Latest News Releases 23 June

Researchers at Karolinska Institutet and SciLifeLab in Sweden describe in a study published in Science how they have improved the ability of a protein to repair oxidative DNA damage and created a new protein function. Their innovative technique can lead to improved drugs for diseases involving oxidative stress, such as cancer, Alzheimer’s disease and lung diseases, but the researchers believe it has even greater potential.

Human activity is rapidly altering how much sediment flows from rivers worldwide into the oceans and seas, researchers report. Their findings also highlight sediment flux changes specific to key regions: while damming activity has decreased the amount of sediment flux in rivers across the global north, in the global south, increased erosion, likely driven by land use change, has increased sediment flux. Because sediment flux is crucial to river health and the stability of the economic and ecological services they provide, these new observations could help inform policy decisions and future planning and mitigation efforts. Across scales, riverine sediment flux plays a vital role in shaping landscape morphology and river, wetland, and coastal ecosystems. However, sediment flux worldwide is changing due to various human activities and impacts, including increased erosion from changing land use, sediment trapping from dam building, and compounding hydrological and sedimentological alterations due to climate change. Across many basins and particularly at the global scale, the current and future impacts of each of these changes are poorly understood, largely due to insufficient monitoring. To fill this knowledge gap, Evan Dethier and colleagues present an analysis of flux changes for 414 rivers worldwide. Deither et al. used more than 130,000 field measurements and a suite of algorithms to calibrate satellite images from 1984-2020, creating a monthly record of suspended sediment concentration (SSC) in global rivers spanning nearly 40 years. The findings show that dams have dramatically reduced sediment flux in rivers throughout the global north, resulting in SSC declines to 49% of pre-dam conditions. Across the global south, however, extensive land use change has increased erosion, increasing SSC on average by about 41% since 1980. “Although similar techniques have been used locally before, the scale, both spatial and temporal, and extensive verification of the work by Diether et al. is unprecedented, which allows the most detailed and comprehensive analysis of these trends in the data,” write Christiane Zarfl and Frances Dunn in a related Perspective.

Across two studies, researchers investigated aging in cold-blooded tetrapods, revealing surprisingly little evidence of senescence, or physical aging, in several turtle species. Together the two studies’ findings challenge assumptions of some evolutionary models that suggest senescence is an unescapable fate. In nature, some species live exceptionally long lives, seemingly avoiding senescence – the gradual process of deterioration of functional characteristics of an organism with age. This is particularly true for Testudines, an order of reptiles encompassing turtles, terrapins, and tortoises, some of which can live to be more than 100 years old. Here, in two studies, researchers investigate the impacts and patterns of aging in these and other closely related species that vary greatly in their aging rates, despite other fundamental similarities. “By investigating the nature of [this] variation, something new may be learned about aging in humans,” write Steven Austad and Caleb Finch in a related Perspective. In one analysis, Beth Reinke and colleagues provide a comparative study of aging rates and lifespan across wild cold-blooded tetrapods. Using data from long-term field studies of 77 species from 107 wild populations, including turtles, amphibians, snakes, crocodilians and tortoises, the authors evaluated how thermoregulatory mode, environmental temperature, protective adaptations, and pace of life history contribute to physical aging. Compared to birds and mammals, Reinke et al. found greater diversity in aging rates in the group studied. Ectotherm longevity (estimated as the number of years after first reproduction when 95% of adults have died) ranged from 1 to 137 years. For comparison, primate longevity ranges from 4 to 84 years. The authors also found little evidence of aging in multiple chelonian species, in some salamanders and in the tuatara. Protective adaptations and life history strategies – like bony shells and a relatively slow pace of life, in the case of turtles – help to explain the negligible aging in these long-lived species. In another study, Rita da Silva and colleagues examined mortality rate changes with age in captive animals , focusing on 52 turtle, terrapin, and tortoise species in zoo populations. Similarly, da Silva et al. found that senescence was slow or negligible in roughly 75% of the species evaluated. Moreover, roughly 80% experienced aging rates lower than that of modern humans. Unlike humans and other species, the findings in controlled settings also suggest that some turtle and tortoise species may reduce physical aging in response to better environmental conditions, in which – as conditions improve – they can allocate more energy to survival rather than protection, thereby extending their lifespans.

