Unveiling the co-phylogeny signal between plunderfish Harpagifer spp. and their gut microbiomes across the Southern Ocean

Understanding the factors that sculpt fish gut microbiome is challenging, especially in natural populations characterized by high environmental and host genomic complexity. However, closely related hosts are valuable models for deciphering the contribution of host evolutionary history to microbiome assembly, through the underscoring of phylosymbiosis and co-phylogeny patterns. Here, we propose that the recent diversification of several Harpagifer species across the Southern Ocean would allow the detection of robust phylogenetic congruence between the host and its microbiome. We characterized the gut mucosa microbiome of 77 individuals from four field-collected species of the plunderfish Harpagifer (Teleostei, Notothenioidei), distributed across three biogeographic regions of the Southern Ocean. We found that seawater physicochemical properties, host phylogeny, and geography collectively explained 35% of the variation in bacterial community composition in Harpagifer gut mucosa. The core microbiome of Harpagifer spp. gut mucosa was characterized by a low diversity, mostly driven by selective processes, and dominated by a single Aliivibrio Operational Taxonomic Unit (OTU) detected in more than 80% of the individuals. Nearly half of the core microbiome taxa, including Aliivibrio, harbored co-phylogeny signal at microdiversity resolution with host phylogeny, indicating an intimate symbiotic relationship and a shared evolutionary history with Harpagifer. The clear phylosymbiosis and co-phylogeny signals underscore the relevance of the Harpagifer model in understanding the role of fish evolutionary history in shaping the gut microbiome assembly. We propose that the recent diversification of Harpagifer may have led to the diversification of Aliivibrio, exhibiting patterns that mirror the host phylogeny.

IMPORTANCE

Although challenging to detect in wild populations, phylogenetic congruence between marine fish and its microbiome is critical, as it highlights intimate associations between hosts and ecologically relevant microbial symbionts. Our study leverages a natural system of closely related fish species in the Southern Ocean to unveil new insights into the contribution of host evolutionary trajectory on gut microbiome assembly, an underappreciated driver of the global marine fish holobiont. Notably, we unveiled striking evidence of co-diversification between Harpagifer and its microbiome, demonstrating both phylosymbiosis of gut bacterial communities and co-phylogeny of some specific bacterial symbionts, mirroring the host diversification patterns. Given Harpagifer's significance as a trophic resource in coastal areas and its vulnerability to climatic and anthropic pressures, understanding the potential evolutionary interdependence between the hosts and its microbiome provides valuable microbial candidates for future monitoring, as they may play a pivotal role in host species acclimatization to a rapidly changing environment.

Revealing the hidden biodiversity of Antarctic and the Magellanic Sub-Antarctic Ecoregion: A comprehensive study of aquatic invertebrates from the BASE Project

Background

Antarctica, its outlying archipelagoes and the Magellanic Subantarctic (MSA) ecoregion are amongst the last true wilderness areas remaining on the planet. Therefore, the publication, citation and peer review of their biodiversity data are essential. The new Millennium Institute Biodiversity of Antarctic and Subantarctic Ecosystems (BASE), a Chilean scientific initiative funded by the National Agency of Research and Innovation, contributes 770 new records of aquatic invertebrates as a point of reference for present-day biodiversity research at these latitudes.

New information

The occurrence dataset presented here has never been released before and is the result of the systematic recording of occurrences of several taxa across the Antarctic, Subantarctic and Magellanic Subantarctic ecoregions. We collected data from marine and freshwater invertebrates across numerous samplings from 2008 to 2023. From the 770 occurrences, we identified 160 taxa, 125 at species level and 35 at the genus level. The database has been registered in the Global Biodiversity Information Facility (GBIF). The publication of this data paper was funded by the Belgian Science Policy Office (BELSPO, contract n°FR/36/AN1/AntaBIS) in the Framework of EU-Lifewatch as a contribution to the SCAR Antarctic biodiversity portal (biodiversity.aq).

Diversity of Microbial Functional Genes Should Be Considered During the Interpretation of the qPCR Melting Curves

Soil microorganisms play an essential role in biogeochemical cycles. One approach to study these microbial communities is quantifying functional genes by quantitative PCR (qPCR), in which a melting curve analysis is usually assessed to confirm that a single PCR product is being quantified. However, the high diversity of functional genes in environmental samples could generate more than one peak in those curves, so the presence of two or multiple peaks does not always indicate nonspecific amplification. Here, we analyzed the taxonomic diversity of soil microorganisms harboring functional genes involved in nitrogen (N) and phosphorus (P) cycles, based on a database of genomes and metagenomes, and predicted the melting curve profiles of these genes. These functional genes were spread across many bacterial phyla, but mainly Proteobacteria and Actinobacteria. In general, the melting curves exhibited more than one peak or peaks with shoulders, mainly related to the variation of the nucleotide composition of the genes and the expected size of the amplicons. These results indicate that the melting curves of functional genes from environmental samples should be carefully evaluated, being in silico analyses a cost-effective way to identify inherent sequence diversity and avoid interpreting multiple peaks always as unspecific amplifications.

