Clinical characteristics with inflammation profiling of long COVID and association with 1-year recovery following hospitalisation in the UK: a prospective observational study

BACKGROUND

No effective pharmacological or non-pharmacological interventions exist for patients with long COVID. We aimed to describe recovery 1 year after hospital discharge for COVID-19, identify factors associated with patient-perceived recovery, and identify potential therapeutic targets by describing the underlying inflammatory profiles of the previously described recovery clusters at 5 months after hospital discharge.

METHODS

The Post-hospitalisation COVID-19 study (PHOSP-COVID) is a prospective, longitudinal cohort study recruiting adults (aged ≥18 years) discharged from hospital with COVID-19 across the UK. Recovery was assessed using patient-reported outcome measures, physical performance, and organ function at 5 months and 1 year after hospital discharge, and stratified by both patient-perceived recovery and recovery cluster. Hierarchical logistic regression modelling was performed for patient-perceived recovery at 1 year. Cluster analysis was done using the clustering large applications k-medoids approach using clinical outcomes at 5 months. Inflammatory protein profiling was analysed from plasma at the 5-month visit. This study is registered on the ISRCTN Registry, ISRCTN10980107, and recruitment is ongoing.

FINDINGS

2320 participants discharged from hospital between March 7, 2020, and April 18, 2021, were assessed at 5 months after discharge and 807 (32·7%) participants completed both the 5-month and 1-year visits. 279 (35·6%) of these 807 patients were women and 505 (64·4%) were men, with a mean age of 58·7 (SD 12·5) years, and 224 (27·8%) had received invasive mechanical ventilation (WHO class 7-9). The proportion of patients reporting full recovery was unchanged between 5 months (501 [25·5%] of 1965) and 1 year (232 [28·9%] of 804). Factors associated with being less likely to report full recovery at 1 year were female sex (odds ratio 0·68 [95% CI 0·46-0·99]), obesity (0·50 [0·34-0·74]) and invasive mechanical ventilation (0·42 [0·23-0·76]). Cluster analysis (n=1636) corroborated the previously reported four clusters: very severe, severe, moderate with cognitive impairment, and mild, relating to the severity of physical health, mental health, and cognitive impairment at 5 months. We found increased inflammatory mediators of tissue damage and repair in both the very severe and the moderate with cognitive impairment clusters compared with the mild cluster, including IL-6 concentration, which was increased in both comparisons (n=626 participants). We found a substantial deficit in median EQ-5D-5L utility index from before COVID-19 (retrospective assessment; 0·88 [IQR 0·74-1·00]), at 5 months (0·74 [0·64-0·88]) to 1 year (0·75 [0·62-0·88]), with minimal improvements across all outcome measures at 1 year after discharge in the whole cohort and within each of the four clusters.

INTERPRETATION

The sequelae of a hospital admission with COVID-19 were substantial 1 year after discharge across a range of health domains, with the minority in our cohort feeling fully recovered. Patient-perceived health-related quality of life was reduced at 1 year compared with before hospital admission. Systematic inflammation and obesity are potential treatable traits that warrant further investigation in clinical trials.

FUNDING

UK Research and Innovation and National Institute for Health Research.

Patellar tendon ultrasonography in asymptomatic active athletes reveals hypoechoic regions: a study of 320 tendons. Victorian Institute of Sport Tendon Study Group

OBJECTIVE

To compare patellar tendon sonographic findings in active, currently asymptomatic, elite athletes with those in nonathletic controls.

DESIGN

Cross-sectional cohort study with convenience control sample.

SETTING

The Victorian Institute of Sport Tendon Study Group, an institutional elite athlete study group in Australia.

PATIENTS AND PARTICIPANTS

Two hundred elite male and female athletes from the sports of basketball, cricket, netball, and Australian rules football. Forty athletes who had current symptoms of jumper's knee were excluded from analysis, leaving 320 subject tendons in athletes who were currently asymptomatic. Twenty-seven nonathletic individuals served as controls.

