Post-invasion events after infection with Staphylococcus aureus are strongly dependent on both the host cell type and the infecting S. aureus strain

Host cell invasion is a major feature of Staphylococcus aureus and contributes to infection development. The intracellular metabolically active bacteria can induce host cell activation and death but they can also persist for long time periods. In this study a comparative analysis was performed of different well-characterized S. aureus strains in their interaction with a variety of host cell types. Staphylococcus aureus (strains 6850, USA300, LS1, SH1000, Cowan1) invasion was compared in different human cell types (epithelial and endothelial cells, keratinocytes, fibroblasts, osteoblasts). The number of intracellular bacteria was determined, cell inflammation was investigated, as well as cell death and phagosomal escape of bacteria. To explain strain-dependent differences in the secretome, a proteomic approach was used. Barrier cells took up high amounts of bacteria and were killed by aggressive strains. These strains expressed high levels of toxins, and possessed the ability to escape from phagolysosomes. Osteoblasts and keratinocytes ingested less bacteria, and were not killed, even though the primary osteoblasts were strongly activated by S. aureus. In all cell types S. aureus was able to persist. Strong differences in uptake, cytotoxicity, and inflammatory response were observed between primary cells and their corresponding cell lines, demonstrating that cell lines reflect only partially the functions and physiology of primary cells. This study provides a contribution for a better understanding of the pathomechanisms of S. aureus infections. The proteomic data provide important basic knowledge on strains commonly used in the analysis of S. aureus-host cell interaction.

The chloroplast division protein FtsZ is encoded by a nucleomorph gene in cryptomonads

Guillardia theta is a cryptomonad alga, whose phototrophic symbiont was acquired by secondary endocytobiosis. The nucleomorph, the vestigial nucleus of the eukaryotic endosymbiont, harbors three linear chromosomes with a total coding capacity of 515 kb. Sequencing of the nucleomorph genome reveals that it encodes an ORF homologous to the bacterial cell division protein FtsZ, supporting the hypothesis that FtsZ is common in chloroplasts. We show that the nucleomorph-encoded ftsZ gene is transcribed. The transcript is polyadenylated and therefore shows features typical of eukaryotic transcripts. However, 3' processing of nucleomorph mRNA is inaccurate. Transcripts of nucleomorph genes in G. theta overlap with neighboring UTRs and coding regions. We demonstrate that the reading frame encoding NmFtsZ is not interrupted by introns. Subcellular localization of the protein reveals that FtsZ is localized exclusively in the chloroplast of G. theta, demonstrating that FtsZ is imported into the organelle.