Wide distribution of extracellular electron transfer functionality in natural proteinaceous organic materials for microbial reductive dehalogenation

Extracellular electron transfer materials (EETMs) in the environment, such as humic substances and biochar, are formed from the humification/heating of natural organic materials. However, the distribution of extracellular electron transfer (EET) functionality in fresh natural organic materials has not yet been explored. In the present study, we reveal the wide distribution of EET functionality in proteinaceous materials for the first time using an anaerobic pentachlorophenol dechlorinating consortium, whose activity depends on EETM. Out of 11 natural organic materials and 13 reference compounds, seven proteinaceous organic materials (albumin, beef, milk, pork, soybean, yolk, and bovine serum albumin) functioned as EETMs. Carbohydrates and lipids did not function as EETMs. Comparative spectroscopic analyses suggested that a β-sheet secondary structure was essential for proteins to function as EETMs, regardless of water solubility. A high content of reduced sulfur was potentially involved in EET functionality. Although proteinaceous materials have thus far been considered simply as nutrients, the wide distribution of EET functionality in these materials provides new insights into their impact on biogeochemical cycles. In addition, structural information on EET functionality can provide a scientific basis for the development of eco-friendly EETMs.

The Emergence of Extracellular Electron Mediating Functionality in Rice Straw-Artificial Soil Mixture during Humification

This study aimed to elucidate the origin of extracellular electron mediating (EEM) functionality and redox-active center(s) in humic substances, where they are ubiquitously distributed. Here, we show the emergence of EEM functionality during the humification of rice straw in artificial soil (kaolin and sand) with a matric potential of -100 cm at 20 °C for one year. We used the dechlorination activity of an EEM material-dependent pentachlorophenol-dechlorinating anaerobic microbial consortium as an index of the EEM functionality. Although rice straw and its mixture with artificial soil did not initially have EEM functionality, it emerged after one month of humification and increased until six months after which the functionality was maintained for one year. Chemical and electrochemical characterizations demonstrated that the emergence and increase in EEM functionality were correlated with the degradation of rice straw, formation of quinone structures, a decrease in aromatic structures, an increase in nitrogenous and aliphatic structures, and specific electric capacitance during humification. The newly formed quinone structure was suggested as a potential redox-active center for the EEM functionality. These findings provide novel insights into the dynamic changes in EEM functionality during the humification of organic materials.

Prognostic value of estimating appendicular muscle mass in heart failure using creatinine/cystatin C

Objectives

As heart failure with concomitant sarcopenia has a poor prognosis, simple methods for evaluating the appendicular skeletal muscle mass index (ASMI) are required. Recently, a model incorporating anthropometric data and the sarcopenia index, that is, the ratio of serum creatinine to cystatin C (Cre/CysC), was developed to estimate the appendicular skeletal muscle mass. We hypothesized that this model would be superior to the previous model, which uses only anthropometric data to predict the prognosis. This study aimed to compare the prognostic value of low ASMI as defined by the biomarker and anthropometric models in patients with heart failure.

Methods

Among 847 patients, we estimated ASMI using an anthropometric model consisting of age, body weight, and height in 791 patients and a biomarker model that incorporates age, body weight, hemoglobin, and Cre/CysC in 562 patients. Patients were divided into low and non-low ASMI groups according to the ASMI estimated by each model, using the cut-off proposed by the Asian Working Group for Sarcopenia. The primary outcome was all-cause mortality.

Results

Overall, 53.4% and 39.1% of patients were diagnosed with low ASMI by anthropometric and biomarker models, respectively. The agreement of the diagnosis of low ASMI between the two models was poor, with a kappa coefficient of 0.56 (95% confidence interval: 0.49–0.63). Kaplan-Meier curves showed that a low ASMI was significantly associated with all-cause death in both models. However, this association was retained after adjustment for other covariates in the biomarker model (hazard ratio: 2.60, p=0.003), but not in the anthropometric model (hazard ratio: 0.70, p=0.257).

