A new cyanobacterial genus Altericista and three species, A. lacusladogae sp. nov., A. violacea sp. nov., and A. variichlora sp. nov., described using a polyphasic approach.

Several strains of unicellular cyanobacteria from the culture collection of St. Petersburg State University, St. Petersburg, Russia (CALU), which were preliminary identified as Synechocystis sp., are reclassified in the new genus Altericista. Three new species are proposed, A. lacusladogae, A. violacea, and A. variichlora. The last species produces accessory chlorophylls d and f in cultures illuminated by far-red light, an attribute rarely observed in cyanobacteria, especially in unicellular strains. This genus is morphologically similar to Synechocysis having coccoid cells that divide in two successive planes at right angles, containing no sheath or capsule, and having the lamellar system represented by peripheral concentric thylakoids. Altericista shows ecological, biochemical, and physiological characters unlike those in Synechocystis and has the distinguishing phenotypic characters as follows: freshwater, non-halotolerant ecotype; palmitate and α-linoleate as major fatty acids; and the ability to photoacclimate, including several types of complementary chromatic adaptation. Genetic differences from Synechocystis sp. include 16S rRNA, rpoC1, and rbcL gene sequences, as well as sequence and folding of 16S-23S ITS.

The ambiguity of the basic terms related to eukaryotes and the more consistent etymology based on eukaryotic signatures in Asgard archaea.

The endosymbiosis theory most widely accepted variant surmises the engulfment of a bacterial cell by an archaeal cell. For decades, this scenario was reputed to be an unconfirmed hypothesis, and only recently it has obtained an indirect proof in Asgard archaea environmental DNA encoding eukaryotic signatures - actin cytoskeleton, small GTPases, and ESCRT complex. In view of growing interest to this aspect of the endosymbiosis theory, it seemed timely to revisit the basic terms eukaryotic cell/eukaryotes/nucleated organisms. The article highlights the ambiguous applications of these terms, and seeks for their consistency with regard to phylogeny and taxonomy. Additionally, new name Caryosignifera is proposed for the phylum represented by: (1) the underexplored Asgard archaea manifested by above-mentioned environmental DNA; (2) cultured species of engulfing Asgard archaea; (3) eukaryotic host cells in nucleated organisms (protists, algae, plants, fungi, and animals).

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.

Testing culture purity in prokaryotes: criteria and challenges.

Reliance on pure cultures was introduced at the beginning of microbiology as a discipline and has remained significant although their adaptive properties are essentially dissimilar from those of mixed cultures and environmental populations. They are needed for (i) taxonomic identification; (ii) diagnostics of pathogens; (iii) virulence and pathogenicity studies; (iv) elucidation of metabolic properties; (v) testing sensitivity to antibiotics; (vi) full-length genome assembly; (vii) strain deposition in microbial collections; and (viii) description of new species with name validation. Depending on the specific task there are alternative claims for culture purity, i.e., when conventional criteria are satisfied or when looking deeper is necessary. Conventional proof (microscopic and plating controls) has a low resolution and depends on the observer's personal judgement. Phenotypic criteria alone cannot prove culture purity and should be complemented with genomic criteria. We consider the possible use of DNA high-throughput culture sequencing data to define criteria for only one genospecies, axenic state detection panel and only one genome. The second and third of these are preferable, although their resolving capacity (depth) is limited. Because minor contaminants may go undetected, even with deep sequencing, the reliably pure culture would be a clonal culture launched from a single cell or trichome (multicellular bacterium). Although this type of culture is associated with technical difficulties and cannot be employed on a large scale (the corresponding inoculums may have low chances of growth when transferred to solid media), it is hoped that the high-throughput culturing methods introduced by 'culturomics' will overcome this obstacle.

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 1490/1T (CALU1027). The produced draft genome assembly (5.5 Mb) contains 3737 protein-coding genes and 114 RNA genes.

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).