MAIN OUTCOME MEASURE

Sonographic patellar tendon appearance. We measured the dimensions of subject tendons and noted the presence or absence of hypoechoic regions and tendon calcification. Dimensions of hypoechoic regions were measured, and approximate cross-sectional areas were calculated. Chi-squared analysis was used to test the prevalence of hypoechoic regions in subjects and controls and men and women.

RESULTS

In currently asymptomatic subjects, hypoechoic regions were more prevalent in athlete tendons (22%) than in controls (4%), in male subject tendons (30%) than in female subjects (14%), and in basketball players (32%) than in other athletes (9%) (all p < 0.01). Bilateral tendon abnormalities were equally prevalent in men and women but more prevalent in basketball players (15%) than in other athletes (3%) (p < 0.05). Sonographic hypoechoic regions were present in 35 of 250 (14%) patellar tendons in athletes who had never had anterior knee pain.

CONCLUSIONS

Patellar tendon sonographic hypoechoic areas were present in asymptomatic patellar tendons of a proportion of elite athletes but rarely present in controls. This has implications for clinicians managing athletes with anterior knee pain.

The macrophage - a novel system to deliver gene therapy to pathological hypoxia

The use of activated macrophages in the treatment of cancer has been largely ineffectual. By 'arming' these cells with the ability to express a therapeutic gene we demonstrate significant advances in the efficacy of this approach. We have used a hypoxia-regulated adenoviral vector to transduce human macrophages with either a reporter or a therapeutic gene encoding human cytochrome P4502B6 (CYP2B6). Infiltration of transduced macrophages into a tumour spheroid results in induction of gene expression. We demonstrate significant tumour cell killing only in the presence of cyclophosphamide via activation by P4502B6 and show that this can be further targeted to tumours through hypoxia regulated gene expression. Gene Therapy (2000) 7, 255-262.

Patellar tendinopathy in junior basketball players: a controlled clinical and ultrasonographic study of 268 patellar tendons in players aged 14-18 years

Anterior knee pain is a common presenting complaint amongst adolescent athletes. We hypothesised that patellar tendinopathy may occur at a younger age than is generally recognised. Thus, we studied the patellar tendons in 134 elite 14- to 18-year-old female (n=64) and male (n=70) basketball players and 29 control swimmers (17 female, 12 male) clinically and with ultrasonography. We found that of 268 tendons, 19 (7%) had current patellar tendinopathy on clinical grounds (11% in males, 2% in females). Twenty-six percent of the basketball players' patellar tendons contained an ultrasonographic hypoechoic region. Ultrasonographic abnormality was more prevalent in the oldest tertile of players (17-18 years) than the youngest tertile (14-15.9 years). Of tendons categorised clinically as 'Never patellar tendinopathy', 22% had an ultrasonographic hypoechoic region nevertheless. This study indicates that patellar tendinopathy can occur in 14- to 18-year-old basketball players. Ultrasonographic tendon abnormality is 3 times as common as clinical symptoms.

Latent equid herpesviruses 1 and 4: detection and distinction using the polymerase chain reaction and co-cultivation from lymphoid tissues

The polymerase chain reaction (PCR) and co-cultivation were used to identify the lymphoreticular system as the site of latency of equid herpesvirus I (EHV-1). Primers for PCR were designed from aligned nucleotide sequences of the glycoprotein gB genes to amplify the same region of both the EHV-1 and EHV-4 genomes. Subsequent restriction digests using specific enzymes distinguished the amplified fragments of the EHV-1 genome from those of the EHV-4 genome. Ten weeks following an experimental infection of five ponies with EHV-1, latent virus was detected by PCR and recovered by co-cultivation, predominantly from lymphoid tissues draining the respiratory tract. Significantly, latent EHV-1 also persisted in peripheral blood leukocytes (PBL). Latent EHV-4, presumably from a preceding natural infection, was also detected in some tissues, including PBL, from all animals. Of additional interest was the recovery of EHV-1 and -4 only in the presence of the ubiquitous EHV-2.

