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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Direct extracellular electron transfer for high electricity production by a new type of marine microalgae Nannochloropsis sp. HDY2

A growing number of autotrophic microalgae have been found to have extracellular electron transfer (EET) capabilities. However, the mechanism and function of EET pathway in microalgae have not thoroughly investigated. This study presents evidence of direct extracellular electron transfer (DEET) for impressive electricity production by a new type of marine microalgae Nannochloropsis sp. HDY2 in the single and double-chamber photosynthetic microbial fuel cells (PFMCs). The electricity generation of Nannochloropsis sp. is strongly inhibited by photosynthetic inhibitors, suggesting that electrons involved in the extracellular electron transfer (EET) of Nannochloropsis sp. are derived from photosynthesis. The results of dialysis bag and supernatant experiments suggest that Nannochloropsis sp. produce electricity by DEET. The lack of typical redox peaks in cyclic voltammetry (CV) analysis and the appearance of extracellular filamentous component (EFC) around cells support this finding. Under high light conditions, the chlorophyll a and carotenoid content of Nannochloropsis sp. rapidly decreased while the fatty acid synthesis and electricity generation increased, suggesting that the DEET pathway play an active role in the resistance to photooxidation of Nannochloropsis sp. In conclusion, this study provides the first evidence that Nannochloropsis has the capability of performing EET and sheds new light on the positive role of DEET on the environmental adaptation of Nannochloropsis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

How Does Escherichia coli Allocate Proteome?

Microorganisms are shown to actively partition their intracellular resources, such as pro- teins, for growth optimization. Recent experiments have begun to reveal molecular com- ponents unpinning the partition; however, it remains unclear quantitatively how individual parts orchestrate to yield precise resource allocation that is both robust and dynamic. Here we developed a coarse-grained mathematical framework that centers on guanosine pentaphosphate (ppGpp)-mediated regulation, and used it to systematically uncover the design principles of proteome allocation in Escherichia coli. Our results showed that cellular ability of resource partition lies in an ultrasensitive, negative feedback control- ling topology with the ultrasensitivity arising from zero-order amino acid kinetics and the negative feedback from ppGpp-controlled ribosome synthesis. In addition, together with the time-scale separation between slow ribosome kinetics and fast turnovers of ppGpp and amino acids, the network topology confers the organism an optimization mechanism which mimics sliding mode control, a nonlinear optimization strategy that is widely used in man-made systems. We further showed that such a controlling mechanism is robust against parameter variations and molecular fluctuations, and is also efficient for biomass production over time. Furthermore, this work elucidates the fundamental controlling mechanism of E. coli proteome allocation, thereby providing insights into quantitative microbial physiology as well as the design of synthetic gene networks.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Quaternized chitosan as a biopolymer sanitizer for leafy vegetables: synthesis, characteristics, and traditional vs. dry nano-aerosol applications

A series of quaternary dimethyl-(alkyl)-ammonium chitosan derivatives (QACs) was synthesized and studied for physicochemical properties and bioactivity. The QACs tended to spontaneously self-assembly into nanoaggregates. Antimicrobial activity was examined in vitro on Gram-negative Escherichia coli (E. coli) and Gram-positive Listeria innocua (L. innocua) bacteria as well as phytopathogenic fungus Botrytis cinerea. The hexyl chain-substituted QAC-6 demonstrated the highest potency causing 3.0- and 4.5-log CFU mL-1 reduction of E. coli and L. innocua, respectively. QAC-6 was tested for antimicrobial activity on stainless steel coupons and fresh spinach leaves. A traditional ‘wet’ application (spray) and dry Engineered Water Nanostructure (EWNS) approach were used for spinach decontamination. With both approaches, significant reduction of microbial load on the treated produce was achieved. Finally, the wet application showed a greater reduction of microbial load, while the advantages of EWNS were reaching the antimicrobial effect with miniscule dose of active agent leaving treated surface visibly dry.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Real-time bioelectronic sensing of environmental contaminants