On sunken leaves in the waters of a Caribbean mangrove swamp, researchers discovered a bacterium that challenges the prevailing view of bacterial cell size; counter to the notion that microbes are only visible with a microscope, this one – named Thiomargarita magnifica – is larger than all other known giant bacteria by ~50-fold, and can be seen by the naked eye, the study’s authors say. It’s also quite complex in its structure, further challenging traditional concepts of bacterial cells. “This discovery adds to the group of large sulfur bacteria and helps to solve the puzzle of what factors limit cell size,” writes Petra Anne Levin in a related Perspective. Bacteria are commonly thought of as microscopic single cells with DNA free-floating in their cytoplasm. As a group, however, they often show a surprising range of diversity. In this study, Jean-Marie Volland et al. add to this diversity by reporting the discovery and characterization of a sulfur-oxidizing bacterium that can grow orders of magnitude over theoretical limits for bacterial cell size, with a complex membrane organization that likely allowed it to grow to such size, circumventing typical biophysical and bioenergetic limitations. The organism was first discovered growing as thin white filaments on the surfaces of decaying mangrove leaves in shallow tropical marine mangrove swamps in Guadeloupe, Lesser Antilles. Using a range of techniques, Volland and colleagues aimed to characterize it. Though bacteria are typically visible only with a compound microscope capable of magnifying 100 to 1,000 times, this one – reaching one centimeter in length – is visible without a microscope. And, instead of its DNA floating freely inside the cell as happens in other bacteria, the DNA is compartmentalized within membrane-bound structures, an innovation characteristic of more complex cells. These membrane-bound compartments are metabolically active, the authors’ analyses show, with activity occurring throughout the bacterium cell length, as opposed to just at its growing tip. It is possible that this unique spatial organization and bioenergetic membrane system, which indicate a gain of complexity in the Thiomargarita lineage, may have allowed T. magnifica to overcome size- and volume-related limitations typically associated with bacteria. Why these organisms need to be so large is an intriguing, open question, says Levin in the related Perspective, where she also suggests it unlikely that T. magnifica represents the upper limit of bacterial cell size. “… bacteria are endlessly adaptable and always surprising—and should never be underestimated,” writes Levin. The authors conclude: “The discovery…suggests that large and more complex bacteria may be hiding in plain sight.” ***A related embargoed news briefing was held at 11:00 a.m. U.S. ET on 21 June 2022, as a Zoom Webinar. Recordings of the briefing can be found here: https://www.dropbox.com/sh/ob7tbnedqdkby7j/AABp8b2F3W6EaahMjJOrTwwIa?dl=0.***

A model analysis reconstructing the growth of preindustrial forests in the upper Midwest United States shows a steady increase in forest biomass over thousands of years, driven by forest expansion and changing species composition as climate in the region changed following deglaciation. The findings challenge previous conclusions that forest biomass in this region and, by extension, the accumulated carbon, remained relatively static in the millennia before industrialization. Strikingly, the model results also show that what took nearly 8,000 years to accumulate was lost in only 150 years of post-industrial logging and agriculture. Forests represent one of the largest pools of terrestrial carbon. However, the strength and pacing of forest biomass carbon accumulation over centuries to millennia aren’t well understood. As such, estimations of terrestrial carbon fluxes before industrial-era disturbance are uncertain, as is their role in future long-term projections of the carbon climate system. By combining historical data from preindustrial forest surveys and fossil pollen records, Ann Raiho and colleagues developed ReFAB (Reconstructing Forest Aboveground Biomass), a Bayesian statistical model, and used it to reconstruct changes in biomass in the Midwest U.S. over the last 10,000 years. Raiho et al. found that forest biomass in this region was not stable before industrialization, as has been previously believed. Instead, after an initial decline due to postglacial climate change, woody biomass increased slowly yet consistently, nearly doubling over the subsequent 8,000 years and storing as much as 1,800 teragrams of carbon. According to the authors, this steady biomass accumulation was made possible by spatial expansion of forest area following deglaciation and ecological succession to high-biomass tree species. Raiho et al. suggest that the findings could inform forest management strategies that seek to emulate the natural processes that enhanced carbon sequestration throughout the preindustrial Holocene to buffer climate change well into the Anthropocene.