Escherichia coli K-12 genes essential for the synthesis of c-type cytochromes and a third nitrate reductase located in the periplasm

The 'aeg46.5' operon was originally detected as an 'anaerobically expressed gene' located at minute 46.5 on the Escherichia coli linkage map. Subsequent results from the E. coli Genome Sequencing Project revealed that the 'aeg46.5' promoter was located in the centisome 49 (minute 47) region. Downstream from this promoter are 15 genes, seven of which are predicted to encode a periplasmic nitrate reductase and eight encode proteins homologous to proteins essential for cytochrome c assembly in other bacteria. All of these genes, together with the 'aeg46.5' promoter, have been subcloned on a 20kb EcoRI fragment from Kohara phage 19D1. Evidence is presented that, as predicted, the region includes structural genes for two c-type cytochromes of mass 16kDa and 24 kDa, which are transcribed from the previously described 'aeg46.5' promoter, and that the first seven genes encode a functional nitrate reductase. We, therefore, propose that they should be designated nap (nitrate reductase in the periplasm) genes. Plasmids encoding the entire 20kb region, or only the downstream eight genes, complemented five mutations resulting in total absence of all five known c-type cytochromes in E coli, providing biochemical evidence that these are ccm (for cytochrome c maturation) genes. The ccm region was transcribed both from the FNR-dependent, NarL- and NarP-regulated nap promoter (formerly the 'aeg46.5' promoter) and from constitutive or weakly regulated promoters apparently located within the downstream nap and ccm genes.

A seven-gene operon essential for formate-dependent nitrite reduction to ammonia by enteric bacteria

The DNA sequence of the regulatory region and the structural gene, nrfA, for cytochrome c552 of Escherichia coli K-12 have been reported. We have now established that nrfA is the first gene in a seven-gene operon, designated the nrf operon, at least five of which are essential for formate-dependent nitrite reduction to ammonia. This operon terminates just upstream of the previously sequenced gltP gene encoding a sodium-independent, glutamate and aspartate transporter. Expression of lac fused to nrfA, nrfE or nrfG is regulated by oxygen repression, FNR-dependent anaerobic induction, nitrite induction and nitrate repression during anaerobic growth, exactly as previously reported for the nrfA promoter. In contrast, expression of the gltP-lac fusion was FNR-independent. The open reading frame immediately downstream of nrfA encodes NrfB, a hydrophilic, penta-haem cytochrome c with an M(r) of 20,714. The structure of the N-terminal region is typical of a signal peptide for a periplasmic protein: cleavage at the putative signal peptide cleavage site, Ala-26, would result in a periplasmic cytochrome with a molecular mass of 18 kDa. The NrfC polypeptide, M(r) 24,567, contains 16 cysteine residues arranged in four clusters typical of the CooF super-family of non-haem iron-sulphur proteins. The NrfD sequence predicts a 318-residue hydrophobic protein with a distribution of acidic and basic amino acids which suggests that NrfD is an integral transmembrane protein with loops in both the periplasm and the cytoplasm. Proteins most similar to NrfD include the PsrC subunit of polysulphide reductase from Wolinella, but, as seven of the 10 most similar proteins are NADH-ubiquinone oxidoreductases, we propose that NrfD participates in the transfer of electrons from the quinone pool into the terminal components of the Nrf pathway. NrfE, M(r) 60,851, is predicted to be another hydrophobic, integral membrane protein homologous to the CdI1 protein of Rhodobacter capsulatus, which has been implicated in the assembly of periplasmic c-type cytochromes. The sequence of the 127 residue NrfF polypeptide, M(r) 14,522, is strikingly similar to the CcI2 protein of R. capsulatus, especially in the putative haem-binding motif, RCPQCQNQN.(ABSTRACT TRUNCATED AT 400 WORDS)

Asymptomatic hypoechoic regions on patellar tendon ultrasound: A 4-year clinical and ultrasound followup of 46 tendons

