higher metabolic diversity and activity in their carbon utilization profiles in rhizosphere sediments than the bulk sediments. This baseline information on benthic archaea and their environmental drivers would be useful to assess the impact of anthropogenic and natural pressures on these communities and associated biogeochemical cycles.

Bell, E., Sherry, A., Pilloni, G., Suárez-Suárez, A., Cramm, M.A., Cueto, G., Head, I.M., Hubert, C.R.J., 2020. Sediment cooling triggers germination and sulfate reduction by heat-resistant thermophilic spore-forming bacteria. Environmental Microbiology 22, 456-465.

https://doi.org/10.1111/1462-2920.14866 The Laurentian Great Lakes are a vast, interconnected freshwater system spanning strong physicochemical gradients, thus constituting a powerful natural laboratory for addressing fundamental questions about microbial ecology and evolution. We present a comparative analysis of pelagic microbial communities across all five Laurentian Great Lakes, focusing on Bacterial and Archaeal picoplankton characterized via 16S rRNA amplicon sequencing. We collected samples throughout the water column from the major basins of each lake in Alphaproteobacteria spring and summer over 2 years. Two oligotypes, classified as LD12 ( ) and acI-B1 Actinobacteria ( ), were among the most abundant in every sample. At the same time, microbial communities showed distinct patterns with depth during summer stratification. Deep hypolimnion samples were frequently Chloroflexi dominated by a oligotype that reached up to 19% relative abundance. Stratified surface communities differed between the colder, less productive upper lakes (Superior, Michigan, Huron) and warmer, Actinobacteria more productive lower lakes (Erie, Ontario), in part due to an oligotype (acI-C2) that averag ed 7.7% of sequences in the lower lakes but <0.2% in the upper lakes. Together, our findings suggest that both hydrologic connectivity and local selective pressures shape microbial communities in the Great Lakes and establish a framework for future investigations.

Bellucci, J.J., Whitehouse, M.J., Nemchin, A.A., Snape, J.F., Kenny, G.G., Merle, R.E., Bland, P.A., Benedix, G.K., 2020. Tracing martian surface interactions with the triple O isotope compositions of meteoritic phosphates. Earth and Planetary Science Letters 531, 115977.

http://www.sciencedirect.com/science/article/pii/S0012821X19306697 The triple oxygen isotope compositions of phosphate grains in six martian meteorites have been measured by Secondary Ion Mass Spectrometry (SIMS) and combined together with their chlorine isotope and halogen concentrations have been used to constrain hydrosphere-lithosphere interactions on Mars. These samples include three enriched shergottites (Zagami, Roberts Massif 04262 and Larkman Nunatak 12011), one depleted shergottite (Tissint), an orthopyroxenite (Allan Hills 84001), and a regolith breccia (Northwest Africa 7533). 18 16 18 16 3 The phosphates measured here have a range in δ18O [( O/ O) /( O/ O) -1] × 10 ] from +1.0 to sample Standard +6.8‰ and could be a result of indigenous mantle values, mixing with martian water, or replacement reactions 0.528 taking place on the surface of Mars. Three samples have a Δ17O [δ17O - 1000(1 + δ18O /1000) -1] in equilibrium with the martian mantle (ALH 84001, Tissint, and Zagami), while three samples (LAR 12011, RBT 04262, and NWA7533) have an elevated positive Δ17O outside of analytic al uncertainty of the martian fractionation line (MFL). The phosphates in the latter group also have positive and negative δ37Cl 37 35 37 35 3 [( Cl/ Cl) /( Cl/ Cl) - 1] × 10 ] and enrichments in halogens not seen in the rest of the sample suite. sample standard Perchlorate formation on Earth fractionates Cl in both positive and negative directions and generates a correlated positive Δ17O. Further, perchlorate has been detected in wt% amounts on the martian surface. Thus, these results strongly suggest the presence of multiple Cl isotope reservoirs on the martian surface that have interacted with the samples studied here over the last ca. 2 Ga of geologic time. The weighted average of Δ17O measurements from phosphate grains (n = 13) in NWA7533, which are the explicit result of exchange reactions σ on the martian surface, yields a statistically robust mean value of 1.39 ± 0.19‰ (2 , MSWD= 1.5, p = 0.13). This value likely represents an accurate estimate for an oxidized surface reservoir on Mars.