The impact of mindfulness on working memory-related brain activation in breast cancer survivors with cognitive complaints

PURPOSE

Cancer-related cognitive impairment (CRCI) has been associated with altered brain activation after chemotherapy in areas related to working memory. Hence, improving working memory capacity and associated brain activation might aid in the recovery of CRCI. In this study, we investigated the potential of a mindfulness-based intervention (MBI) to impact working memory-related brain activation.

METHODS

Female breast cancer survivors reporting cognitive complaints (N=117) were randomized into a mindfulness (n=43; MBI), physical training (n=36; PT), or waitlist control condition (n=38; WL). Participants completed MRI scans before the intervention, immediately after, and three months post-intervention. Task-based functional MRI was used to measure differences between groups over time in working memory-related brain activation while performing a visual-verbal n-back task.

RESULTS

Data of 83 participants (32/26/25 MBI/PT/WL) was included. Compared to the waitlist group, MBI participants showed reduced task-related activation in the right middle frontal and angular gyrus and increased activation in the right dorsal posterior cingulate cortex over time. Compared to the physical training group, MBI participants showed reduced brain activation in the bilateral superior parietal lobule and right dorsal anterior cingulate cortex over time. No differences between physical training and no intervention were identified.

CONCLUSION

This study showed that an 8-week mindfulness-based intervention can significantly alter brain activation across brain regions involved in working memory, attentional control, and emotion processing during performance of a working memory task. This might aid in the recovery of CRCI.

IMPLICATIONS FOR CANCER SURVIVORS

Mindfulness might alter brain activation patterns while performing a working memory task, which might ultimately aid in restoring higher order cognitive functions.

The effect of universal school-based mindfulness on anhedonia and emotional distress and its underlying mechanisms: A cluster randomised controlled trial via experience sampling in secondary schools

This cluster randomised controlled trial examined the effectiveness of universal school-based mindfulness training (MT; vs. passive control) to lower anhedonia and emotional distress among mid-adolescents (15-18 years). It further examined three potential mechanisms: dampening of positive emotions, non-acceptance/suppression of negative emotions, and perceived social pressure not to experience/express negative emotions. Adolescents (ncontrol = 136, nintervention = 95) participated in three assessment points (before, after and two/three months after the in-class MT), consisting of Experience Sampling (ES) assessments and self-report questionnaires (SRQs) to corroborate the ES assessments. Analyses were based on general linear modelling and multilevel modelling. Overall, no evidence was found for a significant beneficial and long-lasting impact of the MT on adolescents' mental health. Importantly, some barriers inherently linked to universal MT approaches (low engagement in and mixed attitudes towards the MT) may have tempered the effectiveness of the MT in the current trial. Further research should prioritise overcoming these barriers to optimise programme implementation. Additionally, given the potential complex interplay of moderators at micro- (home practice), meso- (school climate), and macro-level (broader context), research should simultaneously focus on alternative ways of delivering MT at schools to strengthen adolescents' mental health.

A blended preconception lifestyle programme for couples undergoing IVF: lessons learned from a multicentre randomized controlled trial

STUDY QUESTION

What is the effect of a blended preconception lifestyle programme on reproductive and lifestyle outcomes of couples going through their first 12 months of IVF as compared to an attention control condition?

SUMMARY ANSWER

This randomized controlled trial (RCT) was stopped prematurely because of the coronavirus disease 2019 (Covid-19) pandemic but the available data did not suggest that a blended preconception lifestyle programme could meaningfully affect time to ongoing pregnancy or other reproductive and lifestyle outcomes.

WHAT IS KNOWN ALREADY

Increasing evidence shows associations between a healthy lifestyle and IVF success rates. Lifestyle programmes provided through a mobile phone application have yet to be evaluated by RCTs in couples undergoing IVF.

STUDY DESIGN SIZE DURATION

A multicentre RCT (1:1) was carried out. The RCT started in January 2019 and was prematurely stopped because of the Covid-19 pandemic, leading to a reduced sample size (211 couples initiating IVF) and change in primary outcome (cumulative ongoing pregnancy to time to ongoing pregnancy).

