Can nearby eutrophic reservoirs sustain a differentiated biodiversity of planktonic microcrustaceans in a tropical semiarid basin?

ABSTRACT This paper aims to compare alpha and beta diversities of planktonic microcrustaceans from three reservoirs located nearby in a tropical semiarid basin. Our hypothesis was that alpha and beta diversities of the community are different, although the ecosystems are located close to each other. We carried out two sampling campaigns: dry and rainy seasons. The sampling of microcrustaceans and environmental variables (dissolved oxygen, chlorophyll a and nutrient) was performed at twelve stations and were distributed throughout the three zones (river, transition, and lacustrine), using a plankton net (45 µm). The reservoirs showed different uses and types of nitrogen predominance: Cachoeira (supply/nitrate), Borborema (sewage/ammonia) and Saco (aquaculture/ammonia). Seventeen species were recorded whose richness was assessed as particularly specific to each one of the studied reservoirs. Seasonally, both reservoirs with high anthropogenic alteration showed greater richness in the dry season. The three reservoirs located in a same basin showed different richness and composition, but the diversity did not differ between the zones of the reservoirs. Although communities are close to each other, their composition and richness were found to be distinct for each reservoir. This may be in response to the peculiar particularities, such as nitrogen sources and the different uses.

One year weekly dynamics of limnological conditions and phytoplankton in Lake Bonilla, Costa Rica

Abstract:The detailed response of tropical lake phytoplankton to weather variations has been little studied, but it seems that composition varies in response to rain and wind variability over the course of the year. In order to gather more evidence on this variation, the weekly variability of phytoplankton composition was studied in Lake Bonilla, a low land (380 masl) 30 m deep tropical lake, from April 2010 to May 2011. Temperature variation at several depths was recorded automatically, and measurements of dissolved oxygen, water transparency, and nutrients were performed several times during the study period. The lake showed a warm monomictic pattern, with deep mixing occurring during the hemispherical winter, especially after a heavy rain period in December 2010. Phytoplankton was dominated by a few species: a colonial Cyanobacteria (Aphanocapsa sp., functional group F) and two colonial Chlorococcaceae (Botryococcus braunii and Eutetramorus tetrasporus, both in the functional group K). Their relative dominance shifted throughout the year, following changes in water column conditions in response to weather variations. Although changes in main functional groups indicate a shift in resource availability rather than energy, it was clear that attention should also be given to particular species adaptations beyond those used for establishing functional groups. Rev. Biol. Trop. 64 (4): 1771-1781. Epub 2016 December 01.

Resumen:La respuesta detallada del fitoplancton de lagos tropicales a las variaciones climáticas ha sido poco estudiada, sin embargo al parecer la composición de especies varía en respuesta a la variabilidad de la precipitación y de los vientos a lo largo del año. Con el fin de recabar más evidencia de esta variación, se estudió semanalmente la composición del fitoplancton en el lago Bonilla, un lago tropical de zonas bajas (380 msnm), de 30 m de profundidad, entre abril 2010 y mayo 2011. Se registró la temperatura del agua a varias profundidades, y se realizaron mediciones de oxígeno disuelto en la columna de agua, trasparencia del agua y concentración de nutrientes varias veces a lo largo del año de estudio. El lago es monomíctico cálido, con una mezcla profunda durante el invierno hemisférico, especialmente luego de un periodo de fuertes precipitaciones en diciembre 2010. El fitoplancton estuvo dominado por pocas especies: una Cyanobacteria colonial (Aphanocapsa sp., grupo funcional F), y dos Chlorococcaceae coloniales (Botryococcus braunii y Eutetramorus tetrasporus, ambas del grupo funcional K). Sus abundancias relativas cambiaron a lo largo del año, siguiendo los cambios en las condiciones de la columna de agua que es influenciada por variaciones en el tiempo atmosférico. Aunque los cambios en los grupos funcionales indican que hubo un cambio en la disponibilidad de recursos en vez de energía radiante, fue evidente que se debe prestar también atención a las adaptaciones particulares de las especies más allá de las que se usan normalmente para establecer los grupos funcionales.

