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<jats:p> Cells of most bacterial species are around 2 micrometers in length, with some of the largest specimens reaching 750 micrometers. Using fluorescence, x-ray, and electron microscopy in conjunction with genome sequencing, we characterized <jats:italic>Candidatus</jats:italic> ( <jats:italic>Ca.</jats:italic> ) Thiomargarita magnifica, a bacterium that has an average cell length greater than 9000 micrometers and is visible to the naked eye. These cells grow orders of magnitude over theoretical limits for bacterial cell size, display unprecedented polyploidy of more than half a million copies of a very large genome, and undergo a dimorphic life cycle with asymmetric segregation of chromosomes into daughter cells. These features, along with compartmentalization of genomic material and ribosomes in translationally active organelles bound by bioenergetic membranes, indicate gain of complexity in the <jats:italic>Thiomargarita</jats:italic> lineage and challenge traditional concepts of bacterial cells. </jats:p>

<jats:p>Comparative studies of mortality in the wild are necessary to understand the evolution of aging; yet, ectothermic tetrapods are underrepresented in this comparative landscape, despite their suitability for testing evolutionary hypotheses. We present a study of aging rates and longevity across wild tetrapod ectotherms, using data from 107 populations (77 species) of nonavian reptiles and amphibians. We test hypotheses of how thermoregulatory mode, environmental temperature, protective phenotypes, and pace of life history contribute to demographic aging. Controlling for phylogeny and body size, ectotherms display a higher diversity of aging rates compared with endotherms and include phylogenetically widespread evidence of negligible aging. Protective phenotypes and life-history strategies further explain macroevolutionary patterns of aging. Analyzing ectothermic tetrapods in a comparative context enhances our understanding of the evolution of aging.</jats:p>

<jats:p>Is senescence inevitable and universal for all living organisms, as evolutionary theories predict? Although evidence generally supports this hypothesis, it has been proposed that certain species, such as turtles and tortoises, may exhibit slow or even negligible senescence—i.e., avoiding the increasing risk of death from gradual deterioration with age. In an extensive comparative study of turtles and tortoises living in zoos and aquariums, we show that ~75% of 52 species exhibit slow or negligible senescence. For ~80% of species, aging rates are lower than those in modern humans. We find that body weight positively relates to adult life expectancy in both sexes, and sexual size dimorphism explains sex differences in longevity. Unlike humans and other species, we show that turtles and tortoises may reduce senescence in response to improvements in environmental conditions.</jats:p>

<jats:p>Oxidative DNA damage is recognized by 8-oxoguanine (8-oxoG) DNA glycosylase 1 (OGG1), which excises 8-oxoG, leaving a substrate for apurinic endonuclease 1 (APE1) and initiating repair. Here, we describe a small molecule (TH10785) that interacts with the phenylalanine-319 and glycine-42 amino acids of OGG1, increases the enzyme activity 10-fold, and generates a previously undescribed β,δ-lyase enzymatic function. TH10785 controls the catalytic activity mediated by a nitrogen base within its molecular structure. In cells, TH10785 increases OGG1 recruitment to and repair of oxidative DNA damage. This alters the repair process, which no longer requires APE1 but instead is dependent on polynucleotide kinase phosphatase (PNKP1) activity. The increased repair of oxidative DNA lesions with a small molecule may have therapeutic applications in various diseases and aging.</jats:p>

<jats:p> Class 2 CRISPR effectors Cas9 and Cas12 may have evolved from nucleases in IS200/IS605 transposons. IscB is about two-fifths the size of Cas9 but shares a similar domain organization. The associated ωRNA plays the combined role of CRISPR RNA (crRNA) and trans-activating CRISPR RNA <jats:bold>(</jats:bold> tracrRNA) to guide double-stranded DNA (dsDNA) cleavage. Here we report a 2.78-angstrom cryo–electron microscopy structure of IscB-ωRNA bound to a dsDNA target, revealing the architectural and mechanistic similarities between IscB and Cas9 ribonucleoproteins. Target-adjacent motif recognition, R-loop formation, and DNA cleavage mechanisms are explained at high resolution. ωRNA plays the equivalent function of REC domains in Cas9 and contacts the RNA-DNA heteroduplex. The IscB-specific PLMP domain is dispensable for RNA-guided DNA cleavage. The transition from ancestral IscB to Cas9 involved dwarfing the ωRNA and introducing protein domain replacements. </jats:p>

<jats:p>Catalyst-controlled site-selective activation of β- and γ-methylene carbon-hydrogen (C–H) bonds of free carboxylic acids is a long-standing challenge. Here we show that, with a pair of palladium catalysts assembled with quinoline-pyridone ligands of different chelate ring sizes, it is possible to perform highly site-selective monolactonization reactions with a wide range of dicarboxylic acids, generating structurally diverse and synthetically useful γ- and δ-lactones via site-selective β- or γ-methylene C–H activation. The remaining carboxyl group serves as a versatile linchpin for further synthetic applications, as demonstrated by the total synthesis of two natural products, myrotheciumone A and pedicellosine, from abundant dicarboxylic acids.</jats:p>

<jats:p>Global-scale surveys of plankton communities using “omics” techniques have revolutionized our understanding of the ocean. Lipidomics has demonstrated the potential to add further essential insights on ocean ecosystem function but has yet to be applied on a global scale. We analyzed 930 lipid samples across the global ocean using a uniform high-resolution accurate-mass mass spectrometry analytical workflow, revealing previously unknown characteristics of ocean planktonic lipidomes. Focusing on 10 molecularly diverse glycerolipid classes, we identified 1151 distinct lipid species, finding that fatty acid unsaturation (i.e., number of carbon-carbon double bonds) is fundamentally constrained by temperature. We predict substantial declines in the essential fatty acid eicosapentaenoic acid over the next century, which are likely to have serious deleterious effects on economically critical fisheries.</jats:p>

<jats:p>Changes in woody biomass over centuries to millennia are poorly known, leaving unclear the magnitude of terrestrial carbon fluxes before industrial-era disturbance. Here, we statistically reconstructed changes in woody biomass across the upper Midwestern region of the United States over the past 10,000 years using a Bayesian model calibrated to preindustrial forest biomass estimates and fossil pollen records. After an initial postglacial decline, woody biomass nearly doubled during the past 8000 years, sequestering 1800 teragrams. This steady accumulation of carbon was driven by two separate ecological responses to regionally changing climate: the spread of forested biomes and the population expansion of high-biomass tree species within forests. What took millennia to accumulate took less than two centuries to remove: Industrial-era logging and agriculture have erased this carbon accumulation.</jats:p>

<jats:p>Changes in the composition of the gut microbiota are associated with many human diseases. So far, however, we have failed to define homeostasis or dysbiosis by the presence or absence of specific microbial species. The composition and function of the adult gut microbiota is governed by diet and host factors that regulate and direct microbial growth. The host delivers oxygen and nitrate to the lumen of the small intestine, which selects for bacteria that use respiration for energy production. In the colon, by contrast, the host limits the availability of oxygen and nitrate, which results in a bacterial community that specializes in fermentation for growth. Although diet influences microbiota composition, a poor diet weakens host control mechanisms that regulate the microbiota. Hence, quantifying host parameters that control microbial growth could help define homeostasis or dysbiosis and could offer alternative strategies to remediate dysbiosis.</jats:p>