Filamentous Cyanobacteria Research Articles

Culture Growth of the Cyanobacterium Phormidium sp. in Various Salinity and Light Regimes and Their Influence on Its Phycocyanin and Other Pigments Content

A strain of the filamentous non N-fixing cyanobacterium Phormidium sp. isolated from the Messolonghi (W. Greece) saltworks, was cultured in the laboratory at six different combinations of salinity (20-40-60 ppt) and illumination (low-2000 lux and high-8000 lux). At salinities of 60 and 40 ppt and in high illumination (XL-8000 lux), the growth rate (μmax) presented the highest values (0.491 and 0.401, respectively) compared to the corresponding at 20 ppt (0.203). In general and at all salinities, the higher illumination (XL) gave the highest growth rates and shorter duplication time (tg) in comparison to the lower illumination (L). On the contrary, phycocyanin, phycoerythrin and allophycocyanin production was extremely increased in the lower illumination (L) in all salinities, from ~14 fold at 40 and 60 ppt to 269 fold at 20 ppt of those corresponding to higher illumination (XL). Similar analogies were also recorded for the other two billiproteins. Chlorophyll-a content was also higher in lower illumination at all salinities in contrast to total carotenoids that did not exhibit such a pattern. The high growth rate and high phycocyanin content along with the rapid sedimentation of its cultured biomass can set this marine Phormidium species as a promising candidate for mass culture.

Quantitative Proteomics Reveals the Protein Regulatory Network of Anabaena sp. PCC 7120 under Nitrogen Deficiency.

Anabaena sp. PCC 7120 (Anabaena 7120) is a photoautotrophic filamentous cyanobacterium capable of fixing atmospheric nitrogen. It is a model organism used for studying cell differentiation and nitrogen fixation. Under nitrogen deficiency, Anabaena 7120 forms specialized heterocysts capable of nitrogen fixation. However, the molecular mechanisms involved in the cyanobacterial adaptation to nitrogen deficiency are not well understood. Here, we employed a label-free quantitative proteomic strategy to systematically investigate the nitrogen deficiency response of Anabaena 7120 at different time points. In total, 363, 603, and 669 proteins showed significant changes in protein abundance under nitrogen deficiency for 3, 12, and 24 h, respectively. With mapping onto metabolic pathways, we revealed proteomic perturbation and regulation of carbon and nitrogen metabolism in response to nitrogen deficiency. Functional analysis confirmed the involvement of nitrogen stress-responsive proteins in biological processes, including nitrogen fixation, photosynthesis, energy and carbon metabolism, and heterocyst development. The expression of 10 proteins at different time points was further validated by using multiple reaction monitoring assays. In particular, many dysregulated proteins were found to be time-specific and involved in heterocyst development, providing new candidates for future functional studies in this model cyanobacterium. These results provide novel insights into the molecular mechanisms of nitrogen stress responses and heterocyst development in Anabaena 7120.

HetF Protein Is a New Divisome Component in a Filamentous and Developmental Cyanobacterium.

ABSTRACTBacterial cell division, with a few exceptions, is driven by FtsZ through a treadmilling mechanism to remodel and constrict the rigid peptidoglycan (PG) layer. Yet different organisms may differ in the composition of the cell division complex (divisome). In the filamentous cyanobacterium Anabaena sp. strain PCC 7120, hetF is required for the initiation of the differentiation of heterocysts, cells specialized in N2 fixation under combined-nitrogen deprivation. In this study, we demonstrate that hetF is expressed in vegetative cells and necessary for cell division under certain conditions. Under nonpermissive conditions, cells of a ΔhetF mutant stop dividing, consistent with increased levels of HetF under similar conditions in the wild type. Furthermore, HetF is a membrane protein located at midcell and cell-cell junctions. In the absence of HetF, FtsZ rings are still present in the elongated cells; however, PG remodeling is abolished. This phenotype is similar to that observed with the inhibition of the septal PG synthase FtsI. We further reveal that HetF is recruited to or stabilized at the divisome by interacting with FtsI and that this interaction is necessary for HetF function in cell division. Our results indicate that HetF is a member of the divisome depending mainly on light intensity and reveal distinct features of the cell division machinery in cyanobacteria that are of high ecological and environmental importance.

