Cyanobacteria of the genus prochlorothrix

Emergence of fractal geometries in the evolution of a metabolic enzyme

Fractals are patterns that are self-similar across multiple length-scales1. Macroscopic fractals are common in nature2-4; however, so far, molecular assembly into fractals is restricted to synthetic systems5-12. Here we report the discovery of a natural protein, citrate synthase from the cyanobacterium Synechococcus elongatus, which self-assembles into Sierpiński triangles. Using cryo-electron microscopy, we reveal how the fractal assembles from a hexameric building block. Although different stimuli modulate the formation of fractal complexes and these complexes can regulate the enzymatic activity of citrate synthase in vitro, the fractal may not serve a physiological function in vivo. We use ancestral sequence reconstruction to retrace how the citrate synthase fractal evolved from non-fractal precursors, and the results suggest it may have emerged as a harmless evolutionary accident. Our findings expand the space of possible protein complexes and demonstrate that intricate and regulatable assemblies can evolve in a single substitution.

Phylogenetic and spectroscopic insights on the evolution of core antenna proteins in cyanobacteria

Light harvesting by antenna systems is the initial step in a series of electron-transfer reactions in all photosynthetic organisms, leading to energy trapping by reaction center proteins. Cyanobacteria are an ecologically diverse group and are the simplest organisms capable of oxygenic photosynthesis. The primary light-harvesting antenna in cyanobacteria is the large membrane extrinsic pigment-protein complex called the phycobilisome. In addition, cyanobacteria have also evolved specialized membrane-intrinsic chlorophyll-binding antenna proteins that transfer excitation energy to the reaction centers of photosystems I and II (PSI and PSII) and dissipate excess energy through nonphotochemical quenching. Primary among these are the CP43 and CP47 proteins of PSII, but in addition, some cyanobacteria also use IsiA and the prochlorophyte chlorophyll a/b binding (Pcb) family of proteins. Together, these proteins comprise the CP43 family of proteins owing to their sequence similarity with CP43. In this article, we have revisited the evolution of these chlorophyll-binding antenna proteins by examining their protein sequences in parallel with their spectral properties. Our phylogenetic and spectroscopic analyses support the idea of a common ancestor for CP43, IsiA, and Pcb proteins, and suggest that PcbC might be a distant ancestor of IsiA. The similar spectral properties of CP47 and IsiA suggest a closer evolutionary relationship between these proteins compared to CP43.

Heterotrophy among Cyanobacteria

Cyanobacteria have been studied in recent decades to investigate the principle mechanisms of plant-type oxygenic photosynthesis, as they are the inventors of this process, and their cultivation and research is much easier compared to land plants. Nevertheless, many cyanobacterial strains possess the capacity for at least some forms of heterotrophic growth. This review demonstrates that cyanobacteria are much more than simple photoautotrophs, and their flexibility toward different environmental conditions has been underestimated in the past. It summarizes the strains capable of heterotrophy known by date structured by their phylogeny and lists the possible substrates for heterotrophy for each of them in a table in the Supporting Information. The conditions are discussed in detail that cause heterotrophic growth for each strain in order to allow for reproduction of the results. The review explains the importance of this knowledge for the use of new methods of cyanobacterial cultivation, which may be advantageous under certain conditions. It seeks to stimulate other researchers to identify new strains capable of heterotrophy that have not been known so far.

Interaction among spring phytoplankton succession, water discharge patterns, and hydrogen peroxide dynamics in the Caloosahatchee River in southwest Florida

Phytoplankton communities are major primary producers in the aquatic realm and are responsible for shaping aquatic ecosystems. The dynamics of algal blooms could be determined by a succession of variable taxonomic groups, which are altered based on complex environmental factors such as nutrient availability and hydraulic factors. In-river structures potentially increase the occurrence of harmful algal blooms (HABs) by increasing water residence time and deteriorating water quality. How flowing water stimulates cell growth and affects the population dynamics of phytoplankton communities is a prioritized question that needs to be addressed for water management tactics. The goal of this study was to determine if an interaction between water flow and water chemistry is present, furthermore, to determine the relationship among phytoplankton community successions in the Caloosahatchee River, a subtropical river strongly influenced by human-controlled water discharge patterns from Lake Okeechobee. Particularly we focused on how phytoplankton community shifts influence the natural abundance of hydrogen peroxide, the most stable reactive oxygen species and a byproduct of oxidative photosynthesis. High-throughput amplicon sequencing using universal primers amplify 23S rRNA gene in cyanobacteria and eukaryotic algal plastids revealed that Synechococcus and Cyanobium were the dominant cyanobacterial genera and their relative abundance ranged between 19.5 and 95.3% of the whole community throughout the monitoring period. Their relative abundance declined when the water discharge increased. On the contrary, the relative abundance of eukaryotic algae sharply increased after water discharge increased. As water temperature increased in May, initially dominant Dolichospermum decreased as Microcystis increased. When Microcystis declined other filamentous cyanobacteria such as Geitlerinema, Pseudanabaena, and Prochlorothreix increased in their relative abundances. Interestingly, a peak of extracellular hydrogen peroxide was observed when Dolichospermum dominance was ended, and M. aeruginosa numbers increased. Overall, phytoplankton communities were strongly impacted by human-induced water discharge patterns.

