Predicting the presence of coronary plaques featuring high-risk characteristics using polygenic risk scores and targeted proteomics in patients with suspected coronary artery disease

BACKGROUND

The presence of coronary plaques with high-risk characteristics is strongly associated with adverse cardiac events beyond the identification of coronary stenosis. Testing by coronary computed tomography angiography (CCTA) enables the identification of high-risk plaques (HRP). Referral for CCTA is presently based on pre-test probability estimates including clinical risk factors (CRFs); however, proteomics and/or genetic information could potentially improve patient selection for CCTA and, hence, identification of HRP. We aimed to (1) identify proteomic and genetic features associated with HRP presence and (2) investigate the effect of combining CRFs, proteomics, and genetics to predict HRP presence.

METHODS

Consecutive chest pain patients (n = 1462) undergoing CCTA to diagnose obstructive coronary artery disease (CAD) were included. Coronary plaques were assessed using a semi-automatic plaque analysis tool. Measurements of 368 circulating proteins were obtained with targeted Olink panels, and DNA genotyping was performed in all patients. Imputed genetic variants were used to compute a multi-trait multi-ancestry genome-wide polygenic score (GPSMult). HRP presence was defined as plaques with two or more high-risk characteristics (low attenuation, spotty calcification, positive remodeling, and napkin ring sign). Prediction of HRP presence was performed using the glmnet algorithm with repeated fivefold cross-validation, using CRFs, proteomics, and GPSMult as input features.

RESULTS

HRPs were detected in 165 (11%) patients, and 15 input features were associated with HRP presence. Prediction of HRP presence based on CRFs yielded a mean area under the receiver operating curve (AUC) ± standard error of 73.2 ± 0.1, versus 69.0 ± 0.1 for proteomics and 60.1 ± 0.1 for GPSMult. Combining CRFs with GPSMult increased prediction accuracy (AUC 74.8 ± 0.1 (P = 0.004)), while the inclusion of proteomics provided no significant improvement to either the CRF (AUC 73.2 ± 0.1, P = 1.00) or the CRF + GPSMult (AUC 74.6 ± 0.1, P = 1.00) models, respectively.

CONCLUSIONS

In patients with suspected CAD, incorporating genetic data with either clinical or proteomic data improves the prediction of high-risk plaque presence.

TRIAL REGISTRATION

https://clinicaltrials.gov/ct2/show/NCT02264717 (September 2014).

Combining Polygenic and Proteomic Risk Scores With Clinical Risk Factors to Improve Performance for Diagnosing Absence of Coronary Artery Disease in Patients With de novo Chest Pain

BACKGROUND

Patients with de novo chest pain, referred for evaluation of possible coronary artery disease (CAD), frequently have an absence of CAD resulting in millions of tests not having any clinical impact. The objective of this study was to investigate whether polygenic risk scores and targeted proteomics improve the prediction of absence of CAD in patients with suspected CAD, when added to the PROMISE (Prospective Multicenter Imaging Study for Evaluation of Chest Pain) minimal risk score (PMRS).

METHODS

Genotyping and targeted plasma proteomics (N=368 proteins) were performed in 1440 patients with symptoms suspected to be caused by CAD undergoing coronary computed tomography angiography. Based on individual genotypes, a polygenic risk score for CAD (PRSCAD) was calculated. The prediction was performed using combinations of PRSCAD, proteins, and PMRS as features in models using stability selection and machine learning.

RESULTS

Prediction of absence of CAD yielded an area under the curve of PRSCAD-model, 0.64±0.03; proteomic-model, 0.58±0.03; and PMRS model, 0.76±0.02. No significant correlation was found between the genetic and proteomic risk scores (Pearson correlation coefficient, -0.04; P=0.13). Optimal predictive ability was achieved by the full model (PRSCAD+protein+PMRS) yielding an area under the curve of 0.80±0.02 for absence of CAD, significantly better than the PMRS model alone (P<0.001). For reclassification purpose, the full model enabled down-classification of 49% (324 of 661) of the 5% to 15% pretest probability patients and 18% (113 of 611) of >15% pretest probability patients.

CONCLUSIONS

For patients with chest pain and low-intermediate CAD risk, incorporating targeted proteomics and polygenic risk scores into the risk assessment substantially improved the ability to predict the absence of CAD. Genetics and proteomics seem to add complementary information to the clinical risk factors and improve risk stratification in this large patient group.