Photogranulation in a Hydrostatic Environment Occurs with Limitation of Iron.

Filamentous cyanobacteria are an essential element of oxygenic photogranules for granule-based wastewater treatment with photosynthetic aeration. Currently, mechanisms for the selection of this microbial group and their development in the granular structure are not well understood. Here, we studied the characteristics and fate of iron in photogranulation that proceeds in a hydrostatic environment with an activated sludge (AS) inoculum. We found that the level of Fe in bulk liquids (FeBL) sharply increased due to the decay of the inoculum but quickly diminished along with the bloom of microalgae and the advent of the oxic environment. Iron linked with extracellular polymeric substances (FeEPS) continued to decline but reached steady low values, which occurred along with the appearance of granular structure. Strong negative correlations were found between FeEPS and the pigments specific for cyanobacteria. Spectroscopies revealed the presence of amorphous ferric oxides in pellet biomass, which seemed to remain unaltered during the photogranulation process. These results suggest that the availability of FeEPS in AS inoculums-after algal bloom-selects cyanobacteria, and the limitation of this Fe pool becomes an important driver for cyanobacteria to granulate in a hydrostatic environment. We therefore propose that the availability of iron has a strong influence on the photogranulation process.

Trichome Lengths of the Heterocystous N2-Fixing Cyanobacteria in the Tropical Marginal Seas of the Western North Pacific

Calothrix rhizosoleniae and Richelia intracellularis are heterocystous cyanobacteria found in the tropical oceans. C. rhizosoleniae commonly live epiphytically on diatom genera Chaetoceros (C-C) and Bacteriastrum (B-C) while R. intracellularis live endosymbiotically within Rhizosolenia (R-R), Guinardia (G-R), and Hemiaulus (H-R); although, they occasionally live freely (FL-C and FL-R). Both species have much shorter trichomes than the other marine filamentous cyanobacteria such as Trichodesmium spp. and Anabaena gerdii. We investigated the trichome lengths of C. rhizosoleniae and R. intracellularis in the South China Sea (SCS) and the Philippine Sea (PS) between 2006 and 2014. On average, H-R had the shortest trichome lengths (3.5 cells/trichome), followed by B-C and C-C (4.9–5.2 cells/trichome) and FL-C (5.9 cells/trichome), and R-R, G-R, and FL-R had the longest trichome lengths (7.4–8.3 cells/trichome). Field results showed the trichome lengths of C-C and B-C did not vary seasonally or regionally. However, FL-C and H-R from the SCS and during the cool season had longer trichomes, where/when the ambient nutrient concentrations were higher. R-R, G-R, and FL-R also showed regional and seasonal variations in trichome length. Ultrastructural analysis found no gas vesicles within the C. rhizosoleniae cells to assist in buoyancy regulation. Results suggest that the trichome lengths of C. rhizosoleniae and R. intracellularis might be regulated by their diatom hosts’ symbiotic styles and by ambient nutrients. Short trichome length might help C. rhizosoleniae and R. intracellularis to stay in the euphotic zone regardless as to whether they are free-living or symbiotic.

Colonization and survival of a stress tolerant cyanobacterium on a heritage monument of Santiniketan, India

Colonization of cyanobacteria and associated algae on a heritage monument (Buddha statue) of Santiniketan, India was studied. The dominating biofilms component is a filamentous cyanobacterium, Scytonema millei, which thrives on the monument, even when the surface temperature exceeds 60 °C during summer. The basic adaptive strategy of S. millei was analysed upon exposure to different temperature range and desiccation based on the changes in growth, morphology, and biochemical analysis. Maximum increase of growth (16.2%), chlorophyll-a (42.2%), carotenoids (24.4%), cellular carbohydrate content (102.2%), extracellular carbohydrate content (643.6%), and SOD activity (134.8%) were observed under stress conditions. The organism was found as desiccation and thermo-adaptive species. S. millei was more tolerant to heat soon after exposure in the dry state than in the wet state. Significant increase in carbohydrate content (cellular and extracellular) and SOD activity upon exposure to stress suggests their main importance in the stress tolerance of S. millei. These findings suggest that the dominating cyanobacteria have developed different defense mechanisms enough to survive in extreme natural conditions of tropical regions as well as in lab conditions.

