https://doi.org/10.1073/pnas.1916109117 Significance: Phosphate is crucial for the origin of life because it is ubiquitous in key biomolecules. A major issue is that prebiotic syntheses use concentrated phosphate to incorporate phosphate into biomolecules, whereas natural waters are generally phosphate-poor because phosphate reacts with calcium to form low- solubility apatite minerals. Here we show that carbonate-rich lakes can concentrate phosphate to >1 molal levels by locking up calcium in carbonate minerals, which prevents phosphate removal by apatite precipitation. Phosphate-rich lakes may have preferentially formed on the prebiotic Earth because of carbonic acid weathering under CO -rich atmospheres and the absence of microbial phosphate consumption. This specifically points to an 2 origin of life in carbonate-rich lakes, and so defines aqueous conditions that prebiotic chemists should consider. Abstract: Phosphate is central to the origin of life because it is a key component of nucleotides in genetic molecules, phospholipid cell membranes, and energy transfer molecules such as adenosine triphosphate. To incorporate phosphate into biomolecules, prebiotic experiments commonly use molar phosphate concentrations to overcome phosphate's poor reactivity with organics in water. However, phosphate is generally limited to micromolar levels in the environment because it precipitates with calcium as low-solubility apatite minerals. This disparity between laboratory conditions and environmental constraints is an enigma known as 'the phosphate problem.' Here we show that carbonate -rich lakes are a marked exception to phosphate-poor natural ∼ waters. In principle, modern carbonate-rich lakes could accumulate up to 0.1 molal phosphate under steady- state conditions of evaporation and stream inflow because calcium is sequestered into carbonate minerals. This prevents the loss of dissolved phosphate to apatite precipitation. Even higher phosphate concentrations (>1 molal) can form during evaporation in the absence of inflows. On the prebiotic Earth, carbonate-rich lakes were likely abundant and phosphate-rich relative to the present day because of the lack of microbial phosphate sinks and enhanced chemical weathering of phosphate minerals under relatively CO -rich atmospheres. Furthermore, 2 the prevailing CO conditions would have buffered phosphate-rich brines to moderate pH (pH 6.5 to 9). The 2 accumulation of phosphate and other prebiotic reagents at concentration and pH levels relevant to experimental prebiotic syntheses of key biomolecules is a compelling reason to consider carbonate-rich lakes as plausible settings for the origin of life.

Turon, M., Uriz, M.J., 2020. New insights into the archaeal consortium of tropical sponges. Frontiers in Marine Science 6, 789. doi: 10.3389/fmars.2019. 00789.

https://www.frontiersin.org/article/10.3389/fmars.2019.00789 Archaea is a poorly studied domain associated with sponges. Many questions that have been addressed for bacteria still remain largely unknown for archaea. In this study, we analyzed the archaeal communities of 17 tropical sponge species from Nha Trang Bay (Vietnam) using archaea specific primers. We recorded patterns of diversity and spatial stability of these microbial communities and compared the results obtained with the bacterial communities, already reported in our previous study. In our study species, Shannon diversity was always lower for archaeal than for bacterial communities. The differences in alpha diversity as well as the presence of indicator phyla reported for the bacterial domain in High Microbial Abundance (HMA) and Low Microbial Abundance (LMA) could not be confirmed for the archaeal communities. Host identity was the main factor structuring the archaeal assemblages. Sponge archaea core was formed by few but very abundant ZOTUs, which contribute with a high proportion to the relative archaea abundance. The inclusion of the obtained sequences into phylogenetic trees allowed finding out whether or not they belonged to the so-called sponge Thaumarchaeota Euryarchaeota clusters (SC). Our results showed that most of the and sequences were more closely related to environmental samples than to SC, suggesting that they might be acquired from the seawater, Woesarchaeota which need to be verified. However, representatives of , which were major members of the archaea microbiome of two sponge species, formed a monophyletic tree, distantly related to any known environmental sequence.

Vaks, A., Mason, A.J., Breitenbach, S.F.M., Kononov, A.M., Osinzev, A.V., Rosensaft, M., Borshevsky, A., Gutareva, O.S., Henderson, G.M., 2020. Palaeoclimate evidence of vulnerable permafrost during times of low sea ice. Nature 577, 221-225.