REGISTRATION

URL: https://www.

CLINICALTRIALS

gov; Unique identifier: NCT02264717.

Diagnostic Yield of Genetic Testing in Young Patients With Atrioventricular Block of Unknown Cause

Background

The cause of atrioventricular block (AVB) remains unknown in approximately half of young patients with the diagnosis. Although variants in several genes associated with cardiac conduction diseases have been identified, the contribution of genetic variants in younger patients with AVB is unknown.

Methods and Results

Using the Danish Pacemaker and Implantable Cardioverter Defibrillator (ICD) Registry, we identified all patients younger than 50 years receiving a pacemaker because of AVB in Denmark in the period from January 1, 1996 to December 31, 2015. From medical records, we identified patients with unknown cause of AVB at time of pacemaker implantation. These patients were invited to a genetic screening using a panel of 102 genes associated with inherited cardiac diseases. We identified 471 living patients with AVB of unknown cause, of whom 226 (48%) accepted participation. Median age at the time of pacemaker implantation was 39 years (interquartile range, 32–45 years), and 123 (54%) were men. We found pathogenic or likely pathogenic variants in genes associated with or possibly associated with AVB in 12 patients (5%). Most variants were found in the LMNA gene (n=5). LMNA variant carriers all had a family history of either AVB and/or sudden cardiac death.

Conclusions

In young patients with AVB of unknown cause, we found a possible genetic cause in 1 out of 20 participating patients. Variants in the LMNA gene were most common and associated with a family history of AVB and/or sudden cardiac death, suggesting that genetic testing should be a part of the diagnostic workup in these patients to stratify risk and screen family members.

Polygenic Risk Score-Enhanced Risk Stratification of Coronary Artery Disease in Patients With Stable Chest Pain

BACKGROUND

Polygenic risk scores (PRSs) are associated with coronary artery disease (CAD), but the clinical potential of using PRSs at the single-patient level for risk stratification has yet to be established. We investigated whether adding a PRS to clinical risk factors (CRFs) improves risk stratification in patients referred to coronary computed tomography angiography on a suspicion of obstructive CAD.

METHODS

In this prespecified diagnostic substudy of the Dan-NICAD trial (Danish study of Non-Invasive testing in Coronary Artery Disease), we included 1617 consecutive patients with stable chest symptoms and no history of CAD referred for coronary computed tomography angiography. CRFs used for risk stratification were age, sex, symptoms, prior or active smoking, antihypertensive treatment, lipid-lowering treatment, and diabetes. In addition, patients were genotyped, and their PRSs were calculated. All patients underwent coronary computed tomography angiography. Patients with a suspected ≥50% stenosis also underwent invasive coronary angiography with fractional flow reserve. A combined end point of obstructive CAD was defined as a visual invasive coronary angiography stenosis >90%, fractional flow reserve <0.80, or a quantitative coronary analysis stenosis >50% if fractional flow reserve measurements were not feasible.

RESULTS

The PRS was associated with obstructive CAD independent of CRFs (adjusted odds ratio, 1.8 [95% CI, 1.5-2.2] per SD). The PRS had an area under the curve of 0.63 (0.59-0.68), which was similar to that for age and sex. Combining the PRS with CRFs led to a CRF+PRS model with area under the curve of 0.75 (0.71-0.79), which was 0.04 more than the CRF model (P=0.0029). By using pretest probability (pretest probability) cutoffs at 5% and 15%, a net reclassification improvement of 15.8% (P=3.1×10^-4) was obtained, with a down-classification of risk in 24% of patients (211 of 862) in whom the pretest probability was 5% to 15% based on CRFs alone.

CONCLUSIONS

Adding a PRS improved risk stratification of obstructive CAD beyond CRFs, suggesting a modest clinical potential of using PRSs to guide diagnostic testing in the contemporary clinical setting. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT02264717.

