Bacterial filaments recover by successive and accelerated asymmetric divisions that allow rapid post-stress cell proliferation

Filamentation is a reversible morphological change triggered in response to various stresses that bacteria might encounter in the environment, during host infection or antibiotic treatments. Here we re-visit the dynamics of filament formation and recovery using a consistent framework based on live-cells microscopy. We compare the fate of filamentous Escherichia coli induced by cephalexin that inhibits cell division or by UV-induced DNA-damage that additionally perturbs chromosome segregation. We show that both filament types recover by successive and accelerated rounds of divisions that preferentially occur at the filaments' tip, thus resulting in the rapid production of multiple daughter cells with tightly regulated size. The DNA content, viability and further division of the daughter cells essentially depends on the coordination between chromosome segregation and division within the mother filament. Septum positioning at the filaments' tip depends on the Min system, while the nucleoid occlusion protein SlmA regulates the timing of division to prevent septum closure on unsegregated chromosomes. Our results not only recapitulate earlier conclusions but provide a higher level of detail regarding filaments division and the fate of the daughter cells. Together with previous reports, this work uncovers how filamentation recovery allows for a rapid cell proliferation after stress treatment.

Genomic characterization and proteomic analysis of the halotolerant Micrococcus luteus SA211 in response to the presence of lithium

Micrococcus luteus SA211, isolated from the Salar del Hombre Muerto in Argentina, developed responses that allowed its survival and growth in presence of high concentrations of lithium chloride (LiCl). In this research, analysis of total genome sequencing and a comparative proteomic approach were performed to investigate the responses of this bacterium to the presence of Li. Through proteomic analysis, we found differentially synthesized proteins in growth media without LiCl (DM) and with 10 (D10) and 30 g/L LiCl (D30). Bi-dimensional separation of total protein extracts allowed the identification of 17 over-synthesized spots when growth occurred in D30, five in D10, and six in both media with added LiCl. The results obtained showed different metabolic pathways involved in the ability of M. luteus SA211 to interact with Li. These pathways include defense against oxidative stress, pigment and protein synthesis, energy production, and osmolytes biosynthesis and uptake. Furthermore, mono-dimensional gel electrophoresis revealed differential protein synthesis at equivalent NaCl and LiCl concentrations, suggesting that this strain would be able to develop different responses depending on the nature of the ion. Moreover, the percentage of proteins with acidic pI predicted and observed was highlighted, indicating an adaptation to saline environments. To the best of our knowledge, this is the first report showing the relationship between protein synthesis and genome sequence analysis in response to Li, showing the great biotechnological potential that native microorganisms present, especially those isolated from extreme environments.

Adaptative transcriptional response of Dietzia cinnamea P4 strain to sunlight simulator

Responses to sunlight exposure of the oil-degrading Dietzia cinnamea P4 strain were evaluated by transcriptional levels of SOS genes, photoreactivation and genes involved in tolerance to high levels of reactive oxygen species. The P4 strain was exposed for 1 and 2 h and the magnitude of level changes in the mRNA was evaluated by qPCR. The results described the activation of the SOS system, with the decline of the repressor lexA gene levels and the concomitant increase of recA and uvrAD genes levels. The genes that participate in the photoreactivation process were also responsive to sunlight. The phrB gene encoding deoxyribodipyrimidine photo-lyase had its expression increased after 1-h exposure, while the phytAB genes showed a progressive increase over the studied period. The protective genes against reactive oxygen species, catalases, superoxides, peroxidases, and thioredoxins, had their expression rates detected under the conditions validated in this study. These results show a fast and coordinated response of genes from different DNA repair and tolerance mechanisms employed by strain P4, suggesting a complex concerted protective action against environmental stressors.