Chironomid larvae destroy cultivated microbial mat in protected Adriatic salterns

Abstract The Sečovlje salterns on the Northern Adriatic coastline encompass both active and abandoned salt pans on the estuary of the Dragonja River. They are protected as a nature park by a governmental decree and by the Ramsar Convention on Wetlands of International Importance. In the Sečovlje salterns, salt is still gathered according to a traditional process originating from the 14th century. The high quality of the traditionally produced salt is attributed to a cultivated microbial mat (called ‘petola’) that covers the floor of the crystallization basins and provides a barrier from the anoxic mud. Every spring, in a process called ‘fertilization’, the microbial mat is covered by a layer of mud, a practice that is supposedly crucial for the maintenance of the petola, but its exact role and underlying mechanisms are not yet fully understood. In early spring 2018 the microbial mat, primarily composed of the filamentous cyanobacterium Coleofasciculus chthonoplastes, was infested by dipteran larvae, which occurred at densities of up to 20,000 m−2. Based on the morphological features of the larvae and imagos, and on DNA analysis of the mitochondrial cytochrome c oxidase subunit I (COI) gene, the newly identified pest was determined to be a chironomid. Under laboratory conditions, larvae fed upon the cyanobacterial mat and destroyed its structure. In the laboratory, the application of a thin layer of saltern mud in a manner typical for the salt production process prevented the development of chironomid larvae and maintained the structure of the microbial mat. In the salterns, omitting the fertilization step resulted in a considerable weakening of the petola layer. The results reveal the possible biological background for the fertilization process and thus provides important knowledge for the conservation of the traditional man‐made aquatic ecosystem of the Sečovlje salterns.

Molecular Components of Nitrogen Fixation Gene Cluster and Associated Enzymatic Activities of Non-Heterocystous Thermophilic Cyanobacterium Thermoleptolyngbya sp.

Thermoleptolyngbya is a genus of non-heterocystous cyanobacteria that are typical inhabitants of hot spring microbial mats. These filamentous cyanobacteria are capable of nitrogen fixation. In this study, we examined the genome sequences of five publicly available Thermoleptolyngbya strains to explore their nitrogen fixation gene cluster. Analysis of the nitrogen-fixation clusters in these extremophilic strains revealed that the cluster is located in a single locus in Thermoleptolyngbyace. The average nucleotide and amino acid identities of the nitrogen-fixation cluster combined with phylogenetic reconstructions support that nitrogen fixation genes in Thermoleptolyngbyaceae are closely related to one another but also heterogeneous within the genus. The strains from Asia, and China more specifically, generate a separate clade within the genus. Among these strains Thermoleptolyngbya sp. PKUAC-SCTB121 has been selected for experimental validation of clade’s nitrogen fixation capacity. The acetylene reduction experiments of that strain shown that the strain can reduce acetylene to ethylene, indicating a fully functional nitrogenase. The activity of nitrogenase has been tested using different gas compositions across 72 h and exhibited a two-phase trend, high nitrogenase activity at the beginning of the assay that slowed down in the second phase of the analysis.

Unravelling the attributes of novel cyanobacteria Jacksonvillea sp. ISTCYN1 by draft genome sequencing

