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1. The recovery of the deep biosphere at the Chicxulub impact crater

   Coolen, M. ( January 2018 , American Geophysical Union Fall Meeting)

   The Chicxulub crater, Mexico, is the site of the asteroid impact that led to the end-Cretaceous mass extinction. While impact events are known to be able to cause severe disruption to surface-dwelling organisms, the effects of such catastrophic perturbations on the deep biosphere are not known. Deep ocean drilling into the peak ring of the Chicxulub impact crater (IODP expedition 364) in 2016 allowed us to study the modern deep biosphere within the (a) high-porosity melt-bearing impact breccia/suevite (617-740 mbsf) emplaced within a day or so of the Cenozoic, (b) the overlying low porosity post-impact marine Cenozoic carbonates (504-617mbsf), and the impacted and fractured granitic basement (740-1334 mbsf). The microbial biomass (~10 cells/g wet weight) was highest in the upper suevite, in underlying non-granitic subvolcanic pre-impact basanite, and at the intercalation of suevite and impact melt rock. Pre-impact sterile conditions of the uplifted granitic basement rocks and mineralogical evidence of impact-induced sterilization suggest that the basement rocks have only been amenable to microbial colonization for less than 66 Myr. Enrichments at in situ 50-60 °C show the presence of heterotrophic lifestyles in the suevite and bacterial sulfate reduction extending into the top of the granitic basement. Cultivation-independent 16S diversity profiling revealed the presence of heterotrophic (fermentative) as well as autotrophic C-fixing thermophilic bacteria in the organic-rich (up to 4 wt % total organic carbon; TOC) Cenozoic sediments. The organic-lean suevite (< 0.1% TOC) showed the unique presence of sequences related to thermophilic Synechococcus (cyanobacteria) and S-oxidizing green sulfur bacteria (chlorobi), and Chloroflexi often associated with organic-poor deep-sea sediments. Alphaproteobacteria, predominated in the upper part of the granitic basement (<1000 mbsf), while putative manganeseoxidising Bacilli (Firmicutes) predominated in the melt-rich granitic basement (>1200 mbsf). Our data suggest that the catastrophe that led to the end-Cretaceous mass extinction caused geological disruption and recolonization of microbial life in the deep subsurface biosphere at the Chicxulub impact site. 

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2. The Habitat of the Nascent Chicxulub Crater

   https://doi.org/10.1029/2020AV000208  

   Bralower, T. J. ; Cosmidis, J. ; Fantle, M. S. ; Lowery, C. M. ; Passey, B. H. ; Gulick, S. P. S. ; Morgan, J. V. ; Vajda, V. ; Whalen, M. T. ; Wittmann, A. ; et al ( November 2020 , AGU Advances)

   An expanded sedimentary section provides an opportunity to elucidate conditions in the nascent Chicxulub crater during the hours to millennia after the Cretaceous‐Paleogene (K‐Pg) boundary impact. The sediments were deposited by tsunami followed by seiche waves as energy in the crater declined, culminating in a thin hemipelagic marlstone unit that contains atmospheric fallout. Seiche deposits are predominantly composed of calcite formed by decarbonation of the target limestone during impact followed by carbonation in the water column. Temperatures recorded by clumped isotopes of these carbonates are in excess of 70°C, with heat likely derived from the central impact melt pool. Yet, despite the turbidity and heat, waters within the nascent crater basin soon became a viable habitat for a remarkably diverse cross section of the food chain. The earliest seiche layers deposited with days or weeks of the impact contain earliest Danian nannoplankton and dinocyst survivors. The hemipelagic marlstone representing the subsequent years to a few millennia contains a nearly monogeneric calcareous dinoflagellate resting cyst assemblage suggesting deteriorating environmental conditions, with one interpretation involving low light levels in the impact aftermath. At the same horizon, microbial fossils indicate a thriving bacterial community and unique phosphatic fossils including appendages of pelagic crustaceans, coprolites and bacteria‐tunneled fish bone, suggesting that this rapid recovery of the base of the food chain may have supported the survival of larger, higher trophic‐level organisms. The extraordinarily diverse fossil assemblage indicates that the crater was a unique habitat in the immediate impact aftermath, possibly as a result of heat and nutrients supplied by hydrothermal activity.

    

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3. Evidence for autotrophic growth of purple sulfur bacteria using pyrite as electron and sulfur source

   https://doi.org/10.1128/aem.00863-24  

   Alarcon, Hugo V ; Mohl, Jonathon E ; Chong, Grace W ; Betancourt, Ana ; Wang, Yi ; Leng, Weinan ; White, Jason C ; Xu, Jie ( July 2024 , Applied and Environmental Microbiology)

   Spear, John R (Ed.)