Real-time chemical sensing is crucial for applications in environmental and health monitoring. Biosensors can detect a variety of molecules through genetic circuits that use these chemicals to trigger the synthesis of a coloured protein, thereby producing an optical signal. However, the process of protein expression limits the speed of this sensing to approximately half an hour, and optical signals are often difficult to detect in situ. Here we combine synthetic biology and materials engineering to develop biosensors that produce electrical readouts and have detection times of minutes. Here we programmed Escherichia coli to produce an electrical current in response to specific chemicals using a modular, eight-component, synthetic electron transport chain. As designed, this strain produced current following exposure to thiosulfate, an anion that causes microbial blooms, within 2 min. This amperometric sensor was then modified to detect an endocrine disruptor. The incorporation of a protein switch into the synthetic pathway and encapsulation of the bacteria with conductive nanomaterials enabled the detection of the endocrine disruptor in urban waterway samples within 3 min. Our results provide design rules to sense various chemicals with mass-transport-limited detection times and a new platform for miniature, low-power bioelectronic sensors that safeguard ecological and human health.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

The anaerobic fungus Neocallimastix californiae shifts metabolism and produces melanin in response to lignin-derived aromatic compounds

Biological deconstruction of lignocellulose for sustainable chemical production offers an opportunity to harness evolutionarily specialized enzymes and organisms for industrial bioprocessing. While hydrolysis of cellulose and hemicellulose by CAZymes yields fermentable sugars, ligninolysis releases a heterogeneous mix of aromatic compounds that likely play a crucial role in shaping microbial communities and microbial metabolism. Here, we interrogated the metabolomic and transcriptomic response of a lignocellulolytic anaerobic fungus, Neocallimastix californiae, to a heterogeneous mixture of aromatic compounds derived from lignin. Through exposing the fungus to both a concentration it might experience in its native environment and an elevated concentration of alkaline lignin, we observe that N. californiae transforms vanillin and that supplying alkaline lignin at 0.125 g/L, alongside cellulose, enhances the growth and polysaccharide-degrading activity of N. californiae. Altogether, our results further suggest that vanillin consumption, increased polymer-degrading activity, increased metabolic activity, and transcriptomic remodeling of amino acid synthesis genes all coincide with increased melanin production by fungal cells. These observations challenge previous notions that aromatics from lignocellulose only inhibit the growth and polymer deconstruction capabilities of the biomass-degrading anaerobic fungi (Neocallimastigomycetes). This study demonstrates that anaerobic fungi have a complex relationship with aromatic chemicals derived from lignin and hemicellulose and shift their metabolism in response to the addition of lignocellulose-derived aromatics to their growth medium. Further, as no known pathways for the biochemical transformation of aromatics were detected in these organisms despite observed transcriptome remodeling in the presence of aromatics, we suggest they might encode novel biochemical routes for scavenging amino acid building blocks from aromatic monomers derived from hemicellulose side chains and lignin.

Anaerobic fungi↗
DOE OSTI2020

Electric field stimulates production of highly conductive microbial OmcZ nanowires

Multifunctional living materials are attractive due to their powerful ability to self-repair and replicate. However, most natural materials lack electronic functionality. Here we show that an electric field, applied to electricity-producing Geobacter sulfurreducens biofilms, stimulates production of cytochrome OmcZ nanowires with 1,000-fold higher conductivity (30 S cm -1 ) and threefold higher stiffness (1.5 GPa) than the cytochrome OmcS nanowires that are important in natural environments. Using chemical imaging-based multimodal nanospectroscopy, we correlate protein structure with function and observe pH-induced conformational switching to β-sheets in individual nanowires, which increases their stiffness and conductivity by 100-fold due to enhanced π-stacking of heme groups; this was further confirmed by computational modeling and bulk spectroscopic studies. These nanowires can transduce mechanical and chemical stimuli into electrical signals to perform sensing, synthesis and energy production. Overall, these findings of biologically produced, highly conductive protein nanowires may help to guide the development of seamless, bidirectional interfaces between biological and electronic systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1992

Gravity effects on cellulose assembly

The effect of microgravity on cellulose synthesis using the model system of Acetobacter xylinum was the subject of recent investigations using The National Aeronautics and Space Administration's Reduced Gravity Laboratory, a modified KC-135 aircraft designed to produce 20 sec of microgravity during the top of a parabolic dive. Approximately 40 parabolas were executed per mission, and a period of 2 x g was integral to the pullout phase of each parabola. Cellulose biosynthesis was initiated on agar surfaces, liquid growth medium, and buffered glucose during parabolic flight and terminated with 2.0% sodium azide or 50.0% ethanol. While careful ground and in-flight controls indicated normal, compact ribbons of microbial cellulose, data from five different flights consistently showed that during progression into the parabola regime, the cellulose ribbons became splayed. This observation suggests that some element of the parabola (the 20 sec microgravity phase, the 20 sec 2 x g phase, or a combination of both) was responsible for this effect. Presumably the cellulose I alpha crystalline polymorph normally is produced under strain, and the microgravity/hypergravity combination may relieve this stress to produce splayed ribbons. An in-flight video microscopy analysis of bacterial motions during a parabolic series demonstrated that the bacteria continue to synthesize cellulose during all phases of the parabolic series. Thus, the splaying may be a reflection of a more subtle alteration such as reduction of intermicrofibrillar hydrogen bonding. Long-term microgravity exposures during spaceflight will be necessary to fully understand the cellulose alterations from the short-term microgravity experiments.