Filamentous cyanobacteria, Jacksonvillea sp. ISTCYN1 was isolated from agriculture field and cultured in BG-11 medium. This study, report the genome sequence of cyanobacteria Jacksonvillea thatto the best of our knowledgeis the firstgenome sequenceof thisgenus. The 5.7 MB draft genome sequence of this cyanobacterium contains 5134 protein-coding genes. The phylogenetic tree was constructed based on genome and Desertifilum sp. IPPAS B-1220 validated the closest relationship with Jacksonvillea sp. ISTCYN1. The growth of strain ISTCYN1 has been reported in the presence of different types of plastic when used as a sole carbon source. SEM analysis revealed biofilm formation by cyanobacterial strain ISTCYN1 on the surface of high and low-density polyethylene and polypropylene. In the presence of these plastics, EPS production has also been reported by this strain. Whole genome sequence analysis reveals the presence of many genes involved in biofilm formation. The presence of key enzymes responsible for plastic degradation laccase, esterase, lipase, thioesterase, and peroxidase have been predicted in the genome analysis. Genome analysis also provides insight into the genes involved in biotin biosynthetic pathways. Furthermore, the presence of many selenoproteins reveals the selenium acquisition by this cyanobacterium.

Quantitative proteomic analysis of marine biofilms formed by filamentous cyanobacterium

Cyanobacterial molecular biology can identify pathways that affect the adhesion and settlement of biofouling organisms and, consequently, obtain novel antifouling strategies for marine applications. Proteomic analyses can provide an essential understanding of how cyanobacteria adapt to different environmental settings. However, only a few qualitative studies have been performed in some cyanobacterial strains. Considering the limited knowledge about protein expression in cyanobacteria in different growing conditions, a quantitative proteomic analysis by LC-MS/MS of biofilm cells from a filamentous strain was performed. Biofilms were also analysed through standard methodologies for following cyanobacterial biofilm development. Biofilms were formed on glass and perspex at two relevant hydrodynamic conditions for marine environments (average shear rates of 4 s−1 and 40 s−1). Biofilm development was higher at 4 s−1 and no significant differences were found between surfaces. Proteomic analysis identified 546 proteins and 41 were differentially expressed. Differences in protein expression were more noticeable between biofilms formed on glass and perspex at 4 s−1. When comparing biofilms formed on different surfaces, results suggest that biofilm development may be related to the expression of several proteins like a beta-propeller domain-containing protein, chaperone DnaK, SLH domain-containing proteins, an OMF family outer membrane protein, and/or additional uncharacterized proteins. Regarding the hydrodynamic effect, biofilm development can be related to SOD enzyme expression, to proteins related to photosynthetic processes and to a set of uncharacterized proteins with calcium binding domains, disordered proteins, and others involved in electron transfer activity. Studies that combine distinct approaches are essential for finding new targets for antibiofilm agents. The characterisation performed in this work provides new insights into how shear rate and surface affect cyanobacterial biofilm development and how cyanobacteria adapt to these different environmental settings from a macroscopic standpoint to a proteomics context.

Reading and surviving the harsh conditions in desert biological soil crust: the cyanobacterial viewpoint.

Biological soil crusts (BSCs) are found in drylands, cover ∼12% of the Earth's surface in arid and semi-arid lands and their destruction is considered an important promoter of desertification. These crusts are formed by the adhesion of soil particles to polysaccharides excreted mostly by filamentous cyanobacteria, which are the pioneers and main primary producers in BSCs. Desert BSCs survive in one of the harshest environments on Earth, and are exposed to daily fluctuations of extreme conditions. The cyanobacteria inhabiting these habitats must precisely read the changing conditions and predict, for example, the forthcoming desiccation. Moreover, they evolved a comprehensive regulation of multiple adaptation strategies to enhance their stress tolerance. Here, we focus on what distinguishes cyanobacteria able to revive after dehydration from those that cannot. While important progress has been made in our understanding of physiological, biochemical and omics aspects, clarification of the sensing, signal transduction and responses enabling desiccation tolerance are just emerging. We plot the trajectory of current research and open questions ranging from general strategies and regulatory adaptations in the hydration/desiccation cycle, to recent advances in our understanding of photosynthetic adaptation. The acquired knowledge provides new insights to mitigate desertification and improve plant productivity under drought conditions.