Conclusions and implications

Among patients hospitalized with heart failure, a low ASMI estimated using the biomarker model, but not the anthropometric model, was significantly associated with all-cause mortality.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Japan Agency for Medical Research and Development

Promotion of Nitrogen Fixation of Diverse Heterotrophs by Solid-Phase Humin

Although biological nitrogen fixation (BNF) proceeds under mild conditions compared to the energy-intensive Haber–Bosch process, the slow kinetics of BNF necessitate the promotion of BNF activity in its practical application. The BNF promotion using purified nitrogenases and using genetically modified microorganisms has been studied, but these enzymes are unstable and expensive; moreover, designing genetically modified microorganisms is also a difficult task. Alternatively, the BNF promotion in non-modified (wild-type) microorganisms (enriched consortia) with humin has been shown, which is a humic substance insoluble at any pH and functions as an extracellular electron mediator. However, the taxonomic distribution of the diazotrophs promoted by humin, the levels of BNF promotion, and the underlying mechanism in BNF promotion with humin remain unknown. In this study, we show that taxonomically diverse heterotrophic diazotrophs, harboring nifH clusters I, II, and III, promoted their BNF by accepting extracellular electrons from humin, based on the characterization of the individual responses of isolated diazotrophs to humin. The reduced humin increased the acetylene reduction activity of the diazotrophs by 194–916% compared to the level achieved by the organic carbon source, causing adenosine triphosphate (ATP) synthesis in the diazotroph cells without increase in the CO₂ production and direct electron donation to the MoFe protein of the nitrogenase in the cells without relying on the biological electron transfer system. These would result in BNF promotion in the wild-type diazotroph cells beyond their biochemical capacity. This significant promotion of BNF with humin would serve as a potential basis for sustainable technology for greener nitrogen fixation.

Promotion of biological H2 (Bio-H2) production by the nitrogen-fixing anaerobic microbial consortia using humin, a solid-phase humic substance

Dark fermentative biological hydrogen (Bio-H₂) production is expected to be a clean and sustainable H₂ production technology, and the technologies have been studied to increase in the product yield as index. This study achieved high product yields of Bio-H₂ using nitrogen-fixing consortia under nitrogen-deficient conditions with glucose or mannitol as substrate and humin as the extracellular electron mediator: 4.12 mol-H₂/mol-glucose and 3.12 mol-H₂/mol-mannitol. The high Bio-H₂ production was observed under the conditions where both nitrogenase and hydrogenase were active in the presence of humin. Nitrogenase activity was confirmed by acetylene reduction activity and hydrogenase activity by Bio-H₂ production under nitrogenase-inhibiting conditions with NH₄NO₃. [Fe-Fe] hydrogenase detected by a specific PCR and acetate, butyrate, formate, lactate, and pyruvate produced as by-products suggested the involvement of both pyruvate-ferredoxin-oxidoreductase and pyruvate formate lyase pathways in Bio-H₂ production. Humin promoted the Bio-H₂ production beyond the capacity of the consortium, which had reached saturation with the optimum concentrations of glucose and mannitol. Carbon balance suggested the concurrent H₂ consumption by hydrogenotrophic methanogenesis and acetogenesis. Bio-H₂ production of the washed and starved consortium with reduced humin under conditions with or without NH₄NO₃ suggests that humin promoted hydrogenase and nitrogenase activity by donating extracellular electrons. Clostridium and Ruminococcus in the consortia were considered major hydrogen producers. Thus, this study demonstrated the outstanding potential of nitrogen-fixing consortia under nitrogen-deficient conditions with humin as an extracellular electron mediator for dark fermentative Bio-H₂ production with high yields.

Effect of Humin and Chemical Factors on CO2-Fixing Acetogenesis and Methanogenesis

Acetogenesis and methanogenesis have attracted attention as CO₂-fixing reactions. Humin, a humic substance insoluble at any pH, has been found to assist CO₂-fixing acetogenesis as the sole electron donor. Here, using two CO₂-fixing consortia with acetogenic and methanogenic activities, the effect of various parameters on these activities was examined. One consortium utilized humin and hydrogen (H₂) as electron donors for acetogenesis, either separately or simultaneously, but with a preference for the electron use from humin. The acetogenic activity was accelerated 14 times by FeS at 0.2 g/L as the optimal concentration, while being inhibited by MgSO₄ at concentration above 0.02 g/L and by NaCl at concentrations higher than 6 g/L. Another consortium did not utilize humin but H₂ as electron donor, suggesting that humin was not a universal electron donor for acetogenesis. For methanogenesis, both consortia did not utilize extracellular electrons from humin unless H₂ was present. The methanogenesis was promoted by FeS at 0.2 g/L or higher concentrations, especially without humin, and with NaCl at 2 g/L or higher concentrations regardless of the presence of humin, while no significant effect was observed with MgSO₄. Comparative sequence analysis of partial 16S rRNA genes suggested that minor groups were the humin-utilizing acetogens in the consortium dominated by Clostridia, while Methanobacterium was the methanogen utilizing humin with H₂.