Peltigera frigida Lichens and Their Substrates Reduce the Influence of Forest Cover Change on Phosphate Solubilizing Bacteria

Phosphorus (P) is one of the most critical macronutrients in forest ecosystems. More than 70 years ago, some Chilean Patagonian temperate forests suffered wildfires and the subsequent afforestation with foreign tree species such as pines. Since soil P turnover is interlinked with the tree cover, this could influence soil P content and bioavailability. Next to soil microorganisms, which are key players in P transformation processes, a vital component of Patagonian temperate forest are lichens, which represent microbial hotspots for bacterial diversity. In the present study, we explored the impact of forest cover on the abundance of phosphate solubilizing bacteria (PSB) from three microenvironments of the forest floor: Peltigera frigida lichen thallus, their underlying substrates, and the forest soil without lichen cover. We expected that the abundance of PSB in the forest soil would be strongly affected by the tree cover composition since the aboveground vegetation influences the edaphic properties; but, as P. frigida has a specific bacterial community, lichens would mitigate this impact. Our study includes five sites representing a gradient in tree cover types, from a mature forest dominated by the native species Nothofagus pumilio, to native second-growth forests with a gradual increase in the presence of Pinus contorta in the last sites. In each site, we measured edaphic parameters, P fractions, and the bacterial potential to solubilize phosphate by quantifying five specific marker genes by qPCR. The results show higher soluble P, labile mineral P, and organic matter in the soils of the sites with a higher abundance of P. contorta, while most of the molecular markers were less abundant in the soils of these sites. Contrarily, the abundance of the molecular markers in lichens and substrates was less affected by the tree cover type. Therefore, the bacterial potential to solubilize phosphate is more affected by the edaphic factors and tree cover type in soils than in substrates and thalli of P. frigida lichens. Altogether, these results indicate that the microenvironments of lichens and their substrates could act as an environmental buffer reducing the influence of forest cover composition on bacteria involved in P turnover.

Diversity of microbial communities and genes involved in nitrous oxide emissions in Antarctic soils impacted by marine animals as revealed by metagenomics and 100 metagenome-assembled genomes

Antarctic soils generally have low temperatures and limited availability of liquid water and nutrients. However, animals can increase the nutrient availability of ice-free areas by transferring nutrients from marine to terrestrial ecosystems, mainly through their excreta. In this study, we employed shotgun metagenomics and population genome binning techniques to study the diversity of microbial communities in Antarctic soils impacted by marine pinnipeds and birds relative to soils with no evident animal presence. We obtained ~285,000 16S rRNA gene-carrying metagenomic reads representing ~60 phyla and 100 metagenome-assembled genomes (MAGs) representing eight phyla. Only nine of these 100 MAGs represented previously described species, revealing that these soils harbor extensive novel diversity. Proteobacteria, Actinobacteria, and Bacteroidetes were the most abundant phyla in all samples, with Rhodanobacter being one of the most abundant genera in the bird-impacted soils. Further, the relative abundance of genes related to denitrification was at least double in soils impacted by birds than soils without animal influence. These results advance our understanding of the microbial populations and their genes involved in nitrous oxide emissions in ice-free coastal Antarctic soils impacted by marine animals and reveal novel microbial diversity associated with these ecosystems.

Exploring the Microdiversity Within Marine Bacterial Taxa: Toward an Integrated Biogeography in the Southern Ocean

Most of the microbial biogeographic patterns in the oceans have been depicted at the whole community level, leaving out finer taxonomic resolution (i.e., microdiversity) that is crucial to conduct intra-population phylogeographic study, as commonly done for macroorganisms. Here, we present a new approach to unravel the bacterial phylogeographic patterns combining community-wide survey by 16S rRNA gene metabarcoding and intra-species resolution through the oligotyping method, allowing robust estimations of genetic and phylogeographic indices, and migration parameters. As a proof-of-concept, we focused on the bacterial genus Spirochaeta across three distant biogeographic provinces of the Southern Ocean; maritime Antarctica, sub-Antarctic Islands, and Patagonia. Each targeted Spirochaeta operational taxonomic units were characterized by a substantial intrapopulation microdiversity, and significant genetic differentiation and phylogeographic structure among the three provinces. Gene flow estimations among Spirochaeta populations support the role of the Antarctic Polar Front as a biogeographic barrier to bacterial dispersal between Antarctic and sub-Antarctic provinces. Conversely, the Antarctic Circumpolar Current appears as the main driver of gene flow, connecting sub-Antarctic Islands with Patagonia and maritime Antarctica. Additionally, historical processes (drift and dispersal limitation) govern up to 86% of the spatial turnover among Spirochaeta populations. Overall, our approach bridges the gap between microbial and macrobial ecology by revealing strong congruency with macroorganisms distribution patterns at the populational level, shaped by the same oceanographic structures and ecological processes.

The multi metal-resistant bacterium Cupriavidus metallidurans CH34 affects growth and metal mobilization in Arabidopsis thaliana plants exposed to copper

Copper (Cu) is important for plant growth, but high concentrations can lead to detrimental effects such as primary root length inhibition, vegetative tissue chlorosis, and even plant death. The interaction between plant-soil microbiota and roots can potentially affect metal mobility and availability, and, therefore, overall plant metal concentration. Cupriavidus metallidurans CH34 is a multi metal-resistant bacterial model that alters metal mobility and bioavailability through ion pumping, metal complexation, and reduction processes. The interactions between strain CH34 and plants may affect the growth, metal uptake, and translocation of Arabidopsis thaliana plants that are exposed to or not exposed to Cu. In this study, we looked also at the specific gene expression changes in C. metallidurans when co-cultured with Cu-exposed A. thaliana. We found that A. thaliana’s rosette area, primary and secondary root growth, and dry weight were affected by strain CH34, and that beneficial or detrimental effects depended on Cu concentration. An increase in some plant growth parameters was observed at copper concentrations lower than 50 µM and significant detrimental effects were found at concentrations higher than 50 µM Cu. We also observed up to a 90% increase and 60% decrease in metal accumulation and mobilization in inoculated A. thaliana. In turn, copper-stressed A. thaliana altered C. metallidurans colonization, and cop genes that encoded copper resistance in strain CH34 were induced by the combination of A. thaliana and Cu. These results reveal the complexity of the plant-bacteria-metal triad and will contribute to our understanding of their applications in plant growth promotion, protection, and phytoremediation strategies.

