Life cycle as a stable trait in the evaluation of diversity of Nostoc from biofilms in rivers

Polyphasic Approach and Potential Cyanotoxin Production by Planktothrix from the Río Grande de Comitán and Montebello Lakes National Park, Southern Mexico

The development of anthropic activities during recent years has led to an increase in nutrient fluxes in the Río Grande de Comitán and Montebello Lakes National Park, Mexico. In turn, this has modified the dynamics of the biotic community, specifically favoring the presence of cyanobacteria tolerant to contamination. The continual and massive presence of Planktothrix species (spp.) in the system suggests a potential detrimental impact for economic issues and human health. In this study, we identify the morphological and molecular characteristics of Planktothrix populations from seven tropical (1,380-1,740 masl, 23.0-25.5°C) and calcareous lakes and two ponds from a water treatment plant. We also assess the ecological drivers that could be related to the presence of cyanotoxins in the system. The ecological preferences, morphology, 16S rRNA structure, and 16S-23S rRNA internal transcribed spacer found evidence for three species: P. agardhii distributed in neutral to slightly basic water (pH = 7.7-8.7), and P. spiroides and Planktothrix sp. in alkaline waters (pH = 9.1). The presence of the mcyE gene and its validation by liquid chromatography confirmed the presence of two microcystin variants (MC-RR and MC-LR) in at least three populations of P. agardhii. These microcystins put the health of the ecosystem and its inhabitants at risk, a condition that should be addressed and resolved with a water management and detoxification strategy in the basin.

Description of two new species of Nostoc (Nostocales, Cyanobacteria) from central Mexico, using morphological, ecological, and molecular attributes

The present study describes two new Nostoc species, N. montejanii and N. tlalocii, based on a polyphasic approach that combines morphological, ecological, and genetic characteristics. The five investigated populations, including those from newly collected material from central Mexico, were observed to possess morphological features characteristic of the Nostoc genus. Results showed that both new species are strictly associated with running water, and they show clear differences in their habitat preferences. The 16S rRNA gene sequences of the five strains displayed between 98% and 99% similarity to the genus Nostoc sensu stricto. The 16S rRNA gene phylogenetic analyses inferred using Bayesian inference, maximum likelihood, and parsimony methods, placed these five strains in two separate clades distinct from other Nostoc species. The secondary structures of the 16S-23S internal transcribed spacer rRNA region in the two new species showed >10.5% dissimilarities in the operons when compared with other Nostoc species. In addition, clear morphological differences were observed between the two Mexican species, including the color of the colonies (black in N. montejanii and green in N. tlalocii), the size of the cells (greater in N. montejanii), and the number of polyphosphate granules present in the cells (one in N. montejanii and up to four in N. tlalocii).

How diverse a genus can be: An integrated multi-layered analysis into Desmonostoc (Nostocaceae, Cyanobacteriota)

Cyanobacteria (Phylum Cyanobacteriota) are Gram-negative bacteria capable of performing oxygenic photosynthesis. Although the taxonomic classification of cyanobacteria was for a long time based primarily on morphological characters, the application of other techniques (e.g. molecular phylogeny), especially in recent decades, has contributed to a better resolution of cyanobacteria systematics, leading to a revision of the phylum. Although Desmonostoc occurs as a new genus/cluster and some species have been described recently, relatively few studies have been carried out to elucidate its diversity, which encompasses strains from different ecological origins, or examine the application of new characterization tools. In this context, the present study investigated the diversity within Desmonostoc, based on morphological, molecular, metabolic, and physiological characteristics. Although the usage of physiological parameters is unusual for a polyphasic approach, they were efficient in the characterization performed here. The phylogenetic analysis based on 16S rRNA gene sequences put all studied strains (25) into the D1 cluster and indicated the emergence of novel sub-clusters. It was also possible to observe that nifD and nifH exhibited different evolutionary histories within the Desmonostoc strains. Collectively, metabolic and physiological data, coupled with the morphometric data, were in general, in good agreement with the separation based on the phylogeny of the 16S rRNA gene. Furthermore, the study provided important information on the diversity of Desmonostoc strains collected from different Brazilian biomes by revealing that they were cosmopolitan strains, acclimatized to low luminous intensities, with a large metabolic diversity and great biotechnological potential.