Sortilin as a Biomarker for Cardiovascular Disease Revisited

Genetic variants in the genomic region containing SORT1 (encoding the protein sortilin) are strongly associated with cholesterol levels and the risk of coronary artery disease (CAD). Circulating sortilin has therefore been proposed as a potential biomarker for cardiovascular disease. Multiple studies have reported association between plasma sortilin levels and cardiovascular outcomes. However, the findings are not consistent across studies, and most studies have small sample sizes. The aim of this study was to evaluate sortilin as a biomarker for CAD in a well-characterized cohort with symptoms suggestive of CAD. In total, we enrolled 1,173 patients with suspected stable CAD referred to coronary computed tomography angiography. Sortilin was measured in plasma using two different technologies for quantifying circulating sortilin: a custom-made enzyme-linked immunosorbent assay (ELISA) and OLINK Cardiovascular Panel II. We found a relative poor correlation between the two methods (correlation coefficient = 0.21). In addition, genotyping and whole-genome sequencing were performed on all patients. By whole-genome regression analysis of sortilin levels measured with ELISA and OLINK, two independent cis protein quantitative trait loci (pQTL) on chromosome 1p13.3 were identified, with one of them being a well-established risk locus for CAD. Incorporating rare genetic variants from whole-genome sequence data did not identify any additional pQTLs for plasma sortilin. None of the traditional CAD risk factors, such as sex, age, smoking, and statin use, were associated with plasma sortilin levels. Furthermore, there was no association between circulating sortilin levels and coronary artery calcium score (CACS) or disease severity. Sortilin did not improve discrimination of obstructive CAD, when added to a clinical pretest probability (PTP) model for CAD. Overall, our results indicate that studies using different methodologies for measuring circulating sortilin should be compared with caution. In conclusion, the well-known SORT1 risk locus for CAD is linked to lower sortilin levels in circulation, measured with ELISA; however, the effect sizes are too small for sortilin to be a useful biomarker for CAD in a clinical setting of low- to intermediate-risk chest-pain patients.

Genetic Risk of Coronary Artery Disease, Features of Atherosclerosis, and Coronary Plaque Burden

Background

Polygenic risk scores (PRSs) based on risk variants from genome‐wide association studies predict coronary artery disease (CAD) risk. However, it is unknown whether the PRS is associated with specific CAD characteristics.

Methods and Results

We consecutively included 1645 patients with suspected stable CAD undergoing coronary computed tomography angiography. A multilocus PRS was calculated as the weighted sum of CAD risk variants. Plaques were evaluated using an 18‐segment model and characterized by stenosis severity and composition (soft [0%‐19% calcified], mixed‐soft [20%‐49% calcified], mixed‐calcified [50%‐79% calcified], or calcified [≥80% calcified]). Coronary artery calcium score and segment stenosis score were used to characterize plaque burden. For each standard deviation increase in the PRS, coronary artery calcium score increased by 78% (P=4.1e‐26) and segment stenosis score increased by 16% (P=2.4e‐29) in the fully adjusted model. The PRS was associated with a higher prevalence of obstructive plaques (odds ratio [OR]: 1.78, P=5.6e‐16), calcified (OR: 1.69, P=6.5e‐17), mixed‐calcified (OR: 1.67, P=7.3e‐9), mixed‐soft (OR: 1.45, P=1.6e‐6), and soft plaques (OR: 1.49, P=2.5e‐6), and a higher prevalence of plaque in each coronary vessel (all P<1.0e‐4). However, when analyzing data on a plaque level (3007 segments with plaque in 849 patients) the PRS was not associated with stenosis severity, plaque composition, or localization (all P>0.05).

Conclusions

Our results suggest that polygenic risk based on large genome‐wide association studies increases CAD risk through an increased burden of coronary atherosclerosis rather than promoting specific plaque features.

Clinical Trial Registration

URL: https://www.clinicaltrials.gov. Unique identifier: NCT02264717.

The biodiversity of predominant lactic acid bacteria in dolo and pito wort for the production of sorghum beer

AIM

To quantify and identify the predominant lactic acid bacteria (LAB) in dolo and pito wort processing, and to examine their biodiversity at strain level.

