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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...

Two isolates of Oculatella from biological soil crusts in the arid and semi-arid tropical upland region of Mexico were characterized using a polyphasic approach which included morphology, ecology, 16S rRNA and 16S-23S ITS phylogenetic analysis, percent identity of 16S rRNA gene sequence, percent dissimilarity of 16S-23S ITS sequence, and secondary structure of conserved ITS domains. The two species shared the generic synapomorphy of a reddish granule at the tip of mature apical cells, and possessed a single ribosomal operon with both tRNA genes (tRNAIle and tRNAAla) based upon our analysis and the analysis of the other species in the genus. After characterization, the strains were compared with 10 previously described and similarly characterized species in the genus, and based upon the evidence obtained, the strains were described as two new species, O. dilatativagina and O. leona. O. dilatativagina has an extensively widened sheath, and thus is morphologically separated from all other taxa described thus far. O. leona is morphologically highly similar to soil species found in North and South America, and should be considered a cryptic species among these taxa. The recently developed criterion for species recognition using percent dissimilarity among ITS gene sequences in orthologous ribosomal operons was found to be effective in separating cryptic species of Oculatella, and has consistently been useful and sufficient for separation of closely related species in other cyanobacterial genera.

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.

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.

ResumenEl presente trabajo describe la diversidad algal del manantial geotermal Los Hervideros, Michoacán, México, así como su distribución en relación con el gradiente de temperatura. Este manantial forma parte del sistema hidrotermal Los Azufres, localizado en el mismo estado, el cual es afectado por la actividad volcánica de la Faja Neovolcánica Transmexicana. La identificación de las especies fue morfológica y se midieron parámetros fisicoquímicos como la temperatura, la conductividad específica y el pH. La temperatura del agua osciló entre los 22.2 y 85.2°C, presentó una conductividad específica de 3,400 a 4,430μS cm-1 y un pH de 7.5 a 8.0. Las especies que dominaron los crecimientos fueron de la clase Cyanophyceae, con los géneros: Arthrospira sp., Synechococcus sp. y Synechocystis sp. en temperaturas de 22 a 76°C. En cuanto a las especies de Bacillariophyceae, se registraron: Achnanthidium exiguum, Halamphora veneta, Anomoeoneis costata, Diploneis elliptica y Pinnularia viridis en temperaturas de 22 a 55°C. También se registró una especie de la clase Chlorophyceae, Oedogonium sp., en temperaturas de 30 a 35°C. Este manantial se caracteriza por presentar cambios drásticos de temperatura en trayectos cortos, que pueden ser de menos de 1m, lo cual se observó reflejado en una distribución heterogénea de las especies algales.AbstractIn this work we describe the algal diversity, which is in Los Hervideros geothermal spring, in Michoacán, Mexico, and its spatial distribution related with the thermal gradient. This spring forms a part of Los Azufres system, which is affected by volcanic activity from the Transversal Neovolcanic Belt. The species identification was morphological and physical and chemical parameters were measured as temperature, specific conductivity and pH. The temperature recorded was between 22.2 to 85.2°C. The specific conductivity is as high as 3,400 to 4,430μS cm-1, while the pH is 7.5 to 8.0. The growth were dominated by the next Cyanophyceae species: Arthrospira sp., Synechococcus sp. and Synechocystis sp. in temperatures from 22 to 76°C, respectively. As far as the Bacillariophyceae, we registered: Achnanthidium exiguum, Halamphora veneta, Anomoeoneis costata, Diploneis elliptica and Pinnularia viridis in temperatures from 22 to 55°C. We also registered one Chlorophyceae species, Oedogonium sp. (30 to 35°C). This spring is characterized by the presence of great changes of temperate in a few centimeters, which is reflected in a heterogeneous distribution of the algal species.

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.

Twelve strains of Leptolyngbya-like filaments were isolated from biological soil crust samples from two localities in the Central Region of Mexico. The strains were morphologically distinguished from most Synechococcalean species by the obligate presence of a blackish sheath. Phylogenetic analysis based on 16S rRNA gene sequence placed all strains into a strongly supported single clade sister to Scytolyngbya. The genetic identity between our strains and all other Synechococcales, including Scytolyngbya, was less than 95%, and the strains were further distinguished by morphology and terrestrial ecology. The conserved domains of the 16S-23S ITS region had secondary structures distinct from all other closely related genera, which included Scytolyngbya, Stenomitos, Chamaethrix, and Pantanalinema. Based on the combination of morphological, molecular, and ecological evidence, we here describe two species: Chroakolemma opaca gen. et sp. nov. and C. pellucida gen. et sp. nov. Based on the ability to form blackish sheaths, these two species are morphologically similar to Leptolyngbya edaphica, Chamaethrix vaginata and Trichocoleus badius. The latter two species have been sequenced and are phylogenetically distant from Chroakolemma. Leptolyngbya edaphica is a soil species described from Russia and shares other morphological similarities with Chroakolemma, including wide sheaths, coiled filaments, pale blue-green trichomes, and constricted cross-walls. We consider these characteristics diagnostic of Chroakolemma, and accordingly propose Chroakolemma edaphica comb. nov.