Spectrofluorometric Insights into the Application of PAM Fluorometry in Photosynthetic Research

Although pulse amplitude modulation (PAM) fluorometry has revolutionized photosynthetic studies, Photosynthetic Electron Transport Rate (ETR) cannot be measured using PAM technology in some organisms. We compare in vivo absorbance information on a selection of photosynthetic organisms using an integrating sphere spectrophotometry on a variety of oxygenic and nonoxygenic photo-organisms and provide fluorescence data to help in understanding why PAM technology is unsuccessful on some organisms, particularly cyanobacteria. The study includes anoxygenic photosynthetic bacteria: Afifella marina, Rhodopseudomonas palustris and Thermochromatium which are all RC-2 type photosynthetic bacteria (Bacteriochlorophyll a or BChl a) which are known to have measureable delayed fluorescence, Yield and hence measureable ETR. The common unicellular green alga, Chlorella sp (Chl a + b) uses the same primary photosynthetic pigments as vascular plants. Comparisons are made to some other representative oxygenic unicellular organisms: Trebouxia (Chlorophyta, Chl a + b), Chaetoceros (a diatom, Chl a + c₁ c₂ ) and the unusual cyanobacterium Acaryochloris marina which has Chl d + a but uses Chl d as its primary photosynthetic pigment. Synechococcus R-2 (Cyanobacteria) has only Chl a. Its fluorescence is outside the range normally used for measuring photosynthesis using PAM technology: delayed fluorescence is not readily detectable.

Chloroplast history clarified by the criterion of light-harvesting complex

Bacterial essence of mitochondria and chloroplasts was initially proclaimed in general outline. Later, the remarkable insight gave way to an elaborate hypothesis. Finally, it took shape of a theory confirmed by molecular biology data. In particular, the rrn operon, which is the key phylogeny marker, locates chloroplasts on the tree of Cyanobacteria. Chloroplast ancestry and diversity can be also traced with the rpoС and psbA genes, rbc operon, and other molecular criteria of prime importance. Another criterion, also highly reliable, is light-harvesting complex (LHC). LHC pigment and protein moieties specify light acclimation strategies in evolutionary retrospect and modern biosphere. The onset of symbiosis between eukaryotic host and pre-chloroplast, as well as further mutual adjustment of partners depended on physiological competence of LHC. In this review, the criterion of LHC is applied to the origin and diversity of chloroplasts. In particular, ancient cyanobacterium possessing tandem antenna (encoded by the cbp genes and the pbp genes, correspondingly), and defined as a prochlorophyte, is argued to be chloroplast ancestor.

Draft genome of Prochlorothrix hollandica CCAP 1490/1T (CALU1027), the chlorophyll a/b-containing filamentous cyanobacterium

Prochlorothrix hollandica is filamentous non-heterocystous cyanobacterium which possesses the chlorophyll a/b light-harvesting complexes. Despite the growing interest in unusual green-pigmented cyanobacteria (prochlorophytes) to date only a few sequenced genome from prochlorophytes genera have been reported. This study sequenced the genome of Prochlorothrix hollandica CCAP 1490/1^T (CALU1027). The produced draft genome assembly (5.5 Mb) contains 3737 protein-coding genes and 114 RNA genes.

Diversity and Activity of Communities Inhabiting Plastic Debris in the North Pacific Gyre

Marine plastic debris has become a significant concern in ocean ecosystems worldwide. Little is known, however, about its influence on microbial community structure and function. In 2008, we surveyed microbial communities and metabolic activities in seawater and on plastic on an oceanographic expedition through the "great Pacific garbage patch." The concentration of plastic particles in surface seawater within different size classes (2 to 5 mm and >5 mm) ranged from 0.35 to 3.7 particles m^-3 across sampling stations. These densities and the particle size distribution were consistent with previous values reported in the North Pacific Ocean. Net community oxygen production (NCP = gross primary production - community respiration) on plastic debris was positive and so net autotrophic, whereas NCP in bulk seawater was close to zero. Scanning electron microscopy and metagenomic sequencing of plastic-attached communities revealed the dominance of a few metazoan taxa and a diverse assemblage of photoautotrophic and heterotrophic protists and bacteria. Bryozoa, Cyanobacteria, Alphaproteobacteria, and Bacteroidetes dominated all plastic particles, regardless of particle size. Bacteria inhabiting plastic were taxonomically distinct from the surrounding picoplankton and appeared well adapted to a surface-associated lifestyle. Genes with significantly higher abundances among plastic-attached bacteria included che genes, secretion system genes, and nifH genes, suggesting enrichment for chemotaxis, frequent cell-to-cell interactions, and nitrogen fixation. In aggregate, our findings suggest that plastic debris forms a habitat for complex microbial assemblages that have lifestyles, metabolic pathways, and biogeochemical activities that are distinct from those of free-living planktonic microbial communities. IMPORTANCE Marine plastic debris is a growing concern that has captured the general public's attention. While the negative impacts of plastic debris on oceanic macrobiota, including mammals and birds, are well documented, little is known about its influence on smaller marine residents, including microbes that have key roles in ocean biogeochemistry. Our work provides a new perspective on microbial communities inhabiting microplastics that includes its effect on microbial biogeochemical activities and a description of the cross-domain communities inhabiting plastic particles. This study is among the first molecular ecology, plastic debris biota surveys in the North Pacific Subtropical Gyre. It has identified fundamental differences in the functional potential and taxonomic composition of plastic-associated microbes versus planktonic microbes found in the surrounding open-ocean habitat. Author Video: An author video summary of this article is available.

