New insights into the effects of several environmental parameters on the relative fitness of a numerically dominant class of evolved niche specialist

Adaptive radiation in bacteria has been investigated using Wrinkly Spreaders (WS), a morphotype which colonises the air-liquid (A-L) interface of static microcosms by biofilm formation with a significant fitness advantage over competitors growing lower down in the O2-limited liquid column. Here, we investigate several environmental parameters which impact the ecological opportunity that the Wrinkly Spreaders exploit in this model system. Manipulation of surface area/volume ratios suggests that the size of the WS niche was not as important as the ability to dominate the A-L interface and restrict competitor growth. The value of this niche to the Wrinkly Spreaders, as determined by competitive fitness assays, was found to increase as O2 flux to the A-L interface was reduced, confirming that competition for O2 was the main driver of WS fitness. The effect of O2 on fitness was also found to be dependent on the availability of nutrients, reflecting the need to take up both for optimal growth. Finally, the meniscus trap, a high-O2 region formed by the interaction of the A-L interface with the vial walls, was also important for fitness during the early stages of biofilm formation. These findings reveal the complexity of this seemingly simple model system and illustrate how changes in environmental physicality alter ecological opportunity and the fitness of the adaptive morphotype

Penetrating the air-liquid interface is the key to colonization and wrinkly spreader fitness

In radiating populations of Pseudomonas fluorescens SBW25, adaptive wrinkly spreader (WS) mutants are able to gain access to the air–liquid (A–L) interface of static liquid microcosms and achieve a significant competitive fitness advantage over other non-biofilm-forming competitors. Aerotaxis and flagella-based swimming allows SBW25 cells to move into the high-O2 region located at the top of the liquid column and maintain their position by countering the effects of random cell diffusion, convection and disturbance (i.e. physical displacement). However, wild-type cells showed significantly lower levels of enrichment in this region compared to the archetypal WS, indicating that WS cells employ an additional mechanism to transfer to the A–L interface where displacement is no longer an issue and a biofilm can develop at the top of the liquid column. Preliminary experiments suggest that this might be achieved through the expression of an as yet unidentified surface active agent that is weakly associated with WS cells and alters liquid surface tension, as determined by quantitative tensiometry. The effect of physical displacement on the colonization of the high-O2 region and A–L interface was reduced through the addition of agar or polyethylene glycol to increase liquid viscosity, and under these conditions the competitive fitness of the WS was significantly reduced. These observations suggest that the ability to transfer to the A–L interface from the high-O2 region and remain there without further expenditure of energy (through, for example, the deployment of flagella) is a key evolutionary innovation of the WS, as it allows subsequent biofilm development and significant population increase, thereby affording these adaptive mutants a competitive fitness advantage over non-biofilm-forming competitors located within the liquid column

Adaptive radiation of <i>Pseudomonas fluorescens</i> SBW25 in experimental microcosms provides an understanding of the evolutionary ecology and molecular biology of A-L interface biofilm formation

Combined experimental evolutionary and molecular biology approaches have been used to investigate the adaptive radiation of Pseudomonas fluorescens SBW25 in static microcosms leading to the colonisation of the air-liquid interface by biofilm–forming mutants such as the Wrinkly Spreader. In these microcosms, the ecosystem engineering of the early wild-type colonists establish the niche space for subsequent WS evolution and colonisation. Random WS mutations occurring in the developing population that de-regulate diguanylate cyclases and c-di-GMP homeostasis result in cellulose-based biofilms at the air-liquid interface. These structures allow Wrinkly Spreaders to intercept O2 diffusing into the liquid column and limit the growth of competitors lower down. As the biofilm matures, competition increasingly occurs between WS lineages, and niche divergence within the biofilm may support further diversification before system failure when the structure finally sinks. A combination of pleiotropic and epistasis effects, as well as secondary mutations, may explain variations in WS phenotype and fitness. Understanding how mutations subvert regulatory networks to express intrinsic genome potential and key innovations providing a selective advantage in novel environments is key to understanding the versatility of bacteria, and how selection and ecological opportunity can rapidly lead to substantive changes in phenotype and in community structure and function