Microenvironmental Conditions Drive the Differential Cyanobacterial Community Composition of Biocrusts from the Sahara Desert

The Sahara Desert is characterized by extreme environmental conditions, which are a unique challenge for life. Cyanobacteria are key players in the colonization of bare soils and form assemblages with other microorganisms in the top millimetres, establishing biological soil crusts (biocrusts) that cover most soil surfaces in deserts, which have important roles in the functioning of drylands. However, knowledge of biocrusts from these extreme environments is limited. Therefore, to study cyanobacterial community composition in biocrusts from the Sahara Desert, we utilized a combination of methodologies in which taxonomic assignation, for next-generation sequencing of soil samples, was based on phylogenetic analysis (16S rRNA gene) in parallel with morphological identification of cyanobacteria in natural samples and isolates from certain locations. Two close locations that differed in microenvironmental conditions were analysed. One was a dry salt lake (a “chott”), and the other was an extension of sandy, slightly saline soil. Differences in cyanobacterial composition between the sites were found, with a clear dominance of Microcoleus spp. in the less saline site, while the chott presented a high abundance of heterocystous cyanobacteria as well as the filamentous non-heterocystous Pseudophormidium sp. and the unicellular cf. Acaryochloris. The cyanobacteria found in our study area, such as Microcoleus steenstrupii, Microcoleus vaginatus, Scytonema hyalinum, Tolypothrix distorta, and Calothrix sp., are also widely distributed in other geographic locations around the world, where the conditions are less severe. Our results, therefore, indicated that some cyanobacteria can cope with polyextreme conditions, as confirmed by bioassays, and can be considered extremotolerant, being able to live in a wide range of conditions.

Issues in cyanobacterial taxonomy: comprehensive case study of unbranched, false branched and true branched heterocytous cyanobacteria

The order Nostocales is represented by morphologically diverse forms with respect to the branching patterns and polarity of the filaments. With growing understanding of taxonomy and systematics, members of the order Nostocales have also undergone multiple taxonomic revisions. The last decade has seen a surge in the description of new genera and families within the order Nostocales. In this study, we discuss the taxonomic status of all the newly described and reclassified taxa of some of the prominent morphological forms within the order Nostocales by constructing comprehensive phylogenetic trees. Further, we propose certain strategies that would contribute to resolving the taxonomic complexities arising due to inadequate taxon sampling.

Phylogenetic evaluation of the genus Nostoc and description of Nostoc neudorfense sp. nov., from the Czech Republic

Cyanobacterial strain ARC8 was isolated from seepage coming into the river Dračice, Františkov, Czech Republic, and was characterized using a polyphasic approach. Strain ARC8 showed a typical Nostoc -like morphology and in-depth morphological characterization indicated that it is a member of the genus Nostoc . Furthermore, in the 16S rRNA gene phylogeny inferred using Bayesian inference, maximum likelihood and neighbour joining methods, strain ARC8 clustered within the Nostoc sensu stricto clade. The phylogenetic distance and the positioning of strain ARC8 also indicated that it is a member of the genus Nostoc . Furthermore, the rbcL gene phylogeny along with the 16S–23S ITS secondary structure analysis also supported the findings from the 16S rRNA gene tree. In accordance with the International Code of Nomenclature for Algae, Fungi and Plants we describe a novel species of Nostoc with the name Nostoc neudorfense sp. nov.

Physiological and thylakoid ultrastructural changes in cyanobacteria in response to toxic manganese concentrations

In this study, two cyanobacterial strains (morphologically identified as Microcystis novacekii BA005 and Nostoc paludosum BA033) were exposed to different Mn concentrations: 7.0, 10.5, 15.7, 23.6 and 35.4 mg L^-1 for BA005; and 15.0, 22.5, 33.7, 50.6, and 76.0 mg L^-1 for BA033. Manganese toxicity was assessed by growth rate inhibition (EC₅₀), chlorophyll a content, quantification of Mn accumulation in biomass and monitoring morphological and ultrastructural effects. The Mn EC₅₀ values were 16 mg L^-1 for BA005 and 39 mg L^-1 for BA033, respectively. Reduction of chlorophyll a contents and ultrastructural changes were observed in cells exposed to Mn concentrations greater than 23.6 and 33.7 mg L^-1 for BA005 and BA033. Damage to intrathylakoid spaces, increased amounts of polyphosphate granules and an increased number of carboxysomes were observed in both strains. In the context of the potential application of these strains in bioremediation approaches, BA005 was able to remove Mn almost completely from aqueous medium after 96 h exposure to an initial concentration of 10.5 mg L^-1, and BA033 was capable of removing 38% when exposed to initial Mn concentration of 22.5 mg L^-1. Our data shed light on how these cyanobacterial strains respond to Mn stress, as well as supporting their utility as organisms for monitoring Mn toxicity in industrial wastes and potential bioremediation application.

