Biology subjects

Heo, H.

Publications and source records attributed to Heo, H..

5 recordsLinked to original sources

bioRxiv2025

Searching for influencers among placental immune cells in preeclampsia.

Cells in maternal and fetal immune systems may communicate, leading to immune tolerance during pregnancy; however, this hypothesis remains controversial. Here, we profiled single-cell transcriptional signatures in placental layers comprising the maternal-fetal interface and deep placenta, then searched for genes associated with preeclampsia. To investigate the underlying principle of the failure of immune tolerance, we started by clarifying the systemic framework, comprising models of immune interaction frequency (IIF) and specific triggers (i.e., influencers) of tolerance (IT). We generated single-cell transcriptional profiles of normal term (Norms) and preeclampsia preterm (PePT) parturitions. Fetal and maternal cells are admixed across the placenta, for both Norms and PePTs, rejecting the IIF model of immune failure during pregnancy posed by excessive interactions between fetomaternal cells. Whereas placental layers are well mixed with maternal cells, we identified a conserved gradual immune transition of fetal T-cells in both PePT and Norm, disproving the IIF model. To search for influencers of PePT in the IT model, we established and validated a classification model for PePT and Norm immune cells, including T-cells, and then prioritized major contributors to the classifier model, which are highly enriched in ligands and receptors (p = 5.98e-5). Among the prioritized ligand receptors, SPP1 and CD44 are suggested as influencers of inflammation signatures and were experimentally validated by the exclusive colocalization of SPP1- and CD44-expressing cells in the PePT placentas. Different interleukin-4 and interferon-{psi} levels in the serum and urine of PePTs further support the contribution of SPP1 to associated pathways, including allograft rejection. Our findings provide insight into the influence of specific immune interactions between cells in the human placenta and their influencer-derived impact on PePT.

bioinformatics↗

bioRxiv2024

Hydrogen-dependent dissimilatory nitrate reduction to ammonium enables growth of Campylobacterota isolates

Dissimilatory nitrate reduction to ammonium (DNRA) is a key process in global nitrogen cycling, supporting the energy conservation of diverse microbes. For a long time, DNRA has been thought to primarily depend on organic electron donors, and thus to be governed by carbon-to-nitrogen (C:N) ratios. However, recent studies suggest that inorganic electron donors, such as sulfur compounds and iron, may also facilitate DNRA. The coupling of DNRA with molecular hydrogen (H2) oxidation is theoretically feasible, but largely unexplored microbial process. Here, we report the isolation of two Campylobacterota strains, Aliarcobacter butzleri hDNRA1 and Sulfurospirillum sp. hDNRA2, that grow by using H2 as an electron donor for DNRA. In both batch and continuous cultures, DNRA sensu stricto, i.e., NO2--to-NH + reduction, depended on the presence of H2 and was stoichiometric with H2 oxidation. The electrons for NO - reduction were clearly derived from H, and hydrogenotrophic DNRA was largely unaffected by the ratio of either carbon or electron donor to NO -/NO -. Genomic and transcriptomic analyses indicate that group 1b [NiFe]-hydrogenase and cytochrome c552 nitrite reductase are the key enzymes catalyzing hydrogenotrophic DNRA. These findings reveal novel physiological mechanisms enabling anaerobic bacterial growth, challenge the traditional C:N ratio paradigm, and uncover new biogeochemical processes and mediators controlling the global nitrogen and hydrogen cycles.

microbiology↗

bioRxiv2023

Suggested role of NosZ in preventing N2O inhibition of dissimilatory nitrite reduction to ammonium

Climate change and nutrient pollution are among the most urgent environmental issues. Enhancing the abundance and/or the activity of beneficial organisms is an attractive strategy to counteract these problems. Dissimilatory nitrate reduction to ammonium (DNRA), which theoretically improves nitrogen retention in soils, has been suggested as a microbial process that may be harnessed, especially since many DNRA-catalyzing organisms have been found to possess clade II nosZ genes and the ability to respire N2O. However, the selective advantages that may favor these nosZ-harboring DNRA-catalyzing organisms is not well understood. Here, the effect of N2O on Nrf-mediated DNRA was examined in a recently isolated soil bacterium, Bacillus sp. DNRA2, possessing both nrfA and nosZ genes. The DNRA metabolism of this bacterium was observed in the presence of C2H2, a NosZ inhibitor, with or without N2O, and the results were compared with C2H2-free controls. Cultures were also exposed to repeated oxic-anoxic transitions in the sustained presence of N2O. The NO2--to-NH4+ reduction following oxic-to-anoxic transition was significantly delayed in NosZ-inhibited C2H2-amended cultures, and the inhibition was more pronounced with repeated oxic-anoxic transitions. The possible involvement of C2H2 was dismissed since the cultures continuously flushed with C2H2/N2 mixed gas after initial oxic incubation did not exhibit a similar delay in DNRA progression as that observed in the culture flushed with N2O-containing gas. The findings provide novel ecological and evolutionary insights into the oft-observed presence of nosZ genes in DNRA-catalyzing microorganisms. ImportanceDissimilatory nitrate/nitrite reduction to ammonium (DNRA) is a microbial energy-conserving process that reduces NO3- and/or NO2- to NH4+. Interestingly, many DNRA-catalyzing microorganisms possessing nrfA genes harbor nosZ genes encoding nitrous oxide reductases, i.e., the only group of enzymes capable of removing the potent greenhouse gas N2O. Here, through a series of physiological experiments examining DNRA metabolism in one of such microorganisms, Bacillus sp. DNRA2, we have discovered that N2O may delay transition to DNRA upon an oxic-to-anoxic transition, unless timely removed by the nitrous oxide reductases. These observations suggest a novel explanation as to why some nrfA-possessing microorganisms have retained nosZ genes that had probably been acquired via horizontal gene transfers: to remove N2O that may otherwise interfere with the transition from O2 respiration to DNRA.