Humin: No longer inactive natural organic matter

The discovery of the function of humin (HM), an insoluble fraction of humic substances (HSs), as an extracellular electron mediator (EEM) in 2012 has provided insight into the role of HM in nature and its potential for in situ bioremediation of pollutants. The EEM function is thought to enable the energy network of various microorganisms using HM. Recently, a number of studies on the application of HM as EEM in anaerobic microbial cultures have been conducted. Even so, there is a need for developing a holistic view of HM EEM function. In this paper, we summarize all the available information on the properties of HM EEM function, its applications, possible redox-active structures, and the interaction between HM and microbial cells. We also suggest scopes for future HM research.

Promotion of biological nitrogen fixation activity of an anaerobic consortium using humin as an extracellular electron mediator

Nitrogen fertiliser is manufactured using the industrial Haber–Bosch process, although it is extremely energy-consuming. One sustainable alternative technology is the electrochemical promotion of biological nitrogen fixation (BNF). This study reports the promotion of BNF activity of anaerobic microbial consortia by humin, a solid-phase humic substance, at any pH, functioning as an extracellular electron mediator, to levels of 5.7–11.8 times under nitrogen-deficient conditions. This was evidenced by increased acetylene reduction activity and total nitrogen content of the consortia. Various humins from different origins promoted anaerobic BNF activity, although the degree of promotion differed. The promotion effected by humin differed from the effects of chemical reducing agents and the effects of supplemental micronutrients and vitamins. The promotion of anaerobic BNF activity by only reduced humin without any other electron donor suggested that humin did not serve as organic carbon source but as extracellular electron mediator, for electron donation to the nitrogen-fixing microorganisms. The next generation sequencing (NGS) of partial 16S rRNA genes showed the predominance of Clostridiales (Firmicutes) in the consortia. These findings suggest the effectiveness of humin as a solid-phase extracellular electron mediator for the promotion of anaerobic BNF activity, potentially to serve for the basis for a sustainable technology.

Obstructive sleep apnoe and cardiovascular, heart failure and mortality outcomes with empagliflozin versus placebo in the EMPA-REG OUTCOME trial

Background/Introduction

Obstructive sleep apnoe (OSA) and type 2 diabetes (T2D) occurs more frequently in persons with obesity, and both OSA and T2D are associated with metabolic disturbances that increases the risk for cardiovascular disease (CVD). In EMPA-REG OUTCOME, a randomized placebo-controlled outcome trial involving 7020 patients with T2D and CVD, the sodium glucose co-transporter (SGLT)-2 inhibitor empagliflozin reduced HbA1c, systolic blood pressure, waist circumference, and weight, and also reduced the risk of 3-point major adverse CV events (3P- MACE) by 14%, CV death by 38% and hospitalization for heart failure (HHF) by 35%.

Purpose

We investigated incidence rates of CV, HHF, and mortality outcomes in patients with or without OSA at baseline, and the treatment effect of empagliflozin, in EMPA-REG OUTCOME.

Methods

The trial included patients from 42 countries with T2D (with HbA1c 7.0–9.0% for drug-naïve patients and 7.0–10.0% for those on stable glucose-lowering therapy), established CVD, and estimated glomerular filtration rate >30 mL/min/1.73 m2. Patients were randomised (1:1:1) to receive empagliflozin 10 mg, empagliflozin 25 mg, or placebo once daily in addition to standard of care. All CV outcomes were independently adjudicated and events were pooled for the 10 and 25mg doses. In this post-hoc analysis, OSA were assessed based on investigator reports using MedDRA 18.0 and incidence rates for outcomes were reported by adjusted event-rates per 100 patient-years. Analysis of effects on outcomes were performed using Cox regression models with multivariable adjustments.