Differences in the Cyanobacterial Community Composition of Biocrusts From the Drylands of Central Mexico. Are There Endemic Species?

In drylands worldwide, biocrusts, topsoil microbial communities, are prevalent, contributing to the biostabilization of soils and allowing the subsequent establishment and growth of vascular plants. In early successional biocrusts, cyanobacteria are the first dominant colonizers of bare ground, largely determining their functioning. However, there are large gaps in our knowledge of the cyanobacterial diversity in biocrusts, particularly in understudied geographic regions, such as the tropical latitudes. We analyzed the diversity of the cyanobacteria inhabiting the biocrusts of semideserts from Central Mexico in two localities belonging to the same desert system (Chihuahuan Desert) that are separated by a cordillera that crosses the center of Mexico. Morphological identification of the cyanobacteria was carried out after cultivation in parallel with the direct observation of the environmental samples and was supported by genetic characterization through analysis of the 16S rRNA gene of the isolated strains and by next-generation sequencing of the soil samples. Taxonomic assignment revealed a clear dominance of heterocystous cyanobacteria at one of the studied locations (Actopan, Hidalgo state). Although heterocystous forms were abundant at the other location (Atexcac, Puebla state), almost a third of the cyanobacterial phylotypes were represented by unicellular/colonial cyanobacteria, mostly Chroococcidiopsis spp. Only 28.4% of the phylotypes were found to be common to both soils. Most of the other taxa, however, were biocrust-type specific, and approximately 35% of the phylotypes were found to be unique to the soil they were collected in. In addition, differences in the abundances of the shared cyanobacteria between the locations were also found. These differences in the cyanobacterial distribution were supported by the distinct responses of the isolated strains representative of the sites to extreme heat and desiccation in bioassays. Some cyanobacteria with high abundance or only present at the hottest Actopan site, such as Scytonema hyalinum, Scytonema crispum, Nostoc commune, Nostoc sp., and Calothrix parietina, survived extreme heat and desiccation. However, Tolypothrix distorta and Chroococcidiopsis spp. were clearly sensitive to these extreme conditions in relation to their lower abundances at Actopan as opposed to Atexcac. Since novel biocrust-associated phylotypes were also found, the emergence of endemic cyanobacterial taxa is discussed.

Polyphasic evaluation of key cyanobacteria in biocrusts from the most arid region in Europe

Cyanobacteria are key microbes in topsoil communities that have important roles in preventing soil erosion, carbon and nitrogen fixation, and influencing soil hydrology. However, little is known regarding the identity and distribution of the microbial components in the photosynthetic assemblages that form a cohesive biological soil crust (biocrust) in drylands of Europe. In this study, we investigated the cyanobacterial species colonizing biocrusts in three representative dryland ecosystems from the most arid region in Europe (SE Spain) that are characterized by different soil conditions. Isolated cyanobacterial cultures were identified by a polyphasic approach, including 16S rRNA gene sequencing, phylogenetic relationship determination, and morphological and ecological habitat assessments. Three well-differentiated groups were identified: heterocystous-cyanobacteria (Nostoc commune, Nostoc calcicola, Tolypothrix distorta and Scytonema hyalinum), which play an important role in N and C cycling in soil; nonheterocystous bundle-forming cyanobacteria (Microcoleus steenstrupii, Trichocoleus desertorum, and Schizothrix cf. calcicola); and narrow filamentous cyanobacteria (Leptolyngbya frigida and Oculatella kazantipica), all of which are essential genera for initial biocrust formation. The results of this study contribute to our understanding of cyanobacterial species composition in biocrusts from important and understudied European habitats, such as the Mediterranean Basin, a hotspot of biodiversity, where these species are keystone pioneer organisms.

