Ozone pollution contributes to the yield gap for beans in Uganda, East Africa, and is co-located with other agricultural stresses

Air quality negatively impacts agriculture, reducing the yield of staple food crops. While measured data on African ground-level ozone levels are scarce, experimental studies demonstrate the damaging impact of ozone on crops. Common beans (Phaseolus vulgaris), an ozone-sensitive crop, are widely grown in Uganda. Using modelled ozone flux, agricultural surveys, and a flux-effect relationship, this study estimates yield and production losses due to ozone for Ugandan beans in 2015. Analysis at this scale allows the use of localised data, and results can be presented at a sub-regional level. Soil nutrient stress, drought, flood risk, temperature and deprivation were also mapped to investigate where stresses may coincide. Average bean yield losses due to ozone were 17% and 14% (first and second growing season respectively), equating to 184 thousand tonnes production loss. However, for some sub-regions, losses were up to 27.5% and other crop stresses also coincided in these areas. This methodology could be applied widely, allowing estimates of ozone impact for countries lacking air quality and/or experimental data. As crop productivity is below its potential in many areas of the world, changing agricultural practices to mitigate against losses due to ozone could help to reduce the crop yield gap.

AB0395 DE-ESCALATION OF DMARDs IN ELDERLY PATIENTS WITH RA

Background

Rheumatoid Arthritis is the most common form of inflammatory arthritis in older adults, with the mainstay of treatment being the conventional DMARDs (Tutuncu & Kavanaugh, 2007). These drugs are not without side effects, and as elderly people have higher rates of adverse drug reactions and less long-term benefits, the risk/benefit ratio is different compared to other age groups. This research sought to evaluate if the rheumatology department at Southend hospital was sufficiently acknowledging the changing circumstances of their elderly patients and de-escalating conventional DMARDs accordingly. As the average age of rheumatology patients is only likely to increase in the future, contextualising a patients treatment plan for their rheumatological disorder with their overall health status will become an increasingly important skill for clinicians and the observations from this study will be applicable to all who treat elderly patients with inflammatory disorders.

Objectives

1. Evaluate if major new diagnoses were acknowledged in the rheumatology clinic and if conventional DMARD treatment was reduced in response. 2. Record and compare the outcomes of when conventional DMARD was stopped abruptly vs when it was tapered down slowly.

Methods

Evaluated 10 year’s worth of clinic letters from rheumatology and other specialities in 50 patients with a diagnosis of RA over the age of 89. Noted new diagnoses of dementia, cancer and frailty (multiple falls, care home admission or becoming newly house bound) as well as acute hospital admissions and declining renal function and evaluated if this was acknowledged in clinic letters and whether treatment was changed in response. Recorded all instances where conventional DMARDs were stopped or had a dose reduction and evaluated if these dose drops were successful (patient stayed at reduced dose with no flares in disease activity), semi-successful (patient had mild RA flare treated with short course corticosteroids, or stayed at reduced dose for at least a year before returning to original dose) or unsuccessful (patient suffered flare and went back to original dose within 1 year.)

Results

Of the 50 patients, 31 received methotrexate monotherapy, 12 methotrexate and other conventional DMARDs, and 5 DMARDs other than methotrexate. 36 out of 45 patients receiving methotrexate had some decrease in dose by the end of the 10 year period, with the median decrease being 5mg. Patients on multiple DMARDs saw a greater average decrease in methotrexate compared to those on monotherapy. 15 abrupt cessations in methotrexate were recorded, with acute hospital admission being the most common trigger. Of these 3 were successful, 5 were semi-successful and 7 were unsuccessful. 55 planned methotrexate dose reductions in the rheumatology clinic were recorded, with 38 being successful, 9 being semi-successful and 8 being unsuccessful (Figure 1.). Clinic letters did generally acknowledge both new physical diagnoses and changes in social circumstances, but some diagnoses were more likely to trigger a change in treatment, for example in 8 new cancer diagnoses, there were 5 changes to treatment, whereas in 12 dementia diagnoses there were 3 changes to treatment. 6 patients received more methotrexate than guidelines suggest for their level of CKD, with 3 of these having it acknowledged in clinic letters.

Conclusion

Most patients had a reduction in dose of methotrexate over a 10 year period. Planned de-escalations were mostly successful, whereas abrupt stops to treatment were generally less successful. Rheumatologists are good at acknowledging changes to health status but were more likely to change DMARD therapy in response to a cancer diagnosis than a dementia diagnosis or frailty. There is still some work to be done in acknowledging declining renal function and changing methotrexate in response. Overall, these results suggest de-escalation is mostly successful and clinicians can be confident in further expanding this into their day to day practice.

References

[1]Tutuncu, Z. and Kavanaugh, A., 2007. Treatment of elderly rheumatoid arthritis. Future Rheumatology, 2(3), pp.313-319.

Acknowledgements

Many thanks to my supervisor Dr Fiona Hayes and the rest of the rheumatology team at Southend University Hospital for being so welcoming and allowing me to make full use of the tea supplies.

Disclosure of Interests

None declared

Clinical frailty score as an independent predictor of outcome in COVID-19 hospitalised patients

PURPOSE OF THE STUDY

We explored potential predictive variables associated with outcomes using baseline clinical parameters of 500 hospitalised patients with COVID -19 in a single centre, UK.

METHODS

Retrospective study collecting demographic and clinical characteristics of patients admitted at Southend University Hospital from 20th February to 7th May 2020.

