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We analysed and characterized the cyanobacteria in microbialites of Alchichica crater lake over a depth gradient, from 3 to 30 m. A polyphasic approach was followed using morphometry, optical and e...

Only two complete genomes of the cyanobacterial genus Gloeobacter from two very different regions of the world currently exist. Here, we present the complete genome sequence of a third member of the genus isolated from a waterfall cave in Mexico. Analysis of the average nucleotide identities (ANIs) between published Gloeobacter genomes revealed that the complete genome of this new member is only 92.7% similar to Gloeobacter violaceus and therefore we determined it to be a new species. We propose to name this new species Gloeobacter morelensis after the location in Mexico where it was isolated. The complete genome consists of one circular chromosome (4,921,229 bp), one linear plasmid (172,328 bp), and one circular plasmid (8,839 bp). Its genome is the largest of all completely sequenced genomes of Gloeobacter species. Pangenomic comparisons revealed that G. morelensis encodes 759 genes not shared with other Gloeobacter species. Despite being more closely related to G. violaceus, it features an extremely divergent psbA gene encoding an atypical D1 core subunit of Photosystem II previously only found within the genome of Gloeobacter kilaueensis. In addition, we detected evidence of concerted evolution of psbA genes encoding identical D1 in all three Gloeobacter genomes, a characteristic that seems widespread in cyanobacteria and may therefore be traced back to their last common ancestor.

Gloeobacter violaceus is a simple unicellular cyanobacterium believed to be basal to all cyanobacteria. It is unique among the cyanobacteria in various features, but most significantly in the absence of thylakoids and a circadian clock. We found additional features which support the basal status of the clade of G. violaceus in samples from a wet wall in a waterfall cave in central Mexico. We encountered a high morphological and morphometric variability in the populations studied. In trying to explain the reasons for this, we discovered that it can be attributed basically to two phenomena: a lack of synchronicity, circadian or other, in the cell cycles of the organisms; and the presence of a scheme with three simultaneous reproductive options. These two characteristics interfere with the development of a life cycle comparable to that found in other organisms. We coined the term “reproductive routes” for the alternative to a life cycle and discuss the consequences of having several routes instead of a cycle. Our results open avenues for studies to understand how the rest of the cyanobacteria acquired circadian clocks, organized life cycles and evolved complex regulating mechanisms.

Although neglected for a long time by freshwater-ecology research, springs are very important habitats for biodiversity conservation. They are multiple ecotones, and are characterized by a remarkable variety of environmental conditions (e.g., from highly-shaded to UV exposed, from permanent discharge to intermittent flow, from still water to strong currents, from extremely-soft to carbonate-precipitating water, etc.). Moreover, springs are often amongst the last high-integrity, oligotrophic freshwater habitats in densely populated areas. Because of the high quality of their waters, the main impact affecting springs is capturing and water diversion. Climate-change driven reduction in precipitations in many areas is likely to determine an aggravation of this impact. It is thus important to document the rich and peculiar biodiversity of springs, also to establish reference conditions for bioassessment methods. Especially in non-acidic springs with running water, and coarse lithic substrata, cyanobacteria are often one of the most taxa-rich and abundant groups of photoautotrophs. The relatively-scarce information available in the literature is mostly referred to similar habitats, and not to spring habitats in the narrower sense. Papers dealing with the cyanobacteria of ambient springheads (=eucrenal) worldwide are still very rare. These were reviewed separating ambient springs in temperate and warm climate, and with special attention to key species, to cyanobacterial strategies allowing survival in oligotrophic headwaters (e.g., nitrogen fixation, phosphatases, anti-UV compounds, etc.), and to distribution patterns. The review also hopes to bolster new interest and research on this topic, and suggests some promising research directions.

New approaches in taxonomy and the introduction of molecular tools have substantially changed the taxonomy of cyanobacteria, leading to new genera and species being defined based on genetic and morphological investigations. In addition, molecular tools have confirmed several previously defined cyanobacteria genera, including some based on morphological and ecological features. Several of them have also been split into new generic entities, such as Brasilonema. In the central region of Mexico, several populations have been identified to share some traits with this new genus. In the region of Tolantongo, Hidalgo (Hgo), we found cyanobacteria populations that correspond to Brasilonema description (Fiore et al. 2007), however the development of trichomes and hormogonia did not agree with the diagnosis of Brasilonema. We describe and analyze the cyanobacteria populations that we found in Tolantongo, and compare their features with the diagnostic generic features and those of several Brasilonema species. The results of morphological analyses were tested using molecular phylogenetic data derived from 16S RNA gene sequencing and the use of marker cpcBA-IGS for phycocyanin operon. From our analyses we conclude that the strain from Tolantongo belongs to the genus Brasilonema, and the differences observed are sufficient to propose a new species.