Results

Of 7020 patients with T2D and CVD, OSA was reported in 391 (5.6% [placebo 5.4%; pooled empagliflozin doses 5.7%]. Compared with patients without OSA at baseline, those with OSA were more frequent males (82.9% vs 70.8%), living in region North-America (63.2% vs 17.3%), and had more obesity (BMI ≥35 kg/m2: 55.2% vs 18.2%) and more coronary artery disease (88.0 vs 74.9%). Over a median 3.1 years, individuals with OSA at baseline relative to those without OSA in the placebo group, experienced 1.3–2.0 fold higher event rates for 3P-MACE (OSA vs no OSA: 6.49 vs 4.27/100-patient-year), CV death (2.57 vs 1.99), HHF (2.71 vs 1.38) and all-cause mortality (4.29 vs 2.78). Empagliflozin improved CV, HHF, and mortality outcomes regardless of presence of OSA at baseline (p-for interactions >0.05 [Figure 1]).

Conclusions

In this post-hoc exploratory analysis, patients with OSA had higher frequency of events for 3P-MACE, HHF and mortality. The cardio-protective effects of empagliflozin was consistent in those with and without OSA at baseline.

Figure 1. Sleep apnea and empagliflozin

Funding Acknowledgement

Type of funding source: Private company. Main funding source(s): Boehringer Ingelheim and Eli Lilly Diabetes Alliance

Prognostic significance of 2019 Asian Working Group for Sarcopenia update on definition of sarcopenia

Background/Introduction

Sarcopenia plays a major role in the pathophysiology of frailty and is associated with worse outcome in the elderly population including patients with heart failure. A recent update of the most common definition of sarcopenia in Asia, Asian Working Group for Sarcopenia (AWGS2019), included significant changes in the diagnostic algorithm with newly dividing sarcopenia into severe and “non-severe” sarcopenia.

Purpose

The objective of this study was to evaluate the differences between AWGS2014 and AWGS2019 in patients with heart failure.

Methods

In the multicenter prospective FRAGILE-HF registry, which included elderly (≥65 years old) patients who were hospitalized with heart failure, we studied 865 patients (80±8 years old, 42% female). All-cause death in 1-year follow-up was tracked.

Results

Based on the original version of AWGS (AWGS2014), 183 patients (21%) were diagnosed with sarcopenia, which was associated with higher age, lower physical performance, less muscle mass, and greater heart failure risk (all p<0.001) as well as higher rate of all-cause death (HR 1.90, p=0.004 after adjustment by multivariable regression). Those patients with sarcopenia by AWGS2014 were reclassified mainly to severe sarcopenia (155, 84.7%) by AWGS2019, and 25 (13.7%) and 2 (1.1%) were classified into sarcopenia and non-sarcopenia. Meanwhile, 24 (3.5%) and 4 (0.6%) of patients without sarcopenia by AWGS2014 were reclassified into sarcopenia and severe sarcopenia, respectively. Although severe sarcopenia by AWGS2019 was associated with higher age, lower physical performance, less muscle mass, and greater heart failure risk (all p<0.001), patients with “non-severe” sarcopenia was rather younger (p<0.001) and had better physical performance (p=0.021) despite less muscle mass (p<0.001) than those without sarcopenia. Multivariate Cox analysis demonstrated severe sarcopenia by AWGS2019 was an independent prognostic factor (HR 1.77, p=0.014), but “non-severe” sarcopenia was not (HR 1.52, p=0.37). The prognosis of patients who were reclassified from non-sarcopenia to sarcopenia or severe sarcopenia were comparable to those remained non-sarcopenia. When added to other risk factors, the prognostic predictability of AWGS2019 was significantly lower than AWGS2014 (net reclassification improvement −0.26, p=0.025).

Conclusions

About a half of “non-severe” sarcopenia in AWGS2019 were patients without sarcopenia in AWGS2014. The prognosis of such patients who were newly diagnosed as sarcopenia was good, resulting in low overall prognostic predictability of AWGS2019. A further consideration for diagnostic algorithms of sarcopenia may be warranted in patients with heart failure.

Funding Acknowledgement

Type of funding source: Foundation. Main funding source(s): Japan Heart Foundation

Validation and comparison of BIOSTAT risk score and AHEAD score for patients with acute heart failure

Background/Introduction

Acute heart failure (AHF) is one of the major causes of mortality, and identifying the patients at high risk of mortality at the time of admission is crucial to improve clinical outcomes. Although some risk prediction models for patients with AHF have been proposed mainly from randomized clinical trials, the patients in such studies tend not to be similar to those in the real world. Recently, BIOSTAT risk score and AHEAD score derived from two large-scale registry dataset are proposed as useful risk stratification tools for patients with AHF. However, these scores have not been well externally validated and their prognostic prediction performance has not been directly compared.

