Biology subjects

Nikolic, N.

Publications and source records attributed to Nikolic, N..

3 recordsLinked to original sources

bioRxiv2023

Bacterial toxin-antitoxin system MazEF as a native defense mechanism against RNA phages in Escherichia coli

Bacteria have evolved a wide range of defense strategies to protect themselves against bacterial viruses (phages). However, the known mechanisms almost exclusively target phages with DNA genomes. While several bacterial toxin-antitoxin systems have been considered to cleave single-stranded bacterial RNA in response to stressful conditions, their role in protecting bacteria against phages with single-stranded RNA genomes has not been studied. Here we investigate the role of a representative toxin-antitoxin system, MazEF, in protecting Escherichia coli against two RNA phages - MS2 and Q{beta}. Our population-level experiments revealed that a mazEF deletion strain is more susceptible to RNA phage infection than the wild-type. At the single-cell level, deletion of the mazEF locus significantly shortened the time to lysis of individual bacteria challenged with RNA phage. At the genomic level, we found that the adenine-cytosine-adenine sequence, directly recognized and cleaved by the MazF toxin, is systematically underrepresented in the genomes of RNA phages that are known to infect E. coli, indicating selection for decreased probability of cleavage. These results suggest that in addition to other physiological roles, RNA-degrading toxin-antitoxin modules can function as a primitive immune system against RNA phages.

microbiology↗

bioRxiv2022

Real-time dynamics of individual chemoreceptor mRNA molecules reveals translation hotspots at the inner membrane of Escherichia coli

Since bacteria lack a nucleus, the location of mRNA molecules is determined by the different characteristics of the encoded proteins, and the transcriptome is spatially arranged into cytosolic and membrane-associated mRNA. While translation of membrane protein-encoding mRNA has been studied in great mechanistic detail using biochemical methods, the spatiotemporal dynamics of this process remains poorly understood at the subcellular level. Here, we investigate the dynamics of individual fluorescently labelled mRNA molecules encoding the transmembrane serine chemoreceptor Tsr, to probe the mechanism of membrane protein translation. Analysis of tsr mRNA diffusion in the proximity of the plasma membrane revealed distinct diffusive modes that reflect the state of the mRNA molecule and its involvement in the process of active translation into the Sec secretion system. We find that the composition, and hence the fluidity of the membrane affects diffusion of membrane targeted mRNAs. Moreover, Tsr translation occurs in localized membrane regions, similar to eukaryotic hotspots. The hotspot localization coincides with the physical location of the transcribed gene, which itself is displaced towards the inner membrane. These findings suggest that inner membrane protein translation is a spatially defined process that occurs in hotspots, indicative of long-lived transertion sites. Our results show an additional layer of spatio-temporal structuring within the bacterial cell, thus revealing a qualitatively different understanding of the basic process of transcription and translation in bacteria. Significance StatementA large fraction of the bacterial proteome is directly synthesized into the inner membrane, and this process shapes the overall distribution of mRNA transcripts within the cell. Although highly dynamic in their nature, bacterial transcriptomes have mostly been studied in fixed cells. Here, we track individual mRNA molecules encoding the serine chemoreceptor in living bacterial cells and find that translation occurs in membrane hotspots that were previously exclusive to eukaryotes. Our results indicate an additional layer of spatio-temporal structuring within the bacterial cell that impacts our understanding of transcription and translation in bacteria.

microbiology↗

bioRxiv2022

Nutrient and salt depletion synergistically boosts glucose metabolism in individual Escherichia coli cells

The interaction between a cell and its environment shapes fundamental intracellular processes such as cellular metabolism. In most cases growth rate is treated as a proximal metric for understanding the cellular metabolic status. However, changes in growth rate might not reflect metabolic variations in individuals responding to environmental fluctuations. Here we use single-cell microfluidics-microscopy combined with transcriptomics, proteomics and mathematical modelling to quantify the accumulation of glucose within Escherichia coli cells. In contrast to the current consensus, we reveal that environmental conditions which are comparatively unfavourable for growth, where both nutrients and salinity are depleted, increase glucose accumulation rates in individual bacteria and population subsets. We find that these changes in metabolic function are underpinned by variations at the translational and posttranslational level but not at the transcriptional level and are not dictated by changes in cell size. The metabolic response-characteristics identified greatly advance our fundamental understanding of the interactions between bacteria and their environment and have important ramifications when investigating cellular processes where salinity plays an important role.

microbiology↗