Conyza bonariensis as an alternative host for Colletotrichum species in Argentina

AIMS

This study investigated the diversity of Colletotrichum isolates recovered from Conyza bonariensis leaves through the use of morphological characteristics, growth rate, carbon sources utilization and phylogenetic analysis.

METHODS AND RESULTS

In all, 30 Colletotrichum isolates recovered from C. bonariensis leaves showing symptoms of disease were included in the present study. Based on the analysis of morphology and sequences, the isolates were distributed into six Colletotrichum species complexes. The concatenated alignment of GAPDH and ITS sequences showed that 20 out of 30 isolates were included in four species complexes which comprise the most important pathogens causing anthracnose in soybean or anthracnose and stalk rot in maize: C. truncatum, C. orchidearum, C. gloeosporioides and C. graminicola. The remaining 10 isolates were included in the C. boninense and C. destructivum species complexes or could not be assigned to any complex with the available information.

CONCLUSION

Weeds belonging to genus Conyza are host to soybean and maize potential pathogenic species of Colletotrichum and could have a role as inoculum reservoir for cross contamination in the agroecosystem.

SIGNIFICANCE AND IMPACT OF THE STUDY

The combined use of morphological, kinetics and physiological parameters of growth and phylogenetic analysis in Colletotrichum isolates from Conyza leaves allowed the detection of species complexes previously not identified in Argentina.

The Bacterial Community of the Foliose Macro-lichen Peltigera frigida Is More than a Mere Extension of the Microbiota of the Subjacent Substrate

Lichens host highly diverse microbial communities, with bacteria being one of the most explored groups in terms of their diversity and functioning. These bacteria could partly originate from symbiotic propagules developed by many lichens and, perhaps more commonly and depending on environmental conditions, from different sources of the surroundings. Using the narrowly distributed species Peltigera frigida as an object of study, we propose that bacterial communities in these lichens are different from those in their subjacent substrates, even if some taxa might be shared. Ten terricolous P. frigida lichens and their substrates were sampled from forested sites in the Coyhaique National Reserve, located in an understudied region in Chile. The mycobiont identity was confirmed using partial 28S and ITS sequences. Besides, 16S fragments revealed that mycobionts were associated with the same cyanobacterial haplotype. From both lichens and substrates, Illumina 16S amplicon sequencing was performed using primers that exclude cyanobacteria. In lichens, Proteobacteria was the most abundant phylum (37%), whereas soil substrates were dominated by Acidobacteriota (39%). At lower taxonomic levels, several bacterial groups differed in relative abundance among P. frigida lichens and their substrates, some of them being highly abundant in lichens but almost absent in substrates, like Sphingomonas (8% vs 0.2%), and others enriched in lichens, as an unassigned genus of Chitinophagaceae (10% vs 2%). These results reinforce the idea that lichens would carry some components of their microbiome when propagating, but they also could acquire part of their bacterial community from the substrates.

Characterization of the Gut Microbiota of the Antarctic Heart Urchin (Spatangoida) Abatus agassizii

Abatus agassizii is an irregular sea urchin species that inhabits shallow waters of South Georgia and South Shetlands Islands. As a deposit-feeder, A. agassizii nutrition relies on the ingestion of the surrounding sediment in which it lives barely burrowed. Despite the low complexity of its feeding habit, it harbors a long and twice-looped digestive tract suggesting that it may host a complex bacterial community. Here, we characterized the gut microbiota of specimens from two A. agassizii populations at the south of the King George Island in the West Antarctic Peninsula. Using a metabarcoding approach targeting the 16S rRNA gene, we characterized the Abatus microbiota composition and putative functional capacity, evaluating its differentiation among the gut content and the gut tissue in comparison with the external sediment. Additionally, we aimed to define a core gut microbiota between A. agassizii populations to identify potential keystone bacterial taxa. Our results show that the diversity and the composition of the microbiota, at both genetic and predicted functional levels, were mostly driven by the sample type, and to a lesser extent by the population location. Specific bacterial taxa, belonging mostly to Planctomycetacia and Spirochaetia, were differently enriched in the gut content and the gut tissue, respectively. Predictive functional profiles revealed higher abundance of specific pathways, as the sulfur cycle in the gut content and the amino acid metabolism, in the gut tissue. Further, the definition of a core microbiota allowed to obtain evidence of specific localization of bacterial taxa and the identification of potential keystone taxa assigned to the Desulfobacula and Spirochaeta genera as potentially host selected. The ecological relevance of these keystone taxa in the host metabolism is discussed.

Seabird and pinniped shape soil bacterial communities of their settlements in Cape Shirreff, Antarctica

Seabirds and pinnipeds play an important role in biogeochemical cycling by transferring nutrients from aquatic to terrestrial environments. Indeed, soils rich in animal depositions have generally high organic carbon, nitrogen and phosphorus contents. Several studies have assessed bacterial diversity in Antarctic soils influenced by marine animals; however most have been conducted in areas with significant human impact. Thus, we chose Cape Shirreff, Livingston Island, an Antarctic Specially Protected Area designated mainly to protect the diversity of marine vertebrate fauna, and selected sampling sites with different types of animals coexisting in a relatively small space, and where human presence and impact are negligible. Using 16S rRNA gene analyses through massive sequencing, we assessed the influence of animal concentrations, via their modification of edaphic characteristics, on soil bacterial diversity and composition. The nutrient composition of soils impacted by Antarctic fur seals and kelp gulls was more similar to that of control soils (i.e. soils without visible presence of plants or animals), which may be due to the more active behaviour of these marine animals compared to other species. Conversely, the soils from concentrations of southern elephant seals and penguins showed greater differences in soil nutrients compared to the control. In agreement with this, the bacterial communities of the soils associated with these animals were most different from those of the control soils, with the soils of penguin colonies also possessing the lowest bacterial diversity. However, all the soils influenced by the presence of marine animals were dominated by bacteria belonging to Gammaproteobacteria, particularly those of the genus Rhodanobacter. Therefore, we conclude that the modification of soil nutrient composition by marine vertebrates promotes specific groups of bacteria, which could play an important role in the recycling of nutrients in terrestrial Antarctic ecosystems.