Filamentous cyanobacteria from western ghats of North Kerala, India

Cyanobacteria are Gram negative, photosynthetic and nitrogen fixing microorganisms which contribute much to our present-day life as medicines, foods, biofuels and biofertilizers. Western Ghats are the hotspots of biodiversity with rich combination of microbial flora including cyanobacteria. Though cosmopolitan in distribution, their abundance in tropical forests are not fully exploited. To fill up this knowledge gap, the present research was carried out on the cyanobacterial flora of Peruvannamuzhi forest and Janaki forests of Western Ghats in Kozhikode District, North Kerala State, India. Extensive specimen collections were conducted during South-West monsoon (June to September) and North-East monsoon (October to December) in the year 2019. The highest diversity of cyanobacteria was found on rock surfaces. A total of 18 cyanobacterial taxa were identified. Among them filamentous heterocystous forms showed maximum diversity with 10 species followed by non- heterocystous forms with 8 species. The highest number of cyanobacteria were identified from Peruvannamuzhi forest with 15 taxa followed by Janaki forest with 3 taxa. The non- heterocystous cyanobacterial genus Oscillatoria Voucher ex Gomont showed maximum abundance with 4 species. In this study we reported Planktothrix planktonica (Elenkin) Agagnostidis & Komárek 1988, Oscillatoria euboeica Anagnostidis 2001 and Nostoc interbryum Sant’Anna et al. 2007 as three new records from India.
 Bangladesh J. Plant Taxon. 28(1): 83-95, 2021 (June)

Development of a method for phycocyanin recovery from filamentous cyanobacteria and evaluation of its stability and antioxidant capacity

BackgroundMost commercial phycocyanins are extracted from a filamentous cyanobacterium, Arthrospira (Spirulina) platensis. Owing to the expenses of culture and complexities of the physical and chemical methods of phycocyanin purification, a more effective and simple method is required.ResultsWe developed a new method for efficiently recovering the blue pigment protein, phycocyanin, from unique filamentous cyanobacteria, Pseudanabaena sp. ABRG5-3 and Limnothrix sp. SK1-2-1. The cells were cultivated in economy medium BG11 and lysed by adding water in a 1:16 ratio of wet cells to water. After extraction and purification, 28–30% dry cell weight of phycocyanin was obtained and its purity was confirmed. The stabilities of the phycocyanins at different pH in the presence of high temperature and light conditions and their antioxidant abilities were assessed. Results indicated that the phycocyanins were stable and possessed antioxidant properties. Interestingly, the Pseudanabaena phycocyanin was less likely to deteriorate under acidic conditions.ConclusionsOverall, we developed a promising and novel method for producing high functional phycocyanin concentrations at a low cost. The possibilities of adapting this new phycocyanin biorefinery to unique bioreactor utilization have also been discussed.

Evaluation of lemna minor and cyanobacteria effect in aerated and non-aerated conditions on biological oxygen demand (BOD),dissolved chemical oxygen (COD),total coliform and faecal coliform of municipal and industrial wastewater

ABSTRACT Water scarcity and its growing demand, especially in arid and semi-arid countries, put a lot of pressure on water resources and with the increasing limitation of water resources, the use of wastewater is considered as an unconventional water source and the only sustainable source of water for irrigation of agricultural products. In this study, the performance of Lemna minor and filamentous cyanobacteria in the treatment of two types of industrial and municipal effluents were investigated separately. The experiment was performed as a factorial experiment in a randomised complete block design with three replications. The experiment was performed as a factorial experiment in a randomised complete block design with three replications. The highest reduction for BOD and COD factors was observed in the presence of lemna minor, and cyanobacteria showed a more favourable effect on total coliform factor, while both treatments could not reduce the total coliforms to the desired level and it seems that they need time or complementary methods for optimal treatment and reuse in nature. It is worth noting that the lemna minor was very successful in reducing faecal coliform and reduced it to 100% in the first five days. In general, lemna minor was more successful than cyanobacteria. It seems that cyanobacteria need more time for optimal results because the best results of cyanobacteria occurred in a period of 10 to 15 days.