microbiology↗

bioRxiv2020

Enhancement of nitrous oxide emissions in soil microbial consortia via copper competition between proteobacterial methanotrophs and denitrifiers

Unique means of copper scavenging have been identified in proteobacterial methanotrophs, particularly the use of methanobactin, a novel ribosomally synthesized post-translationally modified polypeptide that binds copper with very high affinity. The possibility that copper sequestration strategies of methanotrophs may interfere with copper uptake of denitrifiers in situ and thereby enhance N2O emissions was examined using a suite of laboratory experiments performed with rice paddy microbial consortia. Addition of purified methanobactin from Methylosinus trichosporium OB3b to denitrifying rice paddy soil microbial consortia resulted in substantially increased N2O production, with more pronounced responses observed for soils with lower copper content. The N2O emission-enhancing effect of the soils native mbnA-expressing Methylocystaceae methanotrophs on the native denitrifiers was then experimentally verified with a Methylocystaceae-dominant chemostat culture prepared from a rice paddy microbial consortium as the inoculum. Lastly, with microcosms amended with varying cell numbers of methanobactin-producing Methylosinus trichosporium OB3b before CH4 enrichment, microbiomes with different ratios of methanobactin-producing Methylocystaceae to gammaproteobacterial methanotrophs incapable of methanobactin production were simulated. Significant enhancement of N2O production from denitrification was evident in both Methylocystaceae-dominant and Methylococcaceae-dominant enrichments, albeit to a greater extent in the former, signifying the comparative potency of methanobactin-mediated copper sequestration while implying the presence of alternative copper abstraction mechanisms for Methylococcaceae. These observations support that copper-mediated methanotrophic enhancement of N2O production from denitrification is plausible where methanotrophs and denitrifiers cohabit. ImportanceProteobacterial methanotrophs, groups of microorganisms that utilize methane as source of energy and carbon, have been known to utilize unique mechanisms to scavenge copper, namely utilization of methanobactin, a polypeptide that binds copper with high affinity and specificity. Previously the possibility that copper sequestration by methanotrophs may lead to alteration of cuproenzyme-mediated reactions in denitrifiers and consequently increase emission of potent greenhouse gas N2O has been suggested in axenic and co-culture experiments. Here, a suite of experiments with rice paddy soil slurry cultures with complex microbial compositions were performed to corroborate that such copper-mediated interplay may actually take place in environments co-habited by diverse methanotrophs and denitrifiers. As spatial and temporal heterogeneity allow for spatial coexistence of methanotrophy (aerobic) and denitrification (anaerobic) in soils, the results from this study suggest that this previously unidentified mechanism of N2O production may account for significant proportion of N2O efflux from agricultural soils.

microbiology↗

bioRxiv2020

Physiological characterization of nitrate ammonifying bacteria isolated from rice paddy soils via a newly developed high-throughput screening method

Dissimilatory nitrate/nitrite reduction to ammonium (DNRA) has recently gained attention as a nitrogen retention pathway that may potentially be harnessed to alleviate nitrogen loss resulting from denitrification. Until recently, ecophysiology of DNRA bacteria inhabiting agricultural soils has remained largely unexplored, due to the difficulty in targeted enrichment and isolation of DNRA microorganisms. In this study, >100 microbial isolates capable of DNRA have been isolated from rice paddy soil with apparent dominance of denitrification using a novel high-throughput screening method. Six of these isolates, each assigned to a disparate genus, was examined to improve understanding of DNRA physiology. All isolates carried nrfA and/or nirB, and an isolate affiliated to Bacillus possessed a clade II nosZ gene and was capable of N2O reduction. A common prominent physiological feature observed in all DNRA isolates was NO2- accumulation observed before NH4+ production, which was further examined with Citrobacter sp. DNRA3 (possessing nrfA and nirB) and Enterobacter sp. DNRA5 (possessing only nirB). In both organisms, NO2--to-NH4+ reduction was inhibited by submillimolar NO3-, and nrfA or nirB transcription was down-regulated when NO3- was being reduced to NO2-. Both batch and chemostat incubations of these isolates with excess organic electron donors produced NH4+ from reduction of NO3-; however, incubation with excess NO3- resulted in NO2- buildup but no substantial NH4+ production, presumably due to NO3- presence. This previously overlooked link between NO3- repression of NO2--to-NH4+ reduction and the C-to-N ratio regulation of DNRA activity may be a key mechanism underpinning denitrification-vs-DNRA competition in soil. IMPORTANCEDissimilatory nitrate/nitrite reduction to ammonium (DNRA) is an anaerobic microbial pathway that competes with denitrification for common substrates NO3- and NO2-. Unlike denitrification leading to nitrogen loss and N2O emission, DNRA reduces NO3- and NO2- to NH4+, a reactive nitrogen with higher tendency to be retained in soil matrix. Therefore, stimulation of DNRA has often been proposed as a strategy to improve fertilizer efficiency and reduce greenhouse gas emissions. Such attempts have been hampered by lack of insights into soil DNRA ecophysiology. Here, we have developed a novel high-throughput screening method for isolating DNRA-catalyzing organisms from agricultural soils without apparent DNRA activity. Physiological characteristics of six DNRA isolates were closely examined, disclosing a previously overlooked link between NO3- repression of NO2--to-NH4+ reduction and the C-to-N ratio regulation of DNRA activity, which may be key to understanding why significant DNRA activity is rarely observed in nitrogen-rich agricultural soils.

microbiology↗