Nitrogen-Fixing Bacteria Associated with Peltigera Cyanolichens and Cladonia Chlorolichens

Lichens have been extensively studied and described; however, recent evidence suggests that members of the bacterial community associated with them could contribute new functions to the symbiotic interaction. In this work, we compare the nitrogen-fixing guild associated with bipartite terricolous lichens with different types of photobiont: Peltigera cyanolichens and Cladonia chlorolichens. Since cyanobacteria contribute nitrogen to the symbiosis, we propose that chlorolichens have more diverse bacteria with the ability to fix nitrogen compared to cyanolichens. In addition, since part of these bacteria could be recruited from the substrate where lichens grow, we propose that thalli and substrates share some bacteria in common. The structure of the nitrogen-fixing guild in the lichen and substrate bacterial communities of both lichens was determined by terminal restriction fragment length polymorphism (TRFLP) of the nifH gene. Multivariate analyses showed that the nitrogen-fixing bacteria associated with both types of lichen were distinguishable from those present in their substrates. Likewise, the structure of the nitrogen-fixing bacteria present in the cyanolichens was different from that of chlorolichens. Finally, the diversity of this bacterial guild calculated using the Shannon index confirms the hypothesis that chlorolichens have a higher diversity of nitrogen-fixing bacteria than cyanolichens.

Substrates of Peltigera Lichens as a Potential Source of Cyanobionts

Photobiont availability is one of the main factors determining the success of the lichenization process. Although multiple sources of photobionts have been proposed, there is no substantial evidence confirming that the substrates on which lichens grow are one of them. In this work, we obtained cyanobacterial 16S ribosomal RNA gene sequences from the substrates underlying 186 terricolous Peltigera cyanolichens from localities in Southern Chile and maritime Antarctica and compared them with the sequences of the cyanobionts of these lichens, in order to determine if cyanobacteria potentially available for lichenization were present in the substrates. A phylogenetic analysis of the sequences showed that Nostoc phylotypes dominated the cyanobacterial communities of the substrates in all sites. Among them, an overlap was observed between the phylotypes of the lichen cyanobionts and those of the cyanobacteria present in their substrates, suggesting that they could be a possible source of lichen photobionts. Also, in most cases, higher Nostoc diversity was observed in the lichens than in the substrates from each site. A better understanding of cyanobacterial diversity in lichen substrates and their relatives in the lichens would bring insights into mycobiont selection and the distribution patterns of lichens, providing a background for hypothesis testing and theory development for future studies of the lichenization process.

Intrinsic factors of Peltigera lichens influence the structure of the associated soil bacterial microbiota

Definition of lichens has evolved from bi(tri)partite associations to multi-species symbioses, where bacteria would play essential roles. Besides, although soil bacterial communities are known to be affected by edaphic factors, when lichens grow upon them these could become less preponderant. We hypothesized that the structure of both the lichen microbiota and the microbiota in the soil underneath lichens is shaped by lichen intrinsic and extrinsic factors. In this work, intrinsic factors corresponded to mycobiont and cyanobiont identities of Peltigera lichens, metabolite diversity and phenoloxidase activity and extrinsic factors involved the site of the forest where lichens grow. Likewise, the genetic and metabolic structure of the lichen and soil bacterial communities were analyzed by fingerprinting. Among the results, metabolite diversity was inversely related to the genetic structure of bacterial communities of lichens and soils, highlighting the far-reaching effect of these substances; while phenoloxidase activity was inversely related to the metabolic structure only of the lichen bacterial microbiota, presuming a more limited effect of the products of these enzymes. Soil bacterial microbiota was different depending on the site and, strikingly, according to the cyanobiont present in the lichen over them, which could indicate an influence of the photobiont metabolism on the availability of soil nutrients.

Fungal communities as an experimental approach to Darwin's naturalization hypothesis

Darwin's naturalization hypothesis suggests that the success of an invasive species will be lower when colonizing communities are formed by phylogenetically related rather than unrelated species due to increased competition. Although microbial invasions are involved in both natural and anthropogenic processes, factors affecting the success of microbial invaders are unknown. A biological invasion assay was designed using Trichoderma cf. harzianum as the invader and two types of recipient communities assembled in microcosm assays: communities phylogenetically related to the invader, and communities phylogenetically unrelated to it. Both types of communities were invaded by T. cf. harzianum, and the success of colonization was monitored by qPCR; its effect on the genetic structure of recipient fungal communities was then assessed by DGGE profiles. T. cf. harzianum established itself in both communities, reaching 1000-10,000 times higher copy numbers in the non-related communities. However, invader establishment does not affect the structure of the invaded communities. These results suggest that the composition of recipient communities and their phylogenetic relationship to the invader affect the success of colonization by T. cf. harzianum. While this approach represents a very simplified assay, these microcosms enable an experimental test of Darwin's hypothesis in order to understand the biological invasion process in microbial communities.

