyrenoid. In the cells of CCM-mutant, cia3, the Cah3 protein was much less abundant, and it was evenly distributed throughout the pyrenoid matrix. The results support our hypothesis that CO(2) might be generated from HCO(3)(-) by Cah3 in the thylakoid lumen with the following CO(2) diffusion into the pyrenoid, where the CO(2) fixing Rubisco is located. This ensures the maintenance of active photosynthesis under CO(2)-limiting conditions, and, as a result, the active growth of cells. The relationships between the induction of CCM and restructuring of the photosynthetic membranes, as well as the involvement of the Cah3 of the pyrenoid in these events, are discussed. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.

[Allelic polymorphism of the IL-2and IL-4 genes in herpesvirus infection]

Herpesvirus infection is accompanied by imbalance of peripheral mononuclear production of cytokines, by polarizing an immune response by the Th2 pathway. The homozygous TT genotype of T330G polymorphism in the IL-2 gene is an immunogenetic factor that has a protective activity against susceptibility to herpesvirus infection. The risk of progression, the recurrent course of the infection and its poor outcome is positively associated with the heterozygous TG genotype in the IL-2 gene T-330G promoter region and with the homozygous CC type and C allele in the IL-4 gene C-590T promoter region.

[Effects of recurrent herpetic infection on functional activity of T-cells in patients with rheumatoid arthritis]

AIM

To evaluate effects of recurrent herpetic infection on functional activity of regulatory cell subpopulations in patients with rheumatoid arthritis.

MATERIAL AND METHODS

We studied in vitro production of marker cytokines of type 1 T-helpers (IL-2), type 2 T-helpers (IL-4), type 3 T-helpers TGFbeta and type 1 T-regulators (IL-10) and counted CD4+CD25+ T-cells in the blood of patients with recurrent herpetic infection and having no clinical manifestations of Herpes virus reactivation.

RESULTS

Patients with recurrent herpes had more active production of IL-10, but reduced count of CD4+CD25+ lymphocytes.

CONCLUSION

IL-10 hyperproduction observed in recurrent herpetic infection may contribute to progression of rheumatoid arthritis.

The thylakoid carbonic anhydrase associated with photosystem II is the component of inorganic carbon accumulating system in cells of halo- and alkaliphilic cyanobacterium Rhabdoderma lineare

The organization of carbonic anhydrase (CA) system in halo- and alkaliphilic cyanobacterium Rhabdoderma lineare was studied by Western blot analysis and immunocytochemical electron microscopy. The presence of putative extracellular alpha-CA of 60 kDa in the glycocalyx, forming a tight sheath around the cell, and of two intracellular beta-CA is reported. We show for the first time that the beta-CA of 60 kDa is expressed constitutively and associated with polypeptides of photosystem II (beta-CA-PS II). Another soluble beta-CA of 25 kDa was induced in low-bicarbonate medium. Induction of synthesis of the latter beta-CA was accompanied by an increase in the intracellular pool of inorganic carbon, which suggests an important role of this enzyme in the functioning of a CO(2)-concentrating mechanism.

[Carbonic anhydrase of the alkaliphilic cyanobacterium Microcoleus chthonoplastes]

The activity of carbonic anhydrase (CA) was studied in different cell fractions of the alkaliphilic cyanobacterium Microcoleus chthonoplastes. The activity of this enzyme was found in the soluble and membrane protein fractions, as well as in intact cells and in a thick glycocalyx layer enclosing the cyanobacterium cells. The localization of CA in glycocalyx of M. chthonoplastes was shown by the western blot analysis and by immunoelectron microscopy studies with antibodies to the thylakoid CA from Chlamydomonas reinhardtii (Cah3). At least one of the CA forms occurring in M. chthonoplastes CA was shown to be an alpha-type enzyme. A possible mechanism of the involvement of the glycocalyx CA in calcification of cyanobacteria is discussed.