manned↗
NASA NTRS2019

Lipid Decontamination Procedures for Life Detection Missions

Molecular biosignatures are key targets for current, proposed, and future life detection missions. With the high accuracy and low limit of detection (LOD) that new and future instruments will require, decontamination of life detection hardware is necessary to prevent false positives. Lipids are a molecular biosignature of interest, as they are ubiquitous to all life as we know it, can survive unaltered in the geologic record for longer than any other biomolecule (i.e. billions of years), and form through both biotic and abiotic processes. Lipids display origin-diagnostic molecular patterns that can reveal biotic or abiotic synthesis, so finding them and ascertaining their molecular features is important for potentially detecting evidence of life elsewhere. Traditional methods of decontamination, or contamination control (CC), primarily clean hardware through fabrication in sterile (cleanroom) environments, killing microbes, and removing/flushing contaminants off instrument and spacecraft components. However, research suggests that some standard cleaning methods are either unlikely to remove lipid contaminants or are incompatible with life detection instrument materials. To solve this problem, I propose to find, test, and verify a decontamination method that thoroughly cleans instruments by destroying lipid molecules, but is simultaneously compatible with major materials used in these instruments. I will study the effects of traditional CC methods (including Dry Heat Microbial Reduction and Vapor phase Hydrogen Peroxide) and experimental CC methods (Electron Beam Irradiation) on lipid molecules for application to life detection instrumentation. I will then develop a CC plan for a novel lipid detector (ExCALiBR, Extractor for Chemical Analysis of Lipid Biomarkers in Regolith) searching for lipids in either soil or icy world scenarios. This plan will uphold planetary protection regulation requirements and validate experimental analyses of in-situ life detection tests.

Decontamination↗
DOE OSTI2024

Complete biosynthesis of QS-21 in engineered yeast

QS-21 is a potent vaccine adjuvant and remains the only saponin-based adjuvant that has been clinically approved for use in humans. However, owing to the complex structure of QS-21, its availability is limited. Today, the supply depends on laborious extraction from the Chilean soapbark tree or on low-yielding total chemical synthesis. Here we demonstrate the complete biosynthesis of QS-21 and its precursors, as well as structural derivatives, in engineered yeast strains. The successful biosynthesis in yeast requires fine-tuning of the host’s native pathway fluxes, as well as the functional and balanced expression of 38 heterologous enzymes. The required biosynthetic pathway spans seven enzyme families—a terpene synthase, P450s, nucleotide sugar synthases, glycosyltransferases, a coenzyme A ligase, acyl transferases and polyketide synthases—from six organisms, and mimics in yeast the subcellular compartmentalization of plants from the endoplasmic reticulum membrane to the cytosol. Finally, by taking advantage of the promiscuity of certain pathway enzymes, we produced structural analogues of QS-21 using this biosynthetic platform. This microbial production scheme will allow for the future establishment of a structure–activity relationship, and will thus enable the rational design of potent vaccine adjuvants.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS2011

Copolyimide Surface Modifying Agents for Particle Adhesion Mitigation

Marine biofouling, insect adhesion on aircraft surfaces, microbial contamination of sterile environments, and particle contamination all present unique challenges for which researchers have adopted an array of mitigation strategies. Particulate contamination is of interest to NASA regarding exploration of the Moon, Mars, asteroids, etc.1 Lunar dust compromised seals, clogged filters, abraded visors and space suit surfaces, and was a significant health concern during the Apollo missions.2 Consequently, NASA has instituted a multi-faceted approach to address dust including use of sacrificial surfaces, active mitigation requiring the use of an external energy source, and passive mitigation utilizing materials with an intrinsic resistance to surface contamination. One passive mitigation strategy is modification of a material s surface energy either chemically or topographically. The focus of this paper is the synthesis and evaluation of novel copolyimide materials with surface modifying agents (SMA, oxetanes) enabling controlled variation of surface chemical composition.