   Purple sulfur bacteria (PSB) are capable of anoxygenic photosynthesis via oxidizing reduced sulfur compounds and are considered key drivers of the sulfur cycle in a range of anoxic environments. In this study, we show thatAllochromatium vinosum(a PSB species) is capable of autotrophic growth using pyrite as the electron and sulfur source. Comparative growth profile, substrate characterization, and transcriptomic sequencing data provided valuable insight into the molecular mechanisms underlying the bacterial utilization of pyrite and autotrophic growth. Specifically, the pyrite-supported cell cultures (“py”’) demonstrated robust but much slower growth rates and distinct patterns from their sodium sulfide-amended positive controls. Up to ~200-fold upregulation of genes encoding variousc- andb-type cytochromes was observed in “py,” pointing to the high relevance of these molecules in scavenging and relaying electrons from pyrite to cytoplasmic metabolisms. Conversely, extensive downregulation of genes related to LH and RC complex components indicates that the electron source may have direct control over the bacterial cells’ photosynthetic activity. In terms of sulfur metabolism, genes encoding periplasmic or membrane-bound proteins (e.g., FccAB and SoxYZ) were largely upregulated, whereas those encoding cytoplasmic proteins (e.g., Dsr and Apr groups) are extensively suppressed. Other notable differentially expressed genes are related to flagella/fimbriae/pilin(+), metal efflux(+), ferrienterochelin(−), and [NiFe] hydrogenases(+). Characterization of the biologically reacted pyrite indicates the presence of polymeric sulfur. These results have, for the first time, put the interplay of PSB and transition metal sulfide chemistry under the spotlight, with the potential to advance multiple fields, including metal and sulfur biogeochemistry, bacterial extracellular electron transfer, and artificial photosynthesis.

   Microbial utilization of solid-phase substrates constitutes a critical area of focus in environmental microbiology, offering valuable insights into microbial metabolic processes and adaptability. Recent advancements in this field have profoundly deepened our knowledge of microbial physiology pertinent to these scenarios and spurred innovations in biosynthesis and energy production. Furthermore, research into interactions between microbes and solid-phase substrates has directly linked microbial activities to the surrounding mineralogical environments, thereby enhancing our understanding of the relevant biogeochemical cycles. Our study represents a significant step forward in this field by demonstrating, for the first time, the autotrophic growth of purple sulfur bacteria using insoluble pyrite (FeS2) as both the electron and sulfur source. The presented comparative growth profiles, substrate characterizations, and transcriptomic sequencing data shed light on the relationships between electron donor types, photosynthetic reaction center activities, and potential extracellular electron transfer in these organisms capable of anoxygenic photosynthesis. Furthermore, the findings of our study may provide new insights into early-Earth biogeochemical evolutions, offering valuable constraints for understanding the environmental conditions and microbial processes that shaped our planet’s history.

    

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4. Emerging investigator series: a multispecies analysis of the relationship between oxygen content and toxicity in graphene oxide

   https://doi.org/10.1039/d0en01264e  

   Barrios, Ana C. ; Cahue, Yaritza P. ; Wang, Yan ; Geiger, Jason ; Puerari, Rodrigo C. ; Matias, William Gerson ; Melegari, Silvia Pedroso ; Gilbertson, Leanne M. ; Perreault, François ( June 2021 , Environmental Science: Nano)

   null (Ed.)

   The toxicity of graphene oxide (GO) has been documented for multiple species. However, GO has variable surface chemistry, and it is currently unclear whether changes in oxygen content impact GO-organism interactions the same way across species. In this study, a modified Hummer's GO (ARGO) was systematically reduced by thermal annealing at 200, 500, or 800 °C and toxicity towards bacteria ( Escherichia coli ), alga ( Scenedesmus obliquus ), cyanobacteria ( Microcystis aeruginosa ), and invertebrates ( Daphnia magna ) was assessed by measuring the effective concentrations inducing 50% inhibition (EC 50 ). The EC 50 –carbon/oxygen ratio relationships show similar trends for bacteria and invertebrates, where toxicity increases as the material is reduced. Conversely, cyanobacterial inhibition decreases as GO is reduced. Further testing supports differences in cell-GO interactions between bacteria and cyanobacteria. Cyanobacteria showed a decrease in metabolic activity, evidenced by a 69% reduction in esterase activity after ARGO exposure but no oxidative stress, measured by 2′,7′-dichlorodihydrofluorescein diacetate (H 2 DCFDA) fluorescence and catalase activity. In contrast, ARGO induced a 55% increase in H 2 DCFDA fluorescence and 342% increase in catalase activity in bacteria. These changes in cell–material interactions propose different mechanisms of action, a physical mechanism occurring in cyanobacteria, and a chemical mechanism in bacteria. The differences in GO toxicity observed in different organisms emphasize the need to differentiate the safe-by-design guidelines made for GO in relation to the potential organisms exposed. 

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5. How Does Photosynthesis Wake up in the Morning?

   https://doi.org/10.3389/frym.2022.785172  

   Townsend, Hope ; Imes, Avery ; Wang, Xin ( June 2022 , Frontiers for Young Minds)

   In photosynthesis, plants use energy from sunlight to turn carbon from CO 2 in the air into a solid form of carbon that can build the plant’s body. Photosynthesis consists of two portions: the reactions that absorb sunlight energy and another set of reactions called the Calvin-Benson-Bassham (CBB) cycle. When the plant “wakes up” in the morning, after a night of darkness, these two processes do not wake up at the same pace, which can damage the plant cells. However, plant cells prevent this problem by regulating these two processes carefully. To understand how photosynthetic organisms switch from night to day, a type of photosynthetic bacteria called cyanobacteria were used to explore how another pathway, called the oxidative pentose phosphate (OPP) pathway, helps with this dark-to-light transition. Our research found that the OPP pathway can help photosynthesis quickly reactivate when light is available and can prevent cell damage from too much light. 

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