Discovery of nondiazotrophic Trichodesmium species abundant and widespread in the open ocean

Filamentous and colony-forming cells within the cyanobacterial genus Trichodesmium might account for nearly half of nitrogen fixation in the sunlit ocean, a critical mechanism that sustains plankton’s primary productivity. Trichodesmium has long been portrayed as a diazotrophic genus. By means of genome-resolved metagenomics, here we reveal that nondiazotrophic Trichodesmium species not only exist but also are abundant and widespread in the open ocean, benefiting from a previously overlooked functional lifestyle to expand the biogeography of this prominent marine genus. Near-complete environmental genomes for those closely related candidate species reproducibly shared functional features including a lack of genes related to nitrogen fixation, hydrogen recycling, and hopanoid lipid production concomitant with the enrichment of nitrogen assimilation genes. Our results elucidate fieldwork observations of Trichodesmium cells fixing carbon but not nitrogen. The Black Queen hypothesis and burden of low-oxygen concentration requirements provide a rationale to explain gene loss linked to nitrogen fixation among Trichodesmium species. Disconnecting taxonomic signal for this genus from a microbial community’s ability to fix nitrogen will help refine our understanding of the marine nitrogen balance. Finally, we are reminded that established links between taxonomic lineages and functional traits do not always hold true.

Establishment of a New Filamentous Cyanobacterial Genus, Microcoleusiopsis gen. nov. (Microcoleaceae, Cyanobacteria), from Benthic Mats in Open Channel, Jiangxi Province, China

Cyanobacterial taxonomic studies performed by using the modern approaches always lead to creation of many new genera and species. During the field survey for cyanobacterial resources in China, a filamentous cyanobacterial strain was successfully isolated from a microbial mat attached to rock surfaces of the Ganfu Channel, Jiangxi Province, China. This strain was morphologically similar to the cyanobacterial taxa belonging to the genera Microcoleus and Phormidium. The phylogenetic analyses based on 16S rRNA gene sequences showed that this strain formed a well-supported clade, close to the filamentous genera Microcoleus, Tychonema, and Kamptonema. The maximum similarity of 16S rRNA gene sequence of this strain with the related genera was 95.04%, less than the threshold for distinguishing bacterial genus. The ITS secondary structures also distinguish this strain from the related cyanobacterial genera. Therefore, combined with morphology, 16S rRNA gene sequence, and ITS secondary structures, a novel cyanobacterial genus here as Microcoleusiopsis was established, with the species type as Microcoleusiopsis ganfuensis.

Quorum-Sensing Signals from Epibiont Mediate the Induction of Novel Microviridins in the Mat-Forming Cyanobacterial Genus Nostoc

The regulation of the production of cyanopeptides beyond microcystin is essential to understand their ecological role in complex microbial communities, e.g., harmful cyanobacterial blooms. The role of chemical communication between the cyanobacterium and the epibionts within its phycosphere is at an initial stage of research, and little is understood about its specificity.

Emendation of the Coccoid Cyanobacterial Genus Gloeocapsopsis and Description of the New Species Gloeocapsopsis diffluens sp. nov. and Gloeocapsopsis dulcis sp. nov. Isolated From the Coastal Range of the Atacama Desert (Chile)

The taxonomy of coccoid cyanobacteria, such as Chroococcidiopsis, Pleurocapsa, Chroococcus, Gloeothece, Gloeocapsa, Gloeocapsopsis, and the related recent genera Sinocapsa and Aliterella, can easily be intermixed when solely compared on a morphological basis. There is still little support on the taxonomic position of some of the addressed genera, as genetic information is available only for a fraction of species that have been described solely on morphology. Modern polyphasic approaches that combine classic morphological investigations with DNA-based molecular analyses and the evaluation of ecological properties can disentangle these easily confusable unicellular genera. By using such an approach, we present here the formal description of two novel unicellular cyanobacterial species that inhabit the Coastal Range of the Atacama Desert, Gloeocapsopsis dulcis (first reported as Gloeocapsopsis AAB1) and Gloeocapsopsis diffluens. Both species could be clearly separated from previously reported species by 16S rRNA and 16S–23S ITS gene sequencing, the resulting secondary structures, p-distance analyses of the 16S–23S ITS, and morphology. For avoiding further confusions emendation of the genus Gloeocapsopsis as well as epitypification of the type species Gloeocapsopsis crepidinum based on the strain LEGE06123 were conducted.

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)

Amazonocrinis nigriterrae gen. nov., sp. nov., Atlanticothrix silvestris gen. nov., sp. nov. and Dendronalium phyllosphericum gen. nov., sp. nov., nostocacean cyanobacteria from Brazilian environments

The cyanobacterial genus Nostoc is an important contributor to carbon and nitrogen bioavailability in terrestrial ecosystems and a frequent partner in symbiotic relationships with non-diazotrophic organisms. However, since this currently is a polyphyletic genus, the diversity of Nostoc -like cyanobacteria is considerably underestimated at this moment. While reviewing the phylogenetic placement of previously isolated Nostoc -like cyanobacteria originating from Brazilian Amazon, Caatinga and Atlantic forest samples, we detected 17 strains isolated from soil, freshwater, rock and tree surfaces presenting patterns that diverged significantly from related strains when ecological, morphological, molecular and genomic traits were also considered. These observations led to the identification of the evaluated strains as representative of three novel nostocacean genera and species: Amazonocrinis nigriterrae gen. nov., sp. nov.; Atlanticothrix silvestris gen. nov., sp. nov.; and Dendronalium phyllosphericum gen. nov., sp. nov., which are herein described according to the rules of the International Code of Nomenclature for algae, fungi and plants. This finding highlights the great importance of tropical and equatorial South American ecosystems for harbouring an unknown microbial diversity in the face of the anthropogenic threats with which they increasingly struggle.

Description of Stenomitos kolaenensis and S. hiloensis sp. nov. (Leptolyngbyaceae, Cyanobacteria) with an emendation of the genus

Stenomitos is a recently established cyanobacterial genus, some species of which appear to be cryptic. Here we describe two new species in this genus, Stenomitos kolaensis sp. nov. isolated from the Al-Fe humic podzols of a boreal forest near Nikel town, Murmansk region, Russia and S. hiloensis sp. nov. isolated from a basaltic seep wall on Akeola Road, Hilo, Hawaii, USA. Phylogenetic analyses were conducted on the 16S and 16S-23S ITS rRNA gene regions using Bayesian Inference, and Maximum Likelihood. Phylogenetic analysis of the 16S-23S ITS rRNA region resulted in both S. kolaensis and S. hiloensis forming separate clades from other Stenomitos lineages. Antarctic strains of Stenomitos frigidus (previously reported as “Leptolyngbya frigida”) show that species to be polyphyletic and in need of revision. The structure of the conserved ITS regions (Box-B, D1-D1ʹ, V2 and V3 helices) provided support for separation of the species, and the p-distances among aligned ITS regions further confirmed that a number of species exist within the genus. S. kolaensis and S. hiloensis can be distinguished from other described Stenomitos species (S. rutilans and S. tremulus) by their geographical distribution, habitat preference, 16S rRNA phylogeny, and differences in the secondary structure of the 16S-23S ITS region.