RESULTS

The mean age of the cohort admitted to hospital with Covid-19 was 69.4 and 58% were over 70. Comorbidities were more frequently observed in non-survivors, whose mean Clinical Frailty Scale was significantly higher (5 vs 3) than survivors, p < 0.001. In addition, mean C-reactive protein was significantly higher.

CONCLUSION

Older and frailer patients with high inflammatory markers were at risk of poor outcomes. Integrated frailty and age-based risk stratification is essential, in addition to monitoring saturation /FiO2 ratio (SFR) and inflammatory markers throughout the disease course to allow for early intervention to improve patient outcomes. A frailty-based risk-stratification approach, rather than age may prove more valuable when considering interventions in patients with multiple comorbidities.

Patient perceptions of co-morbidities in inflammatory arthritis

Objective

Longer life expectancy has resulted in people living with an increasing number of co-morbidities. The average individual with inflammatory arthritis has two co-morbidities, which contribute to higher mortality, poorer functional outcomes and increased health-care utilization and cost. A number of studies have investigated the prevalence of co-morbidities, whereas this study was designed to look at patient perspectives.

Methods

The study comprised two parts: a patient questionnaire and an interview. Individuals with physician-verified inflammatory arthritis along with one or more Charlson co-morbidities were invited to participate. In-depth data were obtained by interviews with 12 willing participants.

Results

One hundred and forty-six individuals were recruited; 50 (35%) had one co-morbidity, 69 (48%) had two and 25 (17%) had more than four co-morbidities. Seventy-seven individuals (53%) reported that co-morbidities affected their health as much as their arthritis, and 82 (56%) reported dependence on others for activities of daily living. Lack of education was highlighted by 106 (73%) participants. Qualitative data provided further support for the challenges, with participants highlighting the lack of time to discuss complex or multiple problems, with no-one coordinating their care. This, in turn, led to polypharmacy and insufficient discussion around drug and disease interactions, complications and self-help measures.

Conclusion

This study highlights the challenges for individuals with inflammatory arthritis who suffer with multiple co-morbidities. The challenges result from limited resources or support within the current health-care environments. Individuals highlighted the poor quality of life, which is multifactorial, and the need for better educational strategies and coordination of care to improve outcomes.

EP16 The impact of comorbidities on individuals with inflammatory arthritis

Background

Inflammatory arthritis (IA) predisposes to comorbidities (CC) including cardiovascular disease, osteoporosis, depression, infections, and cancer. CC are associated with higher mortality, poorer quality of life, and greater utilisation of health resources. Treating CC can be challenging and their impact is not addressed by current guidelines. The patient’s perspective of living with multiple conditions remains largely unexplored. We explored patient experience, impact of CC and polypharmacy on their quality of life and activities of daily living.

Methods

A mixed methods approach has been used. Patients with a definite diagnosis of IA with at least 1 Charlson comorbidity were invited to answer questionnaires. A sample of patients was invited for an in-depth qualitative interview which was analysed using thematic analysis approach.

Results

146 patients from 3 centres were recruited. 82 (56%) were females. 58 (40%) had 1 CC, 62 (42.5%) had ≥2 CC, 21 (14.5%) had ≥4 CC. Most common CC was hypertension 76 (53%), pulmonary disease 49 (34%), and diabetes 34 (23.5%). 28 (19%) remained in full time employment and 19 (13%) were unemployed. 27 (18.5%) had to cut down hours because of illness. Disease duration was &gt;10 years in 74 (51%), 5-10 years in 29 (20%), 3- 5 yrs in 21 (14%) and &lt;3 years in 22 (15%). Self-rated severity of disease was rated as low (26%), moderate (42%), severe (24%) and very severe (5.5%). Awareness and impact of CC: 77 (53%) expressed that CC affected their health as much as their arthritis. No information on CC was provided in 27 (18%), minimal information in 35 (24%) and detailed information 69 (47%). 68 (47%) were aware that some of the comorbidities could be the result of the disease or medications and 72 (49%) weren’t aware. 82 (56%) needed help from their family members/carers and of those 30% needed help daily due to CC. Polypharmacy: 73 (50%) stated either they were not involved or ‘just a little’ in choice of medication. 23 (15%) needed medication for side effects. 116 (79%) stated that doctors discuss the risks and benefits at follow ups. 130 (89%) take arthritis and CC related medication regularly. Lifestyle advice: 106 (73%) stated that education on CC wasn’t offered. 24 (16%) were not offered smoking cessation and 32 (22%) declined smoking cessation clinics. 43 (30%) weren’t aware that obesity could cause joint pains or increase the risk of diabetes, hypertension or IHD. 95 (65%) said advice on benefits of exercise was provided. Light exercises such as walking for minimum of 30 minutes was undertaken by 75%: reasons for not exercising were pain, fatigue, lack of motivation, low morale and CC.

Conclusion

This novel study provides insight into patient experiences of understanding comorbidities in the context of inflammatory arthritis. CC have a large impact on their lives and current care does not adequately meet their needs with respect to education of CC, understanding the impact, shared decision-making and lifestyle advice.

Disclosures

G.M. Koduri Honoraria; Roche. Grants/research support; Funding from Charity. N. Gullick None. F. Hayes None. A. Kayani None. S. Dubey None. C. Mukhtyar None.