PARTICIPANTS/MATERIALS SETTING METHODS

Heterosexual couples initiating IVF in five fertility clinics were randomized between an attention control arm and an intervention arm for 12 months. The attention control arm received treatment information by mobile phone in addition to standard care. The intervention arm received the blended preconception lifestyle (PreLiFe)-programme in addition to standard care. The PreLiFe-programme included a mobile application, offering tailored advice and skills training on diet, physical activity and mindfulness, in combination with motivational interviewing over the telephone. The primary outcome was 'time to ongoing pregnancy'. Secondary reproductive outcomes included the Core Outcome Measures for Infertility Trials and IVF discontinuation. Changes in the following secondary lifestyle outcomes over 3 and 6 months were studied in both partners: diet quality, fruit intake, vegetable intake, total moderate to vigorous physical activity, sedentary behaviour, emotional distress, quality of life, BMI, and waist circumference. Finally, in the intervention arm, acceptability of the programme was evaluated and actual use of the mobile application part of the programme was tracked. Analysis was according to intention to treat.

MAIN RESULTS AND THE ROLE OF CHANCE

A total of 211 couples were randomized (105 control arm, 106 intervention arm). The hazard ratio of the intervention for time to ongoing pregnancy was 0.94 (95% CI 0.63 to 1.4). Little to no effect on other reproductive or lifestyle outcomes was identified. Although acceptability of the programme was good (6/10), considerable proportions of men (38%) and 9% of women did not actively use all the modules of the mobile application (diet, physical activity, or mindfulness).

LIMITATIONS REASONS FOR CAUTION

The findings of this RCT should be considered exploratory, as the Covid-19 pandemic limited its power and the actual use of the mobile application was low.

WIDER IMPLICATIONS OF THE FINDINGS

This is the first multicentre RCT evaluating the effect of a blended preconception lifestyle programme for women and their partners undergoing IVF on both reproductive and lifestyle outcomes. This exploratory RCT highlights the need for further studies into optimal intervention characteristics and actual use of preconception lifestyle programmes, as well as RCTs evaluating effectiveness.

STUDY FUNDING/COMPETING INTERESTS

Supported by the Research foundation Flanders (Belgium) (FWO-TBM; reference: T005417N). No competing interests to declare.

TRIAL REGISTRATION NUMBER

ClinicalTrials.gov Identifier: NCT03790449.

TRIAL REGISTRATION DATE

31 December 2018.

DATE OF FIRST PATIENT’S ENROLMENT

2 January 2019.

Effect of the INTER-ACT lifestyle intervention on maternal mental health during the first year after childbirth: A randomized controlled trial

We assess whether the INTER-ACT postpartum lifestyle intervention influences symptoms of depression and anxiety, sense of coherence and quality of life during the first year after childbirth. A total of 1047 women of the INTER-ACT RCT were randomized into the intervention (n = 542) or control arm (n = 505). The lifestyle intervention consisted of 4 face-to-face coaching sessions, supported by an e-health app. Anthropometric and mental health data were collected at baseline, end of intervention and 6-months follow-up. We applied mixed models to assess whether the evolution over time of depressive symptoms, anxiety, sense of coherence and quality of life differed between the intervention and control arm, taking into account the women's pre-pregnancy BMI. There was no statistical evidence for a difference in evolution in anxiety or quality of life between intervention and control arm. But an improvement in symptoms of depression and sense of coherence was observed in women who received the intervention, depending on the mother's pre-pregnancy BMI. Women with normal/overweight pre-pregnancy BMI, reported a decrease in EPDS between baseline and end of intervention, and the decrease was larger in the intervention arm (control arm: -0.42 (95% CI, -0.76 to -0.08); intervention arm: -0.71 (95% CI, -1.07 to -0.35)). Women with pre-pregnancy obesity showed an increase in EPDS between baseline and end of intervention, but the increase was less pronounced in the intervention arm (control arm: +0.71 (95% CI, -0.12 to 1.54); intervention arm: +0.42 (95% CI -0.42 to 1.25)). Women with a normal or obese pre-pregnancy BMI in the intervention arm showed a decrease in sense of coherence between baseline and end of intervention (-0.36) (95% CI, -1.60 to 0.88), while women with overweight pre-pregnancy showed an increase in sense of coherence (+1.53) (95% CI, -0.08 to 3.15) between baseline and end of intervention. Receiving the INTER-ACT postpartum lifestyle intervention showed improvement in depressive symptoms, in normal weight or overweight women on the short run, as well as improvement in sense of coherence in women with pre-pregnancy overweight only. Trial registration: ClinicalTrials.gov;NCT02989142.

The impact of mindfulness on cancer-related cognitive impairment in breast cancer survivors with cognitive complaints

BACKGROUND

Interventions that target cancer-related cognitive impairment (CRCI) to improve the quality of life of cancer survivors are needed. In this study, the potential of a mindfulness-based intervention to reduce CRCI in breast cancer survivors, compared with physical training and a wait list control group, was investigated.