Engineered methanotrophic syntrophy in photogranule communities removes dissolved methane

The anaerobic treatment of wastewater leads to the loss of dissolved methane in the effluent of the treatment plant, especially when operated at low temperatures. The emission of this greenhouse gas may reduce or even offset the environmental gain from energy recovery through anaerobic treatment. We demonstrate here the removal and elimination of these comparably small methane concentrations using an ecologically engineered methanotrophic community harbored in oxygenic photogranules. We constructed a syntrophy between methanotrophs enriched from activated sludge and cyanobacteria residing in photogranules and maintained it over a two-month period in a continuously operated reactor. The novel community removed dissolved methane during stable reactor operation by on average 84.8±7.4% (±standard deviation) with an average effluent concentration of dissolved methane of 4.9±3.7 mg CH4∙l−1. The average methane removal rate was 26 mg CH4∙l−1∙d−1, with an observed combined biomass yield of 2.4 g VSS∙g CH4−1. The overall COD balance closed at around 91%. Small photogranules removed methane more efficiently than larger photogranule, likely because of a more favorable surface to volume ratio of the biomass. MiSeq amplicon sequencing of 16S and 23S rRNA revealed a potential syntrophic chain between methanotrophs, non-methanotrophic methylotrophs and filamentous cyanobacteria. The community composition between individual photogranules varied considerably, suggesting cross-feeding between photogranules of different community composition. Methanotrophic photogranules may be a viable option for dissolved methane removal as anaerobic effluent post-treatment.

Alborzia kermanshahica gen. nov., sp. nov. (Chroococcales, Cyanobacteria), isolated from paddy fields in Iran.

In Iran, polyphasic studies of unicellular cyanobacteria are still scarce, with more emphasis being placed on filamentous cyanobacteria in paddy fields and fresh water regions. In an effort to increase the knowledge of the diversity of unicellular cyanobacteria from paddy fields in Iran, we have isolated and characterized a new unicellular cyanobacterium strain. The strain was studied using a polyphasic approach based on morphological, ecological and phylogenetic analyses of the 16S-23S ITS rRNA gene region. Complementarily, we have searched for the presence of cyanotoxin genes and analysed the pigment content of the strain. Results showed that the strain was morphologically indistinguishable from the genus Chroococcus, but phylogenetic analyses based on the Bayesian inference and maximum-likelihood methods placed the strain in a separated monophyletic and highly supported (0.99/98, posterior probability/maximum-likelihood) genus-level cluster, distant from Chroococcus sensu stricto and with Chalicogloea cavernicola as sister taxa. The calculated p-distance for the 16S rRNA gene also reinforced the presence of a new genus, by showing 92 % similarity to C. cavernicola. The D1-D1', Box-B and V3 ITS secondary structures showed the uniqueness of this strain, as it shared no similar pattern with closest genera within the Chroococcales. For all these reasons, and in accordance with the International Code of Nomenclature for Algae, Fungi and Plants, we here proposed the description of a new genus with the name Alborzia gen. nov. along with the description of a new species, Alborzia kermanshahica sp. nov. (holotype: CCC1399-a; reference strains CCC1399-b; MCC 4116).

Comparative Phenotypic Analysis of Anabaena sp. PCC 7120 Mutants of Porinlike Genes.

Porins are essential for the viability of Gram-negative bacteria. They ensure the uptake of nutrients, can be involved in the maintenance of outer membrane integrity and define the antibiotic or drug resistance of organisms. The function and structure of porins in proteobacteria is well described, while their function in photoautotrophic cyanobacteria has not been systematically explored. We compared the domain architecture of nine putative porins in the filamentous cyanobacterium Anabaena sp. PCC 7120 and analyzed the seven candidates with predicted OprB-domain. Single recombinant mutants of the seven genes were created and their growth capacity under different conditions was analyzed. Most of the putative porins seem to be involved in the transport of salt and copper, as respective mutants were resistant to elevated concentrations of these substances. In turn, only the mutant of alr2231 was less sensitive to elevated zinc concentrations, while mutants of alr0834, alr4741 and all4499 were resistant to high manganese concentrations. Notably the mutant of alr4550 shows a high sensitivity against harmful compounds, which is indicative for a function related to the maintenance of outer membrane integrity. Moreover, the mutant of all5191 exhibited a phenotype which suggests either a higher nitrate demand or an inefficient nitrogen fixation. The dependency of porin membrane insertion on Omp85 proteins was tested exemplarily for Alr4550, and an enhanced aggregation of Alr4550 was observed in two omp85 mutants. The comparative analysis of porin mutants suggests that the proteins in parts perform distinct functions related to envelope integrity and solute uptake.