Evidence-based logic chains demonstrate multiple impacts of trace metals on ecosystem services

Trace metals can have far-reaching ecosystem impacts. In this study, we develop consistent and evidence-based logic chains to demonstrate the wider effects of trace metal contamination on a suite of ecosystem services. They demonstrate knock-on effects from an initial receptor that is sensitive to metal toxicity, along a cascade of impact, to final ecosystem services via alterations to multiple ecosystem processes. We developed logic chains to highlight two aspects of metal toxicity: for impacts of copper pollution in soil ecosystems, and for impacts of mercury in freshwaters. Each link of the chains is supported by published evidence, with an indication of the strength of the supporting science. Copper pollution to soils (134 unique chains) showed a complex network of pathways originating from direct effects on a range of invertebrate and microbial taxa and plants. In contrast, mercury pollution on freshwaters (63 unique chains) shows pathways that broadly follow the food web of this habitat, reflecting the potential for mercury bioaccumulation. Despite different pathways, there is considerable overlap in the final ecosystem services impacted by both of these metals and in both ecosystems. These included reduced human-use impacts (food, fishing), reduced human non-use impacts (amenity value) and positive or negative alterations to climate regulation (impacts on carbon sequestration). Other final ecosystem goods impacted include reduced crop production, animal production, flood regulation, drinking water quality and soil purification. Taking an ecosystem services approach demonstrates that consideration of only the direct effects of metal contamination of soils and water will considerably underestimate the total impacts of these pollutants. Construction of logic chains, evidenced by published literature, allows a robust assessment of potential impacts indicating primary, secondary and tertiary effects.

The climate benefits of high-sugar grassland may be compromised by ozone pollution

High sugar ryegrasses (HSG) have been developed to improve the uptake, digestion and nitrogen (N)-utilisation of grazing stock, with the potential to increase production yields and benefit climate by reducing methane (CH4) and nitrous oxide (N2O) emissions from livestock farming. In this study, the effects of tropospheric ozone pollution on the seasonal growth dynamics of HSG pasture mesocosms containing Lolium perenne cv. AberMagic and Trifolium repens cv. Crusader were investigated. Species-specific ozone (O3) dose-response relationships (seasonal means: 35, 41, 47, 51, 59 & 67ppb) based on the Phytotoxic Ozone Dose (PODy) were constructed for above and below ground biomass, injury, N-fixation and forage quality. The dynamics of effects of ozone exposure on HSG pasture changed over the course of a season, with the strongest responses occurring in the first 4-8weeks. Overall, strong negative responses to ozone flux were found for root biomass, root nodule mass and N-fixation rates, and ozone adversely impacted a range of forage quality parameters including total sugar content and relative and consumable food values. These results indicate that increasing ozone pollution could decrease the N-use efficiency and reduce the sugar content of managed pasture, and thereby partially detract from some of the suggested benefits of HSG.

BVOC responses to realistic nitrogen fertilization and ozone exposure in silver birch

Emission of BVOC (Biogenic Volatile Organic Compounds) from plant leaves in response to ozone exposure (O3) and nitrogen (N) fertilization is poorly understood. For the first time, BVOC emissions were explored in a forest tree species (silver birch, Betula pendula) exposed for two years to realistic levels of O3 (35, 48 and 69 ppb as daylight average) and N (10, 30 and 70 kg ha(-1) yr(-1), applied weekly to the soil as ammonium nitrate). The main BVOCs emitted were: α-pinene, β-pinene, limonene, ocimene, (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT) and hexanal. Ozone exposure increased BVOC emission and reduced total leaf area. The effect on emission was stronger when a short-term O3 metric (concentrations at the time of sampling) rather than a long-term one (AOT40) was used. The effect of O3 on total leaf area was not able to compensate for the stimulation of emission, so that responses to O3 at leaf and whole-plant level were similar. Nitrogen fertilization increased total leaf area, decreased α-pinene and β-pinene emission, and increased ocimene, hexanal and DMNT emission. The increase of leaf area changed the significance of the emission response to N fertilization for most compounds. Nitrogen fertilization mitigated the effects of O3 exposure on total leaf area, while the combined effects of O3 exposure and N fertilization on BVOC emission were additive and not synergistic. In conclusion, O3 exposure and N fertilization have the potential to affect global BVOC via direct effects on plant emission rates and changes in leaf area.

N-fixation in legumes--An assessment of the potential threat posed by ozone pollution

The growth, development and functioning of legumes are often significantly affected by exposure to tropospheric ozone (O3) pollution. However, surprisingly little is known about how leguminous Nitrogen (N) fixation responds to ozone, with a scarcity of studies addressing this question in detail. In the last decade, ozone impacts on N-fixation in soybean, cowpea, mung bean, peanut and clover have been shown for concentrations which are now commonly recorded in ambient air or are likely to occur in the near future. We provide a synthesis of the existing literature addressing this issue, and also explore the effects that may occur on an agroecosystem scale by predicting reductions in Trifolium (clovers) root nodule biomass in United Kingdom (UK) pasture based on ozone concentration data for a "high" (2006) and "average" ozone year (2008). Median 8% and 5% reductions in clover root nodule biomass in pasture across the UK were predicted for 2006 and 2008 respectively. Seasonal exposure to elevated ozone, or short-term acute concentrations >100 ppb, are sufficient to reduce N-fixation and/or impact nodulation, in a range of globally-important legumes. However, an increasing global burden of CO2, the use of artificial fertiliser, and reactive N-pollution may partially mitigate impacts of ozone on N-fixation.

Highlighting the threat from current and near-future ozone pollution to clover in pasture

Globally, the legume-rhizobia symbiosis, contained within specialised organs called root nodules, is thought to add at least 30 Tg N annually to agricultural land. The growth and functioning of a modern white clover (Trifolium repens cv. Crusader) and red clover (T. pratense cv. Merviot) cultivar were investigated in current and future ozone scenarios in solardomes. Both cultivars developed leaf injury and had significant reductions in root biomass and root nodule number in response to ozone, with Crusader also displaying a reduced size and mass of nodules. In-situ measurements of N-fixation in Crusader by acetylene reduction assay revealed reduced N-fixation rates in a future scenario with an increased background and moderate peaks of ozone. The implications for the sustainability of temperate pasture are discussed.