METHODS

Breast cancer survivors with cognitive complaints (N = 117) were randomly allocated to a mindfulness (n = 43), physical training (n = 36), or wait list control condition (n = 38). Participants completed neuropsychological tests and questionnaires before the intervention, immediately after, and 3 months after intervention. The primary outcome measure was the change in cognitive complaints over time. Secondary outcomes were objective cognitive impairment and psychological well-being. All outcomes were compared between groups over time using linear mixed models, including participants with missing values.

RESULTS

Of the 117 included participants, 96 completed the three assessments. Participants in the three groups reported decreased cognitive complaints after intervention, without group differences. There were no between-group differences in objective cognitive impairment after intervention compared with baseline. Compared with the wait list control group, participants reported increased mindfulness skills and reduced emotional distress after mindfulness and reduced emotional distress and fatigue after physical training.

CONCLUSION

Contrary to the hypothesis, all groups reported an improvement in cognitive complaints over time. It is suggested that priming and acknowledgment of CRCI might alter the experience of cognitive impairment. Additionally, both mindfulness-based intervention and physical training can improve psychological well-being of breast cancer survivors with cognitive complaints.

Mindfulness-Based Interventions and Body Awareness

Body awareness (BA) has long been proposed as a working mechanism of mindfulness-based interventions (MBIs), yet research on the mediating role of BA is scarce. Hence, the present study assesses the impact of an 8-week MBI on self-reported and indirect measures of BA, investigates the potential mediating role of BA in the relationship between an MBI and symptomatology, evaluates the impact of an MBI on important psychological processes (i.e., experiential avoidance, rumination, self-efficacy, and self-discrepancy), and explores whether these variables act alongside BA in mediating the relationship between an MBI and symptomatology. A non-randomized controlled trial was conducted with 148 participants (n = 89 in the MBI group; n = 59 in the control group) who completed questionnaires assessing BA and the above-mentioned psychological processes before and after an MBI. A sub-sample of participants (n = 86) completed a task that evaluates BA indirectly. Results showed a significant effect of MBI on the self-reported BA but not on the indirect measure of BA. The MBI significantly reduced symptomatology, and this effect was mediated by regulatory and belief-related dimensions of BA. Multiple mediator models showed a significant mediation via various pathways involving improved BA and various transdiagnostic psychological processes.

Evaluation of a stand-alone mobile mindfulness app in people experiencing infertility: the protocol for an exploratory randomised controlled trial (MoMiFer-RCT)

INTRODUCTION

Infertility and its treatment bring a considerable emotional burden. Increasing evidence demonstrates the effectiveness of smartphone-delivered mindfulness apps for reducing symptoms of emotional distress in both clinical and non-clinical populations. Evidence on this topic in women, men and couples experiencing infertility is currently under-represented. The aim of the MoMiFer study is, therefore, to investigate the efficacy of a stand-alone mobile mindfulness app on symptoms of emotional distress and fertility-related quality of life in people experiencing infertility.

METHODS AND ANALYSIS

This study is an exploratory randomised controlled trial (RCT) with open enrollment. The primary outcomes are symptoms of emotional distress and fertility-related quality of life. Secondary outcomes are mindfulness skills, repetitive negative thinking, self-compassion, user-rated quality of the stand-alone mobile mindfulness app and use of the app. Experience sampling method and standardised self-report questionnaires are combined within a repeated measures design to measure the effects of the stand-alone mobile mindfulness app on the primary and secondary outcomes, apart from the use of the app. The latter will be evaluated through app tracking. People, including women, men and couples, experiencing infertility (n=60) will be randomised to an intervention group receiving the stand-alone mobile mindfulness app for 3 months or a wait-list control group. The app follows the format and content of Mindfulness-Based Stress Reduction. Data will be collected at baseline, at 1.5 months and 3 months after randomisation. Analysis will be according to intention to treat and based on general linear modelling and multilevel mixed-effects modelling.

ETHICS AND DISSEMINATION

This study received approval from the Medical Ethical Committee of the Leuven University Hospital (Belgium). The findings of this exploratory RCT will be disseminated through presentations at public lectures, scientific institutions and meetings, and through peer-reviewed scientific articles.

TRIAL REGISTRATION NUMBER

NCT04143828.

Study protocol for You.Mind!: boosting first-line mental health care for YOUngsters suffering from chronic conditions with mindfulness: a randomised staggered within-subjects design

INTRODUCTION

Adolescents with chronic conditions often experience high levels of stress, anxiety and depression, and reduced quality of life. Mindfulness-based interventions (MBIs) have been found to improve emotional distress in clinical and non-clinical populations and are a promising technique to support adolescents with chronic conditions in managing their symptoms and ultimately enhance their quality of life.