Purpose

To validate and compare prognostication of BIOSTAT risk score and AHEAD score in AHF patients.

Methods

Patients who consecutively admitted to the cardiac intensive-care unit in our institution with a diagnosis of AHF from 2007 to 2011 were analyzed. Among them, patients with acute coronary syndrome, dialysis, malignancy were excluded. BIOSTAT risk score was calculated using 5 factors (age, blood urea nitrogen, BNP, hemoglobin, prescription of beta blockers), and AHEAD score was also calculated with 5 factors (atrial fibrillation, hemoglobin, age, creatinine, and diabetes mellitus). We also developed AHEAD + BNP model incorporating BNP into AHEAD score. Endpoint was 1-year all-cause death.

Results

Overall, 591 eligible patients were enrolled (mean age was 70±14 years old, 64.8% were male) and 96 patients (16.2%) died during the follow-up of 1-year. The median [interquartile range] of AHEAD score and BIOSTAT risk score were 2 [1–3] and 3 [2–4], respectively. The areas under the curves of receiver operating characteristic curve (AUC) were 0.66 for AHEAD, 0.68 for AHEAD + BNP, and 0.72 for BIOSTAT, respectively. The calibration plots for AHEAD, AHEAD + BNP, and BIOSTAT models showed good calibration (Hosmer-Lemeshow test: p=0.89, 0.74, and 0.74, respectively). The BIOSTAT model's AUC was significantly higher compared to AHEAD (p=0.018) and marginally statistically higher compared to AHEAD + BNP (p=0.054). However, BIOSTAT model showed statistically significant net reclassification improvement compared to both AHEAD (NRI: 0.43, p<0.001) and AHEAD + BNP (NRI: 0.43, p<0.001).

Conclusion

The BIOSTAT score comprised of five readily available clinical variables predict 1-year mortality of patients with AHF with good discrimination and calibration.

ROC curves

Funding Acknowledgement

Type of funding source: None

Social frailty provides additive prognostic impact on one-year outcome in aged patients with congestive heart failure

Background

Frailty is associated with multisystem declines in physiologic reserve and increased vulnerability to stressors, resulting in increased risks of adverse clinical outcomes in patients with heart failure (HF). Although frailty is conceptualized as an accumulation of deficits in multiple areas, most of the studies have focused mainly on physical frailty, and the social domains is one of the least investigated area.

Objectives

We prospectively evaluated the incidence and prognostic implication of social frailty (SF) in older patients with HF.

Methods

The FRAGILE-HF is a multicenter, prospective cohort study including patients hospitalized for HF and aged ≥65 years old. We defined SF by Makizako's 5 items, which are 5 questions proposed and validated to be associated with future disability. The primary endpoint of this study was a composite of death from any cause and rehospitalization due to HF. The impact of SF on all-cause mortality alone was also evaluated.

Results

Among 1,240 hospitalized HF patients, 5 simple questions revealed that 825 (66.5%) were in SF. During 1-year observation period after the discharge, the combined endpoint was observed in 399 (32.2%) patients, and 145 (11.7%) patients died. Kaplan-Meier analysis showed that SF patients had significantly higher rates of both the combined endpoint and all-cause mortality than those without SF (Log-rank test: p<0.05 for both, Figures). Moreover, SF remained independently associated with higher event rate of the combined endpoint (hazard ratio: 1.30; 95% confidence interval: 1.02 to 1.66; p=0.038) and all-cause mortality (hazard ratio: 1.53; 95% confidence interval: 1.01 to 2.30; p=0.044), even after adjusting for other covariates. Significant incremental prognostic value was shown when information on social frailty was added to known risk factors for combined endpoint (NRI: 0.189, 95% confidence interval: 0.063–0.316, p=0.003) and all-cause mortality (NRI: 0.234, 95% confidence interval: 0.073–0.395, p=0.004).

Conclusions

Among older hospitalized patients with heart failure, two-thirds of the population was with SF. Evaluating SF provides additive prognostic information in elderly patients with heart failure.

