Studies on diversity and coexistence in an experimental microbial community

Biodiversity and the coexistence of species have puzzled and fascinated biologists since decades and is a hotspot in todays’ natural sciences. Preserving this biodiversity is a great challenge as habitats and environments underlying tremendous changes like climate change and the loss of natural habitats, which are mainly due to anthropogenic influences. The coexistence of numerous species even in homogeneous environments is a stunning feature of natural communities and has been summarized under the term ‘paradox of plankton’. Up to now, there are several mechanisms discussed, which may contribute to local and global diversity of organisms. Several interspecific trade offs have been identified maintaining the coexistence of species like their abilities regarding competition and predator avoidance, their capability to disperse in space and time, and their ability to exploit variable resources. Further, micro-evolutionary dynamics supporting the coexistence of species have been added to our knowledge, and deriving from theoretical deterministic models, non-linear dynamics which describe the temporal fluctuation of abundances of organisms. Whereas competition and predation seem to be clue structural elements within interacting organisms, the intrinsic dynamic behavior – by means of temporal changes in abundance - plays an important role regarding coexistence within a community. The present work sheds light on different factors affecting the coexistence of species using experimental microbial model systems consisting of a bacterivorous ciliate as the predator and two bacteria strains as prey organism. Additionally, another experimental setup consisting of two up to five bacteria species competing for one limiting resource was investigated. Highly controllable chemostat systems were established to exclude extrinsic disturbances. According to theoretical analyses I was able to show - experimentally and theoretically - that phenotypic plasticity of one species within a microbial one-predator-two-prey food web enlarges the range of possible coexistence of all species under different dynamic conditions, compared to a food web without phenotypic plasticity. This was accompanied by non-linear (chaotic) population dynamics within all experimental systems showing phenotypic plasticity. The experiments on the interplay of competition, predation and invasion showed that all aspects have an influence on species coexistence. Under undisturbed controlled conditions all aspects were analyzed in detail and in combination. Populations showed oscillations which were shown by quasi-chaotic attractors in phase space diagrams. Competition experiments with two up to five bacteria species competing for one limiting resource showed that all organisms were able to coexist which was mediated by species oscillations entering a regime of chaos. Besides that fact it was found, that the productivity (biomass) as well as the total cell numbers – under the same nutrition supply – increased by an increasing number of species in the experimental systems. Up to now, the occurrence of non-linear dynamics in well controlled experimental studies has been recognized several times and this phenomenon seemed to be more common in natural systems than generally assumed

Role of Suppressor of Cytokine Signaling-1 In Murine Atherosclerosis

BACKGROUND: While the impact of inflammation as the substantial driving force of atherosclerosis has been investigated in detail throughout the years, the influence of negative regulators of pro-atherogenic pathways on plaque development has remained largely unknown. Suppressor of cytokine signaling (SOCS)-1 potently restricts transduction of various inflammatory signals and, thereby modulates T-cell development, macrophage activation and dendritic cell maturation. Its role in atherogenesis, however has not been elucidated so far. METHODS AND RESULTS: Loss of SOCS-1 in the low-density lipoprotein receptor deficient murine model of atherosclerosis resulted in a complex, systemic and ultimately lethal inflammation with increased generation of Ly-6C(hi) monocytes and activated macrophages. Even short-term exposure of these mice to high-cholesterol dieting caused enhanced atherosclerotic plaque development with accumulation of M1 macrophages, Ly-6C positive cells and neutrophils. CONCLUSION: Our data not only imply that SOCS-1 is athero-protective but also emphasize the fundamental, regulatory importance of SOCS-1 in inflammation-prone organisms

Temperature-dependent ranges of coexistence in a model of a two-prey-one-predator microbial food web

The objective of our study was to analyze the effects of temperature on the population dynamics of a three-species food web consisting of two prey bacteria (Pedobacter sp. and Acinetobacter johnsonii) and a protozoan predator (Tetrahymena pyriformis) as model organisms. We assessed the effects of temperature on the growth rates of all three species with the objective of developing a model with four differential equations based on the experimental data. The following hypotheses were tested at a theoretical level: Firstly, temperature changes can affect the dynamic behavior of a system by temperature-dependent parameters and interactions and secondly, food web response to temperature cannot be derived from the single species temperature response. The main outcome of the study is that temperature changes affect the parameter range where coexistence is possible within all three species. This has significant consequences on our ideas regarding the evaluation of effects of global warming

Differential modulation of valence and arousal in high- alexithymic and low-alexithymic individuals

a High-alexithymic individuals are characterized by an impaired ability to identify and communicate emotions whereas low-alexithymic individuals have a wide-ranging ability to deal with emotions. This study examined the hypothesis that valence and arousal modifications of emotional stimuli differentially modulate cortical regions in high-alexithymic and low-alexithymic individuals. To this end, 28 high-alexithymic and 25 low-alexithymic individuals were investigated with event-related fMRI using visual emotional stimuli. We found differential neural activations in the dorsal anterior cingulate, the insula and the amygdala. We suggest that these differences may account for the impaired ability of high-alexithymic individuals to appropriately handle emotional stimuli

Body Weight of Mice on Chow and High-Cholesterol Diet.