METHODS AND ANALYSIS

To test the effects of an MBI on emotional distress and quality of life and delineate the underlying mechanisms, the You.Mind! study uses a randomised staggered within-subjects design. Thirty adolescents with a chronic condition will be randomised to a baseline phase of 14-28 days followed by an MBI, consisting of four online group sessions and online support spread over 8 weeks. Outcomes will be assessed by short, repeated measurements throughout the baseline, intervention and follow-up phases and by standardised questionnaires and experience sampling measures before randomisation, at postintervention and at 3-months follow-up. Analysis will be based on general linear modelling and multilevel mixed-effects modelling.

ETHICS AND DISSEMINATION

Ethical approval was obtained from the Ethics Committee Research UZ/KU Leuven and the Ethics Committee of Ghent University Hospital and Ghent University (S63485). Results will be disseminated through presentations at public lectures, scientific institutions and meetings, and through publication in peer-reviewed journals.

TRIAL REGISTRATION NUMBER

NCT04359563.

Effects of a mindfulness-based intervention on cancer-related cognitive impairment: Results of a randomized controlled functional magnetic resonance imaging pilot study

BACKGROUND

Many breast cancer survivors suffer from cognitive complaints after cancer treatment, affecting their quality of life. The objective of this pilot study was to investigate the effect of a blended-care mindfulness-based intervention (MBI) on chemotherapy-related cognitive impairment and functional brain changes. Furthermore, correlations between changes in cognitive functioning and self-reported behavioral factors were investigated.

METHODS

Breast cancer survivors (n = 33) who reported cognitive impairment were randomly allocated to a mindfulness condition (n = 18) or a waitlist control condition (n = 15). Patients completed questionnaires on cognitive impairment, emotional distress, and fatigue; neuropsychological tests; and resting-state functional magnetic resonance imaging before the start of MBI (time 1 [T1]), immediately after the completion of an 8-week MBI program (T2), and 3 months postintervention (T3). Resting-state functional connectivity was estimated in the default mode network, the dorsal and salience attention networks, and the frontoparietal network. Mixed model repeated-measures analysis was performed to test the intervention effect.

RESULTS

Patients in the mindfulness condition exhibited significantly higher connectivity between the dorsal and salience attention networks after the mindfulness intervention compared with those in the control condition. MBI participants also had reduced subjective cognitive impairment, emotional distress, and fatigue. No intervention effect was observed on neurocognitive tests.

CONCLUSIONS

MBI may induce functional brain changes in networks related to attention and may have a positive effect on subjective measures of cognitive impairment in breast cancer survivors. Therefore, MBI could be a suitable intervention to improve quality of life in this population and deserves further study in this context.

A mindfulness-based intervention for breast cancer patients with cognitive impairment after chemotherapy: study protocol of a three-group randomized controlled trial

Background

Mindfulness has been applied to improve cancer care by enhancing psychological well-being. However, little is known about its impact on cognitive impairment experienced by cancer patients after chemotherapy. Mindfulness may be relevant in tackling cognitive impairment by decreasing emotional distress and fatigue, by decreasing inflammation, and by strengthening functional brain connectivity. The aim of the present study protocol is to evaluate the efficacy and mechanisms of a mindfulness-based intervention to reduce cognitive impairment in breast cancer patients after chemotherapy.

Methods/design

The present study is a three-arm, parallel-group, randomized controlled trial with assessments at baseline, 1 to 3 weeks after the intervention and at 3 months’ follow-up. One hundred and twenty breast cancer patients who ended treatment a minimum of 6 months and a maximum of 5 years before, and who have cognitive complaints, will be enrolled. They will be randomized into one of the following three study arms: (1) a mindfulness-based intervention group (n = 40), (2) an active control condition based on physical training (n = 40), or (3) a treatment as usual (TAU) control group (n = 40). Both the mindfulness-based intervention and the active control condition consist of four group sessions (3 h for the mindfulness condition and 2 h for the physical training) spread over 8 weeks. The primary outcomes will be cognitive symptoms as measured by the Cognitive Failure Questionnaire and changes in functional brain connectivity in the attention network. Secondary outcomes will be (1) levels of emotional distress, fatigue, mindfulness, quality of life; (2) neurocognitive tests; (3) structural and functional brain changes using MR imaging and (4) measures of inflammation.