Patellar tendon ultrasound appearance is commonly used in clinical practice to diagnose patellar tendinopathy and guide management. Using a longitudinal study design we examined whether or not the presence of a hypoechoic ultrasonographic lesion in an asymptomatic patellar tendon conferred a risk for developing jumper's knee compared with a tendon that was ultrasonographically normal. Ultrasonographic, symptomatic and anthropometric assessment was completed at baseline and followup. Magnetic resonance imaging was performed on four tendons that resolved ultrasonographically in the study period. Forty-six patellar tendons were followed over 47+/-11.8 months. Eighteen tendons were hypoechoic at baseline and 28 were ultrasonographically normal. Five tendons resolved ultrasonographically in the study period. Magnetic resonance imaging in four of these tendons was normal. Seven normal patellar tendons at baseline developed a hypoechoic area but only two became symptomatic. Analysis of ultrasonography at baseline and clinical outcome with Fisher's exact test shows there is no association between baseline ultrasound changes and symptoms at followup. In this study there is no statistically significant relationship between ultrasonographic patellar tendon abnormalities and clinical outcome in elite male athletes. Management of jumper's knee should not be solely based on ultrasonographic appearance; clinical assessment remains the cornerstone of appropriate management.

Prospective imaging study of asymptomatic patellar tendinopathy in elite junior basketball players

To evaluate the ability of ultrasonography to predict eventual symptoms in an at-risk population, 52 elite junior basketball players' patellar tendons were studied at baseline and again 16 months later. The group consisted of 10 study tendons (ultrasonographically hypoechoic at baseline) and 42 control tendons (ultrasonographically normal at baseline). By design, all tendons were asymptomatic at baseline. No differences were noted between subjects and controls at baseline for age, height, weight, training hours, and vertical jump. Functional (P < 0.01) and symptomatic outcome (P < 0.05) were poorer for subjects' tendons than for controls. Relative risk for developing symptoms of jumper's knee was 4.2 times greater in case tendons than in control tendons. Men were more likely to develop ultrasonographic changes than women (P < 0.025), and they also had significantly increased training hours per week (P < 0.01) in the study period. Half (50%) of abnormal tendons in women became ultrasonographically normal in the study period. Our data suggest that presence of an ultrasonographic hypoechoic area is associated with a greater risk of developing jumper's knee symptoms. Ultrasonographic patellar tendon changes may resolve, but this is not necessary for an athlete to become asymptomatic. Qualitative or quantitative analysis of baseline ultrasonographic images revealed it was not possible to predict which tendons would develop symptoms or resolve ultrasonographically.

Different physiological roles of two independent pathways for nitrite reduction to ammonia by enteric bacteria

Operon fusion strains and mutants of Escherichia coli K-12 lacking the NADH-dependent nitrite reductase have been used to determine the regulation and physiological roles of two independent pathways for nitrite reduction to ammonia. Both the formate- and NADH-dependent pathways (Nrf and Nir, respectively) were totally repressed during aerobic growth, partially active during anaerobic growth in the absence of nitrite and further induced anaerobically by nitrite. Both were dependent upon a functional Fnr protein (a transcription activator of genes for anaerobic respiration). During anaerobic growth in the presence of nitrate, the Nir pathway was fully induced but Nrf was strongly repressed. Mutants defective in the NarL protein, which induces transcription of nitrate reductase genes but represses fumarate reductase genes in the presence of nitrate, were derepressed for Nrf activity during growth with nitrate, but the Nir enzyme was less active. The synthesis of Nrf components was also sensitive to glucose repression and weak activation by NarL during growth in the absence of nitrate. These data indicate that the Nir pathway provides a mechanism for detoxifying nitrite formed in the cytoplasm as a product of nitrate reduction. In contrast, the electrogenic reduction of nitrite by the Nrf pathway provides a secondary source of energy during anaerobic growth and is consequently repressed by the NarL protein when the thermodynamically more favourable electron acceptor, nitrate, is available. Two short DNA sequences, 5'-TACCAT-3' and 5'-CTCCTT-3', were found in the promoters of operons known to be activated or repressed by the NarL protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Serological detection of equid herpesvirus 1 infections of the respiratory tract