Enhancing Ecological Inference About Forest Species With Remote Sensing and Statistical Advances

Human-caused disturbances and climate change are affecting forest-dependent communities in myriad ways, including through habitat clearing, habitat degradation, and shifted natural disturbance regimes. Our ability to account for impacts to ecological communities relies on long-term monitoring in the face of global change as well as leveraging technological and theoretical advancements to make better use of existing data. This dissertation explores the ecology of forest species in disturbed and pristine environments. Throughout my dissertation, I use a combination of observational, experimental, and statistical methods to characterize ecological communities in temperate forests and examine how these communities respond to disturbance. A theme across these chapters is a focus on how recent advances in remote sensing technologies and statistical modeling allow ecologists to study forests at a scale relevant to a tree&rsquo;s biology and better account for uncertainty in ecological inferences. In my first chapter, I review what forest traits can be measured with drone technology through a literature research, and describe a case study of how ecologists use drone-derived data to estimate aboveground carbon stock. This review illustrates the utility and underutilization of drones in forest and spatial ecology. In chapter two, I describe the interaction of two disturbances (fragmentation and fire) on a Eucalyptus&nbsp;community by combining ground-, satellite-, and drone-based surveys. I assess how prior forest fragmentation changed forest structure and fuel availability so that a subsequent wildfire burned more severely in fragmented forest remnants compared to continuous forest. Finally, in my third chapter, I contribute a statistical framework that better accounts for species classification uncertainty in community datasets with observation error. In this framework, we leverage observed species abundance to estimate occupancy, focusing on a carabid community. These studies demonstrate that drone remote sensing is a helpful tool in forest ecology, disturbance interactions can create unexpected and nonlinear outcomes, and observation error in community surveys can be accounted for more accurately with the advanced statistical tools.</p

Three biofilm types produced by a model pseudomonad are differentiated by structural characteristics and fitness advantage

Model bacterial biofilm systems suggest that bacteria produce one type of biofilm which is then modified by environmental and physiological factors, though diversification of developing populations might result in the appearance of adaptive mutants producing altered structures with improved fitness advantage. Here we compare the air-liquid interface Viscous Mass (VM) biofilm produced by Pseudomonas fluorescens SBW25 and the Wrinkly Spreader (WS) and Complementary Biofilm-forming Strain (CBFS) biofilm-types produced by adaptive SBW25 mutants in order to better understand the link between these physical structures and the fitness advantage they provide in experimental microcosms. Wrinkly Spreader, CBFS and VM biofilms can be differentiated by strength, attachment levels and rheology, as well as by strain characteristics associated with biofilm–formation. Competitive fitness assays demonstrate that they provide similar advantage under static growth conditions but respond differently to increasing levels of physical disturbance. Pairwise competitions between biofilms suggest that these strains must be competing for at least two growth-limiting resources at the air-liquid interface, most probably O2 and nutrients, though VM and CBFS cells located lower down in the liquid column might provide an additional fitness advantage through the colonisation of a less competitive zone below the biofilm. Our comparison of different SBW25 biofilm-types illustrates more generally how varied biofilm characteristics and fitness advantage could become among adaptive mutants arising from an ancestral biofilm–forming strain and raises the question of how significant these changes might be in a range of medical, biotechnological and industrial contexts where diversification and change may be problematic

Biofilm formation and cellulose expression by <i>Bordetella avium</i> 197N, the causative agent of bordetellosis in birds and an opportunistic respiratory pathogen in humans

