The genomic content of outer membrane vesicles (OMVs) in freshwater cyanobacteria

Outer membrane vesicles (OMVs) are secreted by many bacteria, where they are involved in diverse extracellular functions. They contain DNA which has been reported to be a source for lateral gene transfer. However, it is only poorly understood what the natural genetic content of OMVs comprise and how it changes with different environmental conditions. Here, I searched for the existence of OMVs in several cyanobacteria and studied their genomic content. Transmission electron microscopy showed OMVs in the unicellular Synechocystis sp. PCC 6803, as well as in the filamentous Anabaena sp. PCC 7120 and Chlorogloeopsis fritschii PCC 6912 as discrete, spherical blebs having a bilayer membrane. Sequencing revealed the presence of most of the genome including the chromosome and plasmids (if existing) in all three species. Additionally, a temperate phage was identified in C. fritschii PCC 6912. For Syn. sp. PCC 6803, I found that the OMV abundance is significantly higher in bacteria cultured under heat– or high salt– stress in comparison to the control conditions. Sequencing revealed that two small cryptic plasmids were highly overrepresented in the vesicle DNA independent of the growth conditions compared to a genomic DNA sample. I additionally identified overrepresented genes dependent on the growth condition in OMVs. I hypothesize that the enrichment for small plasmids in the vesicles is a stochastic process and a result of their high abundance in the cell, their packed topology, high diffusibility, and location. Further, I speculate that various mechanisms involved in cell cycle, transcription, or gene amplification might increase the likelihood of specific sequences to be packed in OMVs. My observations implicate that OMVs are a transfer mechanism of small plasmids by providing a nuclease protected DNA space and may serve as a mechanism to maintain plasmids and/or important genes for the population

Role of natural transformation in the evolution of small cryptic plasmids in Synechocystis sp. PCC 6803

Small cryptic plasmids have no clear effect on the host fitness and their functional repertoire remains obscure. The naturally competent cyanobacterium Synechocystis sp. PCC 6803 harbours several small cryptic plasmids; whether their evolution with this species is supported by horizontal transfer remains understudied. Here, we show that the small cryptic plasmid DNA is transferred in the population exclusively by natural transformation, where the transfer frequency of plasmid‐encoded genes is similar to that of chromosome‐encoded genes. Establishing a system to follow gene transfer, we compared the transfer frequency of genes encoded in cryptic plasmids pCA2.4 (2378 bp) and pCB2.4 (2345 bp) within and between populations of two Synechocystis sp. PCC 6803 labtypes (termed Kiel and Sevilla). Our results reveal that plasmid gene transfer frequency depends on the recipient labtype. Furthermore, gene transfer via whole plasmid uptake in the Sevilla labtype ranged among the lowest detected transfer rates in our experiments. Our study indicates that horizontal DNA transfer via natural transformation is frequent in the evolution of small cryptic plasmids that reside in naturally competent organisms. Furthermore, we suggest that the contribution of natural transformation to cryptic plasmid persistence in Synechocystis is limited

Tumour stage distribution and survival of malignant melanoma in Germany 2002-2011

Background Over the past two decades, there has been a rising trend in malignant melanoma incidence worldwide. In 2008, Germany introduced a nationwide skin cancer screening program starting at age 35. The aims of this study were to analyse the distribution of malignant melanoma tumour stages over time, as well as demographic and regional differences in stage distribution and survival of melanoma patients. Methods Pooled data from 61 895 malignant melanoma patients diagnosed between 2002 and 2011 and documented in 28 German population-based and hospital-based clinical cancer registries were analysed using descriptive methods, joinpoint regression, logistic regression and relative survival. Results The number of annually documented cases increased by 53.2% between 2002 (N = 4 779) and 2011 (N = 7 320). There was a statistically significant continuous positive trend in the proportion of stage UICC I cases diagnosed between 2002 and 2011, compared to a negative trend for stage UICC II. No trends were found for stages UICC III and IV respectively. Age (OR 0.97, 95% CI 0.97–0.97), sex (OR 1.18, 95% CI 1.11–1.25), date of diagnosis (OR 1.05, 95% CI 1.04–1.06), ‘diagnosis during screening’ (OR 3.24, 95% CI 2.50–4.19) and place of residence (OR 1.23, 95% CI 1.16–1.30) had a statistically significant influence on the tumour stage at diagnosis. The overall 5-year relative survival for invasive cases was 83.4% (95% CI 82.8–83.9%). Conclusions No distinct changes in the distribution of malignant melanoma tumour stages among those aged 35 and older were seen that could be directly attributed to the introduction of skin cancer screening in 2008.

Additional file 3: Table S2. of Tumour stage distribution and survival of malignant melanoma in Germany 2002–2011

Malignant melanoma patients aged 35 years and above by age at diagnosis, sex, UICC stage, year of diagnosis, place of residence and ‘diagnosis during screening’, N = 34 739 (UICC 0 and X excluded) (DOCX 40 kb

Additional file 4: Table S3. of Tumour stage distribution and survival of malignant melanoma in Germany 2002–2011

Relative 5-year survival of malignant melanoma patients diagnosed between 2002 and 2011, overall (UICC 0-IV, X) (N = 60 672) and for patients with invasive tumours (UICC I – IV, X) stratified by age, sex, UICC stage, ‘diagnosis during screening’ and place of residence (N = 49 351) (DOCX 39 kb