An investigation was made of 3 serological tests (virus neutralization, complement fixation and indirect immunofluorescence), which are applicable to epidemiological studies of infections by Equid herpesvirus 1 (EHV-1). Sera from gnotobiotic foals inoculated intranasally with various strains of EHV-1 were unable in some cases to neutralize heterologous strains and these results were not consistent with the existence of clearly-defined subtypes of EHV-1, as previously proposed. The cross-reactions in complement-fixation tests paralleled those with neutralization but immunofluorescence tests were found to be both more sensitive and more broadly reactive than the other two. Complement-fixing antibodies declined more rapidly following experimental infection than did those measured by neutralization or immunofluorescence. The results are discussed in relation to the diagnosis of EHV-1 infection and the significance they may have for the epidemiology of this disease.

The role of endothelial cell infection in the endometrium, placenta and foetus of equid herpesvirus 1 (EHV-1) abortions

One of three mares in the last trimester of pregnancy became paraplegic 7 days after experimental infection with EHV-1 and was killed 10 days after infection (d.p.i.). The other two mares aborted foetuses at 12 and 14 d.p.i. In the first mare, virus was detected by immunofluorescence (IIF) and immunoperoxidase (IP) staining in endothelial cells of the endometrium, placenta and umbilical vein, but not in any other foetal tissues. In the experimentally aborted foetuses, and in two other independent field cases of abortions, endothelial cell infection was also detected in the foetuses, both in major blood vessels and in capillaries or sinusoidal cells associated with parenchymal lesions. In these four cases there were also positive endothelial placental lesions detected by IIF or IP, although it was not always possible to isolate virus from these tissues, as it was from the foetuses. The evidence suggests that infection of maternal endothelial cells has a major role in the pathogenesis of abortion, and that endothelial cells are also involved in dissemination of virus within the foetus.

The prevalence of latent Equid herpesviruses in the tissues of 40 abattoir horses

Equid herpesviruses 1 or 4 (EHV-1 or -4) were isolated by cocultivation from 60% of 40 horses examined at slaughter. The lymph nodes draining the respiratory tract were the most common source of virus. EHV-1 or EHV-4 was never isolated from the trigeminal ganglia (SLG). The polymerase chain reaction (PCR) detected virus in 87.5% of bronchial lymph nodes and a similar level in the trigeminal ganglia that were examined. By both assays approximately one third of the positive animals harboured both viruses. Equid herpesvirus 2 (EHV-2) was isolated from all but one of the horses and from > 75% of the lymph nodes draining the respiratory tract; alpha viruses were isolated only in the presence of EHV-2. The results indicate that latent EHV-1 and EHV-4 are widespread in the equine population and that the primary site of latency is the lymph nodes of the respiratory tract.

Reproducibility and clinical utility of tendon palpation to detect patellar tendinopathy in young basketball players. Victorian Institute of Sport tendon study group

BACKGROUND

Palpation is an important clinical test for jumper's knee.

OBJECTIVES

To (a) test the reproducibility of palpation tenderness, (b) evaluate the sensitivity and specificity of palpation in subjects with clinical symptoms of jumper's knee, and (c) determine whether tenderness to palpation may serve as a useful screening test for patellar tendinopathy. The yardstick for diagnosis of patellar tendinopathy was ultrasonographic abnormality.

METHODS

In 326 junior symptomatic and asymptomatic athletes' tendons, palpation was performed by a single examiner before ultrasonographic examination by a certified ultrasound radiologist. In 58 tendons, palpation was performed twice to test reliability. Tenderness to palpation was scored on a scale from 0 to 3 where 0 represented no pain, and 1, 2, and 3 represented mild, moderate, and severe tenderness respectively.

