Long-range transport of airborne microbes over the global tropical and subtropical ocean

The atmosphere plays a fundamental role in the transport of microbes across the planet but it is often neglected as a microbial habitat. Although the ocean represents two thirds of the Earth’s surface, there is little information on the atmospheric microbial load over the open ocean. Here we provide a global estimate of microbial loads and air-sea exchanges over the tropical and subtropical oceans based on the data collected along the Malaspina 2010 Circumnavigation Expedition. Total loads of airborne prokaryotes and eukaryotes were estimated at 2.2 × 1021 and 2.1 × 1021 cells, respectively. Overall 33–68% of these microorganisms could be traced to a marine origin, being transported thousands of kilometres before re-entering the ocean. Moreover, our results show a substantial load of terrestrial microbes transported over the oceans, with abundances declining exponentially with distance from land and indicate that islands may act as stepping stones facilitating the transoceanic transport of terrestrial microbes.En prens

Global Distribution of Polaromonas Phylotypes - Evidence for a Highly Successful Dispersal Capacity

Bacteria from the genus Polaromonas are dominant phylotypes in clone libraries and culture collections from polar and high-elevation environments. Although Polaromonas has been found on six continents, we do not know if the same phylotypes exist in all locations or if they exhibit genetic isolation by distance patterns. To examine their biogeographic distribution, we analyzed all available, long-read 16S rRNA gene sequences of Polaromonas phylotypes from glacial and periglacial environments across the globe. Using genetic isolation by geographic distance analyses, including Mantel tests and Mantel correlograms, we found that Polaromonas phylotypes are globally distributed showing weak isolation by distance patterns at global scales. More focused analyses using discrete, equally sampled distances classes, revealed that only two distance classes (out of 12 total) showed significant spatial structuring. Overall, our analyses show that most Polaromonas phylotypes are truly globally distributed, but that some, as yet unknown, environmental variable may be selecting for unique phylotypes at a minority of our global sites. Analyses of aerobiological and genomic data suggest that Polaromonas phylotypes are globally distributed as dormant cells through high-elevation air currents; Polaromonas phylotypes are common in air and snow samples from high altitudes, and a glacial-ice metagenome and the two sequenced Polaromonas genomes contain the gene hipA, suggesting that Polaromonas can form dormant cells

The Passive Yet Successful Way of Planktonic Life: Genomic and Experimental Analysis of the Ecology of a Free-Living Polynucleobacter Population

Background: The bacterial taxon Polynucleobacter necessarius subspecies asymbioticus represents a group of planktonic freshwater bacteria with cosmopolitan and ubiquitous distribution in standing freshwater habitats. These bacteria comprise,1 % to 70 % (on average about 20%) of total bacterioplankton cells in various freshwater habitats. The ubiquity of this taxon was recently explained by intra-taxon ecological diversification, i.e. specialization of lineages to specific environmental conditions; however, details on specific adaptations are not known. Here we investigated by means of genomic and experimental analyses the ecological adaptation of a persistent population dwelling in a small acidic pond. Findings: The investigated population (F10 lineage) contributed on average 11 % to total bacterioplankton in the pond during the vegetation periods (ice-free period, usually May to November). Only a low degree of genetic diversification of the population could be revealed. These bacteria are characterized by a small genome size (2.1 Mb), a relatively small number of genes involved in transduction of environmental signals, and the lack of motility and quorum sensing. Experiments indicated that these bacteria live as chemoorganotrophs by mainly utilizing low-molecular-weight substrates derived from photooxidation of humic substances. Conclusions: Evolutionary genome streamlining resulted in a highly passive lifestyle so far only known among free-living bacteria from pelagic marine taxa dwelling in environmentally stable nutrient-poor off-shore systems. Surprisingly, such a lifestyle is also successful in a highly dynamic and nutrient-richer environment such as the water column of the investigate

La selección de la dieta : papel de los compuestos secundarios de las plantas

Los herbívoros seleccionan su dieta tratando, por una parte, de cubrir sus necesidades nutritivas y, por otra, de evitar la ingestión de compuestos tóxicos. En general, la dieta consumida tiene un valor nutritivo superior al valor medio del pasto al que los animales tienen acceso. Ahora bien, los mecanismos que intervienen en la selección de la dieta son aún materia de controversia en la comunidad científica. En este capítulo se tratan las cuatro teorías principales que intentan explicar el comportamiento selectivo: eufagia, hedofagia, características morfofisiológicas y aprendizaje. Además, se analiza el papel que los compuestos secundarios de las plantas pueden jugar en el proceso de aprendizaje y selección de la dieta y la importancia que en ello puede tener la adaptación fisiológica de los rumiantes a la ingestión de estos compuestos

Vertical segregation and phylogenetic characterization of ammonia-oxidizing Archaea in a deep oligotrophic lake