Although bacterial cellulose synthase (bcs) operons are widespread within the Proteobacteria phylum, subunits required for the partial-acetylation of the polymer appear to be restricted to a few γ-group soil, plant-associated and phytopathogenic pseudomonads, including Pseudomonas fluorescens SBW25 and several Pseudomonas syringae pathovars. However, a bcs operon with acetylation subunits has also been annotated in the unrelated β-group respiratory pathogen, Bordetella avium 197N. Our comparison of subunit protein sequences and GC content analyses confirms the close similarity between the B. avium 197N and pseudomonad operons and suggests that, in both cases, the cellulose synthase and acetylation subunits were acquired as a single unit. Using static liquid microcosms, we can confirm that B. avium 197N expresses low levels of cellulose in air–liquid interface biofilms and that biofilm strength and attachment levels could be increased by elevating c-di-GMP levels like the pseudomonads, but cellulose was not required for biofilm formation itself. The finding that B. avium 197N is capable of producing cellulose from a highly-conserved, but relatively uncommon bcs operon raises the question of what functional role this modified polymer plays during the infection of the upper respiratory tract or survival between hosts, and what environmental signals control its production

What are the sources of stress and distress for general practitioners working in England? A qualitative study

OBJECTIVES: This paper reports the sources of stress and distress experienced by general practitioners (GP) as part of a wider study exploring the barriers and facilitators to help-seeking for mental illness and burnout among this medical population. DESIGN: Qualitative study using in-depth interviews with 47 GP participants. The interviews were audio-recorded, transcribed, anonymised and imported into NVivo V.11 to facilitate data management. Data were analysed using a thematic analysis employing the constant comparative method. SETTING: England. PARTICIPANTS: A purposive sample of GP participants who self-identified as: (1) currently living with mental distress, (2) returning to work following treatment, (3) off sick or retired early as a result of mental distress or (4) without experience of mental distress. Interviews were conducted face-to-face or over the telephone. RESULTS: The key sources of stress/distress related to: (1) emotion work-the work invested and required in managing and responding to the psychosocial component of GPs' work, and dealing with abusive or confrontational patients; (2) practice culture-practice dynamics and collegial conflict, bullying, isolation and lack of support; (3) work role and demands-fear of making mistakes, complaints and inquests, revalidation, appraisal, inspections and financial worries. CONCLUSION: In addition to addressing escalating workloads through the provision of increased resources, addressing unhealthy practice cultures is paramount. Collegial support, a willingness to talk about vulnerability and illness, and having open channels of communication enable GPs to feel less isolated and better able to cope with the emotional and clinical demands of their work. Doctors, including GPs, are not invulnerable to the clinical and emotional demands of their work nor the effects of divisive work cultures-culture change and access to informal and formal support is therefore crucial in enabling GPs to do their job effectively and to stay well

Barriers, facilitators, and survival strategies for GPs seeking treatment for distress:a qualitative study

BACKGROUND: GPs are under increasing pressure due to a lack of resources, a diminishing workforce, and rising patient demand. As a result, they may feel stressed, burnt out, anxious, or depressed. AIM: To establish what might help or hinder GPs experiencing mental distress as they consider seeking help for their symptoms, and to explore potential survival strategies. DESIGN AND SETTING: The authors recruited 47 GP participants via e-mails to doctors attending a specialist service, adverts to local medical committees (LMCs) nationally and in GP publications, social media, and snowballing. Participants self-identified as either currently living with mental distress, returning to work following treatment, off sick or retired early as a result of mental distress, or without experience of mental distress. Interviews were conducted face to face or over the telephone. METHOD: Transcripts were uploaded to NVivo 11 and analysed using thematic analysis. RESULTS: Barriers and facilitators were related to work, stigma, and symptoms. Specifically, GPs discussed feeling a need to attend work, the stigma surrounding mental ill health, and issues around time, confidentiality, and privacy. Participants also reported difficulties accessing good-quality treatment. GPs also talked about cutting down or varying work content, or asserting boundaries to protect themselves. CONCLUSION: Systemic changes, such as further information about specialist services designed to help GPs, are needed to support individual GPs and protect the profession from further damage