RESULTS

Patellar tendon palpation was a reliable examination for a single examiner (Pearson r = 0.82). In symptomatic tendons, the positive predictive value of palpation was 68%. As a screening examination in asymptomatic subjects, the positive predictive value of tendon palpation was 36-38%. Moderate and severe palpation tenderness were better predictors of ultrasonographic tendon pathology than absent or mild tenderness (p<0.001). Tender and symptomatic tendons were more likely to have ultrasound abnormality than tenderness alone (p<0.01).

CONCLUSIONS

In this age group, palpation is a reliable test but it is not cost effective in detecting patellar tendinopathy in a preparticipation examination. In symptomatic tendons, palpation is a moderately sensitive but not specific test. Mild tenderness in the patellar tendons in asymptomatic jumping athletes should be considered normal.

Platelet-derived endothelial cell growth factor thymidine phosphorylase in tumour growth and response to therapy

Angiogenesis plays an important role in the growth and metastasis of solid tumours. Platelet-derived endothelial cell growth factor (PD-ECGF) is known to be chemotactic for endothelial cells in vitro and angiogenic in vivo. It is also known as gliostatin, a factor promoting neuronal survival, and thymidine phosphorylase (dThdPase), which catalyses the reversible phosphorylation of thymidine to thymine and 2-deoxyribose-1-phosphate. This enzymatic activity is critical for angiogenic activity. PD-ECGF protein is highly expressed in tumours compared with most normal tissues and has been correlated with tumour growth, invasion and metastasis in clinical studies. In addition, dThdPase activity (by inference PD-ECGF) has been found to be a major determinant of the toxicity of 5-fluorouracil and its prodrugs, which are extensively studied clinically as anti-cancer agents. This review attempts to summarize recent gains in understanding the nature, location and action of PD-ECGF and its specific relevance to tumour biology.

Regulation and sequence of the structural gene for cytochrome c552 from Escherichia coli: not a hexahaem but a 50 kDa tetrahaem nitrite reductase

The structural gene, nrfA, for cytochrome c552, which is the terminal reductase of the formate-dependent pathway for nitrite reduction to ammonia, has been located at co-ordinate 4366 on the physical map of the Escherichia coli chromosome. The DNA sequence of nrfA encodes a tetrahaem c-type cytochrome with a predicted M(r) for the unprocessed product of 53,788. Cleavage of the putative signal peptide at Ala-26 would result in a mature, periplasmic cytochrome of M(r) 50,580 rather than a larger hexahaem cytochrome, as has been widely reported previously. A cytochrome of this size was detected by staining SDS-polyacrylamide gels for covalently bound haem. This cytochrome was partially purified by anion exchange chromatography and confirmed to be cytochrome c552 by difference spectroscopy. Similar cytochromes were detected in five other E. coli strains including strain ST 249, which was used previously to purify and characterize the protein. A plasmid with an in-phase deletion within nrfA directed the synthesis of a truncated haemoprotein of the predicted mass. In-phase translational fusions to lacZ were used to locate the nrfA translation start, and the transcription start site was found by S1 mapping. Expression from the FNR-dependent nrfA promoter was almost totally repressed during aerobic growth, partially induced during anaerobic growth in the absence of nitrite or in the presence of nitrate, but fully induced only during anaerobic growth in the presence of nitrite. No nitrate repression was detected in a narL mutant, but nitrite induction was unaffected, indicating that the nitrite-sensing mechanism is independent of the NarL protein. Expression from the nrfA promoter was subject to glucose repression but regulation was independent of the CRP-cAMP complex.