Wohl, Christopher J.↗
DOE OSTI2023

Insights into the physiological and genomic characterization of three bacterial isolates from a highly alkaline, terrestrial serpentinizing system

The terrestrial serpentinite-hosted ecosystem known as “The Cedars” is home to a diverse microbial community persisting under highly alkaline (pH ~ 12) and reducing (Eh < -550 mV) conditions. This extreme environment presents particular difficulties for microbial life, and efforts to isolate microorganisms from The Cedars over the past decade have remained challenging. Herein, we report the initial physiological assessment and/or full genomic characterization of three isolates: Paenibacillus sp. Cedars (‘Paeni-Cedars’), Alishewanella sp. BS5-314 (‘Ali-BS5-314’), and Anaerobacillus sp. CMMVII (‘Anaero-CMMVII’). Paeni-Cedars is a Gram-positive, rod-shaped, mesophilic facultative anaerobe that grows between pH 7–10 (minimum pH tested was 7), temperatures 20–40°C, and 0–3% NaCl concentration. The addition of 10–20 mM CaCl 2 enhanced growth, and iron reduction was observed in the following order, 2-line ferrihydrite > magnetite > serpentinite ~ chromite ~ hematite. Genome analysis identified genes for flavin-mediated iron reduction and synthesis of a bacillibactin-like, catechol-type siderophore. Ali-BS5-314 is a Gram-negative, rod-shaped, mesophilic, facultative anaerobic alkaliphile that grows between pH 10–12 and temperatures 10–40°C, with limited growth observed 1–5% NaCl. Nitrate is used as a terminal electron acceptor under anaerobic conditions, which was corroborated by genome analysis. The Ali-BS5-314 genome also includes genes for benzoate-like compound metabolism. Anaero-CMMVII remained difficult to cultivate for physiological studies; however, growth was observed between pH 9–12, with the addition of 0.01–1% yeast extract. Anaero-CMMVII is a probable oxygen-tolerant anaerobic alkaliphile with hydrogenotrophic respiration coupled with nitrate reduction, as determined by genome analysis. Based on single-copy genes, ANI, AAI and dDDH analyses, Paeni-Cedars and Ali-BS5-314 are related to other species (P. glucanolyticus and A. aestuarii, respectively), and Anaero-CMMVII represents a new species. The characterization of these three isolates demonstrate the range of ecophysiological adaptations and metabolisms present in serpentinite-hosted ecosystems, including mineral reduction, alkaliphily, and siderophore production.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS2016

Permanent Draft Genome of Strain ESFC-1: Ecological Genomics of a Newly Discovered Lineage of Filamentous Diazotrophic Cyanobacteria

The nonheterocystous filamentous cyanobacterium, strain ESFC-1, is a recently described member of the order Oscillatoriales within the Cyanobacteria. ESFC-1 has been shown to be a major diazotroph in the intertidal microbial mat system at Elkhorn Slough, CA, USA. Based on phylogenetic analyses of the 16S RNA gene, ESFC-1 appears to belong to a unique, genus-level divergence; the draft genome sequence of this strain has now been determined. Here we report features of this genome as they relate to the ecological functions and capabilities of strain ESFC-1. The 5,632,035 bp genome sequence encodes 4914 protein-coding genes and 92 RNA genes. One striking feature of this cyanobacterium is the apparent lack of either uptake or bi-directional hydrogenases typically expected within a diazotroph. Additionally, a large genomic island is found that contains numerous low GC-content genes and genes related to extracellular polysaccharide production and cell wall synthesis and maintenance.

R Craig Everroad↗
DOE OSTI2021

Eight Metagenome-Assembled Genomes Provide Evidence for Microbial Adaptation in 20,000- to 1,000,000-Year-Old Siberian Permafrost