Plant species sensitivity distributions for ozone exposure

This study derived Species Sensitivity Distributions (SSD), representing a cumulative stressor-response distribution based on single-species sensitivity data, for ozone exposure on natural vegetation. SSDs were constructed for three species groups, i.e. trees, annual grassland and perennial grassland species, using species-specific exposure-response data. The SSDs were applied in two ways. First, critical levels were calculated for each species group and compared to current critical levels for ozone exposure. Second, spatially explicit estimates of the potentially affected fraction of plant species in Northwestern Europe were calculated, based on ambient ozone concentrations. We found that the SSD-based critical levels were lower than for the current critical levels for ozone exposure, with conventional critical levels for ozone relating to 8-20% affected plant species. Our study shows that the SSD concept can be successfully applied to both derive critical ozone levels and estimate the potentially affected species fraction of plant communities along specific ozone gradients.

Identification of the Minimal Replicon of Lactococcus lactis subsp. lactis UC317 Plasmid pCI305

Replication functions of the stable, cryptic 8.7-kilobase (kb) plasmid pCI305 from multi-plasmid-containing Lactococcus lactis subsp. lactis UC317 were studied. Analysis of this replicon was facilitated by the construction of replication probe vectors that consisted of the pBR322 replication region, a pUC18-derived multiple cloning site, and either the cat gene of pC194 (pCI341; 3.1 kb) or the erm gene of pAMbeta1 (pCI3330; 4.0 kb). Plasmid pCI305 was introduced into plasmid-free L. lactis subsp. lactis MG1363Sm, a streptomycin-resistant derivative of MG1363, by a transformation procedure with the 75-kb lactose-proteinase plasmid pCI301 of UC317 as a marker plasmid. A combination of transposon Tn5 mutagenesis and subcloning in pCI341 and pCI3330 with individual Tn5 insertions around the replication region facilitated the identification of a 1.6-kb minimal replicon on pCI305. This region was separable into two domains: (i) a 1.3-kb region (repB) encoding a trans-acting function (in vitro transcription-translation studies suggested the involvement of a 48-kilodalton protein); and (ii) a 0.3-kb region (repA) sufficient to direct replication when provided with repB in trans and thus probably containing the origin of replication. Lactococcus-Escherichia coli shuttle vectors based on the pCI305 replication region were constructed.

Effects of ozone on inter- and intra-species competition and photosynthesis in mesocosms of Lolium perenne and Trifolium repens

Trifolium repens and Lolium perenne were exposed as both monocultures and two-species mixtures to an episodic rural ozone regime in large, well-watered containers within solardomes for 12 weeks. There were reductions in biomass for T. repens, but not L. perenne, and the proportion of T. repens decreased in ozone-exposed mixtures compared to the control. In addition, leaf biomass of T. repens was maintained at the expense of biomass partitioning to the stolons. The decreased growth corresponded with decreased photosynthetic capacity for T. repens, however, by the end of the exposure there was also decreased photosynthetic capacity of L. perenne, a species previously considered insensitive to ozone. The observed decreases in photosynthetic efficiency and capacity in elevated ozone indicate that the ability of such ubiquitous vegetation to act as a sink for atmospheric carbon may be reduced in future climates.

Identifying ozone-sensitive communities of (semi-)natural vegetation suitable for mapping exceedance of critical levels

Using published data on the responses of individual species to ozone, 54 EUNIS (European Nature Information System) level 4 communities with six or more ozone-sensitive species (%OS) and c. 20% or more species tested for ozone sensitivity, were identified as potentially ozone-sensitive. The largest number of these communities (23) was associated with Grasslands, with Heathland, scrub and tundra, and Mires, bogs and fens having the next highest representation at 11 and 8 level 4 communities each respectively. Within the grasslands classification, E4 (Alpine and sub-alpine grasslands), E5 (Woodland fringes and clearings) and E1 (Dry grasslands) were the most sensitive with 68.1, 51.6 and 48.6%OS respectively. It is feasible to map the land-cover for these and other communities at level 2, but it may not be currently possible to map the land-cover for all communities identified to be ozone-sensitive at levels 3 and 4.

Meta-analysis of the relative sensitivity of semi-natural vegetation species to ozone

This study identified 83 species from existing publications suitable for inclusion in a database of sensitivity of species to ozone (OZOVEG database). An index, the relative sensitivity to ozone, was calculated for each species based on changes in biomass in order to test for species traits associated with ozone sensitivity. Meta-analysis of the ozone sensitivity data showed a wide inter-specific range in response to ozone. Some relationships in comparison to plant physiological and ecological characteristics were identified. Plants of the therophyte lifeform were particularly sensitive to ozone. Species with higher mature leaf N concentration were more sensitive to ozone than those with lower leaf N concentration. Some relationships between relative sensitivity to ozone and Ellenberg habitat requirements were also identified. In contrast, no relationships between relative sensitivity to ozone and mature leaf P concentration, Grime's CSR strategy, leaf longevity, flowering season, stomatal density and maximum altitude were found. The relative sensitivity of species and relationships with plant characteristics identified in this study could be used to predict sensitivity to ozone of untested species and communities.