Diversity and bioactivities of nostocacean cyanobacteria isolated from paddy soil in Vietnam

Nostocacean cyanobacteria are one of the important components of paddy fields due to their ability to fix atmospheric nitrogen and supply phytohormones for crop growth. In this study, 13 Nostoc strains isolated from paddy soils in Vietnam were classified using a polyphasic approach. The results showed a high diversity of the isolated strains that represented seven morphotypes corresponding to five genotypes, with 16S rRNA gene sequence similarity values ranging between 94.97-99.78% compared to the available sequences from GenBank. Bioassay assessment revealed that 11 out of 13 strains possessed antibacterial activities, three of which exhibited cytotoxic activities on MCF7 and HCT116 cells with an IC₅₀ ranging from 47.8μgmL^-1 to 232.0μgmL^-1. Interestingly, strains with identical 16S rRNA gene sequences displayed different antibacterial and cytotoxic activity profiles.

Nostoc thermotolerans sp. nov., a soil-dwelling species of Nostoc (Cyanobacteria)

A filamentous, soil-dwelling cyanobacterial strain (9C-PST) was isolated from Mandsaur, Madhya Pradesh, India, and is described as a new species of the genus Nostoc. Extensive morphological and molecular characterization along with a thorough assessment of ecology was performed. The style of filament orientation, type and nature of the sheath (e.g. distribution and visibility across the trichome), and vegetative and heterocyte cell dimensions and shape were assessed for over one year using both the laboratory grown culture and the naturally occurring samples. Sequencing of the 16S rRNA gene showed 94 % similarity with Nostocpiscinale CENA21 while analyses of the secondary structures of the 16S-23S ITS region showed unique folding patterns that differentiated this strain from other species of Nostoc. The level of rbcl and rpoC1 gene sequence similarity was 91 and 94 % to Nostocsp. PCC 7524 and Nostocpiscinale CENA21, respectively, while the nifD gene sequence similarity was found to be 99 % with Nostocpiscinale CENA21. The phenotypic, ecological, genetic and phylogenetic observations indicate that the strain 9C-PST represents a novel species of the genus Nostoc with the name proposed being Nostoc thermotolerans sp. nov. according to the International Code of Nomenclature for Algae, Fungi, and Plants.

Nitrogen fixation in a non-heterocystous cyanobacterial mat from a mountain river

In situ nitrogen fixation was investigated in a cyanobacterial mat growing on the bed of rocks of the Muga River, Spain. The filamentous non-heterocystous cyanobacterium Schizothrix dominated the mat, showing nitrogenase activity in the light at similar rates to those found in nearby heterocystous Rivularia colonies. N2 fixation in the light was significantly increased by an inhibitor of PSII and oxygen evolution, DCMU (3-[3,4-dichlorophenyl]-1,1-dimethylurea), and anaerobic conditions. However, no nitrogenase activity was found in the dark. Addition of fructose as a respiratory substrate induced nitrogenase activity in samples incubated under aerobic conditions in the dark but not in anaerobic conditions. Microelectrode oxygen profiles showed internal microaerobic microzones where nitrogen fixation might concentrate. Analyses of the 16S rRNA gene revealed only the presence of sequences belonging to filamentous non-heterocystous cyanobacteria. nifH gene diversity showed that the major phylotypes also belonged to this group. One of the three strains isolated from the Schizothrix mat was capable of fixing N2 and growing in the absence of combined N. This was consistent with the nifH gene analysis. These results suggest a relevant contribution of non-heterocystous cyanobacteria to nitrogen fixation in these mats.

Halotia gen. nov., a phylogenetically and physiologically coherent cyanobacterial genus isolated from marine coastal environments

Nostoc is a common and well-studied genus of cyanobacteria and, according to molecular phylogeny, is a polyphyletic group. Therefore, revisions of this genus are urged in an attempt to clarify its taxonomy. Novel strains isolated from underexplored environments and assigned morphologically to the genus Nostoc are not genetically related to the ‘true Nostoc’ group. In this study, four strains isolated from biofilms collected in Antarctica and five strains originated from Brazilian mangroves were evaluated. Despite their morphological similarities to other morphotypes of Nostoc , these nine strains differed from other morphotypes in ecological, physiological and genetic aspects. Based on the phylogeny of the 16S rRNA gene, the Antarctic sequences were grouped together with the sequences of the Brazilian mangrove isolates and Nostoc sp. Mollenhauer 1 : 1-067 in a well-supported cluster (74 % bootstrap value, maximum-likelihood). This novel cluster was separated phylogenetically from the ‘true Nostoc’ clade and from the clades of the morphologically similar genera Mojavia and Desmonostoc. The 16S rRNA gene sequences generated in this study exhibited 96 % similarity to sequences from the nostocacean genera mentioned above. Physiologically, these nine strains showed the capacity to grow in a salinity range of 1–10 % NaCl, indicating their tolerance of saline conditions. These results provide support for the description of a new genus, named Halotia gen. nov., which is related morphologically to the genera Nostoc , Mojavia and Desmonostoc. Within this new genus, three novel species were recognized and described based on morphology and internal transcribed spacer secondary structures: Halotia branconii sp. nov., Halotia longispora sp. nov. and Halotia wernerae sp. nov., under the provisions of the International Code of Nomenclature for Algae, Fungi and Plants.