An account of the intricate history of the taxonomy and nomenclature of the genus Dermocarpella (Cyanobacteria / Cyanophyceae / Cyanoprokaryota) is provided. Detailed observations at the population level have allowed the detection of different stages of the life cycle of two species of this genus and have helped to solve some of the uncertainties in the validation of this genus. The species described are D. gardneri as a new name for Dermocarpa hemisphaerica Setchell et Gardner and Dermocarpella stellata sp. nov. An identification key and a comparative table of the diagnostic features of the species of the genus are included.

Summary: Second article of the series of studies about the cyanoprokaryotic (cyanophycean, cyanobacterial) species, growing epiphytically on submersed filamentous algae in central Mexico. The traditional genus Xenococcus was found to be heterogeneous and the stability and frequency of inter- and intrageneric characters was studied in natural populations from central Mexican streaming waters, sampled in the period from 1983 to 1993. The types of cellular binary,fission and nanocytic cell division were particularly studied, and from them were derived different life-cycle strategies. The genus Xenothotos gen.n. was separated from the genus Xenococcus on the basis of these results, and seven species were studied from both genera (one new species of Xenococcus and three new species of Xenotholos were described). Characteristics of all species studied are included. Another group of traditional Xenococcus -species, which does not correspond morphologically either to Xenococcus or to Xenotnotos , and cells of which never divide by multiple fission, must be also separated from the genus Xenococcus ( X. minimus type).

Since James Hutton established the principle of uniformitarism in 1788, direct comparisons between ancient and present processes have been key elements in geological and paleontological observations. Lyell and Darwin successfully applied uniformitarism using reasoning and inference to obtain the missing data from incomplete evidence (Gould, 1983). This actualistic approach has also permeated the study of stromatolites and their living analogs, modern microbial mats. As early as 1908, Kalkowsky (1908), who coined the term stromatolites, recognized not only the organic nature of stromatolites, but also the participation of microbial life in their construction (Riding, 2008, and references therein), as he wrote: ‘stromatolites have a fine more or less even layered fabric.…and the participation of simple plants gave rise to limestone precipitation’ (translation from Prof. J. Paul, 2008). The structural similarity between algal mats and intertidal stromatolites was documented since the beginning of the twentieth century; Walcott (1914) even presumed the participation of cyanobacteria by then (Awramik and Grey, 2005). The early observations of Black (1933) also included the participation of cyanobacteria in the modern marine microbialites from the Bahamas. The precipitation of calcium carbonate, erosive boring, and binding of sediments were identified as main processes in these algal carbonates (Fritsch, 1945; Pettijohn, 1957; Sharp, 1970). Later Logan et al. (1964) proposed a popular general classification system to group the main morphologies found in ‘algal stromatolites’ when he analyzed recent stromatolites from Shark Bay in Australia.

Summary Three freshwater, epiphytic species of the cyanoprocaryotic (cyanophycean, cyanobacterial) genera Cyanocystis (C. mexicana spec. nova) and Xenococcus (X. willei GARDNER, X. bicudoi spec. nova), which occur commonly in streaming, unpolluted waters of central Mexico, were studied and documented. The generic diacritical features of Cyanocystis and Xenococcus are discussed.

Although toxic cyanobacteria are commonly described worldwide, only one recent paper on the toxicity of cyanobacteria in Mexico has been published reporting the occurrence of cylindrospermopsin and saxitoxins. Microcystins are the most commonly studied cyanotoxins in many countries and those that may cause the most dramatic problems in terms of human health. In this paper, we studied the occurrence of potentially toxic cyanobacteria in different ecosystems in Central Mexico. Samples were collected in natural lakes (Zumpango, Laguna Atotonilco and Cienega Chica), reservoirs (Los Angeles and Valle de Bravo), man-made channels (Cuemanco, Tlameleca) and urban lakes (Chapultepec). A multi-technique approach was applied by the use of molecular, immunological and chemical techniques. Cyanobacteria were found in all the sites, ranging from 1.6 x 10(3) cells/mL in Tlameleca to 7.5 x 10(6) cells/mL in Chapultepec Grande, representing between 67 and 100% of the total phytoplankton density. The concentration of total microcystins varied between 4.9 and 78.0 microg MC-LR eq/L. The results revealed the occurrence of MC-LR in all the sites analyzed by MALDI-TOF, and MC-FR, MC-RR and MC-H(4)YR in two sites. Most of the studied sites are used either as a source of drinking water, as a recreational area, or for agriculture irrigation purposes, so the risk for human health may be high if not properly monitored. This is the first report on the MC profiles and concentrations in blooms collected in Mexico.