A comparative molecular analysis of water‐filled limestone sinkholes in north‐eastern Mexico

Sistema Zacatón in north‐eastern Mexico is host to several deep, water‐filled, anoxic, karstic sinkholes (cenotes). These cenotes were explored, mapped, and geochemically and microbiologically sampled by the autonomous underwater vehicle deep phreatic thermal explorer (DEPTHX). The community structure of the filterable fraction of the water column and extensive microbial mats that coat the cenote walls was investigated by comparative analysis of small‐subunit (SSU) 16S rRNA gene sequences. Full‐length Sanger gene sequence analysis revealed novel microbial diversity that included three putative bacterial candidate phyla and three additional groups that showed high intra‐clade distance with poorly characterized bacterial candidate phyla. Limited functional gene sequence analysis in these anoxic environments identified genes associated with methanogenesis, sulfate reduction and anaerobic ammonium oxidation. A directed, barcoded amplicon, multiplex pyrosequencing approach was employed to compare ～100 000 bacterial SSU gene sequences from water column and wall microbial mat samples from five cenotes in Sistema Zacatón. A new, high‐resolution sequence distribution profile (SDP) method identified changes in specific phylogenetic types (phylotypes) in microbial mats at varied depths; Mantel tests showed a correlation of the genetic distances between mat communities in two cenotes and the geographic location of each cenote. Community structure profiles from the water column of three neighbouring cenotes showed distinct variation; statistically significant differences in the concentration of geochemical constituents suggest that the variation observed in microbial communities between neighbouring cenotes are due to geochemical variation.     

Effect of tree plantations on the functional composition of Odonata species in the highlands of southern Brazil

Marine benthic microalgae are a promising bioindicator of contamination. To date, however, investigations on the microbenthic communities subjected to multiple stressors in natural environments are still very rare. To assess whether the benthic processes of primary production and oxygen consumption, and the structure of active and resting microbenthos, were affected by sediment contamination, seven stations were sampled in different zones of the port of Trieste, subjected to multiple and diffuse contamination, and a reference site in the Marine Reserve of Miramare. No major differences in total abundance of active microbenthos were observed among sites, but the dominance of stress-resistant species and the reduction of more sensitive ones, were registered nearby the main productive activities. The densities of resting microbenthos were higher in polluted areas, and represented by key dinoflagellate species that were clearly linked to contamination. The analysis of similarity applied to both active and resting communities significantly separated the most contaminated stations from the other ones. The photosynthetic capability of active microbenthos did not seem to be affected by contamination. The maximum oxygen consumption rates observed in sediments nearby the productive activities were likely ascribable to high organic C contents and the presence of metals in reduced chemical form.     

The genetics of lantibiotic biosynthesis

The lantibiotics are a rapidly expanding group of biologically active peptides produced by a variety of Gram-positive bacteria, and are so-called because of their content of the thioether amino acids lanthionine and β-methyllanthionine. These amino acids, and indeed a number of other unusual amino acids found in the lantibiotics, arise following post-translational modification of a ribosomally synthesised precursor peptide. A number of genes involved in the biosynthesis of these highly modified peptides have been identified, including genes encoding the precursor peptide, enzymes responsible for specific amino acid modifications, proteases able to remove the leader peptide, ABC-superfamily transport proteins involved in lantibiotic translocation, regulatory proteins controlling lantibiotic biosynthesis and proteins that protect the producing strain from the action of its own lantibiotic. Analysis of these genes and their products is allowing greater understanding of the complex mechanism(s) of the biosynthesis of these unique peptides.