Azole resistance in Candida spp. isolated from Catú Lake, Ceará, Brazil: an efflux-pump-mediated mechanism

Abstract Since, there is no study reporting the mechanism of azole resistance among yeasts isolated from aquatic environments; the present study aims to investigate the occurrence of antifungal resistance among yeasts isolated from an aquatic environment, and assess the efflux-pump activity of the azole-resistant strains to better understand the mechanism of resistance for this group of drugs. For this purpose, monthly water and sediment samples were collected from Catú Lake, Ceará, Brazil, from March 2011 to February 2012. The obtained yeasts were identified based on morphological and biochemical characteristics. Of the 46 isolates, 37 were Candida spp., 4 were Trichosporon asahii, 3 were Cryptococcus laurentii, 1 Rhodotorula mucilaginosa, and 1 was Kodamaea ohmeri. These isolates were subjected to broth microdilution assay with amphotericin B, itraconazole, and fluconazole, according to the methodology standardized by the Clinical and Laboratory Standards Institute (CLSI). The minimum inhibitory concentrations (MICs) of amphotericin B, itraconazole, and fluconazole were 0.03125–2 µg/mL, 0.0625 to ≥16 µg/mL, and 0.5 to ≥64 µg/mL, respectively, and 13 resistant azole-resistant Candida isolates were detected. A reduction in the azole MICs leading to the phenotypical reversal of the azole resistance was observed upon addition of efflux-pump inhibitors. These findings suggest that the azole resistance among environmental Candida spp. is most likely associated with the overexpression of efflux-pumps.

Enhanced alkaline cellulases production by the thermohalophilic Aspergillus terreus AUMC 10138 mutated by physical and chemical mutagens using corn stover as substrate

Abstract A thermohalophilic fungus, Aspergillus terreus AUMC 10138, isolated from the Wadi El-Natrun soda lakes in northern Egypt was exposed successively to gamma and UV-radiation (physical mutagens) and ethyl methan-sulfonate (EMS; chemical mutagen) to enhance alkaline cellulase production under solid state fermentation (SSF) conditions. The effects of different carbon sources, initial moisture, incubation temperature, initial pH, incubation period, inoculum levels and different concentrations of NaCl on production of alkaline filter paper activity (FPase), carboxymethyl cellulase (CMCase) and β-glucosidase by the wild-type and mutant strains of A. terreus were evaluated under SSF. The optimum conditions for maximum production of FPase, CMCase and β-glucosidase were found to be the corn stover: moisture ratio of 1:3(w/v), temperature 45 °C, pH range, 9.0–11.0, and fermentation for 4, 4 and 7 day, respectively. Inoculum levels of 30% for β-glucosidase and 40% for FPase, CMCase gave the higher cellulase production by the wild-type and mutant strains, respectively. Higher production of all three enzymes was obtained at a 5% NaCl. Under the optimized conditions, the mutant strain A. terreus M-17 produced FPase (729 U/g), CMCase (1,783 U/g), and β-glucosidase (342 U/g), which is, 1.85, 1.97 and 2.31-fold higher than the wild-type strain. Our results confirmed that mutant strain M-17 could be a promising alkaline cellulase enzyme producer employing lignocellulosics especially corn stover.

Planktonic production and respiration in a subtropical lake dominated by Cyanobacteria / Produção e respiração planctônicas em uma lagoa subtropical dominada por cianobactérias

Planktonic primary production and respiration rates were estimated in a subtropical coastal lake dominated by Cyanobacteria in order to investigate the temporal and vertical variation in this lake and to evaluate its relationships with limnological variables and phytoplankton. Light and dark bottles were incubated at four different depths in the central part of the lake and were performed bimonthly from June/2009 to December/2010. No significant difference was evident among depths in relation to phytoplankton, limnological variables and metabolic rates. However, the highest production rates were recorded at the surface, and decreased towards the bottom, coupled with phytoplanktonic photosynthetic capacity. Wind induced mixing in Peri Lake played an important role in nutrient and phytoplankton redistribution, characterizing this lake as polymictic. According to density and biovolume, the phytoplankton community was dominated by filamentous Cyanobacteria, especially Cylindrospermopsis raciborskii (Woloszynska) Seenayya and Subba-Raju. This study has shown that both water temperature and nutrient availability drive phytoplankton growth and consequently the temporal variation in metabolic rates, where respiration is higher than primary production.

