The nitrogen isotopic composition (δ 15 N) of amino acids is potentially useful as an alternative method for estimating the trophic levels of organisms in food webs. However, because this "amino acid method" has been constructed from the observations of only a few case studies of food-consumer combinations in previous studies, the universality of the approach remains unclear. In this study, we investigated the δ 15 N signatures of amino acids in 17 photoautotrophs and the trophic relationships during four controlled feeding experiments using green algae, zooplankton, and fish. The results are consistent with those reported in previous studies, implying that the amino acid method can be applied to a variety of organisms. From these and previously published data, we estimate the two factors (β, isotope differences among amino acids in primary producers; Δ, the 15 N-enrichment factor for each trophic level) required to calculate the trophic level. Based on the lowest error (1σ = 0.12) in the estimated trophic level, we conclude that a comparison of the δ 15 N values for glutamic acid and phenylalanine is most useful in calculating precise estimates of the trophic level, using the following equation: trophic level (TL Glu/Phe ) = (δ 15 N Glu -δ 15 N Phe -3.4)/7.6 + 1.

Setting out to isolate uncultivated deep marine sediment microorganisms, we engineered and operated a methane-fed continuous-flow bioreactor system for more than 2,000 days to enrich such organisms from anaerobic marine methane-seep sediments 15 (Supplementary Note 1). We successfully enriched many phylogenetically diverse yetto-be cultured microorganisms, including Asgard archaea members (Loki-, Heimdall-and Odinarchaeota) 15. For further enrichment and isolation, samples of the bioreactor community were inoculated in glass tubes with simple substrates and basal medium. After approximately one year, we found faint cell turbidity in a culture containing casamino acids supplemented with four bacteria-suppressing antibiotics (Supplementary Note 2) that was incubated at 20 °C. Clone librarybased small subunit (SSU) rRNA gene analysis revealed a simple community that contained Halodesulfovibrio and a small population of Lokiarchaeota (Extended Data Table 1). In pursuit of this archaeon, which we designated strain MK-D1, we repeated subcultures when MK-D1 reached maximum cell densities as measured by quantitative PCR (qPCR). This approach gradually enriched the archaeon, which has an extremely slow growth rate and low cell yield (Fig. 1a). The culture consistently had a 30-60-day lag phase and required more

A deep sleep in coal beds Deep below the ocean floor, microorganisms from forest soils continue to thrive. Inagaki et al. analyzed the microbial communities in several drill cores off the coast of Japan, some sampling more than 2 km below the seafloor (see the Perspective by Huber). Although cell counts decreased with depth, deep coal beds harbored active communities of methanogenic bacteria. These communities were more similar to those found in forest soils than in other deep marine sediments. Science , this issue p. 420 ; see also p. 376

Compound-specific isotopic analysis of amino acids (CSIA-AA) has emerged in the last decade as a powerful approach for tracing the origins and fate of nitrogen in ecological and biogeochemical studies. This approach is based on the empirical knowledge that source AAs (i.e., phenylalanine), fractionate 15 N very little (<0.5‰) during trophic transfer, whereas trophic AAs (i.e., glutamic acid), are greatly (~6-8‰) enriched in 15 N during each trophic step. The differential fractionation of these two AA groups can provide a valuable estimate of consumer trophic position that is internally indexed to the baseline δ 15 N value of the integrated food web. In this paper, we critically review the analytical methods for determining the nitrogen isotopic composition of AAs by gas chromatography/isotope-ratio mass spectrometry. We also discuss methodological considerations for accurate trophic position assessment of organisms using CSIA-AA. We then discuss the advantages and challenges of the CSIA-AA approach by examining published studies including trophic position assessment in various ecosystems, reconstruction of ancient human diets, reconstruction of animal migration and environmental variability, and assessment of marine organic matter dynamics. It is clear that the CSIA-AA approach can provide unique insight into the sources, cycling, and trophic modification of organic nitrogen as it flows through systems. However, some uncertainty still exists in how biochemical, physiological, and ecological mechanisms affect isotopic fractionation of trophic AAs. We end this review with a call for continued exploration of the mechanisms of AA isotopic fractionation, through various studies to promote the evolution of the rapidly growing field of CSIA-AA.

The abundance, diversity, activity, and composition of microbial communities in sulfide structures both of active and inactive vents were investigated by culture-independent methods. These sulfide structures were collected at four hydrothermal fields, both on-and off-axis of the back-arc spreading center of the Southern Mariana Trough. The microbial abundance and activity in the samples were determined by analyzing total organic content, enzymatic activity, and copy number of the 16S rRNA gene. To assess the diversity and composition of the microbial communities, 16S rRNA gene clone libraries including bacterial and archaeal phylotypes were constructed from the sulfide structures. Despite the differences in the geological settings among the sampling points, phylotypes related to the Epsilonproteobacteria and cultured hyperthermophilic archaea were abundant in the libraries from the samples of active vents. In contrast, the relative abundance of these phylotypes was extremely low in the libraries from the samples of inactive vents. These results suggest that the composition of microbial communities within sulfide structures dramatically changes depending on the degree of hydrothermal activity, which was supported by statistical analyses. Comparative analyses suggest that the abundance, activity and diversity of microbial communities within sulfide structures of inactive vents are likely to be comparable to or higher than those in active vent structures, even though the microbial community composition is different between these two types of vents. The microbial community compositions in the sulfide structures of inactive vents were similar to those in seafloor basaltic rocks rather than those in marine sediments or the sulfide structures of active vents, suggesting that the microbial community compositions on the seafloor may be constrained by the available energy sources. Our findings provide helpful information for understanding the biogeography, biodiversity and microbial ecosystems in marine environments.