Discussion

The study will examine the impact of a mindfulness-based intervention on cognitive impairment in breast cancer patients. If the findings of this study confirm the effectiveness of a mindfulness-based program to reduce cognitive impairment, it will be possible to improve quality of life for ex-cancer patients. We will inform health care providers about the potential use of a mindfulness-based intervention as a non-pharmaceutical, low-threshold mental health intervention to improve cognitive impairment after cancer.

Trial registration

ClinicalTrials.gov, ID: NCT03736460. Retrospectively registered on 8 November 2018.

Effectiveness of a mobile preconception lifestyle programme in couples undergoing in vitro fertilisation (IVF): the protocol for the PreLiFe randomised controlled trial (PreLiFe-RCT)

INTRODUCTION

Infertility and in vitro fertilisation (IVF; with or without intracytoplasmic sperm injection) result in considerable emotional and financial burden. Increasing evidence suggests that lifestyle factors, including diet, physical activity and personal well-being, are associated with IVF-success rates. Currently, IVF is not routinely combined with a lifestyle programme. The preconception lifestyle (PreLiFe) randomised controlled trial (RCT) assesses the effects of a new mobile PreLiFe programme in couples undergoing IVF.

METHODS AND ANALYSIS

A multicentre RCT including 460 heterosexual couples starting IVF in Belgian fertility clinics. IVF couples are randomised between an attention control group or the PreLiFe programme for a period of 12 months or until an ongoing pregnancy is confirmed by ultrasound. The attention control programme includes a mobile application with treatment information (ie, appointments and medication instructions) in addition to standard care. The PreLiFe programme includes a mobile application with the same treatment information in combination with a lifestyle programme. This new lifestyle programme includes tailored advice and skills training on diet, physical activity and mindfulness in combination with text messages and telephone interaction with a healthcare professional trained in motivational interviewing. The primary outcome of this RCT is the cumulative ongoing pregnancy rate within 12 months after randomisation. Secondary outcomes include changes in diet, physical activity, emotional distress, body mass index, waist circumference, quality of life and other reproductive outcomes including IVF discontinuation, clinical pregnancy rate and time to pregnancy. Additionally, partner support and the feasibility (use and acceptability) of the PreLiFe programme will be evaluated in the intervention group. Analysis will be according to intention to treat.

ETHICS AND DISSEMINATION

This study has been approved by the Medical Ethical Committee of the Leuven University Hospital (Belgium) and the other recruiting clinics. The findings of this RCT will be disseminated through presentations at international scientific meetings and peer-reviewed publications.

TRIAL REGISTRATION NUMBER

NCT03790449; Pre-results.

Processes of change in a school-based mindfulness programme: cognitive reactivity and self-coldness as mediators

The underlying mechanisms of the effectiveness of mindfulness-based interventions for emotional well-being remain poorly understood. Here, we examined the potential mediating effects of cognitive reactivity and self-compassion on symptoms of depression, anxiety and stress using data from an earlier randomised controlled school trial. A moderated time-lagged mediation model based on multilevel modelling was used to analyse the data. The findings showed that post-treatment changes in cognitive reactivity and self-coldness, an aspect of self-compassion, mediated subsequent changes in symptoms of depression, anxiety and stress. These results suggest that cognitive reactivity and self-coldness may be considered as transdiagnostic mechanisms of change of a mindfulness-based intervention programme for youth.

A Mindfulness-Based Intervention for Adolescents and Young Adults After Cancer Treatment: Effects on Quality of Life, Emotional Distress, and Cognitive Vulnerability

PURPOSE

Adolescent and young adult cancer (AYAC) survivors show an elevated risk of distress. Targeted psychosocial interventions for this distinct population are needed. This study examined the potential efficacy of a mindfulness-based intervention (MBI) to alleviate emotional distress and improve quality of life (QoL) in AYAC survivors.

METHODS

Participants were 16 AYAC survivors, aged 14-24, who had completed acute medical treatment. A two-baseline (8 and 1 week before the intervention), post- (1 week after the intervention) and 3 months follow-up within-subjects design was used. Each participant completed two baseline assessments, followed by an 8-week MBI. The primary outcome variables were emotional distress and QoL. Secondary outcomes were cognitive vulnerability factors and mindfulness skills.

RESULTS

Multilevel modeling showed (1) a significant reduction in emotional distress and improvement in QoL at 3 months of follow-up, (2) a significant reduction in negative attitudes toward self (i.e., a cognitive vulnerability factor), and (3) a significant improvement in mindfulness skills.

CONCLUSION

MBI is a promising approach that is used to treat emotional distress and to improve QoL in AYAC survivors. Further research using randomized controlled trials is needed to generalize these findings. Trial registration information: www.trialregister.nl ; NTR4358.