As taxas de produção primária e respiração planctônicas foram estimadas em um lago costeiro subtropical dominado por cianobactérias, com o objetivo de investigar a variação temporal e vertical nesta lagoa e avaliar suas relações com as variáveis limnológicas e os grupos fitoplanctônicos. Garrafas claras e escuras foram incubadas em quatro diferentes profundidades na parte central da lagoa e foram realizadas bimensalmente de junho/2009 a dezembro/2010. Nenhuma diferença significativa foi encontrada entre as profundidades amostradas, em relação ao fitoplâncton, variáveis limnológicas e taxas metabólicas. No entanto, as maiores taxas de produção foram registradas na superfície, diminuindo com o aumento da profundidade, juntamente com a capacidade fotossintética do fitoplâncton. A ação do vento na lagoa do Peri promoveu a homogeneidade de nutrientes e do fitoplâncton na coluna d’água, caracterizando-o como polimítico. De acordo com a densidade e biovolume, a comunidade fitoplanctônica foi dominada por cianobactérias filamentosas, especialmente Cylindrospermopsis raciborskii (Woloszynska) Seenayya and Subba-Raju. Este estudo demonstrou que a temperatura da água combinada com a disponibilidade de nutrientes influencia a comunidade fitoplanctônica, determinando a variação temporal das taxas metabólicas, onde a respiração é maior que a produção primária.

Variación diurna en la composición del bacterioplancton y daño del ADN en la comunidad microbiana de un lago oligotrófico andino / Diurnal variation in bacterioplankton composition and DNA damage in the microbial community from an Andean oligotrophic lake

Laguna Azul is an oligotrophic lake situated at 4,560 m above sea level and subject to a high level of solar radiation. Bacterioplankton community composition (BCC) was analysed by denaturing gradient gel electrophoresis and the impact of solar ultraviolet radiation was assessed by measuring cyclobutane pyrimidine dimers (CPD). Furthermore, pure cultures of Acinetobacter johnsonii A2 and Rhodococcus sp. A5 were exposed simultaneously and CPD accumulation was studied. Gel analyses generated a total of 7 sequences belonging to Alpha-proteobacteria (1 band), Beta-proteobacteria (1 band), Bacteroidetes (2 bands), Actinobacteria (1 band), and Firmicutes (1 band). DGGE profiles showed minimal changes in BCC and no CPD was detected even though a high level of damage was found in biodosimeters. A. johnsonii A2 showed low level of DNA damage while Rhodococcus sp. A5 exhibited high resistance since no CPD were detected under natural UV-B exposure, suggesting that the bacterial community is well adapted to this highly solar irradiated environment.

La Laguna Azul es un ambiente oligotrófico localizado a 4560m de altura y sometido a elevados niveles de radiación solar. La composición de su comunidad bacterioplanctónica fue analizada empleando la técnica de electroforesis en gradiente desnaturalizante y se investigó el impacto de la radiación ultravioleta cuantificando los dímeros de pirimidina (CPD). Además, se expusieron simultáneamente cultivos puros de Acinetobacter johnsonii A2 y Rhodococcus sp. A5 para estudiar la acumulación de CPD. El análisis de los geles mostró siete secuencias pertenecientes a Alpha-proteobacteria (1 banda), Beta-proteobacteria (1 banda), Bacteroidetes (2 bandas), Actinobacteria (1 banda) y Firmicutes (1 banda). A lo largo del día se observaron cambios mínimos en la composición de la comunidad y no se detectaron CPD. A. johnsonii A2 presentó un daño bajo mientras que Rhodococcus sp. A5 no presentó daño en su ADN, sugiriendo que la comunidad bacteriana está muy bien adaptada a este ambiente altamente irradiado

Yeast diversity associated to sediments and water from two Colombian artificial lakes

In Colombia, knowledge of the yeast and yeast-like fungi community is limited because most studies have focused on species with clinical importance. Sediments and water represent important habitats for the study of yeast diversity, especially for yeast species with industrial, biotechnological, and bioremediation potential. The main purpose of this study was to identify and compare the diversity of yeast species associated with sediment and water samples from two artificial lakes in Universidad del Valle (Cali-Colombia). Yeast samplings were performed from fifteen sediment samples and ten water samples. Grouping of similar isolates was initially based on colony and cell morphology, which was then complemented by micro/mini satellite primed PCR banding pattern analysis by using GTG5 as single primer. A representative isolate for each group established was chosen for D1/D2 domain sequencing and identification. In general, the following yeast species were identified: Candida albicans, Candida diversa, Candida glabrata, Candida pseudolambica, Cryptococcus podzolicus, Cryptococcus rajasthanensis, Cryptococcus laurentii, Williopsis saturnus, Hanseniaspora thailandica, Hanseniaspora uvarum, Rhodotorula mucilaginosa, Saccharomyces cerevisiae, Torulaspora delbrueckii, Torulaspora pretoriensis, Tricosporon jirovecii, Trichosporon laibachii and Yarrowia lypolitica. Two possible new species were also found, belonging to the Issatchenkia sp. and Bullera sp. genera. In conclusion, the lakes at the Universidad del Valle campus have significant differences in yeast diversity and species composition between them.