Phylogenetic Diversity of Peltigera Cyanolichens and Their Photobionts in Southern Chile and Antarctica

The lichen genus Peltigera has been mainly revised in the Northern Hemisphere, with most species being recorded in Europe and North America. This study assessed the phylogenetic diversity of the mycobionts and cyanobionts of Peltigera cyanolichens collected in Southern Chile and Antarctica, areas in which lichens are extremely diverse but poorly studied. The operational taxonomic units (OTUs) of each symbiont were defined by analyzing the genetic diversity of the LSU and SSU rDNA of the mycobionts and cyanobionts, respectively, and a phylogenetic approach was used to relate these OTUs with sequences previously reported for Peltigera and Nostoc. Among the 186 samples collected, 8 Peltigera and 15 Nostoc OTUs were recognized, corresponding to sections Peltigera, Horizontales, and Polydactylon, in the case of the mycobionts, and to the Nostoc clade II, in the case of the cyanobionts. Since some of the OTUs recognized in this study had not previously been described in these areas, our results suggest that the diversity of Peltigera reported to date in the regions studied using traditional morphological surveys has underestimated the true diversity present; therefore, further explorations of these areas are recommended.

Designing a SCAR molecular marker for monitoring Trichoderma cf. harzianum in experimental communities

Several species of the fungal genus Trichoderma establish biological interactions with various micro- and macro-organisms. Some of these interactions are relevant in ecological terms and in biotechnological applications, such as biocontrol, where Trichoderma could be considered as an invasive species that colonizes a recipient community. The success of this invasion depends on multiple factors, which can be assayed using experimental communities as study models. Therefore, the aim of this work is to develop a species-specific sequence-characterized amplified region (SCAR) marker to monitor the colonization and growth of T. cf. harzianum when it invades experimental communities. For this study, 16 randomly amplified polymorphic DNA (RAPD) primers of 10-mer were used to generate polymorphic patterns, one of which generated a band present only in strains of T. cf. harzianum. This band was cloned, sequenced, and five primers of 20-23 mer were designed. Primer pairs 2F2/2R2 and 2F2/2R3 successfully and specifically amplified fragments of 278 and 448 bp from the T. cf. harzianum BpT10a strain DNA, respectively. Both primer pairs were also tested against the DNA from 14 strains of T. cf. harzianum and several strains of different fungal genera as specificity controls. Only the DNA from the strains of T. cf. harzianum was successfully amplified. Moreover, primer pair 2F2/2R2 was assessed by quantitative real-time polymerase chain reaction (PCR) using fungal DNA mixtures and DNA extracted from fungal experimental communities as templates. T. cf. harzianum was detectable even when as few as 100 copies of the SCAR marker were available or even when its population represented only 0.1% of the whole community.

Genetic diversity of terricolous Peltigera cyanolichen communities in different conservation states of native forest from southern Chile

Decreasing quality of forest habitats is among the major factors leading to a loss of epiphytic lichen diversity. However, there is little information about how this factor influences the diversity of terricolous lichens, which do not grow over living trees and could be less susceptible to such disturbances. In this work we describe the genetic diversity of Peltigera terricolous cyanolichens and their cyanobiont (Nostoc) from three habitats at the Karukinka Natural Park (Tierra del Fuego, southern Chile), which represent different conservation states: native mature-forest (low disturbance intensity), native young-forest (medium disturbance intensity) and grassland (high disturbance intensity). In both forest contexts, a higher diversity and a higher number of unique OTUs (operational taxonomic units) were found. In contrast, in the grassland, the diversity was lower and the Peltigera species were mostly cosmopolitan. The presence of unique OTUs and the higher diversity of lichens in native forest areas highlight the importance of their preservation, indicating that decreasing forest quality also has a negative impact on terricolous lichens diversity.

Environmental context shapes the bacterial community structure associated to Peltigera cyanolichens growing in Tierra del Fuego, Chile

The structure of the associated bacterial community of bipartite cyanolichens of the genus Peltigera from three different environmental contexts in the Karukinka Natural Park, Tierra del Fuego, Chile, was assessed. The sampling sites represent different habitat contexts: mature native forest, young native forest and grassland. Recently it has been determined that the bacterial community associated to lichens could be highly structured according to the mycobiont or photobiont identities, to the environmental context and/or to the geographic scale. However, there are some inconsistencies in defining which of these factors would be the most significant on determining the structure of the microbial communities associated with lichens, mainly because most studies compare the bacterial communities between different lichen species and/or with different photobiont types (algae vs. cyanobacteria). In this work bipartite lichens belonging to the same genus (Peltigera) symbiotically associated with cyanobacteria (Nostoc) were analyzed by TRFLP to determine the structure of the bacterial community intimately associated with the lichen thalli and the one present in the substrate where they grow. The results indicate that the bacterial community intimately associated differs from the one of the substrate, being the former more influenced by the environmental context where the lichen grows.

