Spatial Distribution and Molecular Diversity of Archaeal Communities in the Extreme Hypersaline Meromictic Brâncoveanu Lake (Transylvanian Basin,Romania)

Dating from the Middle Miocene, the massive halite deposits lying beneath the Transylvanian Basin (Central Romania) have been valuable mineral resources quarried for millennia. Among the numerous hypersaline pit lakes that resulted from this mining, Brâncoveanu Lake is unique by its extreme salinity. Assessment of physicochemical variables, water chemistry and trophic status indicated that Brâncoveanu Lake is a permanently stratified, pH-neutral, NaCl-rich and eutrophied system. We investigated the abundance, molecular diversity and vertical distribution of archaeal community by culture-independent approaches. Additionally, the most relevant environmental parameters shaping the archaeal community composition were evaluated by statistical methods. Archaea appeared to largely outnumber Bacteria; altogether the great prevalence of Halobacteriaceae-related sequences could imply a major contribution of this group to the biogeochemical carbon turnover. The fairly distinct composition of archaeal communities reflects the lake's physicochemical stratification. Among the limnological factors, salinity and oxygen showed a significant impact on determining the composition and structure of archaeal assemblages. Furthermore, Brâncoveanu Lake might harbor novel microorganisms such as members of the recently described phylum Nanohaloarchaea. Overall, this study reported the occurrence of halophilic Archaea in a little explored hydrogeochemical system and provided a better insight into geomicrobiology of meromictic hypersaline pit lakes.     

Structural integrity of the Golgi is temperature sensitive in conditional-lethal mutants with no detectable GM130

At 39.5 °C in the temperature-sensitive, conditional-lethal mutant ldlG, glycoprotein processing is disrupted and secretion is blocked. The ultrastructure of the Golgi apparatus in ldlG cells was examined using immunofluorescence and immunoelectron microscopy. At 34 °C the structure of the Golgi apparatus was normal, whereas after incubation at 39.5 °C for 12 h it disassembled into dispersed vesicles. These reassembled into stacks when cells were returned to 34 °C for 6 h. At both 34 and 39.5 °C, all Golgi markers examined were present at wild-type levels except GM130, which was undetectable (<5% of control). Transfection with GM130 corrected the mutant phenotypes. Although the endogenous gene encoding NSF is apparently normal in ldlG cells, all mutant phenotypes were corrected by transfection with NSF, suggesting that NSF functioned as an extragenic suppressor. These findings provide additional support for a role of GM130 in determining the properties of the Golgi apparatus and for NSF in influencing GM130 stability and function. They also suggest that, at 34 °C, detectable levels of GM130 are not required for normal Golgi morphology and function, but that GM130 – or a GM130-dependent protein(s) – does play a role in protecting the Golgi, and thus the cells, from stress at higher temperatures .     

A Highlights from MBoC Selection: PTP1B-dependent regulation of receptor tyrosine kinase signaling by the actin-binding protein Mena

During breast cancer progression, alternative mRNA splicing produces functionally distinct isoforms of Mena, an actin regulator with roles in cell migration and metastasis. Aggressive tumor cell subpopulations express Mena^INV, which promotes tumor cell invasion by potentiating EGF responses. However, the mechanism by which this occurs is unknown. Here we report that Mena associates constitutively with the tyrosine phosphatase PTP1B and mediates a novel negative feedback mechanism that attenuates receptor tyrosine kinase signaling. On EGF stimulation, complexes containing Mena and PTP1B are recruited to the EGFR, causing receptor dephosphorylation and leading to decreased motility responses. Mena also interacts with the 5′ inositol phosphatase SHIP2, which is important for the recruitment of the Mena-PTP1B complex to the EGFR. When Mena^INV is expressed, PTP1B recruitment to the EGFR is impaired, providing a mechanism for growth factor sensitization to EGF, as well as HGF and IGF, and increased resistance to EGFR and Met inhibitors in signaling and motility assays. In sum, we demonstrate that Mena plays an important role in regulating growth factor–induced signaling. Disruption of this attenuation by Mena^INV sensitizes tumor cells to low–growth factor concentrations, thereby increasing the migration and invasion responses that contribute to aggressive, malignant cell phenotypes.     

Contrasting taxonomic stratification of microbial communities in two hypersaline meromictic lakes

Hypersaline meromictic lakes are extreme environments in which water stratification is associated with powerful physicochemical gradients and high salt concentrations. Furthermore, their physical stability coupled with vertical water column partitioning makes them important research model systems in microbial niche differentiation and biogeochemical cycling. Here, we compare the prokaryotic assemblages from Ursu and Fara Fund hypersaline meromictic lakes (Transylvanian Basin, Romania) in relation to their limnological factors and infer their role in elemental cycling by matching taxa to known taxon-specific biogeochemical functions. To assess the composition and structure of prokaryotic communities and the environmental factors that structure them, deep-coverage small subunit (SSU) ribosomal RNA (rDNA) amplicon sequencing, community domain-specific quantitative PCR and physicochemical analyses were performed on samples collected along depth profiles. The analyses showed that the lakes harbored multiple and diverse prokaryotic communities whose distribution mirrored the water stratification patterns. Ursu Lake was found to be dominated by Bacteria and to have a greater prokaryotic diversity than Fara Fund Lake that harbored an increased cell density and was populated mostly by Archaea within oxic strata. In spite of their contrasting diversity, the microbial populations indigenous to each lake pointed to similar physiological functions within carbon degradation and sulfate reduction. Furthermore, the taxonomy results coupled with methane detection and its stable C isotope composition indicated the presence of a yet-undescribed methanogenic group in the lakes'' hypersaline monimolimnion. In addition, ultrasmall uncultivated archaeal lineages were detected in the chemocline of Fara Fund Lake, where the recently proposed Nanohaloarchaeota phylum was found to thrive.     

Spatio-temporal insights into microbiology of the freshwater-to-hypersaline,oxic-hypoxic-euxinic waters of Ursu Lake

Ursu Lake is located in the Middle Miocene salt deposit of Central Romania. It is stratified, and the water column has three distinct water masses: an upper freshwater-to-moderately saline stratum (0–3 m), an intermediate stratum exhibiting a steep halocline (3–3.5 m), and a lower hypersaline stratum (4 m and below) that is euxinic (i.e. anoxic and sulphidic). Recent studies have characterized the lake's microbial taxonomy and given rise to intriguing ecological questions. Here, we explore whether the communities are dynamic or stable in relation to taxonomic composition, geochemistry, biophysics, and ecophysiological functions during the annual cycle. We found: (i) seasonally fluctuating, light-dependent communities in the upper layer (≥0.987–0.990 water-activity), a stable but phylogenetically diverse population of heterotrophs in the hypersaline stratum (water activities down to 0.762) and a persistent plate of green sulphur bacteria that connects these two (0.958–0.956 water activity) at 3–3.5 to 4 m; (ii) communities that might be involved in carbon- and sulphur-cycling between and within the lake's three main water masses; (iii) uncultured lineages including Acetothermia (OP1), Cloacimonetes (WWE1), Marinimicrobia (SAR406), Omnitrophicaeota (OP3), Parcubacteria (OD1) and other Candidate Phyla Radiation bacteria, and SR1 in the hypersaline stratum (likely involved in the anaerobic steps of carbon- and sulphur-cycling); and (iv) that species richness and habitat stability are associated with high redox-potentials. Ursu Lake has a unique and complex ecology, at the same time exhibiting dynamic fluctuations and stability, and can be used as a modern analogue for ancient euxinic water bodies and comparator system for other stratified hypersaline systems.