A new record of Spirulina subsalsa (Oersted Ex Gomont, 1892) with molecular profile isolated in Vellar Estuary, Portonovo, South East Coast, Tamil Nadu (India)

Spirulina is a filamentous, multi-cellular and autotrophic cyanobacterium having distinct features of helical shape filaments ( i.e. trichomes). An investigation is to isolate a marine, Spirulina subsalsa from Vellar estuary, South East Coast zone of India. The isolated strain sub-cultured in Zarrouk medium with optimum conditions for sustaining growth. Pure cultures were examined in a research microscope for morphometric studies through 16S rRNA sequencing and the sequence was submitted to NCBI-GENBANK, the accession number is MW037197 which displays the maximum similarity as 100% with a diverse sequence in databank i.e. LC 215280. The investigation is the first record for the existence of Spirulina subsalsa in Vellar Estuary, South East Coast, Tamil Nadu (India) as affirmed by a molecular nucleotide sequence.

Phytoplankton responses to meteorological and hydrological forcing at decadal to seasonal time scales

One of the challenges for predicting global change effects on aquatic ecosystems is the vague understanding of the mechanisms of multiple controlling factors affecting phytoplankton dynamics at different time scales. Here we distinguish between hydrometeorological forcing of phytoplankton dynamics at time scales from days to decades based on a 54-year monthly phytoplankton time series from a large shallow Lake Võrtsjärv (58°16′N, 26°02′E) in Estonia, combined with daily data on forcing factors—thermal-, wind-, light- and water-level regimes. By using variance partitioning with linear mixed effect modelling (LME), we found a continuum from the large dominant K-selected filamentous cyanobacteria with strongest decadal scale variation (8–30%) to r-selected phytoflagellates with large stochastic variability (80–96%). External forcing revealed strong seasonal variation (up to 80%), while specifically water level and wind speed had a robust decadal variation (8% and 20%, respectively). The effect of external variables was proportionally manifested in the time scales of phytoplankton variation. Temperature, with a clear seasonal variation, had no impact on the dominant cold tolerant filamentous cyanobacteria in Lake Võrtsjärv. We found the LME as a reliable method for resolving the temporal cross-scale problem. It yielded quantitative results that matched our intuitive understanding of the dynamics of different variables.

Insight into cyanobacterial preservation in shallow marine environments from experimental simulation of cyanobacteria-clay co-aggregation

Clay minerals associated with microbial body and trace fossils in rocks deposited in shallow marine environments have importance in understanding microbial preservation. We show experimentally that the presence of suspended detrital clays in oceanic environments is a crucial control on the formation of co-aggregates between filamentous cyanobacteria and clay minerals and is thus important in the sedimentation and subsequent preservation of cyanobacteria. Strong cyanobacteria-clay co-aggregation occurs over short time periods (3–7 days) in the presence of 10 mg/L of suspended clay minerals (illite, kaolinite and montmorillonite), and the occurrence of co-aggregation is not affected by the type of clay minerals present. The cyanobacteria-clay co-aggregation shows a pronounced effect on preserving the biomass of cyanobacteria. The surface properties of clay minerals and cyanobacteria, specifically the electrostatic attraction between the oppositely charged surfaces of cyanobacteria and clay minerals, are the main drivers of cyanobacteria-clay co-aggregation. Chemical effects, such as the deprotonation of COOH groups in active organic compounds secreted by cyanobacteria and therefore the release of H+, result in local dissolution of clay and slight structure changes in the bulk of clay minerals. Compared with the suspended clay, dissolved ions (Si, Al or Fe ions) are of secondary importance in the formation of cyanobacteria-clay co-aggregates, although these ions further promote this process. Overall, the cyanobacteria-clay co-aggregation not only substantially affects the preservation of cyanobacteria, but also may have potentially important and profound impacts on related geochemical processes such as microbial dissolution of clay minerals and the biogeochemical Si cycle in marine environments.