Permafrost microbes may be metabolically active in microscopic layers of liquid brines, even in ancient soil. Metagenomics can help discern whether permafrost microbes show adaptations to this environment. Thirty-three metagenome-assembled genomes (MAGs) were obtained from six depths (3.5 m to 20 m) of freshly cored permafrost from the Siberian Kolyma-Indigirka Lowland region. These soils have been continuously frozen for ~20,000 to 1,000,000 years. Eight of these MAGs were ≥80% complete with <10% contamination and were taxonomically identified as Aminicenantes, Atribacteria, Chloroflexi, and Actinobacteria within bacteria and Thermoprofundales within archaea. MAGs from these taxa have been obtained previously from nonpermafrost environments and have been suggested to show adaptations to long-term energy starvation, but they have never been explored in ancient permafrost. The permafrost MAGs had greater proportions in the Clusters of Orthologous Groups (COGs) categories of energy production and conversion and carbohydrate transport and metabolism than did their nonpermafrost counterparts. They also contained genes for trehalose synthesis, thymine metabolism, mevalonate biosynthesis, and cellulose degradation, which were less prevalent in nonpermafrost genomes. Furthermore, many of these genes are involved in membrane stabilization and osmotic stress responses, consistent with adaptation to the anoxic, high-ionic-strength, cold environments of permafrost brine films. Our results suggest that this ancient permafrost contains DNA of high enough quality to assemble MAGs from microorganisms with adaptations to survive long-term freezing in this extreme environment.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

MIBiG 4.0: advancing biosynthetic gene cluster curation through global collaboration

Specialized or secondary metabolites are small molecules of biological origin, often showing potent biological activities with applications in agriculture, engineering and medicine. Usually, the biosynthesis of these natural products is governed by sets of co-regulated and physically clustered genes known as biosynthetic gene clusters (BGCs). To share information about BGCs in a standardized and machine-readable way, the Minimum Information about a Biosynthetic Gene cluster (MIBiG) data standard and repository was initiated in 2015. Since its conception, MIBiG has been regularly updated to expand data coverage and remain up to date with innovations in natural product research. Here, we describe MIBiG version 4.0, an extensive update to the data repository and the underlying data standard. In a massive community annotation effort, 267 contributors performed 8304 edits, creating 557 new entries and modifying 590 existing entries, resulting in a new total of 3059 curated entries in MIBiG. Particular attention was paid to ensuring high data quality, with automated data validation using a newly developed custom submission portal prototype, paired with a novel peer-reviewing model. MIBiG 4.0 also takes steps towards a rolling release model and a broader involvement of the scientific community. MIBiG 4.0 is accessible online at https://mibig.secondarymetabolites.org/.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Lipid production from non-sugar compounds in pretreated lignocellulose hydrolysates by Rhodococcus jostii RHA1

Valorization of all carbon sources from biorefinery wastes to biofuels and bioproducts is an attractive but challenging strategy to improve the carbon efficiency of the entire biorefinery process for economic competitiveness. Rhodococcus jostii RHA1 is considered as a promising candidate for conversion of non-sugar compounds in pretreated lignocellulose hydrolysate, which contain aromatic monomers, furans and acids derived from biomass. However, the insufficient understanding of the strain’s complex metabolism network limits its application. In this study, furans (furfural, 5-hydroxymethylfurfural), phenols (vanillin, vanillate), and organic acids (acetic acid), which mimic the complex components of the non-sugar compounds in pretreated biomass hydrolysate, were mixed with benzoate or used individually as carbon sources to investigate the growth and lipid accumulation of R. jostii RHA1. Fermentation kinetics, specific growth rates (h-1) and lipid yield (g(g) -1, g(mmol)-1), for each selected biomass-derived compound were compared for lipid production. The order of the specific growth rates (h-1) was benzoate > acetic acid > vanillate > vanillin. Higher consumption rate of benzoate than that of vanillate, as well as different lipid yield from them, suggested the preference of strain employing two branches of ß-ketoadipate pathway and plausibly distinct carbon routing to lipid biosynthesis. And acetic acid showed the lowest lipid yield (g(mmol)-1) indicating less carbon contributed to lipid production. The highest lipid content (0.46 g lipid/g CDW) was achieved using benzoate as a main carbon source in the presence of 5-hydroxymethylfurfural (5-HMF). The generated lipids predominantly contained C16:0 and C17:0 fatty acids. The concentration of furfural and 5-HMF in fermentation broth decreased individually or simultaneously with benzoate catabolism. NMR results revealed the oxidation of furfural and 5-HMF by R. jostii RHA1. This study provides new insights into the catabolism and metabolism of non-sugar compounds derived from biomass by Rhodococcus in terms of growth and lipid production, facilitating its application to 2nd generation biofuel production.