12 páginas, 6 figuras, 1 tabla.Freshwater habitats have been identified as one of the largest reservoirs of archaeal genetic diversity, with specific lineages of ammonia-oxidizing archaea (AOA) populations different from soils and seas. The ecology and biology of lacustrine AOA is, however, poorly known. In the present study, vertical changes in archaeal abundance by CARD-FISH, quantitative PCR (qPCR) analyses and identity by clone libraries were correlated with environmental parameters in the deep glacial high-altitude Lake Redon. The lake is located in the central Spanish Pyrenees where atmospheric depositions are the main source of reactive nitrogen. Strong correlations were found between abundance of thaumarchaeotal 16S rRNA gene, archaeal amoA gene and nitrite concentrations, indicating an ammonium oxidation potential by these microorganisms. The bacterial amoA gene was not detected. Three depths with potential ammonia-oxidation activity were unveiled along the vertical gradient, (i) on the top of the lake in winter–spring (that is, the 0 oC slush layers above the ice-covered sheet), (ii) at the thermocline and (iii) the bottom waters in summer—autumn. Overall, up to 90% of the 16S rRNA gene sequences matched Thaumarchaeota, mostly from both the Marine Group (MG) 1.1a (Nitrosoarchaeum-like) and the sister clade SAGMGC−1 (Nitrosotalea-like). Clone-libraries analysis showed the two clades changed their relative abundances with water depth being higher in surface and lower in depth for SAGMGC−1 than for MG 1.1a, reflecting a vertical phylogenetic segregation. Overall, the relative abundance and recurrent appearance of SAGMGC−1 suggests a significant environmental role of this clade in alpine lakes. These results expand the set of ecological and thermal conditions where Thaumarchaeota are distributed, unveiling vertical positioning in the water column as a key factor to understand the ecology of different thaumarchaeotal clades in lacustrine environments.This research was supported by grants CRENYC CGL2006-12058 and PIRENA CGL2009-13318 to EOC, and CONSOLIDER grant GRACCIE CSD2007-00067 from the Spanish Office of Science and Innovation (MICINN). JCA benefits from a Juan de la Cierva postdoctoral fellow (MICINN).Peer reviewe

Spatial and temporal analysis of estuarine bacterioneuston and bacterioplankton using culture-dependent and culture-independent methodologies

Bacterioneuston may play a key role in water–air exchange of gases and in processing organic matter and pollutants that accumulate at the sea-surface microlayer (SML). However, the phylogenetic diversity of bacterioneuston has been poorly characterized. We analyzed 24 samples each from the SML and underlying water (UW) at three sites in the Ria de Aveiro estuary, Portugal. Cultivation and culture-independent techniques were used to compare bacterioneuston and bacterioplankton. Culturable heterotrophic bacteria were enriched in the SML. The culturable community was dominated by Psychrobacter and Acinetobacter. The presence of high numbers of Psychrobacter was a notable result. Differences were confined to a few genera overrepresented in UW samples (Kocuria, Agrococcus and Vibrio). 16S rDNA DGGE profiles were highly stable in terms of number and position of bands between sampling sites and dates but cluster analysis revealed a slight tendency for grouping according to sampled layer. SML-specific DGGE bands affiliated with Actinobacteria, Cyanobacteria, Gammaproteobacteria and Bacteroidetes. Low similarity between nucleotide sequences of DGGE-bands and previously reported sequences suggest the occurrence of SML-specific populations. Enrichment of SML for Pseudomonas and Aeromonas was questioned and the diversity of both communities was analyzed. Consistent differences between SML and UW aeromonads communities were not identified. In terms of Pseudomonas, a culturable operational taxonomic unit was consistently overrepresented within SML samples. Taken together, our results indicate that the similarity between SML and UW communities depends on spatial and temporal factors

Consortia of low-abundance bacteria drive sulfate reduction-dependent degradation of fermentation products in peat soil microcosms

Dissimilatory sulfate reduction in peatlands is sustained by a cryptic sulfur cycle and effectively competes with methanogenic degradation pathways. In a series of peat soil microcosms incubated over 50 days, we identified bacterial consortia that responded to small, periodic additions of individual fermentation products (formate, acetate, propionate, lactate or butyrate) in the presence or absence of sulfate. Under sulfate supplementation, net sulfate turnover (ST) steadily increased to 16–174 nmol cm(–3) per day and almost completely blocked methanogenesis. 16S rRNA gene and cDNA amplicon sequencing identified microorganisms whose increases in ribosome numbers strongly correlated to ST. Natively abundant (⩾0.1% estimated genome abundance) species-level operational taxonomic units (OTUs) showed no significant response to sulfate. In contrast, low-abundance OTUs responded significantly to sulfate in incubations with propionate, lactate and butyrate. These OTUs included members of recognized sulfate-reducing taxa (Desulfosporosinus, Desulfopila, Desulfomonile, Desulfovibrio) and also members of taxa that are either yet unknown sulfate reducers or metabolic interaction partners thereof. Most responsive OTUs markedly increased their ribosome content but only weakly increased in abundance. Responsive Desulfosporosinus OTUs even maintained a constantly low population size throughout 50 days, which suggests a novel strategy of rare biosphere members to display activity. Interestingly, two OTUs of the non-sulfate-reducing genus Telmatospirillum (Alphaproteobacteria) showed strongly contrasting preferences towards sulfate in butyrate-amended microcosms, corroborating that closely related microorganisms are not necessarily ecologically coherent. We show that diverse consortia of low-abundance microorganisms can perform peat soil sulfate reduction, a process that exerts control on methane production in these climate-relevant ecosystems