Lack of phylogeographic structure in the freshwater cyanobacterium Microcystis aeruginosa suggests global dispersal

BACKGROUND

Free-living microorganisms have long been assumed to have ubiquitous distributions with little biogeographic signature because they typically exhibit high dispersal potential and large population sizes. However, molecular data provide contrasting results and it is far from clear to what extent dispersal limitation determines geographic structuring of microbial populations. We aimed to determine biogeographical patterns of the bloom-forming freshwater cyanobacterium Microcystis aeruginosa. Being widely distributed on a global scale but patchily on a regional scale, this prokaryote is an ideal model organism to study microbial dispersal and biogeography.

METHODOLOGY/PRINCIPAL FINDINGS

The phylogeography of M. aeruginosa was studied based on a dataset of 311 rDNA internal transcribed spacer (ITS) sequences sampled from six continents. Richness of ITS sequences was high (239 ITS types were detected). Genetic divergence among ITS types averaged 4% (maximum pairwise divergence was 13%). Preliminary analyses revealed nearly completely unresolved phylogenetic relationships and a lack of genetic structure among all sequences due to extensive homoplasy at multiple hypervariable sites. After correcting for this, still no clear phylogeographic structure was detected, and no pattern of isolation by distance was found on a global scale. Concomitantly, genetic differentiation among continents was marginal, whereas variation within continents was high and was mostly shared with all other continents. Similarly, no genetic structure across climate zones was detected.

CONCLUSIONS/SIGNIFICANCE

The high overall diversity and wide global distribution of common ITS types in combination with the lack of phylogeographic structure suggest that intercontinental dispersal of M. aeruginosa ITS types is not rare, and that this species might have a truly cosmopolitan distribution.

Hidden levels of phylodiversity in Antarctic green algae: further evidence for the existence of glacial refugia

Recent data revealed that metazoans such as mites and springtails have persisted in Antarctica throughout several glacial-interglacial cycles, which contradicts the existing paradigm that terrestrial life was wiped out by successive glacial events and that the current inhabitants are recent colonizers. We used molecular phylogenetic techniques to study Antarctic microchlorophyte strains isolated from lacustrine habitats from maritime and continental Antarctica. The 14 distinct chlorophycean and trebouxiophycean lineages observed point to a wide phylogenetic diversity of apparently endemic Antarctic lineages at different taxonomic levels. This supports the hypothesis that long-term survival took place in glacial refugia, resulting in a specific Antarctic flora. The majority of the lineages have estimated ages between 17 and 84 Ma and probably diverged from their closest relatives around the time of the opening of Drake Passage (30-45 Ma), while some lineages with longer branch lengths have estimated ages that precede the break-up of Gondwana. The variation in branch length and estimated age points to several independent but rare colonization events.

Priority effects in experimental populations of the cyanobacterium Microcystis

The arrival order of colonists in developing populations can have a lasting influence on community and population structure, a phenomenon referred to as priority effects. To explore whether such priority effects are important in determining strain composition of populations of the cyanobacterium Microcystis, four Microcystis strains, isolated from a single lake and differing in functional traits, were grown during 4 weeks in the laboratory in all possible pairwise combinations, with the two strains either inoculated at the same time or with a time lag of 1 week, in the presence or absence of grazing Daphnia magna. The relative abundance of strains in the mixtures was assessed using denaturing gradient gel electrophoresis, and the growth rate of each strain in the mixtures was determined for the last 2 weeks of the experiment. We observed strong effects of inoculation order on the final population structure, and these effects were influenced by grazing Daphnia. The priority effects were strain-specific and occurred in two directions: some of the strains grew slower while others grew faster when inoculated second compared with when inoculated first. Our results indicate that priority effects may have a profound impact on strain composition of Microcystis populations.

The power of species sorting: local factors drive bacterial community composition over a wide range of spatial scales

There is a vivid debate on the relative importance of local and regional factors in shaping microbial communities, and on whether microbial organisms show a biogeographic signature in their distribution. Taking a metacommunity approach, spatial factors can become important either through dispersal limitation (compare large spatial scales) or mass effects (in case of strongly connected systems). We here analyze two datasets on bacterial communities [characterized by community fingerprinting through denaturing gradient gel electrophoresis (DGGE)] in meso- to eutrophic shallow lakes to investigate the importance of spatial factors at three contrasting scales. Variation partitioning on datasets of both the bacterial communities of 11 shallow lakes that are part of a strongly interconnected and densely packed pond system <1 km apart, three groups of shallow lakes approximately 100 km apart, as well as these three groups of shallow lakes combined that span a large part of a North-South gradient in Europe (>2,500 km) shows a strong impact of local environmental factors on bacterial community composition, with a marginal impact of spatial distance. Our results indicate that dispersal is not strongly limiting even at large spatial scales, and that mass effects do not have a strong impact on bacterial communities even in physically connected systems. We suggest that the fast population growth rates of bacteria facilitate efficient species sorting along environmental gradients in bacterial communities over a very broad range of dispersal rates.