MATERIALS AND RESULTS

The processing of dolo and pito wort was studied at four production sites in Burkina Faso and Ghana. The succession of dominant micro-organisms, pH and titratable acidity were determined from sorghum malt through mashing and acidification to final wort. In the sorghum malt and during mashing, the LAB counts were 5.7-7.5 log CFU g(-1). Similar levels of yeasts and gram-negative, catalase-positive bacteria were observed. These levels decreased to 3.7-4.5 log CFU g(-1) and<or=2-3 log CFU g(-1), respectively, at the end of mashing, including a mild heat treatment. During acidification at ambient temperature (30-33 degrees C) lasting for 12-16 h, LAB counts increased to 8.8-9.9 log CFU g(-1), pH decreased from 5.55+/-0.12 to 3.72+/-0.24, and the titratable acidity calculated as lactic acid, increased from 0.13% to 0.61%. The gram-negative, catalase-positive bacteria and yeasts observed in the malt and during mashing were no longer detected. A total of 556 strains of LAB were isolated and purified. The LAB isolates were characterized and identified by a polyphasic approach based on phenotypic and genotypic methods, such as carbohydrate fermentation patterns using API 50 CHL, intergenic transcribed spacers-polymerase chain reaction/restriction fragment length polymorphism (ITS-PCR/RFLP), pulsed-field gel electrophoresis (PFGE) and 16S rRNA gene sequencing. Lactobacillus fermentum was identified as the dominant LAB species in the malt during mashing and during acidification. The other species observed during acidification were Lactobacillus delbrueckii ssp. delbrueckii, Lact. delbrueckii ssp. bulgaricus and Pediococcus acidilactici. These bacteria comprised a minor fraction of the bacterial population and no distinct microbial succession was observed for the LAB. At species level, the LAB profiles were similar for the four production sites; however, a pronounced diversity was observed at strain level. For one site, which had implemented a cleaning procedure between batches only, Lact. fermentum was found.

CONCLUSION

Lact. fermentum was found to be the dominant LAB species throughout the entire process to final dolo and pito wort, including the acidification. Lact. delbrueckii ssp. delbrueckii, Lact. delbrueckii ssp. bulgaricus and P. acidilactici occurred in low numbers. At strain level, a high diversity based on PFGE-RFLP was observed for Lact. fermentum within and between sites.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study for the first time gives details of the involvement of LAB in the production of dolo and pito wort, for West African traditional sorghum beer production. One species, Lact. fermentum was predominant throughout the process, and seems to harbour potential starter cultures to be selected according to technological characteristics determined at strain level.

Case study of the distribution of mucosa-associated Bifidobacterium species, Lactobacillus species, and other lactic acid bacteria in the human colon

The distribution of mucosa-associated bacteria, bifidobacteria and lactobacilli and closely related lactic acid bacteria, in biopsy samples from the ascending, transverse, and descending parts of the colon from four individuals was investigated by denaturing gradient gel electrophoresis (DGGE). Bifidobacterial genus-specific, Lactobacillus group-specific, and universal bacterial primers were used in a nested PCR approach to amplify a fragment of the 16S rRNA gene. DGGE profiles of the bifidobacterial community were relatively simple, with one or two amplicons detected at most sampling sites in the colon. DGGE profiles obtained with Lactobacillus group-specific primers were complex and varied with host and sampling site in the colon. The overall bacterial community varied with host but not sampling site.

DNA typing methods for differentiation of Debaryomyces hansenii strains and other yeasts related to surface ripened cheeses

The discriminative power of ITS-PCR, ITS-PCR RFLP and mitochondrial (mt)-DNA RFLP were evaluated for differentiation of yeasts of importance for surface ripened cheeses. In total 60 isolates were included. Of these, 40 strains of the following species, Debaryomyces hansenii var. hansenii, D. hansenii var. fabryi, Saccharomyces cerevisiae, Candida zeylanoides, Kluyveromyces lactis and Yarrowia lipolytica, were obtained from culture collections and 20 isolates of D. hansenii representing six different phenotypes were collected from seven Danish producers of surface ripened cheeses. ITS-PCR was evaluated for differentiation at species level on the 40 strains obtained from culture collections. Ten strains of each variety of D. hansenii and five strains of each of the above mentioned species were analysed. For each of the investigated species, a specific ITS1-5.8S rDNA-ITS2 region size was observed. Accordingly ITS-PCR was found valuable for differentiation at species level of yeasts of importance for surface ripened cheeses. ITS-PCR RFLP was investigated for the purpose of strain typing of D. hansenii. Ten CBS strains of each variety of D. hansenii were analysed. Only one enzyme (TaqI) out of several investigated (BamHI, DpnI, Fnu4HI, HaeIII, HindIII, HpaII, NlaII, Sau3AI, TaqI) demonstrated genetic diversity within the strains. This enzyme divided the 20 strains in three groups. Sequence analysis of the ITS1-5.8S rDNA-ITS2 region for the type strains of each variety of D. hansenii showed an identity of 99.84%, corresponding to a difference in one basepair. Based on these results, ITS-PCR RFLP was found ineffective for strain typing of D. hansenii. MtDNA RFLP using HaeIII and HpaII was evaluated for strain typing of D. hansenii on the 20 CBS strains of D. hansenii. The CBS strains were divided into 16 groups according to their restriction profiles, which proved the method useful for typing of D. hansenii at subspecies level. The 20 dairy isolates showed a lower genetic variability than the CBS strains as they were divided into eight groups. Cluster analysis of the 20 CBS strains and the 20 dairy isolates based on their mtDNA restriction profiles showed (max. similarity level = 52%) that the dairy isolates only clustered with the CBS strains of D. hansenii var. hansenii. For some of the dairies more than one strain of D. hansenii were found to be involved in the ripening process, indicating that the method could be useful for subspecies typing and investigation of the microbial succession between strains of D. hansenii during the ripening process of surface ripened cheeses.