C-type asteroids1 are considered to be primitive small Solar System bodies enriched in water and organics, providing clues to the origin and evolution of the Solar System and the building blocks of life. C-type asteroid 162173 Ryugu has been characterized by remote sensing2–7 and on-asteroid measurements8,9 with Hayabusa2 (ref. 10). However, the ground truth provided by laboratory analysis of returned samples is invaluable to determine the fine properties of asteroids and other planetary bodies. We report preliminary results of analyses on returned samples from Ryugu of the particle size distribution, density and porosity, spectral properties and textural properties, and the results of a search for Ca–Al-rich inclusions (CAIs) and chondrules. The bulk sample mainly consists of rugged and smooth particles of millimetre to submillimetre size, confirming that the physical and chemical properties were not altered during the return from the asteroid. The power index of its size distribution is shallower than that of the surface boulder observed on Ryugu11, indicating differences in the returned Ryugu samples. The average of the estimated bulk densities of Ryugu sample particles is 1,282 ± 231 kg m−3, which is lower than that of meteorites12, suggesting a high microporosity down to the millimetre scale, extending centimetre-scale estimates from thermal measurements5,9. The extremely dark optical to near-infrared reflectance and spectral profile with weak absorptions at 2.7 and 3.4 μm imply a carbonaceous composition with indigenous aqueous alteration, matching the global average of Ryugu3,4 and confirming that the sample is representative of the asteroid. Together with the absence of submillimetre CAIs and chondrules, these features indicate that Ryugu is most similar to CI chondrites but has lower albedo, higher porosity and more fragile characteristics.

34The origin of eukaryotes remains enigmatic. Current data suggests that eukaryotes may 35 have risen from an archaeal lineage known as "Asgard archaea". Despite the eukaryote-36 like genomic features found in these archaea, the evolutionary transition from archaea to 37 eukaryotes remains unclear due to the lack of cultured representatives and corresponding 38 physiological insight. Here we report the decade-long isolation of a Lokiarchaeota-related 39Asgard archaeon from deep marine sediment. The archaeon, "Candidatus 40Prometheoarchaeum syntrophicum strain MK-D1", is an anaerobic, extremely slow-41 growing, small cocci (~550 nm), that degrades amino acids through syntrophy. Although 42 eukaryote-like intracellular complexities have been proposed for Asgard archaea, the 43 isolate has no visible organella-like structure. Ca. P. syntrophicum instead displays 44 morphological complexity -unique long, and often, branching protrusions. Based on 45 cultivation and genomics, we propose an "Entangle-Engulf-Enslave (E 3 ) model" for 46 eukaryogenesis through archaea-alphaproteobacteria symbiosis mediated by the physical 47 complexities and metabolic dependency of the hosting archaeon. 48 49 How did the first eukaryotic cell emerge? So far, among various competing evolutionary 50 models, the most widely accepted are the symbiogenetic models in which an archaeal 51 host cell and an alphaproteobacterial endosymbiont merged to become the first eukaryotic 52 cell 1-4 . Recent metagenomic discovery of Lokiarchaeota (and the Asgard archaea 53 superphylum) led to the theory that eukaryotes originated from an archaeon closely 54 related to Asgard archaea 5,6 . The Asgard archaea genomes encode a repertory of proteins 55 hitherto only found in Eukarya (eukaryotic signature proteins -ESPs), including those 56 involved in membrane trafficking, vesicle formation/transportation, ubiquitin and 57 cytoskeleton formation 6 . Subsequent metagenomic studies have suggested that Asgard 58 archaea have a wide variety of physiological properties, including hydrogen-dependent 59 anaerobic autotrophy 7 , peptide or short-chain hydrocarbon-dependent organotrophy 8-11 60 and rhodopsin-based phototrophy 12,13 . A recent study suggests that an ancient Asgard 61 archaea degraded organic substances and syntrophically handed off reducing equivalents 62 (e.g., hydrogen and electrons) to a bacterial partner, and further proposes a symbiogenetic 63 model for the origin of eukaryotes based on this interaction 14 . However, at present, no 64 single representative of the Asgard archaea has been cultivated and, thus, the physiology 65 and cell biology of this clade remains unclear. In an effort to close this knowledge gap, 66 3 we successfully isolated the first Asgard archaeon and here report the physiological 67 characteristics, potentially key insights into the evolution of eukaryotes. 68 69 Isolation of an Asgard archaeon 70Setting out to isolate uncultivated deep marine sediment microorganisms, we engineered 71 and operated a methane-fed continuous-fl...

The asymmetric synthesis of amino acid precursors from complex organics have been performed. A gaseous mixture of carbon monoxide, ammonia and water (molecules which are among those identified in the interstellar medium) was irradiated with 3.0 MeV protons to obtain amino acid precursors within high-molecular-weight complex organics of up to 3,000 Da. The amino acid precursor products synthesized were then irradiated with right (R-) or left (L-) ultraviolet circularly polarized light (UV-CPL) obtained from a synchrotron radiation (SR) source. Glycine was a predominant product, and number of chiral amino acids including alanine were identified following acid hydrolysis. R-UV-CPL preferentially produced D-alanine, while L-UV-CPL yielded more L-alanine. Enantiomeric excesses (% D - % L) of + 0.44 % and - 0.65 % were obtained by R-UV-CPL and L-UV-CPL, respectively. These results imply that the origins of chirality in meteoritic amino acids could be accounted for by the formation of asymmetric amino acid precursors from extraterrestrial complex organics by CPL in space