Bacterial community composition in Lake Tanganyika: vertical and horizontal heterogeneity

Vertical and latitudinal differences in bacterial community composition (BCC) in Lake Tanganyika were studied during the dry season of 2002 by means of denaturing gradient gel electrophoresis analysis of PCR-amplified 16S RNA fragments. Dominant bands were sequenced and identified as members of the Cyanobacteria, Actinobacteria, Nitrospirae, green nonsulfur bacteria, and Firmicutes divisions and the Gamma- and Deltaproteobacteria subdivisions. The BCC in the lake displayed both vertical and latitudinal variation. Vertical changes in BCC were related to the thermal water column stratification, which influences oxygen and nutrient concentrations. Latitudinal variation was related to upwelling of deep water and increased primary production in the south of the lake. The number of bands per sample increased with bacterial production in the epilimnion of the lake, suggesting a positive diversity-productivity relationship.

Characterization of bacterial communities in four freshwater lakes differing in nutrient load and food web structure

The phylogenetic composition of bacterioplankton communities in the water column of four shallow eutrophic lakes was analyzed by partially sequencing cloned 16S rRNA genes and by PCR-DGGE analysis. The four lakes differed in nutrient load and food web structure: two were in a clearwater state and had dense stands of submerged macrophytes, while two others were in a turbid state characterized by the occurrence of phytoplankton blooms. One turbid and one clearwater lake had very high nutrient levels (total phosphorus > 100 microg/l), while the other lakes were less nutrient rich (total phosphorus < 100 microg/l). Cluster analysis, multidimensional scaling and ANOSIM (analysis of similarity) were used to investigate differences among the bacterial community composition in the four lakes. Our results show that each lake has its own distinct bacterioplankton community. The samples of lake Blankaart differed substantially from those of the other lakes; this pattern was consistent throughout the year of study. The bacterioplankton community composition in lake Blankaart seems to be less diverse and less stable than in the other three lakes. Clone library results reveal that Actinobacteria strongly dominated the bacterial community in lake Blankaart. The relative abundance of Betaproteobacteria was low, whereas this group was dominant in the other three lakes. Turbid lakes had a higher representation of Cyanobacteria, while clearwater lakes were characterized by more representatives of the Bacteroidetes. Correlating our DGGE data with environmental parameters, using the BIOENV procedure, suggests that differences are partly related to the equilibrium state of the lake.

Top-down impact of bacterivorous nematodes on the bacterial community structure: a microcosm study

The influence of bacterivorous nematodes (Diplolaimelloides meyli, Diplolaimelloides oschei, Diplolaimella dievengatensis, Panagrolaimus paetzoldi) on the development of a bacterial community growing on decaying cordgrass detritus was studied in laboratory microcosm experiments. Cordgrass leaves were incubated on a sediment surface with a natural bacterial mixture containing bacteria from sediment, cordgrass detritus and habitat water. The four nematode species were applied separately to the microcosms; controls remained without nematodes. Samples were taken seven times over a 65-day period. The bacterial community structure was analysed by means of DGGE of the 16S rRNA genes. Multi Dimensional Scaling showed grouping of the samples per treatment. Analysis of Similarities indicated that the differences between treatments were significantly larger than differences within treatments. Our results suggest that nematodes can have a significant structuring top-down influence on the 'pool' of bacteria growing on the detritus, even at low densities. Dissimilarities were similar between all treatments. Differences in bacterial community composition within the treatments with monhysterids (D. meyli, D. oschei and D. dievengatensis) can be explained by species-specific food preferences. Panagrolaimus paetzoldi on the other hand feeds unselectively, and thus affects the bacterial community differently. A top-down effect of the nematodes on the diversity of the bacterial community was only evident under high grazing pressure, i.e. in the presence of P. paetzoldi.