A new low molecular mass alkaline cyclodextrin glucanotransferase from Amphibacillus sp. NRC-WN isolated from an Egyptian soda lake

Background: Cyclodextrin glucanotransferase (CGTase) is one of the most industrially important enzymes used in the commercial production of cyclodextrins (CDs). Alkaliphilic bacteria have attracted much interest in the last few decades because of their ability to produce extracellular enzymes that are active and stable at high pH values. Here, we report the isolation of a new CGTase from alkaliphilic bacteria collected from Egyptian soda lakes and describe the purification and biochemical characterization of this CGTase. Results: Screening for CGTase-producing alkaliphilic bacteria from sediment and water samples collected from Egyptian soda lakes located in the Wadi Natrun valley resulted in the isolation of a potent CGTase-producing alkaliphilic bacterial strain, designated NRC-WN. Strain NRC-WN was belonging to genus Amplibacullus by 16S rDNA sequence analysis (similarity: ca. 98%). Among the tested nitrogen and carbon sources, peptone (0.15%, w/v) and soluble starch (0.4%, w/v) allowed maximal CGTase production by Amphibacillus sp. NRC-WN. CGTase was successfully purified from Amphibacillus sp. NRC-WN up to 159.7-fold through a combination of starch adsorption and anion exchange chromatography, resulting in a yield of 84.7%. SDS-PAGE analysis indicated that the enzyme was purified to homogeneity and revealed an estimated molecular mass of 36 kDa, which makes it one of the smallest CGTases reported in the literature. The purified enzyme exhibited maximum activity at 50ºC and was stable up to 70ºC, retaining 93% of its initial activity after treatment for 1 hr. Furthermore, Ca2+ ions (10 mM) significantly enhanced the thermal stability of the CGTase. The purified enzyme was active and stable over a wide pH range, showing maximal activity at pH 9.5. The enzyme was significantly stimulated by Zn2+, Ca2+ and Co2+ but was completely inhibited in the presence of Fe3+ and mercaptoethanol. The Km and Vmax values of the purified CGTase were estimated to be 0.0434 mg/ml and 3,333.3 mg β-CD/ml/min, respectively. β-CD was the predominant product of starch degradation by the Amphibacillus sp. NRC-WN CGTase, followed by α-and γ-CDs. Conclusions: A new low molecular mass alkaline CGTase was purified from a newly identified alkaliphilic Amphibacillus sp. NRC-WN isolate from the Egyptian soda lakes. The enzyme showed promising thermal and pH stability and a high affinity toward starch as a natural substrate.

Comparación de técnicas para la extracción de bacterias coliformes del sedimento del lago de Xochimilco, México / [Comparison of techniques for coliform bacteria extraction from sediment of Xochimilco Lake, Mexico].

The need to separate bacteria from sediment in order to appropriately count them has led to test the efficacy of different techniques. In this research, traditional techniques such as manual shaking, homogenization, ultrasonication, and surfactant are compared. Moreover, the possibility of using a set of enzymes (pancreatine) and an antibiotic (ampicillin) for sediment coliform extraction is proposed. Samples were obtained from Xochimilco Lake in Mexico City. The most probable number of coliform bacteria was determined after applying the appropriate separation procedure. Most of the techniques tested led to numbers similar to those of the control (manual shaking). Only with the use of ampicillin, a greater total coliform concentration was observed (Mann-Whitney, z = 2.09; p = 0.03). It is possible to propose the use of ampicillin as a technique for total coliform extraction; however, it is necessary to consider sensitivity of bacteria to the antibiotic.