A reassessment of the range of c-type cytochromes synthesized by Escherichia coli K-12

Five different c-type cytochromes have been detected during anaerobic growth of various Escherichia coli strains in different media. None of these cytochromes was detectable in aerobically-grown cultures. Only a single, 43 kDa cytochrome was synthesized in response to the presence of trimethylamine-N-oxide: synthesis of this cytochrome was unaffected by the presence of nitrate or nitrite, was repressed by oxygen, but was dependent upon a functional tor operon located at minute 22 (coordinate 1070 kb) on the E. coli chromosome. The other four cytochromes, masses 16, 18, 24 and 50 kDa, were induced by nitrite coordinately with formate-dependent nitrite reductase activity, but repressed by oxygen and nitrate. As only the 18 kDa and 50 kDa cytochromes are encoded by the nrf operon located at minute 92 (coordinate 4366 kb), there must be other loci, possibly essential for formate-dependent nitrite reduction, encoding the 16 kDa and 24 kDa cytochromes. No other c-type cytochrome was detected under any growth condition tested.

Transcriptional control, translation and function of the products of the five open reading frames of the Escherichia coli nir operon

Five open reading frames designated nirB, nirD, nirE, nirC and cysG have been identified from the DNA sequence of the Escherichia coli nir operon. Complementation experiments established that the NirB, NirD and CysG polypeptides are essential and sufficient for NADH-dependent nitrite reductase activity (EC 1.6.6.4). A series of plasmids has been constructed in which each of the open reading frames has been fused in-phase with the beta-galactosidase gene, lacZ. Rates of beta-galactosidase synthesis during growth in different media revealed that nirB, -D, -E and -C are transcribed from the FNR-dependent promoter, p-nirB, located just upstream of the nirB gene: expression is co-ordinately repressed by oxygen and induced during anaerobic growth. Although the nirB, -D and -C open reading frames are translated into protein, no translation of nirE mRNA was detected. The cysG gene product is expressed from both p-nirB and a second, FNR-independent promoter, p-cysG, located within the nirC gene. No NADH-dependent nitrite reductase activity was detected in extracts from bacteria lacking either NirB or NirD, but a mixture of the two was as active as an extract from wild-type bacteria. Reconstitution of enzyme activity in vitro required stoichiometric quantities of NirB and NirD and was rapid and independent of the temperature during mixing. NirD remained associated with NirB during the initial stages of purification of the active enzyme, suggesting that NirD is a second structural subunit of the enzyme.

Identification of the formate dehydrogenases and genetic determinants of formate-dependent nitrite reduction by Escherichia coli K12

The formate dehydrogenases of Escherichia coli involved in electron transfer from formate to nitrite (Nrf activity: nitrite reduction by formate) have been identified. No previously undescribed selenoprotein was detected in bacteria grown under conditions optimal for the expression of Nrf activity. The Nrf activities of single mutants defective in either FdhN or FdhH were between 50 and 60% that of the parental strain. A double mutant defective in both FdhN and FdhH retained less than 10% of the activity of the FdhN+ FdhH+ strain. No Nrf activity was detected in a triple mutant defective in FdhN, FdhH and FdhO or in the selC strain. It is concluded that all three of the known formate dehydrogenases of E. coli can contribute to the transfer of electrons from formate to the Nrf pathway. Mutants defective in Nrf activity and cytochrome c552 synthesis were isolated by insertion mutagenesis or identified amongst strains received from the E. coli Genetic Stock Center. The mutations were located in at least three regions of the chromosome, including the 92 to 94 minute region which includes fdhF, the gene encoding FdhH required for formate hydrogenlyase activity. Fine structure mapping by P1 transduction established that the nrf mutations in the fdhF region were due to defects in three separable loci, all of which were independent of but close to fdhF. Clones were isolated from a cosmid library that complemented a deletion extending from fdhF into a region essential for Nrf activity. From these clones, plasmids were isolated that complemented only some of the Nrf- mutations in the 92 to 94 minute region, confirming the presence of different operons essential for Nrf activity and cytochrome c552 synthesis in this region. Suggested reasons for this genetic complexity include the need for proteins involved in electron transfer from the various formate dehydrogenases to cytochrome c552, for the attachment of the haem group to the apocytochrome and for cytochrome c552 export into the periplasm.