Optimization of scanning transmission X-ray microscopy for the identification and quantitation of reinforcing particles in polyurethanes

The morphology, size distributions, spatial distributions, and quantitative chemical compositions of co-polymer polyol-reinforcing particles in a polyurethane have been investigated with scanning transmission X-ray microscopy (STXM). A detailed discussion of microscope operating procedures is presented and ways to avoid potential artifacts are discussed. Images at selected photon energies in the C 1s, N 1s and O 1s regions allow unambiguous identification of styrene-acrylonitrile-based (SAN) copolymer and polyisocyanate polyaddition product-based (PIPA) reinforcing particles down to particle sizes at the limit of the spatial resolution (50 nm). Quantitative analysis of the chemical composition of individual reinforcing particles is achieved by fitting C 1s spectra to linear combinations of reference spectra. Regression analyses of sequences of images recorded through the chemically sensitive ranges of the C 1s, N 1s and O 1s spectra are used to generate quantitative compositional maps, which provide a fast and effective means of investigating compositional distributions over a large number of reinforcing particles. The size distribution of all particles determined by STXM is shown to be similar to that determined by TEM. The size distributions of each type of reinforcing particle, which differ considerably, were obtained by analysis of STXM images at chemically selective energies.

Pentapeptide scanning mutagenesis: encouraging old proteins to execute unusual tricks

Pentapeptide scanning mutagenesis is a facile transposon-based procedure for the random insertion of a variable five amino acid cassette into a target protein. The analysis of a library of proteins harbouring pentapeptide insertions can provide invaluable information on the essential and inessential regions of a target protein, as well as revealing surprising aspects of target protein function and activity.

Development of a multi-factor model for predicting the effects of ambient ozone on the biomass of white clover

Results are presented from the UN/ECE ICP Vegetation (International Cooperative Programme on effects of air pollution on natural vegetation and crops) experiments in which ozone(O(3))-resistant (NC-R) and -sensitive (NC-S) clones of white clover (Trifolium repens cv. Regal) were exposed to ambient O(3) episodes at 14 sites in eight European countries in 1996, 1997 and 1998. The plants were grown according to a standard protocol, and the forage was harvested every 28 days for 4-5 months per year by excision 7 cm above the soil surface. Biomass ratio (NC-S/NC-R) was related to the climatic and pollutant conditions at each site using multiple linear regression (MLR) and artificial neural networks (ANNs). Twenty-one input parameters [e.g. AOT40, 7-h mean O(3) concentration, daylight vapour pressure deficit (VPD), daily maximum temperature] were considered individually and in combination with the aim of developing a model with high r(2) and simple structure that could be used to predict biomass change in white clover. MLR models were generally more complex, and performed less well for unseen data than non-linear ANN models. The ANN model with the best performance had five inputs with an r(2) value of 0.84 for the training data, and 0.71 for previously unseen data. Two inputs to the model described the O(3) conditions (AOT40 and 24-h mean for O(3)), two described temperature (daylight mean and 24-h mean temperature), and the fifth input appeared to be differentiating between semi-urban and rural sites (NO concentration at 17:00). Neither VPD nor harvest interval was an important component of the model. The model predicted that a 5% reduction in biomass ratio was associated with AOT40s in the range 0.9-1.7 ppm x h (microl l(-1) h) accumulated over 28 days, with plants being most sensitive in conditions of low NO(x), medium-range temperature, and high 24-h mean O(3) concentration.

The partition system of multidrug resistance plasmid TP228 includes a novel protein that epitomizes an evolutionarily distinct subgroup of the ParA superfamily

The segregational stability of bacterial, low-copy-number plasmids is promoted primarily by active partition. The plasmid-specified components of the prototypical P1 plasmid partition system consist of two proteins, ParA (44.3 kDa) and ParB (38.5 kDa), which, in conjunction with integration host factor, form a nucleoprotein complex at the plasmid partition site, parS. This complex is the probable substrate for the directed temporal and spatial intracellular movement of plasmids before cell division. The genetic organization of the partition cassette of the multidrug resistance plasmid TP228 differs markedly from that of the P1 paradigm. The TP228 system includes a novel member (ParF; 22.0 kDa) of the ParA superfamily of ATPases, of which the P1 ParA protein is the archetype. However, the ParF protein and its immediate relatives form a discrete subgroup of the ParA superfamily, which evolutionarily is more related to the MinD subgroup of cell division proteins than to ParA of P1. The TP228 and P1 partition modules differ further in that the former does not include a parB homologue, but does specify a protein (ParG; 8.6 kDa) unrelated to ParB. Homologues of the parF gene are widely disseminated on eubacterial genomes, suggesting that ParF-mediated partition may be a common mechanism by which plasmid segregational stability is achieved.

Hyperprolactinaemia: analysis of presentation, diagnosis and treatment in the endocrine service of a general hospital

The charts of 184 patients with clinically significant hyperprolactinaemia who presented to a teaching hospital between 1978-1995 were reviewed, 158 (86%) females and 26 (14%) males. Hyperprolactinaemia was due to a microadenoma or was idiopathic in 36.4%, drug induced in 16%, associated with a macroadenoma in 12%, due to epilepsy in 7%, with other causes each contributing 5% or less. The presenting symptoms were amenorrhoea in 64%, galactorrhoea in 40.5%, infertility in 15%, visual field defect in 9%, with impotence in 30% and, gynaecomastia in 8% of men. One hundred and one patients were treated with bromocriptine (80%), surgery (35.4%) and radiotherapy (10.7%). Twenty-five percent of patients developed side-effects of bromocriptine for which cabergoline, a new long-lasting dopaminergic agonist, was successfully substituted. Presenting features responded to drug treatment in 70-80% of patients.