Do photobiont switch and cephalodia emancipation act as evolutionary drivers in the lichen symbiosis? A case study in the Pannariaceae (Peltigerales)

Lichen symbioses in the Pannariaceae associate an ascomycete and either cyanobacteria alone (usually Nostoc; bipartite thalli) or green algae and cyanobacteria (cyanobacteria being located in dedicated structures called cephalodia; tripartite thalli) as photosynthetic partners (photobionts). In bipartite thalli, cyanobacteria can either be restricted to a well-delimited layer within the thallus ('pannarioid' thalli) or spread over the thallus that becomes gelatinous when wet ('collematoid' thalli). We studied the collematoid genera Kroswia and Physma and an undescribed tripartite species along with representatives of the pannarioid genera Fuscopannaria, Pannaria and Parmeliella. Molecular inferences from 4 loci for the fungus and 1 locus for the photobiont and statistical analyses within a phylogenetic framework support the following: (a) several switches from pannarioid to collematoid thalli occured and are correlated with photobiont switches; the collematoid genus Kroswia is nested within the pannarioid genus Fuscopannaria and the collematoid genus Physma is sister to the pannarioid Parmeliella mariana group; (b) Nostoc associated with collematoid thalli in the Pannariaceae are related to that of the Collemataceae (which contains only collematoid thalli), and never associated with pannarioid thalli; Nostoc associated with pannarioid thalli also associate in other families with similar morphology; (c) ancestors of several lineages in the Pannariaceae developed tripartite thalli, bipartite thalli probably resulting from cephalodia emancipation from tripartite thalli which eventually evolved and diverged, as suggested by the same Nostoc present in the collematoid genus Physma and in the cephalodia of a closely related tripartite species; Photobiont switches and cephalodia emancipation followed by divergence are thus suspected to act as evolutionary drivers in the family Pannariaceae.

Polyphasic characterization of benthic cyanobacterial diversity from biofilms of the Guadarrama river (Spain): morphological, molecular, and ecological approaches(1)

The occurrence and environmental factors responsible for the distribution of benthic cyanobacteria in running waters remain largely unexplored in comparison with those of other aquatic ecosystems. In this study, combined data of ecological characteristics, molecular analysis (based on 16S rRNA gene), and direct microscopic inspection of environmental samples were analyzed in parallel with the morphological characterization of the isolated strains to investigate benthic cyanobacterial diversity in the Guadarrama river (Spain). A total of 17 species were identified that belonged to the genera Aphanocapsa, Pleurocapsa, Chroococcus, Chamaesiphon, Cyanobium, Pseudan-abaena, Leptolyngbya, Phormidium, Nostoc, and Tolypothrix. Phenotypic features were associated with the results of 16S rRNA gene sequencing, complementing existing morphological and genetic databases. A decrease in the cyanobacterial diversity was observed along a pollution gradient in the river. Water quality differed among the sampling sites, and variation in nutrient content was the principal difference among locations. These characteristics were closely associated with an upstream-downstream eutrophic gradient. Canonical correspondence analysis distinguished three groups of species with respect to the eutrophication gradient. The first group (Tolypothrix cf. tenuis, Nostoc punctiforme, Nostoc piscinale, Chamaesiphon investiens, Chroococcus minor, Leptolyngbya nostocorum, and Leptolyngbya tenuis) was characteristic of waters with low levels of nutrients. The second group (Cyanobium sp., Chamaesiphon polymorphus, Leptolyngbya boryana, Phormidium autumnale, Phormidium sp., and Aphanocapsa cf. rivularis) was characteristic of polluted waters, its members appearing mainly in great abundance under eutrophic-hypertrophic conditions. The third group of species (Pseudanabaena catenata, Aphanocapsa muscicola, and Nostoc carneum) was present at upstream and downstream sites.