Consortium of the 'bichlorophyllous' cyanobacterium Prochlorothrix hollandica and chemoheterotrophic partner bacteria: culture and metagenome-based description

'Bacterial consortium' sensu lato applies to mutualism or syntrophy-based systems consisting of unrelated bacteria. Consortia of cyanobacteria have been preferentially studied on Anabaena epibioses; non-photosynthetic satellites of other filamentous or unicellular cyanobacteria were also considered although structure-functional data are few. At the same time, information about consortia of cyanobacteria which have light-harvesting antennae distinct from standard phycobilisome was missing. In this study, we characterized first, via a polyphasic approach, the cultivable consortium of Prochlorothrix hollandica CCAP 1490/1 (filamentous cyanobacterium which contains chlorophylls a, b/carotenoid/protein complex in the absence of phycobilisome) and non-photosynthetic heterotrophic bacteria. The strains of most abundant satellites were isolated and identified. Consortium metagenome reconstructed via 454-pyro and Illumina sequencing was shown to include, except for P. hollandica, several phylotypes of Proteobacteria and Bacteroidetes. The ratio of consortium members was essentially stable irrespective of culture age, and restored after artificially imposed imbalance. The consortium had a complex spatial arrangement as demonstrated by FISH and SEM images of the association, epibiosis, and biofilm type. Preliminary data of metagenome annotation agreed with the hypothesis that satellite bacteria contribute to P. hollandica protection from reactive oxygen species (ROS).

Identification of DXCF cyanobacteriochrome lineages with predictable photocycles

Two specialized subgroups of cyanobacteriochromes with predictable green/blue and blue/orange photocycles are defined by these studies.

Primary endosymbiosis and the evolution of light and oxygen sensing in photosynthetic eukaryotes

The origin of the photosynthetic organelle in eukaryotes, the plastid, changed forever the evolutionary trajectory of life on our planet. Plastids are highly specialized compartments derived from a putative single cyanobacterial primary endosymbiosis that occurred in the common ancestor of the supergroup Archaeplastida that comprises the Viridiplantae (green algae and plants), red algae, and glaucophyte algae. These lineages include critical primary producers of freshwater and terrestrial ecosystems, progenitors of which provided plastids through secondary endosymbiosis to other algae such as diatoms and dinoflagellates that are critical to marine ecosystems. Despite its broad importance and the success of algal and plant lineages, the phagotrophic origin of the plastid imposed an interesting challenge on the predatory eukaryotic ancestor of the Archaeplastida. By engulfing an oxygenic photosynthetic cell, the host lineage imposed an oxidative stress upon itself in the presence of light. Adaptations to meet this challenge were thus likely to have occurred early on during the transition from a predatory phagotroph to an obligate phototroph (or mixotroph). Modern algae have recently been shown to employ linear tetrapyrroles (bilins) to respond to oxidative stress under high light. Here we explore the early events in plastid evolution and the possible ancient roles of bilins in responding to light and oxygen.

Antitumor activity of hierridin B, a cyanobacterial secondary metabolite found in both filamentous and unicellular marine strains

Cyanobacteria are widely recognized as a valuable source of bioactive metabolites. The majority of such compounds have been isolated from so-called complex cyanobacteria, such as filamentous or colonial forms, which usually display a larger number of biosynthetic gene clusters in their genomes, when compared to free-living unicellular forms. Nevertheless, picocyanobacteria are also known to have potential to produce bioactive natural products. Here, we report the isolation of hierridin B from the marine picocyanobacterium Cyanobium sp. LEGE 06113. This compound had previously been isolated from the filamentous epiphytic cyanobacterium Phormidium ectocarpi SAG 60.90, and had been shown to possess antiplasmodial activity. A phylogenetic analysis of the 16S rRNA gene from both strains confirmed that these cyanobacteria derive from different evolutionary lineages. We further investigated the biological activity of hierridin B, and tested its cytotoxicity towards a panel of human cancer cell lines; it showed selective cytotoxicity towards HT-29 colon adenocarcinoma cells.