Faculty of Sciences National Autonomous University of Mexico (UNAM) Ciudad Universitaria, Mexico DF

The distribution of species of Rhodophyta was investigated in 424 stream segments, sampled from 1981–1999 in three river basins from central Mexico. Red algae occurred in 12% of the stream segments sampled, a low frequency compared to major surveys in other parts of the world (18–65%). Sixteen species of freshwater red algae were found, of which the most widespread were Compsopogon coeruleus (24 sites) and Hildenbrandia angolensis (16 sites). Two groups of species were clearly distinguished on the basis of environmental characteristics. The first group, which included Batrachospermum gelatinosum, Paralemanea annulata, P. mexicana and Sirodotia suecica, is found in temperate climates, high altitudes (>1700 m), and cold or temperate waters (12–18°C) that are slightly acidic (pH 5.5–6.5) and of low specific conductivity (77–86 μS . cm–1). The second group, including Chroodactylon ornatum, Compsopogon coeruleus, Hildenbrandia angolensis, Audouinella eugenea, A. huastecana, A. meiospora, Batrachospermum globosporum, Sirodotia huillensis and Thorea hispida, is of subtropical to tropical climates, low altitudes ( 21°C) that are neutral to slightly alkaline (pH 7.0–8.6) and of high specific conductivity (160–1990 μS.cm–1). Half of the species found in this study were exclusively of calcareous sites from within a highly homogeneous limestone region (56% Ca). The rest of the sites with rhodophytes were found in sub-basins with andesitic-basaltic or calcareous substrates, and in temperate to semidesertic climates that provoke dramatic changes in the water level of the river or even the complete absence of permanent rivers. A high percentage of the currents contained an influx of organic material in which populations of Compsopogon coeruleus, described as tolerant of these conditions, could be found. The sub-basins that were most similar and had the least diversity corresponded to high mountain regions of Central Mexico (HP and HB). The overall species composition for streams and rivers of Central Mexico revealed high similarities with other tropical regions and had few species in common with freshwater red algal floras of other continents.

The little known genera of Hydrococcaceae Cyanodermatium, Placoma and Hydrococcus are well represented in the epilithic and epiphytic flora of central Mexico. A new marine species of Cyanodermatium, C. gonzaliensis, is established and three freshwater populations of the genera Hydrococcus, Cyanodermatium and Placoma, that represent new records for Mexico are studied. The morphological characteristics of the development of the thalli in several species of the three genera from populations from both marine and continental habitats are described. These genera differ among each other, in the pattern of cell division and growth that result in a characteristic organization of the pseudofilaments and therefore in the shape of the colonies. The proposal made by KOMAREK & ANAGNOSTIDIS (1998) to separate these genera that do not produce baeocytes from those included in the family Hyellaceae to which they are similar in their pseudofilamentous organisation is supported.

In this paper we present a synthesis of several studies on the reproduction, life cyles and taxonomy of epiphytic baeocyte producing cyanoprokaryotes from central Mexico. We have found that thallus structure is closely related with the mechanism of reproduction (binary fission and/or multiple fission), planes of cell division during development and sheath consistency. We propose characteristics for distinguishing among species belonging to the genera. Xenococcus, Xenotholos, (Xenococcaceae), Cyanocystis, and Dermocarpella (Dermocarpellaceae).

The reproductive stages of Dermocarpella gardneri and D. stellata, which have been reported only once, are described. Formation of baeocytes occurs by cellular divisions that are parallel to the substratum, followed by a series of anticlinal radial divisions. In some cases in D. gardneri, the superior cell, resulting from the first division parallel to the substratum, is liberated prior to radial divisions, and these probably represent the ‘macrogonidia’ originally described by Lemmermann for D. hemisphaerica. The baeocytes are released through a circular apical pore, which develops after the formation of a papilla that eventually dissolves to form a pore.