Comparison of water availability effect on ammonia-oxidizing bacteria and archaea in microcosms of a Chilean semiarid soil

Water availability is the main limiting factor in arid soils; however, few studies have examined the effects of drying and rewetting on nitrifiers from these environments. The effect of water availability on the diversity of ammonia-oxidizing bacteria (AOB) and archaea (AOA) from a semiarid soil of the Chilean sclerophyllous matorral was determined by microcosm assays. The addition of water every 14 days to reach 60% of the WHC significantly increased nitrate content in rewetted soil microcosms (p < 0.001). This stimulation of net nitrification by water addition was inhibited by acetylene addition at 100 Pa. The composition of AOA and AOB assemblages from the soils microcosms was determined by clone sequencing of amoA genes (A-amoA and B-amoA, respectively), and the 16S rRNA genes specific for β-proteobacteria (beta-amo). Sequencing of beta-amo genes has revealed representatives of Nitrosomonas and Nitrosospira while B-amoA clones consisted only of Nitrosospira sequences. Furthermore, all clones from the archaeal amoA gene library (A-amoA) were related to “mesophilic Crenarchaeota” sequences (actually, reclassified as the phylum Thaumarchaeota). The effect of water availability on both microbial assemblages structure was determined by T-RFLP profiles using the genetic markers amoA for archaea, and beta-amo for bacteria. While AOA showed fluctuations in some T-RFs, AOB structure remained unchanged by water pulses. The relative abundance of AOA and AOB was estimated by the Most Probable Number coupled to Polymerase Chain Reaction (MPN-PCR) assay. AOB was the predominant guild in this soil and higher soil water content did not affect their abundance, in contrast to AOA, which slightly increased under these conditions. Therefore, these results suggest that water addition to these semiarid soil microcosms could favor archaeal contribution to ammonium oxidation.

Diversity and activity of denitrifiers of chilean arid soil ecosystems

The Chilean sclerophyllous matorral is a Mediterranean semiarid ecosystem affected by erosion, with low soil fertility, and limited by nitrogen. However, limitation of resources is even more severe for desert soils such as from the Atacama Desert, one of the most extreme arid deserts on Earth. Topsoil organic matter, nitrogen and moisture content were significantly higher in the semiarid soil compared to the desert soil. Although the most significant loss of biologically preferred nitrogen from terrestrial ecosystems occurs via denitrification, virtually nothing is known on the activity and composition of denitrifier communities thriving in arid soils. In this study we explored denitrifier communities from two soils with profoundly distinct edaphic factors. While denitrification activity in the desert soil was below detection limit, the semiarid soil sustained denitrification activity. To elucidate the genetic potential of the soils to sustain denitrification processes we performed community analysis of denitrifiers based on nitrite reductase (nirK and nirS) genes as functional marker genes for this physiological group. Presence of nirK-type denitrifiers in both soils was demonstrated but failure to amplify nirS from the desert soil suggests very low abundance of nirS-type denitrifiers shedding light on the lack of denitrification activity. Phylogenetic analysis showed a very low diversity of nirK with only three distinct genotypes in the desert soil which conditions presumably exert a high selection pressure. While nirK diversity was also limited to only few, albeit distinct genotypes, the semiarid matorral soil showed a surprisingly broad genetic variability of the nirS gene. The Chilean matorral is a shrub land plant community which form vegetational patches stabilizing the soil and increasing its nitrogen and carbon content. These islands of fertility may sustain the development and activity of the overall microbial community and of denitrifiers in particular.

Rhizosphere microbial community structure at different maize plant growth stages and root locations

The aims of the present work were (1) to determine the influence of plant growth stages on the population size of culturable bacteria and fungi associated with rhizoplane and endo-rhizosphere of maize grown in field and (2) to establish the community structure of total culturable bacteria and fungi. Density, diversity and community structure of culturable rhizoplane and endo-rhizosphere populations at different maize plant growth stages were estimated. Plant development did not have influence on total culturable microflora density but it selectively influenced some bacterial and fungal groups present in the rhizosphere. However, the microbial community structure changed markedly over time. This knowledge is relevant for exploring endophytic rhizobacteria potential in the promotion of plant-growth, protection against pathogens and to detect perturbations in natural agro ecosystems.

In vitro influence of bacterial mixtures on Fusarium verticillioides growth and fumonisin B1 production: effect of seeds treatment on maize root colonization

AIMS

Enterobacter cloacae, Microbacterium oleovorans, Pseudomonas solanacearum and Bacillus subtilis were investigated in order to evaluate: (i) the inoculum size of two bacterial mixtures on Fusarium verticillioides growth and fumonisin B1 production in vitro at different water activities and (ii) the efficacy of a seed treatment with the best bacterial mixture on F. verticillioides root colonization in greenhouse studies.

METHODS AND RESULTS

The influence of bacterial mixtures (1 = E. cloacae and M. oleovorans and 2 = P. solanacearum and B. subtilis) to antagonize 13 F. verticillioides strains at different inoculum concentrations (10(8), 10(9) and 10(10) cells ml(-1)) and water activities (0.937, 0.955 and 0.982 aW) were examined. Antibiosis, growth rate and fumonisin B1 production were determined. Bacterial mixture 1 proved to exert the most effective control. Seed treatment with mixture 1 at 10(8) cells ml(-1) had the best inhibitory effect on F. verticillioides root colonization.

CONCLUSIONS

These results suggest that the combination E. cloacae and M. oleovorans has the potential for the biological control of F. verticillioides as a maize seed inoculant.

SIGNIFICANCE AND IMPACT OF THE STUDY

The application of this knowledge contributes to prevent the vertical transmission of F. verticillioides.

Biocontrol of Bacillus subtilis against Fusarium verticillioides in vitro and at the maize root level

Bacillus species as a group offer several advantages over other bacteria for protection against root pathogens because of their ability to form endospores, and because of the broad-spectrum activity of their antibiotics. The objectives of this work were to determine the ability of strains of Bacillus to inhibit Fusarium verticillioides growth and fumonisin B(1) accumulation in vitro, and to evaluate the ability of the best bacterium for preventing rhizosphere and endorhizosphere colonization by F. verticillioides. Bacterial populations from the maize rhizoplane were obtained, and the capacity of ten Bacillus strains to inhibit fungal growth and fumonisin B(1) accumulation in vitro was assayed. According to these results, B. subtilis CE1 was selected as the best antagonist for testing maize root colonization of F. verticillioides. Bacillus subtilis CE1 at 10(8) and 10(7) CFU ml(-1) inocula was able to reduce rhizoplane and endorhizosphere colonization of F. verticillioides in greenhouse trials. The strain B. subtilis CE1 could be a potential biological control agent against F. verticillioides at the root level.