<p><b>Weight of mice on chow (CD) and after high-cholesterol diet (HCD).</b> Age-matched mice were weighted after 4 weeks of CD or HCD. Socs-1^−/− triple KO mice (Socs-1^−/−) on CD and HCD demonstrated a significantly lower weight compared to Ldlr^−/− and Ldlr^−/−;Rag-2^−/− mice. However, Socs-1^−/−triple-KO mice displayed a significant weight gain after 4 weeks of HCD compared to Socs-1^−/−triple-KO mice on CD. Data represent mean±SD, *p<0.05 vs Ldlr^−/− and Ldlr^−/−;Rag-2^−/− mice, #p<0.05 vs Socs-1^−/− triple-KO mice on CD, 13–21 mice/group.</p

SOCS-1 deficiency results in enhanced atherosclerotic plaque formation. A.

<p>Aortas derived from Socs-1^−/− triple-KO mice (Socs-1^−/−) showed significantly enhanced lipid depositions after en face preparation and staining with Oil Red O after 4 weeks of HCD. <b>B.</b> Aortic roots of Socs-1^−/− triple-KO mice also displayed increased lipid depositions after staining with Oil Red O. Horizontal bars represent mean, *p<0.05 vs Ldlr^−/− and Ldlr^−/−;Rag-2^−/− (scale bar: 50 µm). Each dot indicates results for an individual animal. <b>C.</b> Aortic roots derived from Socs-1^−/− triple-KO (Socs-1^−/−) mice showed a significantly enhanced macrophage content after staining with MOMA-2 compared to Ldlr^−/−;Rag-2^−/− and Ldlr^−/− mice after 4 weeks of HCD. Horizontal bars are mean, *p<0.05 vs Ldlr^−/− and Ldlr^−/−;Rag-2^−/−. Each dot indicates results for an individual animal. (scale bar: 500 µm). <b>D.</b> Phenotype analysis of atherosclerotic plaques demonstrated more advanced lesion development in Socs-1^−/−triple-KO (Socs-1^−/−) mice. N = 5–8 mice/group.</p

Cholesterol Levels after 4 Weeks of High-Cholesterol Diet.

<p><b>Cholesterol levels after 4 weeks of high-cholesterol diet (HCD).</b> No differences in lipoprotein fractions between age-matched Ldlr^−/− and Socs-1^−/−triple-KO mice were observed after 4 weeks of HCD. Total cholesterol levels were significantly lower in Ldlr^−/−;Rag-2^−/− mice compared to the other genotypes due to lower LDL and VLDL lipoprotein fractions. *p<0.05 vs Ldlr^−/− and Socs-1^−/−triple-KO mice, data are mean ± SD, N = 7–10 mice/group.</p

Blood Count on Chow and High-Cholesterol Diet.

<p><b>Blood count on chow (CD) and high-cholesterol diet (HCD).</b> Whole blood samples of all three genotypes were taken from age-matched mice after 4 weeks of CD or HCD. Differential blood counts were obtained using an automated blood counter. Ldlr^−/−;Rag-2^−/− and Socs-1^−/−triple-KO mice (Socs-1^−/−) showed a significant leucopenia after correction for granulocytes compared to Ldlr^−/− mice on CD and HCD. Leucopenia in Socs-1^−/− triple-KO mice was compensated by a significant granulocytosis under both conditions compared to Ldlr^−/− mice. Granulocytes mainly consisted of neutrophils. Data represent median with 25^th and 75^th percentiles, #p<0.05 vs Ldlr^−/− and Socs-1^−/− triple-KO mice, *p<0.05 vs Ldlr^−/− mice, N = 13–21 mice/group.</p

Impact of SOCS-1 deficiency on atherosclerotic plaque composition A.

<p>Atherosclerotic plaques from Socs-1^−/− triple-KO (Socs-1^−/−) mice showed an increased CD68 (red);iNOS (green) double-positive cell content. <b>B.</b> CD68 (red); CD206 (green) double-positive cells were hardly detected. <b>C.</b> Atherosclerotic plaques from Socs-1^−/−triple-KO (Socs-1^−/−) mice contained slightly more MOMA-2 (red); Ly-6C (green) double-positive cells after 4 weeks of HCD as well as <b>D.</b> a higher number of Ly-6G positive cells (scale bar A–C: 20 µm, scale bar D:50 µm). N = 5–7 animals per group.</p