This paper is a contribution to the morphological and molecular characterization of the cyanobacterium Brasilonema roberti-lamii from populations found in Central Mexico. The general growth form and the morphological, morphometric and ecological characteristics of the populations studied clearly correspond to those described for Brasilonema roberti-lamii (basionym: Tolypothrix roberti-lamii ) from the French Antilles. Based on molecular data from DNA sequencing of the16S rRNA gene and the IGS of the cpc B- cpc A phycocyanin operon ( cpc BA-IGS), we propose that the populations that we studied are closely related to those of other Brasilonema species, including B. octagenarum UFV-OR1, UFV-E1 and HA4187-MV1-p1F, Brasilonema sennae CENA 114, B . tolantongensis , B . terrestre CENA 116, B . angustatum HA4187-MV1-B2+p1F and HA4187-MV1-B2+p1H and B . bromeliae SPC951. Our findings support the transference of Tolypothrix roberti-lamii , which was made based exclusively on morphological criteria, to Brasilonema . The use of molecular analyses in addition to traditional morphological and ecological criteria, known as polyphasic approach, is a good alternative to describe taxa of cyanobacteria, mainly at the genus and species levels.

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 This is the third study on the cyanoprokaryotic (cyanophycean, cyanobacterial) epiphytes, colonizing submersed substrates (mainly other filamentous algae) in streaming waters in central Mexico. The species of the genus Stichosiphon Geitler 1932 were all made synonyms of S. sansibaricus by Drouet & Daily (1956). We have found six morphotypes, which can be distinguished at the species level, five corresponding to species defined by previous authors and one new species, S. exiguus. The morphological variation of the Mexican populations was studied, and the comparison with the original descriptions of type specimens is presented. The characters applied in the taxonomy of the genus Stichosiphon are discussed. One other species, known from Burma ( Skuja 1949), was redefined according to the present diacritical features for this genus (S. skujae).

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.

Se presentan los resultados del estudio ficofloristico de tres manantiales en la región de la Huasteca Potosina, en el que se reportan 67 especies algales. Se analizan las diferencias y similitudes florísticas y su relación con algunos parámetros ambientales como la iluminación y velocidad de corriente, que fueron los factores más importantes que afectaron las formas de crecimiento predominantes en estos ambientes. En estos manantiales se definieron los microambientes y las principales asociaciones algales que los caracterizan.

Se reseñan las especies algales que se desarrollan en las pozas de El Salto, sobre el cauce del río del mismo nombre. Varias de éstas pozas en época de secas se encuentran aisladas del cauce principal y presentan características similares a las de ambientes lenticos en cuanto a movimiento de agua y formas de crecimiento de las algas. En época de lluvias, éstas pozas quedan incorporadas al cauce principal, lo cual provoca un cambio en las formas de crecimiento predominantes. Se identificaron un total de 68 especies distribuidas de la siguiente forma: 42 especies de la Clase Bacillariophyceae (61.76%), 14 especies de la Clase Chlorophyceae (20.59 %), 3 especies de la Clase Charophyceae (4.41 %), 7 especies de la Clase Cyanophyceae (10.29 %) y las Clases Rhodophyceae y Dinophyceae representadas por 1 especie cada una (1.47 %). Las formas de crecimiento predominantes en las pozas aisladas, al igual que en otros cuerpos de agua estancada, son masas de filamentos flotantes, constituídas principalmente por especies del Orden Zygnematales, además de formas de vida fitoplanctónicas y metafíticas.

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.

A distinctive morphotype consisting of an epilithic, one-layered colony of polarized, 1–3-celled pseudofilaments was recognized in the rocky shores of the state of Oaxaca in the Mexican tropical Pacific. Morphologically, it was not identifiable as any species of a previously described genus. It is similar to species from the former order Chroococcales, recently modified by Komarek et al . (2014), in its sessile heteropolar pseudofilaments. Specifically, it is most similar to the colonial species of the genus Chamaesiphon ; and of Chamaecalyx , but the cells of the Mexican populations divide symmetrically in one or two planes, differentiating them from Chamaesiphon which divides asymmetrically and only in one plane, and from Chamaecalyx , which has multiple fission. The other defining feature is that all cells of the pseudofilament have differentiated mucilaginous structures (pad and/or stipe and cup). It has not been possible to obtain cultures of our material for further studies to complete the polyphasic approach. Nevertheless, its morphological characteristics and life cycle, plus its distinctive extreme biotope, form a unique combination of features that derive in our proposal of the morphogenus Nisada gen . nov ., with the type species, Nisada stipitata , sp . nov . We describe the proposed taxa and the problems and current inconveniences regarding its assignment to higher taxonomic levels. We also discuss the different degrees of complexity of heteropolarity in Nisada and other taxa.