Funding Acknowledgement

Type of funding source: Private grant(s) and/or Sponsorship. Main funding source(s): Novartis Pharma Research Grants, Japan Heart Foundation Research Grant

Changes in the ear canal microbiota of dogs with otitis externa

AIMS

Otitis externa (OE), one of the most common ear diseases in dogs, is caused by bacterial pathogens such as Staphylococcus sp. To understand the network of microbial communities in the canine ear canal affected with OE, we performed a cross-sectional study using next-generation sequencing.

METHODS AND RESULTS

Ear swab samples were collected from 23 OE-affected and 10 healthy control dogs, and the 16S rRNA gene sequenced using Illumina MiSeq. The otic microbiota in the OE-affected dogs showed significantly decreased alpha diversity compared to controls. The community composition also differed in the affected group, with significantly higher relative abundance of the phylum Firmicutes and the genus Staphylococcus (P = 0·01 and 0·04 respectively). Contrary to our expectations, the severity of the disease did not impact the otic microbiota in OE-affected dogs.

CONCLUSIONS

The ear canal microbiota of OE-affected dogs is distinct from that of healthy dogs, irrespective of disease status.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study, one of the few detailed analyses of the otic microbiota, can provide practical information for the appropriate treatment of canine OE.

Humin Assists Reductive Acetogenesis in Absence of Other External Electron Donor

The utilization of extracellular electron transfer by microorganism is highly engaging for remediation of toxic pollutants under “energy-starved” conditions. Humin, an organo-mineral complex of soil, has been instrumental as an external electron mediator for suitable electron donors in the remediative works of reductive dehalogenation, denitrification, and so forth. Here, we report, for the first time, that humin assists microbial acetogenesis as the extracellular electron donor using the electron acceptor CO2. Humin was obtained from Kamajima paddy soil, Japan. The anaerobic acetogenic consortium in mineral medium containing CO2/HCO3− as the inorganic carbon source used suspended humin as the energy source under mesophilic dark conditions. Retardation of acetogenesis under the CO2-deficient conditions demonstrated that humin did not function as the organic carbon source but as electron donor in the CO2-reducing acetogenesis. The consortium with humin also achieved anaerobic dechlorination with limited methanogenic activity. Total electron-donating capacity of humin was estimated at about 87 µeeq/g-humin. The metagenomic sequencing of 16S rRNA genes showed the predominance of Firmicutes (71.8 ± 2.5%) in the consortium, and Lachnospiraceae and Ruminococcaceae were considered as the CO2-reducing acetogens in the consortium. Thus, microbial fixation of CO2 using humin introduces new insight to the holistic approach for sustainable treatment of contaminants in environment.

Anaerobic Dechlorination by a Humin-Dependent Pentachlorophenol-Dechlorinating Consortium under Autotrophic Conditions Induced by Homoacetogenesis

Anoxic aquifers suffer from energy limitations due to the unavailability of organic substrates, as dictated by hydrogen (H2) for various electron-accepting processes. This deficiency often results in the accumulation of persistent organic pollutants, where bioremediation using organic compounds often leads to secondary contamination. This study involves the reductive dechlorination of pentachlorophenol (PCP) by dechlorinators that do not use H2 directly, but rather through a reduced state of humin-a solid-phase humic substance-as the extracellular electron donor, which requires an organic donor such as formate, lactate, etc. This shortcoming was addressed by the development of an anaerobic mixed culture that was capable of reductively dechlorinating PCP using humin under autotrophic conditions induced by homoacetogenesis. Here, H2 was used for carbon-dioxide fixation to acetate; the acetate produced was used for the reduction of humin; and consequently used for dechlorination through reduced humin. The 16SrRNA gene sequencing analysis showed Dehalobacter and Dehalobacterium as the possible dechlorinators, while Clostridium and Oxobacter were identified as the homoacetogens. Thus, this work contributes to the development of an anaerobic consortium that balanced H2 dependency, where efficiency of humin reduction extends the applicability of anaerobic microbial remediation in aquifers through autotrophy, syntrophy, and reductive dechlorination.