Phylogenetic analysis of partial bacterial 16S rDNA sequences of tropical grass pasture soil under Acacia tortilis subsp. raddiana in Senegal

We used direct recovery of bacterial 16S rRNA gene sequences to investigate the bacterial diversity under Acacia tortilis subsp. raddiana, a legume tree naturally growing in the dry land part of Senegal (West Africa). Microbial DNA was purified directly from soil samples and subjected to PCR with primers specific for bacterial 16S rRNA gene sequences. 16S rDNA clone libraries were constructed from two soil samples taken at two dates, i.e. June 25th 1999 (dry season) and August 28th 1999 (rainy season) at depths of 0.25-0.50 m and at 3 m distance from the stem. The 16S rDNA of 117 clones was partially sequenced. Phylogenetic analysis of these sequences revealed extensive diversity (100 phylotypes). Comparative sequence analysis of these clones identified members of the Gammaproteobacteria (35% of the phylotypes) as the most important group, followed by the Firmicutes division with 24%. Alphaproteobacteria, Betaproteobacteria, Acidobacteria and Actinobacteria were found to be less represented. Our data suggest that bacterial communities under Acacia tortilis subsp. raddiana might differ according to the season. The relative compositions of the populations is different in both samples: the Acidobacteria are present in a much higher percentage in the dry season than in the rainy season sample while the inverse effect is observed for the members of the other groups. Within the Gammaproteobacteria we found a shift between the dry season and the rainy season from pseudomonads to Acinetobacter and Escherichia related organisms.

Polymerase chain reaction denaturing gradient gel electrophoresis analysis of the N2-fixing bacterial diversity in soil under Acacia tortilis ssp. raddiana and Balanites aegyptiaca in the dryland part of Senegal

Denaturing gradient gel electrophoresis (DGGE) of amplified nifH gene fragments was used to study the diazotrophic community of soil samples under Acacia tortilis ssp. raddiana (legume tree) and Balanites aegyptiaca (non-legume tree), two dominant plant species growing naturally in the dryland part of Senegal. Samples were taken along transects from the stem up to 10 m distance from it, at depths of 0-0.25 m and 0.25-0.50 m. Sampling was done in the dry season (25 June 1999) and in the rainy season (28 August 1999). The community structure and diversity of the bacterial groups from the different samples was analysed further using different techniques, such as statistical analysis and diversity index evaluation of the band patterns. Diazotrophic diversity was lower under B. aegyptiaca than under A. tortilis ssp. raddiana. Multidimensional scaling (MDS) analysis and ANOSIM tests showed a significant effect of the tree on the diazotroph assemblages. SIMPER analysis showed that the major elements responsible for the dissimilarity are a member of the genus Sinorhizobium, which is characteristic of the samples taken under A. tortilis ssp. raddiana and a member of the cluster Bradyrhizobium for the samples taken under B. aegyptiaca. Forty-four major bands were partially sequenced, yielding 33 different nifH sequences, which were used in phylogenetic reconstructions. Most sequences were affiliated with the alpha- beta- and gamma-proteobacteria. Five nifH sequences were identical to those of Pseudomonas stutzeri, and one sequence showed 100% similarity to that of Azotobacter vinelandii. Four bands were affiliated with the Cyanobacteria and a single one with the Firmicutes. For both trees, there were also clear differences between the samples taken in the dry and rainy seasons. Only for the samples taken under A. tortilis ssp. raddiana was a significant difference found between the two sampling depths.

Rapid screening for freshwater bacterial groups by using reverse line blot hybridization

The identification of phylogenetic clusters of bacteria that are common in freshwater has provided a basis for probe design to target important freshwater groups. We present a set of 16S ribosomal RNA gene-based oligonucleotide probes specific for 15 of these freshwater clusters. The probes were applied in reverse line blot hybridization, a simple method that enables the rapid screening of PCR products from many samples against an array of probes. The optimized assay was made stringent to discriminate at approximately the single-mismatch level. This made 10 of the probes highly specific, with at least two mismatches to the closest noncluster member in the global database. Screening of PCR products from bacterioplankton of 81 diverse lakes from Belgium, The Netherlands, Denmark, Sweden, and Norway showed that the respective probes were reactive against 5 to 100% of the lake samples. Positive reactivity of six highly specific probes showed that bacteria from actinobacterial clusters ACK-M1 and Sta2-30 and from verrucomicrobial cluster CLO-14 occurred in at least 90% of the investigated lakes. Furthermore, bacteria from alpha-proteobacterial cluster LD12 (closely related to the marine SAR11 cluster), beta-proteobacterial cluster LD28 and cyanobacterial cluster Synechococcus 6b occurred in more than 70% of the lakes. Reverse line blot hybridization is a new tool in microbial ecology that will facilitate research on distribution and habitat specificity of target species at relatively low costs.