"El presente trabajo describe la diversidad algal del manantial geotermal Los Hervideros, Michoacán, México, así como su distribución enrelación con el gradiente de temperatura. Este manantial forma parte del sistema hidrotermal Los Azufres, localizado en el mismo estado, el cuales afectado por la actividad volcánica de la Faja Neovolcánica Transmexicana. La identificación de las especies fue morfológica y se midieronparámetros fisicoquímicos como la temperatura, la conductividad específica y el pH. La temperatura del agua osciló entre los 22.2 y 85.2◦C,presentó una conductividad específica de 3,400 a 4,430 S cm-1y un pH de 7.5 a 8.0. Las especies que dominaron los crecimientos fueron dela clase Cyanophyceae, con los géneros: Arthrospira sp., Synechococcus sp. y Synechocystis sp. en temperaturas de 22 a 76◦C. En cuanto a lasespecies de Bacillariophyceae, se registraron: Achnanthidium exiguum, Halamphora veneta, Anomoeoneis costata, Diploneis elliptica y Pinnulariaviridis en temperaturas de 22 a 55◦C. También se registró una especie de la clase Chlorophyceae, Oedogonium sp., en temperaturas de 30 a 35◦C.Este manantial se caracteriza por presentar cambios drásticos de temperatura en trayectos cortos, que pueden ser de menos de 1 m, lo cual seobservó reflejado en una distribución heterogénea de las especies algales.Derechos Reservados © 2016 Universidad Nacional Autónoma de México, Instituto de Biología. Este es un artículo de acceso abierto distribuidobajo los términos de la Licencia Creative Commons CC BY-NC-ND 4.0."

Arid mangroves constitute a particular biotope, with very extreme variations in ecological conditions, mainly temperature and salinity, condition that demand specific adaptations to successfully inhabit this ecosystem. Cyanoprokaryotes have not been well studied in Mexican coasts and this is the first study that contributes to the knowledge of the biodiversity of this group in an arid mangrove in Zacatecas estuary, Baja California Sur, Mexico. Samples of Avicennia germinans pneumatophores from Zacatecas estuary were collected between May 2005 and May 2006. The identification of the most representative Chroococcales produced 10 morphotypes, described mor - phologically and digitally registered for the first time for Mexico. We report species of Aphanocapsa, Chroococ- cus, Hydrococcus, Chamaecalyx, Dermocarpella and Xenococcus. Some taxa have been recorded in brackish or even marine environments from other regions, evidencing the wide geographical distribution and ecological adapt- ability of these organisms, but some others are probably new to science. Some species have a specific seasonal and vertical distribution on the pneumatophore but other have a more ample distribution. Aphanocapsa littoralis and Chroococcus cf. obliteratus are new records for benthic biotopes of Pacific Mexico; Dermocarpella cf. stellata is a new record for the Gulf of California.

Introduction: The Mayan archaeological sites belong to the World cultural heritage. The porous nature of limestone and stucco (calcareous coating) along with the high humidity and temperature typical of Southern Mexico and Central America, make these monuments prone to stone biodeterioration. The Mayan masks and stelae of the North Acropolis Complex (Tikal, Guatemala) are one of the most emblematic and valuable items at this site. As a common practice to keep these items from weathering, archaeologists and restorers build palm roofs over them. A field survey undertaken in august 2006 has shown that the West Mask (WM) semi-protected under a roof was heavily colonized by biofilms and display decayed feature. The East Mask (EM) located in a vault and kept from the exterior environment appears dry and sound. The apparent correlation of biofilm coverage and substratum deterioration led us to hypothesize that biofilm coating the WM had deteriogenic activity. Results: The purpose of this study was to characterize the biofilms colonizing WM, determine efflorescence chemistry and monitor microclimate under the palm roof in order to shed light on the ongoing deterioration phenomena. Contrasting microclimates were observed associated with WM and EM, with varying levels of relative humidity, sunlight and temperature being linked to the former. These conditions allowed the development of biofilm communities dominated by cyanobacteria only on the WM. Some of the detected taxa are recognized endolithic organisms (i.e. Gloecapsa). Fourier-transformed infrared spectroscopy showed that polysaccharides dominated the chemistry of biofilms. X-ray diffraction analyses (XRD) confirmed the presence of halite, gypsum and weddellite in efflorescences associated with the WM. Our results suggest that the joint impact of a varying microclimatic regime and the presence of biofilms promoted the deterioration. Conclusions: The use of palm roofs as protective practice in the Mayan area should be reassessed. Although they prevent deterioration stucco masks and stelae from direct exposure to the environment, they also induce a microclimate suitable for phototrophic biofilms capable of deteriorating directly and indirectly stucco materials. Management of microclimate and biofilm control should be further investigated as additional means to conserve these valuable items.