Loss of receptor regulation by a phospholipase D1 mutant unresponsive to protein kinase C

Activation of phosphatidylcholine-specific phospholipase D (PLD) constitutes an important part of the cellular response to agonist signaling. PLD1 is stimulated in vitro in a direct and synergistic manner by protein kinase C (PKC), ADP-ribosylation factor (ARF) and Rho family members. However, the direct and specific role of each of these effectors in agonist-stimulated PLD activation is poorly understood. We have used transposon mutagenesis to generate a library of PLD1 alleles containing random pentapeptide insertions. Forty-five alleles were characterized to identify functionally important regions. Use of an allele unresponsive to PKC, but otherwise seemingly normal, to examine coupling of PLD1 to a subset of G-protein-coupled receptors demonstrates for the first time direct stimulation of PLD1 in vivo by PKC and reveals that this direct stimulation is unexpectedly critical for PLD1 activation.

Appropriate and inappropriate referrals to a unit of conservative dentistry

Inappropriate referrals to secondary care are an unnecessary cost, notwithstanding the effect on waiting lists. It is essential therefore that only those patients whose referrals are appropriate are actually referred for secondary care. This project aimed to determine whether referrals to a unit of conservative dentistry are appropriate. The records of 120 consecutive new patient referrals who had been examined by one consultant in the unit of conservative dentistry at Glasgow Dental Hospital and School were obtained. A pro forma was designed on which synopses of the relevant clinical findings were written. These synopses were examined by four general dental practitioners (GDPs). A referral was considered appropriate if three or four of the GDPs considered it to be so, a referral was considered inappropriate if three or four of the GDPs concurred. Of the 120 cases examined, a majority of the GDP assessors agreed that 54 warranted referral, with 23 of these being referrals for toothwear. Agreement was not reached in 35 cases, while 31 referrals were considered inappropriate. Of the 31 cases which were considered inappropriate, 27 were thought to be within the scope of general practitioners. In conclusion, the results suggest that around one quarter of referrals to a unit of conservative dentistry are inappropriate. It would appear that a number of GDPs are unable or unwilling to treat a variety of simple conditions in practice and it may be that the development of referral guidelines is necessary to ensure that only those patients who merit a specialist opinion are referred for this service.

A newly identified, essential catalytic residue in a critical secondary structure element in the integrase family of site-specific recombinases is conserved in a similar element in eucaryotic type IB topoisomerases

The integrase family of site-specific recombinases catalyzes conservative rearrangements between defined segments of DNA. A highly conserved tetrad (RHRY) of catalytic residues is essential for this process. This tetrad is dispersed in two motifs in the linear sequence, but is configured appropriately in the catalytic pocket to execute the strand cleavage and rejoining reactions. A third conserved motif has been identified in the Xer subgroup of the integrase family. Mutational analysis of 12 conserved residues in this motif in the XerD protein from Salmonella typhimurium led to the identification of an essential fifth catalytic residue (lysine 172) which is implicated in strand cleavage or exchange. This lysine residue occupies part of the turn of an antiparallel beta-hairpin which forms one side of the catalytic cleft in XerD, and is found at similar positions among evolutionarily diverse integrase family members. Related antiparallel beta-hairpins are present in eucaryotic type IB topoisomerase enzymes which also contain a critical lysine residue in the turn of the hairpin. In both the integrase family and eucaryotic type IB topoisomerases, the catalytic lysine residues are in close contact with the substrates and may play similar roles in influencing the reactivity of the phosphotyrosine intermediates formed during reactions catalyzed by both enzymes.

A family of stability determinants in pathogenic bacteria

A novel segregational stability system was identified on plasmid R485, which originates from Morganella morganii. The system is composed of two overlapping genes, stbD and stbE, which potentially encode proteins of 83 and 93 amino acids, respectively. Homologs of the stbDE genes were identified on the enterotoxigenic plasmid P307 from Escherichia coli and on the chromosomes of Vibrio cholerae and Haemophilus influenzae biogroup aegyptius. The former two homologs also promote plasmid stability in E. coli. Furthermore, the stbDE genes share homology with components of the relBEF operon and with the dnaT gene of E. coli. The organization of the stbDE cassette is reminiscent of toxin-antitoxin stability cassettes.

Structure-function correlations in the XerD site-specific recombinase revealed by pentapeptide scanning mutagenesis

Xer-mediated site-specific recombination contributes to the stability of circular chromosomes in bacteria by resolving plasmid multimers and chromosome dimers to monomers prior to cell division. Two related site-specific recombinases, XerC and XerD, each catalyse one pair of strand exchange during Xer recombination. In order to relate the recently determined structure of XerD to its function, the XerD protein was subjected to pentapeptide scanning mutagenesis, which leads to a variable five amino acid cassette being introduced randomly into the target protein. This has allowed identification of regions of XerD involved in specific DNA binding, in communicating with the partner recombinase, XerC, and in catalysis and its control. The C-terminal domain of XerD, comprising two-thirds of the protein, contains the catalytic active site and comprises ten alpha helices (alphaE to alphaN) and a beta hairpin. A flexible linker connects this domain to the N-terminal domain that comprises four alpha helices (alphaA to alphaD). Pentapeptide insertions into alphaB, alphaD, alphaG, or alphaJ interfered with DNA binding. Helices alphaG and alphaJ comprise a pseudo helix-turn-helix DNA binding motif that may provide specificity of recombinase binding. An insertion in alphaL, adjacent to an active site arginine residue, led to loss of cooperative interactions between XerC and XerD and abolished recombination activity. Other insertions close to active site residues also abolished recombination activity. Proteins with an insertion in the beta hairpin turn bound DNA, interacted cooperatively with XerC and had a phenotype that is consistent with the protein being defective in XerD catalysis. This beta hairpin appears to be highly conserved in related proteins. Insertions at a number of dispersed locations did not impair XerD catalytic activity or DNA binding, but failed to allow XerC catalysis in vivo, indicating that several sites of interaction between XerD and XerC may be important for activation of XerC catalysis by XerD.