Overexpression of the adenylate cyclase gene cyaC facilitates current generation by Shewanella oneidensis in bioelectrochemical systems

Electrochemically active bacteria (EAB) are capable of electrochemical interactions with electrodes via extracellular electron transfer (EET) pathways and serve as essential components in bioelectrochemical systems. Previous studies have suggested that EAB, such as Shewanella oneidensis MR-1, use cyclic AMP (cAMP) receptor proteins to coordinately regulate the expression of catabolic and EET-related genes, prompting us to hypothesize that the intracellular cAMP concentration is an important factor determining the electrochemical activities of EAB. The present study constructed an MR-1 mutant, cyaC-OE, that overexpressed cyaC, a gene encoding a membrane-bound class III adenylate cyclase, and examined its electrochemical and transcriptomic characteristics. We show that the intracellular cAMP concentration in cyaC-OE is more than five times that in wild-type MR-1, and that cya-OE generates approximately two-fold higher current in BES than the wild-type strain. In addition, the expression of genes involved in EET and anaerobic carbon catabolism is up-regulated in cya-OE compared to that in the wild-type strain. These results suggest that increasing the intracellular cAMP level is a promising approach for constructing EAB with high catabolic and electrochemical activities.

Drug-induced oral lichenoid reaction during nivolumab therapy

Oral lichenoid reaction, an immune-related adverse event of immunotherapy, has been reported in very few patients receiving anti-programmed cell death receptor-1 (anti-PD-1) therapy. Here, we describe a case of severe stomatitis (grade ≥3 by the Common Terminology Criteria for Adverse Events, version 4.0) accompanied by pharyngolaryngitis that was observed in a patient receiving nivolumab therapy. The stomatitis was diagnosed as drug-induced lichenoid reaction. Nivolumab therapy was discontinued, and the patient was administered systemic prednisolone (1mg/kg). Most of the patient's mucosal changes in the oral cavity and pharyngolarynx resolved within approximately 3 weeks after starting the prednisolone. Clinicians should be aware that severe oral lichenoid reactions can occur in patients receiving anti-PD-1 therapy.

Electrochemically active bacteria sense electrode potentials for regulating catabolic pathways

Electrochemically active bacteria (EAB) receive considerable attention for their utility in bioelectrochemical processes. Although electrode potentials are known to affect the metabolic activity of EAB, it is unclear whether EAB are able to sense and respond to electrode potentials. Here, we show that, in the presence of a high-potential electrode, a model EAB Shewanella oneidensis MR-1 can utilize NADH-dependent catabolic pathways and a background formate-dependent pathway to achieve high growth yield. We also show that an Arc regulatory system is involved in sensing electrode potentials and regulating the expression of catabolic genes, including those for NADH dehydrogenase. We suggest that these findings may facilitate the use of EAB in biotechnological processes and offer the molecular bases for their ecological strategies in natural habitats.

Long-term clinical impact of serum albumin in coronary artery disease patients with preserved renal function

BACKGROUND AND AIMS

Low serum albumin level is reportedly associated with worse clinical outcomes in patients with chronic kidney disease (CKD). However, associations between decreased serum albumin level and outcomes in non-CKD patients with coronary artery disease (CAD) remain unclear. Therefore, we aimed to evaluate the prognostic value of serum albumin concentrations in stable CAD patients with preserved renal function.

METHODS AND RESULTS

We studied 1316 patients with CAD and preserved renal function (estimated glomerular filtration rate ≥60 mL/min/1.73 m²) who underwent their first PCI between 2000 and 2011 and had data available for pre-procedural serum albumin. Patients were assigned to quartiles based on pre-procedural albumin concentrations. The incidence of major adverse cardiac events (MACE), including all-cause death and non-fatal myocardial infarction, was evaluated. Mean albumin concentration was 4.1 ± 0.4 g/dL. During the median follow-up of 7.5 years, 181 events occurred (13.8%). Kaplan-Meier curves revealed that patients with decreased serum albumin concentrations showed a higher event rate for MACE (log-rank, p < 0.0001). Using the highest tertiles (>4.3 g/dL) as reference, adjusted hazard ratios were 1.97 (95% CI, 1.12-3.55), 1.77 (95% CI, 0.99-3.25), and 1.19 (95% CI, 0.68-2.15) for serum albumin concentrations of <3.9, 3.9-4.0, and 4.1-4.3 g/dL, respectively. Decreased serum albumin concentration was associated with MACE even after adjusting for other independent variables (HR, 2.21 per 1-g/dL decrease; 95% CI, 1.37-3.56, p = 0.001).

