Hns-GFP is excluded from old pole cells in the <i>csrA</i> mutant.

<p><i>csrA</i> mutant cells harboring a plasmid encoding Hns-GFP were grown in microfluidic devices and observed by time-lapse microscopy. (<b>A</b>) shows a temporal montage of still images analogous to <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1005974#pgen.1005974.g003" target="_blank">Fig 3A</a>, showing the entire lifetime of a focal individual. (<b>B</b>) is a quantification of fluorescence intensity of the focal individual (‘ mother cell’, yellow) and its young pole daughter cells (blue), analogous to <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1005974#pgen.1005974.g003" target="_blank">Fig 3B</a>. Hns-GFP reaches similar levels in daughter cells regardless of the mother’s age, but drops dramatically at a cells last division, indicating loss of the mother cell’s chromosome. Error bars denote standard error of the mean.</p

Schiessl_etal_Evolution_dryad

Contains data for Figures 2, 4, 5 and S

Data from: Individual- versus group-optimality in the production of secreted bacterial compounds

How unicellular organisms optimize the production of compounds is a fundamental biological question. While it is typically thought that production is optimized at the individual-cell level, secreted compounds could also allow for optimization at the group level, leading to a division of labor where a subset of cells produces and shares the compound with everyone. Using mathematical modelling, we show that the evolution of such division of labor depends on the cost function of compound production. Specifically, for any trait with saturating benefits, linear costs promote the evolution of uniform production levels across cells. Conversely, production costs that diminish with higher output levels favor the evolution of specialization – especially when compound shareability is high. When experimentally testing these predictions with pyoverdine, a secreted iron-scavenging compound produced by Pseudomonas aeruginosa, we found linear costs and, consistent with our model, detected uniform pyoverdine production levels across cells. We conclude that for shared compounds with saturating benefits, the evolution of division of labor is facilitated by a diminishing cost function. More generally, we note that shifts in the level of selection from individuals to groups do not solely require cooperation, but critically depend on mechanistic factors, including the distribution of compound synthesis costs

Genetic Manipulation of Glycogen Allocation Affects Replicative Lifespan in <i>E</i>. <i>coli</i>

<div><p>In bacteria, replicative aging manifests as a difference in growth or survival between the two cells emerging from division. One cell can be regarded as an aging mother with a decreased potential for future survival and division, the other as a rejuvenated daughter. Here, we aimed at investigating some of the processes involved in aging in the bacterium <i>Escherichia coli</i>, where the two types of cells can be distinguished by the age of their cell poles. We found that certain changes in the regulation of the carbohydrate metabolism can affect aging. A mutation in the carbon storage regulator gene, <i>csrA</i>, leads to a dramatically shorter replicative lifespan; <i>csrA</i> mutants stop dividing once their pole exceeds an age of about five divisions. These old-pole cells accumulate glycogen at their old cell poles; after their last division, they do not contain a chromosome, presumably because of spatial exclusion by the glycogen aggregates. The new-pole daughters produced by these aging mothers are born young; they only express the deleterious phenotype once their pole is old. These results demonstrate how manipulations of nutrient allocation can lead to the exclusion of the chromosome and limit replicative lifespan in <i>E</i>. <i>coli</i>, and illustrate how mutations can have phenotypic effects that are specific for cells with old poles. This raises the question how bacteria can avoid the accumulation of such mutations in their genomes over evolutionary times, and how they can achieve the long replicative lifespans that have recently been reported.</p></div

<i>CsrA</i> mutant cells stop dividing at low pole ages.

<p>(<b>A</b>) illustrates the concept of pole age. Every cell has one pole of age zero that has been formed at the last division (the young pole), and one pole of age one or more (the older pole). We use the older pole to define individuals, and the age of the older pole to assign a pole age to each individual. A new individual emerges from division as a cell with an older pole of age 1. If this cell divides, its older pole segregates to one of the two cells emerging from division, and increases its age to two. We refer to the cell receiving this pole as the same individual that underwent division (since it has the same older pole). This individual can be referred to as the ‘mother’ of the other cell that emerges from division. This other cell—the ‘daughter’–has an older pole of age one. We refer to this other cell as a new individual. In panel A, we use colors to mark individuals. The first individual is light red, and its older pole is dark red. This individual produces two daughters, the blue individual and the green individual. (<b>B</b>) shows a representative lineage tree of a microcolony of <i>csrA</i> mutant cells. Each branching event in the lineage tree corresponds to one cell division. The lineage tree is organized according to pole age. At each cell division, the branch that represents the daughter—the cell with the new cell pole—extends to the left; the branch that represents the mother—the cell with the older pole—extends to the right. Three individuals with old poles stop dividing. Note that these experiments are initiated with single cells whose old and new pole we cannot distinguish; the branches representing the first cell division are thus dashed. In (<b>C</b>), we show that the cumulative probability of <i>csrA</i> mutant cells to stop dividing increases with increasing pole age (orange lines; see <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1005974#sec003" target="_blank">Materials and Methods</a> for how we defined when a cell stops dividing; the median pole age at which <i>csrA</i> mutant cells stop dividing is 4). For wild type (purple) and <i>csrA ΔglgA</i> double mutant cells (green) very few cells were observed to stop dividing. Three independent experiments were performed for <i>csrA</i> mutant cells (N = 38, 71, 23), and two independent replicates were performed for the other two strains (N = 25, 74 for wild type, N = 31, 28 for <i>csrA ΔglgA</i>). (<b>D</b>) shows that the <i>per division</i> probability of <i>csrA</i> mutant cells to stop dividing increases with increasing pole age, for the same three experiments (denoted by different shades of orange). The diameter of the circles is proportional to the sample size at each pole age, i.e., to the number of cells that were still alive. In all three experiments, the probability to stop increases significantly with increasing pole age (logistic regression, p<0.001 for all three experiments, N = 38, 71, 23).</p