Insertion mutagenesis as a tool in the modification of protein function. Extended substrate specificity conferred by pentapeptide insertions in the omega-loop of TEM-1 beta-lactamase

The TEM-1 beta-lactamase enzyme efficiently hydrolyzes beta-lactam antibiotics such as ampicillin but cleaves third generation cephalosporin antibiotics poorly. Variant beta-lactamases that conferred elevated levels of resistance to the cephalosporin ceftazidime were identified in a set of beta-lactamase derivatives previously generated by pentapeptide scanning mutagenesis in which a variable 5-amino acid cassette was introduced randomly in the target protein. This mutagenesis procedure was also modified to allow the direct selection of variant beta-lactamases with pentapeptide insertions that conferred extended substrate specificities. All insertions associated with enhanced resistance to ceftazidime were targetted to the 19-amino acid Omega-loop region, which forms part of the catalytic pocket of the beta-lactamase enzyme. However, pentapeptide insertions in the C- and N-terminal halves of this region had different effects on the ability of the enzyme to hydrolyze ampicillin in vivo. Larger insertions that increased the length of the Omega-loop by up to 2-fold also retained catalytic activity toward ampicillin and/or ceftazidime in vivo. In accord with previous substitution mutation studies, these results emphasize the extreme flexibility of the Omega-loop with regards the primary structure requirements for ceftazidime hydrolysis by beta-lactamase. The potential of pentapeptide scanning mutagenesis in mimicking evolution events that result from the insertion and excision of transposons in nature is discussed.

Salmonella typhimurium specifies a circular chromosome dimer resolution system which is homologous to the Xer site-specific recombination system of Escherichia coli

The Xer site-specific recombination system of Escherichia coli resolves both chromosome dimers and multimers of certain plasmids including those of ColE1. In this manner, Xer site-specific recombination contributes to the accurate distribution of circular chromosomes at cell division. Two related site-specific recombinases, XerC and XerD, are required for this process. The xerC and xerD genes of Salmonella typhimurium LT2 were isolated from libraries of LT2 genomic DNA by genetic complementation of E. coli Xer mutants. The putative proteins specified by the S. typhimurium genes can substitute for and are highly homologous to the corresponding proteins in E. coli. The distribution of amino acid dissimilarities differs, however, between pairs of cognate Xer proteins. The immediate genetic contexts of equivalent xer genes, i.e., in operons with genes of apparently unrelated function, are conserved between the two bacteria. This is the first description of the identification of a pair of functional homologues of the xerC and xerD genes of E. coli.

Pentapeptide scanning mutagenesis: random insertion of a variable five amino acid cassette in a target protein

A new insertion method for probing protein functional organization was developed. The method relies on the random insertion of transposon Tn 4430 and subsequent in vitro deletion of the bulk of the transposon after which a 15 bp insertion remains within the target gene. This results in pentapeptide insertions randomly distributed in the target protein. Characterization of 23 pentapeptide insertions in TEM-1beta-lactamase demonstrated the utility of the method. The phenotypes associated with the mutated beta-lactamase proteins equated both with the sorts of local peptide structures in which the pentapeptide insertions occurred and their position in the three-dimensional structure of the enzyme.

Recombinase binding specificity at the chromosome dimer resolution site dif of Escherichia coli

Xer site-specific recombination functions in Escherichia coli chromosome segregation and cell division apparently by resolving chromosome dimers, which arise through homologous recombination, to monomers. Xer recombination requires two closely related site-specific recombinases, XerC and XerD, which bind cooperatively to the recombination site dif and catalyse separate pairs of strand exchanges. The dif site is an imperfect palindrome whose left and right halves are bound by XerC and XerD, respectively. By using variant dif sites in which the symmetry between the XerC and XerD binding sites was increased incrementally, the determinants in the dif site that specifically direct binding of XerC and XerD to their cognate sites were elucidated. The primary specificity nucleotides in the XerC and XerD binding sites were identified and their relative contributions to specificity assessed. The biological affects of these mutations on site-specific recombination, chromosome segregation and cell division were examined. The specificity determinants are confined to the non-palindromic outer ends of the binding sites. Replacement of the wild-type dif site with mutated dif sites at the normal location in the replication terminus region of the chromosome revealed that the sequence of the dif site can be altered substantially while retaining apparently normal chromosome segregation activity.

The P1 ParA protein and its ATPase activity play a direct role in the segregation of plasmid copies to daughter cells

The P1 ParA protein is an ATPase that recognizes the parA promoter region where it acts to autoregulate the P1 parA-parB operon. The ParB protein is essential for plasmid partition and recognizes the cis-acting partition site parS. The regulatory role of ParA is also essential because a controlled level of ParB protein is critical for partition. However, we show that this regulatory activity is not the only role for ParA in partition. Efficient partition can be achieved without autoregulation as long as Par protein levels are kept within a range of low values. The properties of ParA mutants in these conditions showed that ParA is essential for some critical step in the partition process that is independent of par operon regulation. The putative nucleotide-binding site for the ParA ATPase was identified and disrupted by mutation. The resulting mutant was substantially defective for autoregulation and completely inactive for partition in a system in which the need for autoregulation is abolished. Thus, the ParA nucleotide-binding site appears to be necessary both for the repressor activity of ParA and for some essential step in the partition process itself. We propose that the nucleotide-bound form of the enzyme adopts a configuration that favours binding to the operator, but that the ATPase activity of ParA is required for some energetic step in partition of the plasmid copies to daughter cells.