Altered ganglioside composition in virally transformed rat embryo fibroblasts

The composition of gangliosides was examined in a normal rat embryo fibroblast cell line (REF52) and in two viral transformants: a polyoma transformant (REF52-PyMLV) and a simian viral 40 transformant (REF52-SV40). The distribution of gangliosides in the cell lines was determined using gas-liquid chromatography and high-performance thin-layer chromatography. N-acetylneuraminic acid was the predominant sialic acid species detected in the three cell lines. The total ganglioside concentration (microgram/100 mg dry weight of cells) in the normal, PyMLV, and SV40 lines was 144.7 +/- 10.4, 153.8 +/- 9.2, and 86.1 +/- 6.8, respectively. Gangliosides GM3, GM2, GM1, and GD1a were the major species in the normal and transformed lines. The distribution of these gangliosides, however, differed markedly between the normal and the transformed lines and also between the transformed lines themselves. The transformed cells also differed from the normal cells in growth rate, morphology, and social behavior. The cell line with highest GM3 content (PyMLV) formed islands, whereas the normal and SV40 cell lines, which had lower GM3 levels, grew as monolayers. The findings suggest that PyMLV and SV40 transformation can have multiple and different effects on cellular ganglioside distribution and growth behavior.

Growth factor requirements of normal and polyomavirus middle T gene transformed REF52 cells in serum-free medium: indications of a reduced vasopressin requirement and its relationship to the control of phosphatidylinositol metabolism

The growth factor requirement of normal and polyomavirus middle T gene transformed REF52 cells was studied in serum-free medium in an attempt to elucidate the possible linkage between an altered growth factor requirement and one or more altered physiological properties of the transformed cells. For optimal growth, REF52 cells required vasopressin, epidermal growth factor (EGF), high-density lipoprotein (HDL), hydrocortisone, insulin, transferrin, and fibronectin. Deletion of vasopressin or hydrocortisone from the medium resulted in a 50 to 60% reduction in cell growth and the deletion of HDL, transferrin, or the combination of EGF and vasopressin led to an 80 to 90% growth retardation. The same medium supported the growth of the transformed variant (PyMLV-REF52) at a rate comparable to that of 10% serum, and deletion of hydrocortisone, vasopressin, or the combination of EGF and vasopressin had virtually no effect on PyMLV-REF52 cell growth. In vasopressin-deleted medium, vasopressin elicited a rapid increase of intracellular inositol phosphate levels in REF52 cells and the control of phosphoinositide turnover was strictly regulated. In contrast, both cell proliferation and intracellular inositol phosphate levels of PyMLV-REF52 cells were not affected by vasopressin treatment under identical culture conditions, and control of phosphoinositide metabolism was lost. Thus, a correlation may exist between the trigger of a mitogenic signal and the stimulation of the phosphoinositol pathway by vasopressin in REF52 cells and this relationship was disrupted in PyMLV-REF52 cells.

The penetration of formulated Guthion spray through selected fabrics

A technique for comparing pesticide penetration through fabric was devised. It involved passing fabric swatches through a controlled spray system and measuring the pesticide residue transferring on and through the tested fabric. Six variations in fabric were selected for testing: 100% cotton woven chambray, Scotch-guard treated chambray, Tyvek, Crowntex, and two variations of Gore Tex. Guthion (azinphos-methyl) was chosen as the insecticide for controlled use in this experiment because of its widespread use and relatively high toxicity. Gas chromatographic analysis of the amount of Guthion transferred through the outer fabric was made by the use of analysis of variance (ANOVA) and Duncan's multiple range test. The ANOVA for experiment replication showed no significant difference among the replications of each fabric. The treatment ANOVA was highly significant at the 0.01 level. Duncan's multiple range test further analyzed the differences in the treatment, and three groups were found to be significantly different from each other. The two types of Gore Tex, Tyvek and Crowntex comprised the group permitting the least penetration Scotch-guard treated chambray followed, and untreated chambray allowed the greatest penetration.

Conversion of glutathione to glutathione disulfide, a catalytic function of gamma-glutamyl transpeptidase

A purification procedure, based on that previously used for rat kidney gamma-glutamyl transpeptidase, was used for the purification of glutathione oxidase (which converts glutathione to gluthathione disulfide). The two activities co-purified, the ratio of the activities remaining constant through all steps of the isolation procedure. The purified enzyme was separable into 12 isozymic species by isoelectric focusing. All 12 isozymes exhibited a constant ratio of transpeptidase to glutathione oxidase activities, strongly supporting the conclusion that conversion of glutathione to glutathione disulfide is a catalytic function of gamma-glutamyl transpeptidase. Modulation of oxidase activity by inhibitors and acceptor substrates of transpeptidase is discussed in relation to the possible glutathione binding sites involved in gamma-glutamyl transfer and oxidase activities of the enzyme.