Individual‐ versus group‐optimality in the production of secreted bacterial compounds

How unicellular organisms optimize the production of compounds is a fundamental biological question. While it is typically thought that production is optimized at the individual-cell level, secreted compounds could also allow for optimization at the group level, leading to a division of labor where a subset of cells produces and shares the compound with everyone. Using mathematical modelling, we show that the evolution of such division of labor depends on the cost function of compound production. Specifically, for any trait with saturating benefits, linear costs promote the evolution of uniform production levels across cells. Conversely, production costs that diminish with higher output levels favor the evolution of specialization – especially when compound shareability is high. When experimentally testing these predictions with pyoverdine, a secreted iron-scavenging compound produced by Pseudomonas aeruginosa, we found linear costs and, consistent with our model, detected uniform pyoverdine production levels across cells. We conclude that for shared compounds with saturating benefits, the evolution of division of labor is facilitated by a diminishing cost function. More generally, we note that shifts in the level of selection from individuals to groups do not solely require cooperation, but critically depend on mechanistic factors, including the distribution of compound synthesis costs

GlgA-GFP indicates polar localization of glycogen in <i>csrA</i> mutant cells.

<p><i>CsrA</i> mutant cells harboring a plasmid encoding GlgA-GFP fusion protein were observed by time-lapse microscopy when growing in microfluidic devices. (<b>A</b>) shows a temporal montage of still images from different time points, starting with the emergence of a new individual (‘focal individual’) at time 10 min that produces three daughters and then stops dividing. GlgA-GFP signal accumulates at the old pole and eventually fills the whole cell. The focal individual is the last daughter of the cell at the bottom of the channel. (<b>B</b>) is a quantification of fluorescence intensity of the focal individual (‘mother cell’, yellow) and its young pole daughter cells (blue), for the focal individual’s first, second last, and last division. Fluorescence is extracted as integrated density. GlgA-GFP signal stays approximately the same in all daughter cells, but accumulates in mother cells with increasing pole age. Error bars denote standard error of the mean.</p

Low prevalence of SV40 in Swiss mesothelioma patients after elimination of false-positive PCR results

The association of simian virus 40 (SV40) with malignant pleural mesothelioma is currently under debate. In some malignancies of viral aetiology, viral DNA can be detected in the patients' serum or plasma. To characterize the prevalence of SV40 in Swiss mesothelioma patients, we optimized a real-time PCR for quantitative detection of SV40 DNA in plasma, and used a monoclonal antibody for immunohistochemical detection of SV40 in mesothelioma tissue microarrays. Real-time PCR was linear over five orders of magnitude, and sensitive to a single gene copy. Repeat PCR determinations showed excellent reproducibility. However, SV40 status varied for independent DNA isolates of single samples. We noted that SV40 detection rates by PCR were drastically reduced by the implementation of strict room compartmentalization and decontamination procedures. Therefore, we systematically addressed common sources of contamination and found no cross-reactivity with DNA of other polyomaviruses. Contamination during PCR was rare and plasmid contamination was infrequent. SV40 DNA was reproducibly detected in only 4 of 78 (5.1%) plasma samples. SV40 DNA levels were low and not consistently observed in paired plasma and tumour samples from the same patient. Immunohistochemical analysis revealed a weak but reproducible SV40 staining in 16 of 341 (4.7%) mesotheliomas. Our data support the occurrence of non-reproducible SV40 PCR amplifications and underscore the importance of proper sample handling and analysis. SV40 DNA and protein were found at low prevalence (5%) in plasma and tumour tissue, respectively. This suggests that SV40 does not appear to play a major role in the development of mesothelioma

Cyclin D1 (CCND1) A870G gene polymorphism modulates smoking-induced lung cancer risk and response to platinum-based chemotherapy in non-small cell lung cancer (NSCLC) patients

PURPOSE: The cyclin D1 (CCND1) A870G gene polymorphism is linked to the outcome in patients with resectable non-small cell lung cancer (NSCLC). Here, we investigated the impact of this polymorphism on smoking-induced cancer risk and clinical outcome in patients with NSCLC stages I-IV. METHODS: CCND1 A870G genotype was determined by polymerase chain reaction (PCR) and restriction fragment length polymorphism analysis (RFLP) of DNA extracted from blood. The study included 244 NSCLC patients and 187 healthy control subjects. RESULTS: Patient characteristics were: 70% male, 77% smokers, 43% adenocarcinoma, and 27% squamous cell carcinoma. Eighty-one percent of the patients had stages III-IV disease. Median age at diagnosis was 60 years and median survival was 13 months. Genotype frequencies of patients and controls both conformed to the Hardy Weinberg equilibrium. The GG genotype significantly correlated with a history of heavy smoking (>or=40 py, P=0.02), and patients with this genotype had a significantly higher cigarette consumption than patients with AA/AG genotypes (P=0.007). The GG genotype also significantly correlated with tumor response or stabilization after a platinum-based first-line chemotherapy (P=0.04). Survival analysis revealed no significant differences among the genotypes. CONCLUSION: Evidence was obtained that the CCND1 A870G gene polymorphism modulates smoking-induced lung cancer risk. Further studies are required to explore the underlying molecular mechanisms and to test the value of this gene polymorphism as a predictor for platinum-sensitivity in NSCLC patients