Topological scanning of the P1 plasmid partition site

The parS site of the P1 plasmid promotes active partition of P1 to daughter cells when the P1 ParA and ParB proteins are provided. The structure of parS was modified by substituting portions of the sequence with synthetic oligonucleotides and testing partition activity of the resulting mutants in an in vivo assay. The boundaries of the site were defined. They enclose a 74 bp region with a central integration host factor (IHF) binding region flanked by two arms containing heptamer and hexamer ParB binding motifs. The IHF binding region was shown to be important for partition activity but could be replaced by sequences containing A tracts that induce static bends in the DNA. The properties of sites with spacer sequences of different lengths inserted at one of five different locations led to the following conclusions. (1) The spacing between the heptamer and hexamer ParB binding motifs in both arms is critical for function. (2) Optimum partition activity requires that the parS site arms are bent toward each other with specific faces of the two helices facing each other. (3) Both arms show torsional rigidity in the active complex. (4) The left arm is laterally inflexible and activity is lost when it is extended unless the right arm is similarly extended. (5) The right arm is laterally flexible so that, when it is extended by an integral number of turns of the helix, it can still align properly with a left arm of wild-type length. The results suggest that right-arm flexibility is promoted by an A + T-rich region that is essential for IHF binding and lies adjacent to the IHF binding consensus motif. Inherent flexibility of this A + T-rich region also appears to account for the residual activity of parS sites in which the IHF binding consensus has been destroyed by multiple point mutations. The results are consistent with a proposed structure in which specific alignment of the parS site arms by an IHF-promoted bend allows them to be linked by bifunctional ParB protein binding. We suggest that such a structure might be involved in the specific pairing and unpairing of daughter plasmids during partition by an isomerization reaction.

The homologous operons for P1 and P7 plasmid partition are autoregulated from dissimilar operator sites

The plasmid-partition regions of the P1 and P7 plasmid prophages in Escherichia coli are homologues which each encode two partition proteins, ParA and ParB. The equivalent P1 and P7 proteins are closely related. In each case, the proteins are encoded by an operon that is autoregulated by the ParA and ParB proteins in concert. This regulation is species-specific, as the P1 proteins are unable to repress the P7 par operon and vice versa. The homologous ParA proteins are primarily responsible for repression and bind to regions that overlap the operon promoter in both cases. The DNA-binding domain of the P7 autorepressor lies in the amino-terminal end of the P7 ParA protein. This region includes a helix-turn-helix motif that has a clear counterpart in the P1 ParA sequence. However, despite the common regulatory mechanism and the similarity of the proteins involved in repression, the promoter-operator sequences of these two operons are very different in sequence and organization. The operator is located downstream of the promoter in P1 and upstream of it in P7, and the two regions show little, if any, homology. How these differences may have arisen from a common ancestral form is discussed.

Specificity determinants of the P1 and P7 plasmid centromere analogs

The cis-acting parS sites of P1 and P7 are similar in sequence and promote active partition of their respective plasmid prophages to daughter cells when the cognate Par proteins are supplied. Forty of the 94 relevant bases differ between the P1 and P7 parS sites, and the protein-site interactions show complete species specificity. A method was developed to predict which subset of the differing parS bases is responsible. When the four P1 bases thus identified were substituted into the P7 parS site, a complete switch to P1 specificity was observed. The P1-specific bases constitute two CG dinucleotide elements situated 66 bp apart. They lie within repeats of the TCGCCA sequence implicated in secondary contacts with the P1 ParB protein. The equivalent TC dinucleotides in the P7 site were found to be involved in P7 specificity. However, three other P7 bases can also contribute, including two in the heptamer repeats primarily responsible for ParB binding, and the P7-specific information shows some redundancy. The motifs containing the specificity dinucleotides and the primary ParB binding (heptamer) sites bear no obvious relationship of spacing or orientation to each other. For the ParB protein to contact both types of motif at the same time, the topology of the interaction must be complex.

Fine-structure analysis of the P7 plasmid partition site

The par region of bacteriophage P7 is responsible for active partition of the P7 plasmid prophage into daughter cells. The cis-acting partition site was defined precisely as a 75-bp sequence that was necessary and sufficient to promote correct segregation of an unstable vector plasmid when the two P7 partition proteins, ParA and ParB, were supplied in trans. Roughly the same region was necessary to exert partition-mediated incompatibility. The minimal site contains an integration host factor (IHF) protein binding site bracketed by regions containing heptamer repeat sequences that individually bind ParB. An additional sequence forms the left boundary of the site. Site-directed mutations in the latter sequence, as well as the IHF motif and the rightmost ParB box, blocked site function. Although the P7 site shares 55% sequence identity with its counterpart in bacteriophage P1, functional interactions between the partition sites and the Par proteins of the two plasmids were entirely species specific in vivo. The P1 sequence has similar IHF and ParB binding motifs, but the left boundary sequence differs radically and may define a point of species-specific contact with the Par proteins. No evidence was found for the existence of a functional P7 analog of the P1 parS core, a small subregion of the P1 site that, in isolation, acts as an enfeebled partition site with modified incompatibility properties.