Proposal to consistently apply the International Code of Nomenclature of Prokaryotes (ICNP) to names of the oxygenic photosynthetic bacteria (cyanobacteria), including those validly published under the International Code of Botanical Nomenclature (ICBN)/International Code of Nomenclature for algae, fungi and plants (ICN), and proposal to change Principle 2 of the ICNP.

This taxonomic note was motivated by the recent proposal [Oren & Garrity (2014) Int J Syst Evol Microbiol 64, 309-310] to exclude the oxygenic photosynthetic bacteria (cyanobacteria) from the wording of General Consideration 5 of the International Code of Nomenclature of Prokaryotes (ICNP), which entails unilateral coverage of these prokaryotes by the International Code of Nomenclature for algae, fungi, and plants (ICN; formerly the International Code of Botanical Nomenclature, ICBN). On the basis of key viewpoints, approaches and rules in the systematics, taxonomy and nomenclature of prokaryotes it is reciprocally proposed to apply the ICNP to names of cyanobacteria including those validly published under the ICBN/ICN. For this purpose, a change to Principle 2 of the ICNP is proposed to enable validation of cyanobacterial names published under the ICBN/ICN rules.

Cyanobacteria of the genus prochlorothrix.

Green cyanobacteria differ from the blue-green cyanobacteria by the possession of a chlorophyll-containing light-harvesting antenna. Three genera of the green cyanobacteria namely Acaryochloris, Prochlorococcus, and Prochloron are unicellular and inhabit marine environments. Prochlorococcus marinus attracts most attention due to its prominent role in marine primary productivity. The fourth genus Prochlorothrix is represented by the filamentous freshwater strains. Unlike the other green cyanobacteria, Prochlorothrix strains are remarkably rare: to date, living isolates have been limited to two European locations. Taking into account fluctuating blooms, morphological resemblance to Planktothrix and Pseudanabaena, and unsuccessful attempts to obtain enrichments of Prochlorothrix, the most successful strategy to search for this cyanobacterium involves PCR with environmental DNA and Prochlorothrix-specific primers. This approach has revealed a broader distribution of Prochlorothrix. Marker genes have been found in at least two additional locations. Despite of the growing evidence for naturally occurring Prochlorothrix, there are only a few cultured strains with one of them (PCC 9006) being claimed to be axenic. In multixenic cultures, Prochlorothrix is accompanied by heterotrophic bacteria indicating a consortium-type association. The genus Prochlorothrix includes two species: P. hollandica and P. scandica based on distinctions in genomic DNA, cell size, temperature optimum, and fatty acid composition of membrane lipids. In this short review the properties of cyanobacteria of the genus Prochlorothrix are described. In addition, the evolutionary scenario for green cyanobacteria is suggested taking into account their possible role in the origin of simple chloroplast.

Association of chlorophyll a/b-binding Pcb proteins with photosystems I and II in Prochlorothrix hollandica.

Action spectra for photosystem II (PSII)-driven oxygen evolution and of photosystem I (PSI)-mediated H(2) photoproduction and photoinhibition of respiration were used to determine the participation of chlorophyll (Chl) a/b-binding Pcb proteins in the functions of pigment apparatus of Prochlorothrix hollandica. Comparison of the in situ action spectra with absorption spectra of PSII and PSI complexes isolated from the cyanobacterium Synechocystis 6803 revealed a shoulder at 650 nm that indicated presence of Chl b in the both photosystems of P. hollandica. Fitting of two action spectra to absorption spectrum of the cells showed a chlorophyll ratio of 4:1 in favor of PSI. Effective antenna sizes estimated from photochemical cross-sections of the relevant photoreactions were found to be 192+/-28 and 139+/-15 chlorophyll molecules for the competent PSI and PSII reaction centers, respectively. The value for PSI is in a quite good agreement with previous electron microscopy data for isolated Pcb-PSI supercomplexes from P. hollandica that show a trimeric PSI core surrounded by a ring of 18 Pcb subunits. The antenna size of PSII implies that the PSII core dimers are associated with approximately 14 Pcb light-harvesting proteins, and form the largest known Pcb-PSII supercomplexes.