CONCLUSION

Decreased serum albumin concentration independently predicted worse long-term prognosis in non-CKD patients after PCI. Pre-procedural serum albumin concentration could offer a useful predictor for patients with CAD and preserved renal function.

CpdA is involved in amino acid metabolism in Shewanella oneidensis MR-1

Cyclic 3',5'-adenosine monophosphate (cAMP) phosphodiesterase (CPD) is an enzyme that catalyzes the hydrolysis of cAMP, a signaling molecule affecting diverse cellular and metabolic processes in bacteria. Some CPDs are also known to function in cAMP-independent manners, while their physiological roles remain largely unknown. Here, we investigated physiological roles of CPD in Shewanella oneidensis MR-1, a model environmental bacterium, and report that CPD is involved in amino-acid metabolism. We found that a CPD-deficient mutant of MR-1 (ΔcpdA) showed decreased expression of genes for the synthesis of methionine, S-adenosylmethionine, and histidine and required these three compounds to grow in minimal media. Interestingly, deletion of adenylate cyclases in ΔcpdA did not restore the ability to grow in minimal media, indicating that the amino acid requirements were not due to the accumulation of cAMP. These results suggest that CPD is involved in the regulation of amino acid metabolism in MR-1 in a cAMP-independent manner.

CRP Regulates D-Lactate Oxidation in Shewanella oneidensis MR-1

Shewanella oneidensis MR-1 is a heterotrophic facultative anaerobe that respires using various organic and inorganic compounds. This organism has served as a model to study bacterial metabolic and regulatory systems that facilitate their survival in redox-stratified environments. The expression of many anaerobic respiratory genes in MR-1, including those for the reduction of fumarate, dimethyl sulfoxide, and metal oxides, is regulated by cyclic AMP receptor protein (CRP). However, relatively little is known about how this organism regulates the expression of catabolic enzymes catalyzing the oxidation of organic compounds, including lactate. Here, we investigated transcriptional mechanisms for the lldP (SO_1522) and dld (SO_1521) genes, which encode putative lactate permease and D-lactate dehydrogenase, respectively, and demonstrate that CRP regulates their expression in MR-1. We found that a crp-deletion mutant of MR-1 (Δcrp) showed impaired growth on D-lactate. Complementary expression of dld in Δcrp restored the ability to grow on D-lactate, indicating that the deficient growth of Δcrp on D-lactate is attributable to decreased expression of dld. In vivo transcription and in vitro electrophoretic mobility shift assays reveal that CRP positively regulates the expression of the lldP and dld genes by directly binding to an upstream region of lldP. Taken together, these results indicate that CRP is a global transcriptional regulator that coordinately regulates the expression of catabolic and respiratory pathways in MR-1, including D-lactate dehydrogenase and anaerobic terminal reductases.

Catabolic and regulatory systems in Shewanella oneidensis MR-1 involved in electricity generation in microbial fuel cells

Shewanella oneidensis MR-1 is a facultative anaerobe that respires using a variety of inorganic and organic compounds. MR-1 is also capable of utilizing extracellular solid materials, including anodes in microbial fuel cells (MFCs), as electron acceptors, thereby enabling electricity generation. As MFCs have the potential to generate electricity from biomass waste and wastewater, MR-1 has been extensively studied to identify the molecular systems that are involved in electricity generation in MFCs. These studies have demonstrated the importance of extracellular electron-transfer (EET) pathways that electrically connect the quinone pool in the cytoplasmic membrane to extracellular electron acceptors. Electricity generation is also dependent on intracellular catabolic pathways that oxidize electron donors, such as lactate, and regulatory systems that control the expression of genes encoding the components of catabolic and electron-transfer pathways. In addition, recent findings suggest that cell-surface polymers, e.g., exopolysaccharides, and secreted chemicals, which function as electron shuttles, are also involved in electricity generation. Despite these advances in our knowledge on the EET processes in MR-1, further efforts are necessary to fully understand the underlying intra- and extracellular molecular systems for electricity generation in MFCs. We suggest that investigating how MR-1 coordinates these systems to efficiently transfer electrons to electrodes and conserve electrochemical energy for cell proliferation is important for establishing the biological basis for MFCs.