Intra- and extracellular beta-galactosidases from Bifidobacterium bifidum and B. infantis: molecular cloning, heterologous expression, and comparative characterization

Three beta-galactosidase genes from Bifidobacterium bifidum DSM20215 and one beta-galactosidase gene from Bifidobacterium infantis DSM20088 were isolated and characterized. The three B. bifidum beta-galactosidases exhibited a low degree of amino acid sequence similarity to each other and to previously published beta-galactosidases classified as family 2 glycosyl hydrolases. Likewise, the B. infantis beta-galactosidase was distantly related to enzymes classified as family 42 glycosyl hydrolases. One of the enzymes from B. bifidum, termed BIF3, is most probably an extracellular enzyme, since it contained a signal sequence which was cleaved off during heterologous expression of the enzyme in Escherichia coli. Other exceptional features of the BIF3 beta-galactosidase were (i) the monomeric structure of the active enzyme, comprising 1,752 amino acid residues (188 kDa) and (ii) the molecular organization into an N-terminal beta-galactosidase domain and a C-terminal galactose binding domain. The other two B. bifidum beta-galactosidases and the enzyme from B. infantis were multimeric, intracellular enzymes with molecular masses similar to typical family 2 and family 42 glycosyl hydrolases, respectively. Despite the differences in size, molecular composition, and amino acid sequence, all four beta-galactosidases were highly specific for hydrolysis of beta-D-galactosidic linkages, and all four enzymes were able to transgalactosylate with lactose as a substrate.

16S to 23S rRNA spacer fragment length polymorphism of Salmonella enterica at subspecies and serotype levels

The variation in the lengths of the internal transcribed spacer (ITS) between 16S and 23S rRNA genes of 101 strains representing 58 serotypes of Salmonella enterica (used for Salm. choleraesuis) subsp. enterica (I), salamae (II), arizonae (IIIa), diarizonae (IIIb), houtenae (IV) and indica (VI) was used for typing by PCR amplification. Ten fragment lengths were observed by denaturing polyacrylamide gel electrophoresis on an automatic DNA sequencer resulting in 21 unique fragment patterns. Ten out of the 58 serotypes showed specific patterns but 48 serotypes were not fully differentiated. More than one ITS pattern was observed in seven serotypes. Five of the 21 fragment patterns contained representatives of more than one subspecies. Under non-denaturing electrophoresis conditions, serotype specificity was obtained but precise ITS fragment length determination was not possible. DNA sequence comparison between ITSs of individual rrn operons is needed to further interpret ITS diversity within Salm. enterica at serotype and subspecies levels.

Time to onset of analgesia and analgesic efficacy of effervescent acetaminophen 1000 mg compared to tablet acetaminophen 1000 mg in postoperative dental pain: a single-dose, double-blind, randomized, placebo-controlled study

This randomized, double-blind, placebo-controlled study compared the time to onset of analgesia and the analgesic efficacy of two formulations of acetaminophen 1000 mg--an effervescent solution and tablet--in 242 patients with moderate or severe pain following dental surgery. Onset of analgesia was determined using a two-stopwatch procedure. Analgesia was assessed over a 4-hour period. Treatments were compared using standard indexes of pain intensity and pain relief and summary measures. Both acetaminophen formulations were significantly more effective than their corresponding placebo for all efficacy assessments. The median time to onset of analgesia was significantly shorter with effervescent acetaminophen (20 minutes) compared to tablet acetaminophen (45 minutes). During the first 45 minutes after administration, effervescent acetaminophen was significantly more effective at each scheduled assessment time than tablet acetaminophen. The median time to meaningful pain relief was significantly shorter with effervescent acetaminophen (45 minutes) compared to tablet acetaminophen (60 minutes). At 4 hours after administration, the pain relief was significantly better with tablet acetaminophen than with effervescent acetaminophen. No other significant differences were observed between the active treatments. In conclusion, effervescent acetaminophen produces a significantly faster onset of analgesia than tablet acetaminophen.