Prognostic value of a persistently positive technetium-99m stannous pyrophosphate myocardial scintigram after myocardial infarction

Technetium-99m stannous pyrophosphate myocardial scintigrams were obtained in 138 clinically stable patients 32.7 +/- 47.3 weeks (range 6 to 260) after acute myocardial infarction. Of the 138 patients, 74 (54 percent) had a persistently positive scintigram. Patients with such a scintigram were more likely to have severe angina pectoris, compensated congestive heart failure, anterior location of acute myocardial infarction, Q waves and S-T segment elevation in the electrocardiograms, cardiomegaly, left ventricular dyssynergy (dyskinesia or global dyssynergy), and an ejection fraction of less than 50 percent. During a follow-up period of 11.6 +/- 6.9 months after scintigraphy, 42 percent of the patients with a persistently positive scintigram had either a cardiac death, a nonfatal myocardial infarction, unstable angina pectoris or decompensated congestive heart failure compared with 13 percent of the patients with a negative scintigram (P less than 0.001). Of the 14 patients with cardiac death, 13 (93 percent) had a persistently positive scintigram. A persistently positive scintigram not only was the best single predictor of cardiac death and combined end points, but also added significantly to the predictive ability of the other clinical variables, including age, location of acute myocardial infarct, clinical status, electrocardiographic findings, and chest X-ray findings. It is concluded that technetium-99m stannous pyrophosphate myocardial scintigraphy has prognostic value in patients after acute myocardial infarction.

Systolic time intervals before and after cardioversion of atrial fibrillation

The effect of cardioversion of atrial fibrillation to normal sinus rhythm on systolic time intervals was evaluated in 18 patients. Variable results in the left ventricular ejection time index, the external isovolumic contraction time (EICT), and the ratio of the left ventricular ejection time over the EICT (LVET/EICT) and shortening of the preejection period (PEP) (P less than 0.01), the PEP index (PEPI) (P less than 0.005), and the ratio of PEP/LVET (P less than 0.001) occurred at five hours after cardioversion. Six (33 percent) of the 18 patients developed recurrent atrial fibrillation within one month after cardioversion, and the hearts of 12 (67 percent) of the 18 patients remained in sinus rhythm for one to ten months after cardioversion. Four of five patients in whom the EICT became worse at five hours after cardioversion and two of two patients in whom the PEPI became worse at five hours after cardioversion developed recurrent atrial fibrillation. The EICT and PEPI at five hours after cardioversion may be helpful in predicting subsequent recurrence of atrial fibrillation.

Fasting decreases triiodothyronine receptor capacity

Fasting decreases the ratio of hepatic nuclear to serum triiodothyronine (T3) by diminishing the binding capacity of nuclear T3 receptors. In combination with the lower serum T3 concentration caused by fasting, the decrease in receptor content results in a marked decrease in nuclear T3-receptor complexes. The changes in T3 receptor content and circulating T3 in fasted animals appear to be independent synergistic adaptations for caloric conservation in the fasted state. Unlike changes in hormonal level, the modification of nuclear receptor content provides a mechanism that may protect cells with a low caloric reserve independently of the metabolic status of the whole animal.

Correlation of mean pulmonary artery wedge pressure, left atrial dimention, and PTF-V1 in patients with acute myocardial infarction

The mean pulmonary artery wedge pressure (PAWP), left atrial dimension (LAD) by echocardiography, and PTF-V1 in the electrocardiogram were correlated with each other in 16 patients with acute myocardial infarction in the control period and after therapeutic intervention with either Dextran or furosemide and/or nitroprusside. No significant correlation was found between a normal control PAWP and the LAD. An increased control PAWP correlated well with an increased LAD (r = 0.98). No significant correlation was found between the LAD and the PAWP whether normal or elevated after therapeutic intervention. No significant correlation was found between the PAWP whether normal or elevated and the PTF-V1. No significant correlation was found between the LAD and the PTF-V1. We conclude in acute myocardial infarction 1) the PTF-V1 is not useful in assessing PAWP before or after therapeutic intervention, 2) the LAD correlates poorly with a normal control PAWP but correlates well with an elevated control PAWP, and 3) the LAD cannot be used to assess PAWP after therapeutic intervention.

High reversion of atrial flutter to sinus rhythm after atrial pacing in patients with pulmonary disease

The effect of atrial pacing on atrial flutter was evaluated in 36 consecutive episodes in 33 patients. Seventeen episodes occurred in a pulmonary setting, 14 of these in patients with chronic pulmonary disease. Twenty-four (67 percent) of the 36 episodes converted to sinus rhythm within one minute after atrial pacing. In nine (25 percent) of the 36 episodes, atrial fibrillation developed after atrial pacing. Atrial flutter was not affected by atrial pacing in three (8 percent) of the 36 episodes.n 12 (86 percent) of the 14 patients with chronic pulmonary disease and in 14 (82 percent) of the 17 patients in whom a pulmonary setting was responsible for atrial flutter, atrial pacing caused conversion to sinus rhythm. Atrial pacing may be the treatment of choice for atrial flutter in patients with pulmonary disease because of its excellent rate of success in this subgroup whose risk of cardioversion is increased by poor anesthetic tolerance and hypoxia.

Effect of ethanol on angina pectoris

We evaluated the effect of ethanol on exercise performance until angina in 12 patients in a double-blind, randomized study. The mean resting heart rate times systolic blood pressure was not changed after Fresca but was increased after 2 ounces of ethanol (P less than 0.001) and after 5 ounces of ethanol (P less than 0.01). Compared to the control periods, the mean exercise time until angina was not different after Fresca but was decreased after 2 ounces of ethanol (P less than 0.001) and after 5 ounces of ethanol (P less than 0.001). Compared to the control periods, the mean maximal ischemic ST-segment depression after angina was not changed after Fresca but was increased after 2 ounces of ethanol (P less than 0.01) and after 5 ounces of ethanol (P less than 0.001). Drinking 5 ounces or 2 ounces of ethanol decreases exercise duration until angina and increases ischemic ST-segment depression after angina.