Li, Xiaolu↗
DOE OSTI2025

Architecture, catalysis and regulation of methylthio-alkane reductase for bacterial sulfur acquisition from volatile organic compounds

Bacteria utilize methylthio-alkane reductase (MAR) to acquire sulfur from volatile organic sulfur compounds. Reductive cleavage of methylthio-ethanol and dimethylsulfide liberates methanethiol for methionine synthesis and concomitantly releases ethylene and methane, respectively. Here we show that the native MAR of Rhodospirillum rubrum is a two-component system composed of a MarH ATP-dependent reductase and a MarDK catalytic core, whose architecture parallels nitrogenase. MarS complexes with MarDK to downregulate MAR activity during cellular sulfate influx, based on chromatographic and activity analyses. MarDK possesses complex metallocofactors resembling, but not identical to, nitrogenase P- and iron-only M-clusters, designated as mar1 and mar2 clusters based on metal, spectroscopic and mutagenesis analyses. They exhibit electronic features similar to the iron-only nitrogenase under turnover and, remarkably, are matured by MarB or nitrogenase NifB, resulting in maturase-dependent activity profiles. Altogether, this suggests a broader scope of reactivity, mechanisms and regulation in microbial metabolism for the nitrogenase-like family of enzymes than previously considered.

09 BIOMASS FUELS↗
DOE OSTI2024

Peeling back the many layers of competitive exclusion

Baby chicks administered a fecal transplant from adult chickens are resistant to Salmonella colonization by competitive exclusion. A two-pronged approach was used to investigate the mechanism of this process. First, Salmonella response to an exclusive (Salmonella competitive exclusion product, Aviguard ® ) or permissive microbial community (chicken cecal contents from colonized birds containing 7.85 Log 10 Salmonella genomes/gram) was assessed ex vivo using a S. typhimurium reporter strain with fluorescent YFP and CFP gene fusions to rrn and hilA operon, respectively. Second, cecal transcriptome analysis was used to assess the cecal communities’ response to Salmonella in chickens with low (≤5.85 Log 10 genomes/g) or high (≥6.00 Log 10 genomes/g) Salmonella colonization. The ex vivo experiment revealed a reduction in Salmonella growth and hilA expression following co-culture with the exclusive community. The exclusive community also repressed Salmonella’s SPI-1 virulence genes and LPS modification, while the anti-virulence/inflammatory gene avrA was upregulated. Salmonella transcriptome analysis revealed significant metabolic disparities in Salmonella grown with the two different communities. Propanediol utilization and vitamin B12 synthesis were central to Salmonella metabolism co-cultured with either community, and mutations in propanediol and vitamin B12 metabolism altered Salmonella growth in the exclusive community. There were significant differences in the cecal community’s stress response to Salmonella colonization. Cecal community transcripts indicated that antimicrobials were central to the type of stress response detected in the low Salmonella abundance community, suggesting antagonism involved in Salmonella exclusion. This study indicates complex community interactions that modulate Salmonella metabolism and pathogenic behavior and reduce growth through antagonism may be key to exclusion.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Biogeography of microbial bile acid transformations along the murine gut

Bile acids, which are synthesized from cholesterol by the liver, are chemically transformed along the intestinal tract by the gut microbiota, and the products of these transformations signal through host receptors, affecting overall host health. These transformations include bile acid deconjugation, oxidation, and 7α-dehydroxylation. An understanding of the biogeography of bile acid transformations in the gut is critical because deconjugation is a prerequisite for 7α-dehydroxylation and because most gut microorganisms harbor bile acid transformation capacity. Here, we used a coupled metabolomic and metaproteomic approach to probe in vivo activity of the gut microbial community in a gnotobiotic mouse model. Results revealed the involvement of Clostridium scindens in 7α-dehydroxylation, of the genera Muribaculum and Bacteroides in deconjugation, and of six additional organisms in oxidation (the genera Clostridium, Muribaculum, Bacteroides, Bifidobacterium, Acutalibacter, and Akkermansia). Furthermore, the bile acid profile in mice with a more complex microbiota, a dysbiosed microbiota, or no microbiota was considered. For instance, conventional mice harbor a large diversity of bile acids, but treatment with an antibiotic such as clindamycin results in the complete inhibition of 7α-dehydroxylation, underscoring the strong inhibition of organisms that are capable of carrying out this process by this compound. Finally, a comparison of the hepatic bile acid pool size as a function of microbiota revealed that a reduced microbiota affects host signaling but not necessarily bile acid synthesis. In this study, bile acid transformations were mapped to the associated active microorganisms, offering a systematic characterization of the relationship between microbiota and bile acid composition.

59 BASIC BIOLOGICAL SCIENCES↗