Planktonic Cyanobacteria of the tropical karstic lake Lagartos from the Yucatan Peninsula, Mexico / Las cianobacterias planctónicas del lago tropical cárstico Lagartos de la Península de Yucatán, México

The tropical karstic lakes on the Mexican Caribbean Sea coast are numerous. However, there is an enormous gap of knowledge about their limnological conditions and micro-algae communities. In the present study, surface water samples were collected monthly from November 2007 to September 2008 to provide taxonomical composition and biovolume of planktonic cyanobacteria of the lake Lagartos from State of Quintana Roo, Mexico. Water temperature, pH, conductivity, salinity, soluble reactive phosphorus (SRP), dissolved inorganic nitrogen (DIN), and soluble reactive silica (SRSi) levels were also analyzed. A total of 22 species were identified. Chroococcales and Oscillatoriales dominated the phytoplankton assemblages during the study period. Chroococcus pulcherrimus, Coelosphaerium confertum, Cyanodyction iac, Phormidium pachydermaticum and Planktolyngbya contorta were recorded for the first time in Mexico. A surplus of DIN (mean value of 42.7µM) and low concentrations of SRP (mean value of 1.0µM) promoted the enhanced growth and bloom formation of cyanobacteria. The mean biovolume was 3.22X10(8)µm³/mL, and two biovolume peaks were observed; the first was dominated by Microcystis panniformis in November 2007 (7.40X10(8)µm³/mL), and the second was dominated by Oscillatoria princeps in April 2008 (6.55X10(8)µm³/mL). Water quality data, nitrates enrichment, and trophic state based on biovolume, indicated that Lagartos is a hyposaline, secondarily phosphorus-limited, and eutrophic lake, where the cyanobacteria flora was composed mainly by non-heterocystous groups.

Los lagos cársticos tropicales en la costa del Caribe mexicano son numerosos. Sin embargo, existe un enorme desconocimiento acerca de sus condiciones limnológicas y de las comunidades de microalgas que se desarrollan en ellos. El objetivo del presente estudio fue estudiar las condiciones limnológicas en las que crecen las poblaciones de cianobacterias planctónicas del lago Lagartos, Quintana Roo, México. Las recolectas se realizaron de forma mensual entre noviembre 2007 y septiembre 2008. Las especies fueron identificadas y su biovolumen determinado. Se midieron in situ la temperatura del agua, pH, conductividad y salinidad. También, se analizaron las concentraciones de fósforo reactivo soluble (SRP), nitrógeno inorgánico disuelto (DIN) y sílice reactivo soluble (SRSi). Se identificaron 22 especies de cianobacterias. Chroococcus pulcherrimus, Coelosphaerium confertum, Cyanodyction iac, Phormidium pachydermaticum y Planktolyngbya contorta fueron nuevos registros para México. Un exceso de DIN (valor promedio de 42.7µM) y bajas concentraciones de PRS (valor promedio de 1.0µM) promovieron la proliferación de cianobacterias. El biovolumen presentó dos picos: el primero en noviembre 2007, dominado por Microcystis panniformis (7.40X10(8)µm³/mL) y el segundo en abril 2008, representado por Oscillatoria princeps (6.55X10(8)µm³/mL). Los datos de calidad del agua, el enriquecimiento por nitratos y el estado trófico basado en el biovolumen, indican que Lagartos es un lago hiposalino, eutrófico, con limitación secundaria por fósforo, donde los crecimientos masivos de cianobacterias sin heterocitos fueron recurrentes.

Phospholipid fatty acids analysis of the vertical distribution of microbial communities in eutrophic lake sediments

Vertical distribution of microbial communities in a eutrophic lake sediments of Lake Xuanwu was quantified by phospholipid fatty acids analysis and multivariate statistical analysis was employed to interprete the data. Principle component analysis of sediment characteristics parameters, including total nitrogen, total phosphorus, organic matters and pH produced clustering of sampling sites for two distinct groups. These groups corresponded with the two sampling stations and the levels of nutrient enrichment. Total phospholipid fatty acids concentration, which is indicative of microbial biomass, reduced with depth, however, the relative percentage of anaerobic prokaryotes increased. To assess changes of microbial community along depth, phospholipid fatty acids compositions were analyzed by cluster analysis. Distinct clusters were observed in different sampling stations. Canonical correspondence analysis was carried out to infer the relationship between sediment characteristics and microbial communities. Phospholipid fatty acids samples collected at the same sampling site clustered together. Canonical correspondence analysis revealed that the environmental parameter with the greatest bearing on the phospholipid fatty acids profiles was pH. This study proved the successful application of phospholipid fatty acids and multivariate analysis to investigate the relationship between environment factors and microbial community composition