Sequence variation of the 16S to 23S rRNA spacer region in Salmonella enterica

The possibility for identification of Salmonella enterica serotypes by sequence analysis of the 16S to 23S rRNA internal transcribed spacer was investigated by direct sequencing of polymerase chain reaction-amplified DNA from all operons simultaneously in a collection of 25 strains of 18 different serotypes of S. enterica, and by sequencing individual cloned operons from a single strain. It was only possible to determine the first 117 bases upstream from the 23S rRNA gene by direct sequencing because of variation between the rrn operons. Comparison of sequences from this region allowed separation of only 15 out of the 18 serotypes investigated and was not specific even at the subspecies level of S. enterica. To determine the differences between internal transcribed spacers in more detail, the individual rrn operons of strain JEO 197, serotype IV 43:z4,z23:-, were cloned and sequenced. The strain contained four short internal transcribed spacer fragments of 382-384 bases in length, which were 98.4-99.7% similar to each other and three long fragments of 505 bases with 98.0-99.8% similarity. The study demonstrated a higher degree of interbacterial variation than intrabacterial variation between operons for serotypes of S. enterica.

Screening of probiotic activities of forty-seven strains of Lactobacillus spp. by in vitro techniques and evaluation of the colonization ability of five selected strains in humans

The probiotic potential of 47 selected strains of Lactobacillus spp. was investigated. The strains were examined for resistance to pH 2.5 and 0.3% oxgall, adhesion to Caco-2 cells, and antimicrobial activities against enteric pathogenic bacteria in model systems. From the results obtained in vitro, five strains, Lactobacillus rhamnosus 19070-2, L. reuteri DSM 12246, L. rhamnosus LGG, L. delbrueckii subsp. lactis CHCC 2329, and L. casei subsp. alactus CHCC 3137, were selected for in vivo studies. The daily consumption by 12 healthy volunteers of two doses of 10(10) freeze-dried bacteria of the selected strains for 18 days was followed by a washout period of 17 days. Fecal samples were taken at days 0 and 18 and during the washout period at days 5 and 11. Lactobacillus isolates were initially identified by API 50CHL and internal transcribed spacer PCR, and their identities were confirmed by restriction enzyme analysis in combination with pulsed-field gel electrophoresis. Among the tested strains, L. rhamnosus 19070-2, L. reuteri DSM 12246, and L. rhamnosus LGG were identified most frequently in fecal samples; they were found in 10, 8, and 7 of the 12 samples tested during the intervention period, respectively, whereas reisolations were less frequent in the washout period. The bacteria were reisolated in concentrations from 10(5) to 10(8) cells/g of feces. Survival and reisolation of the bacteria in vivo appeared to be linked to pH tolerance, adhesion, and antimicrobial properties in vitro.

Carbon metabolism regulates expression of the pfl (pyruvate formate-lyase) gene in Escherichia coli

The anaerobic expression of pfl is reduced both in a strain mutated in the pgi gene and in a pfkA pfkB double mutant strain when cells are grown in medium supplemented with glucose. When cells are grown in medium supplemented with either fructose or pyruvate, no reduction is observed in these strains. The amount of pyruvate in the cells may be responsible for the reduced expression of pfl in the strains mutated in the genes encoding the glycolytic enzymes. Because of the lowered oxygen concentration in the medium, the expression of pfl is induced when an exponentially growing culture enters the stationary phase. This induction is increased when the Casamino Acid concentration is raised 10-fold or when the medium is supplemented with NaCl. Superhelicity of DNA is decreased in a pgi mutant strain grown in medium supplemented with glucose. The superhelicity is also changed, but the opposite way, in a wild-type strain grown in medium supplemented with Casamino Acids at a high concentration or 0.3 M sodium chloride. Our data show that changes in superhelicity do not affect the aerobic expression of pfl but might be important for the anaerobic induction of pfl.