Along with functional advances in the use of CRISPR/Cas9 for genome editing, endonuclease-deficient Cas9 (dCas9) has provided a versatile molecular tool for exploring gene functions. In principle, differences in cell phenotypes that result from the RNA-guided modulation of transcription levels by dCas9 are critical for inferring with gene function; however, the effect of intracellular dCas9 expression on bacterial morphology has not been systematically elucidated. Here, we observed unexpected morphological changes in Escherichia coli mediated by dCas9, which were then characterized using RNA sequencing (RNA-Seq) and chromatin immunoprecipitation sequencing (ChIP-Seq). Growth rates were severely decreased, to approximately 50% of those of wild type cells, depending on the expression levels of dCas9. Cell shape was changed to abnormal filamentous morphology, indicating that dCas9 affects bacterial cell division. RNA-Seq revealed that 574 genes were differentially transcribed in the presence of high expression levels of dCas9. Genes associated with cell division were upregulated, which was consistent with the observed atypical morphologies. In contrast, 221 genes were downregulated, and these mostly encoded proteins located in the cell membrane. Further, ChIP-Seq results showed that dCas9 directly binds upstream of 37 genes without single-guide RNA, including fimA, which encodes bacterial fimbriae. These results support the fact that dCas9 has critical effects on cell division as well as inner and outer membrane structure. Thus, to precisely understand gene functions using dCas9-driven transcriptional modulation, the regulation of intracellular levels of dCas9 is pivotal to avoid unexpected morphological changes in E. coli.

Synthetic biology aims to design and construct bacterial genomes harboring the minimum number of genes required for self-replicable life. However, the genome-reduced bacteria often show impaired growth under laboratory conditions that cannot be understood based on the removed genes. The unexpected phenotypes highlight our limited understanding of bacterial genomes. Here, we deploy adaptive laboratory evolution (ALE) to re-optimize growth performance of a genome-reduced strain. The basis for suboptimal growth is the imbalanced metabolism that is rewired during ALE. The metabolic rewiring is globally orchestrated by mutations in rpoD altering promoter binding of RNA polymerase. Lastly, the evolved strain has no translational buffering capacity, enabling effective translation of abundant mRNAs. Multi-omic analysis of the evolved strain reveals transcriptome- and translatome-wide remodeling that orchestrate metabolism and growth. These results reveal that failure of prediction may not be associated with understanding individual genes, but rather from insufficient understanding of the strain’s systems biology.

Microbial cells are versatile hosts for the production of value-added products due to the well-established background knowledge, various genetic tools, and ease of manipulation. Despite those advantages, efficiency of newly incorporated synthetic pathways in microbial cells is frequently limited by innate metabolism, product toxicity, and growth-mediated genetic instability. To overcome those obstacles, a minimal genome harboring only the essential set of genes was proposed, which is a fascinating concept with potential for use as a platform strain. Here, we review the currently available artificial reduced genomes and discuss the prospects for extending use of the genome-reduced strains as programmable chasses. The genome-reduced strains generally showed comparable growth to and higher productivity than their ancestral strains. In Escherichia coli, about 300 genes are estimated as the minimal number of genes under laboratory conditions. However, recent advances revealed that there are non-essential components in essential genes, suggesting that the design principle of minimal genomes should be reconstructed. Current technology is not efficient enough to reduce large amount of interspaced genomic regions or to synthesize the genome. Furthermore, construction of minimal genome frequently has failed due to lack of genomic information. Technological breakthroughs and intense systematic studies on genomes remain tasks.

Background The gut microbiota is associated with diverse age-related disorders. Several rejuvenation methods, such as probiotic administration and faecal microbiota transplantation, have been applied to alter the gut microbiome and promote healthy ageing. Nevertheless, prolongation of the health span of aged mice by remodelling the gut microbiome remains challenging. Results Here, we report the changes in gut microbial communities and their functions in mouse models during ageing and three rejuvenation procedures including co-housing, serum-injection and parabiosis. Our results showed that the compositional structure and gene abundance of the intestinal microbiota changed dynamically during the ageing process. Through the three rejuvenation procedures, we observed that the microbial community and intestinal immunity of aged mice were comparable to those of young mice. The results of metagenomic data analysis underscore the importance of the high abundance of Akkermansia and the butyrate biosynthesis pathway in the rejuvenated mouse group. Furthermore, oral administration of Akkermansia sufficiently ameliorated the senescence-related phenotype in the intestinal systems in aged mice and extended the health span, as evidenced by the frailty index and restoration of muscle atrophy. Conclusions In conclusion, the changes in key microbial communities and their functions during ageing and three rejuvenation procedures, and the increase in the healthy lifespan of aged mice by oral administration of Akkermansia. Our results provide a rationale for developing therapeutic strategies to achieve healthy active ageing.

18Bactericidal antibiotics are powerful drugs due to their ability to not only inhibit essential 19 bacterial functions, but to convert them into toxic (and potentially lethal) processes. 20However, many important bacterial pathogens are remarkably tolerant against 21 bactericidal drugs, due to inducible stress responses that repair antibiotic-induced 22 damage. The mechanistic details of how stress responses promote whole population 23 tolerance in important human pathogens are unknown. The two-component system 24 VxrAB of the diarrheal pathogen Vibrio cholerae, a model system for high-level -lactam 25 2 tolerance, is induced by exposure to cell wall acting antibiotic and controls a gene 26 network encoding highly diverse functions, including cell wall synthesis functions and 27 iron uptake systems. Here, we show that positive control over cell wall synthesis 28 functions only partially explains high level -lactam tolerance. We find that in addition to 29 cell wall damage, -lactam antibiotics inappropriately induce the Fur-regulated iron 30 starvation response, causing an increase in intracellular free iron levels and colateral 31 oxidative damage. We propose that VxrAB reduces antibiotic-induced toxic influx of 32 Fe 2+ and concomitant metabolic perturbations by selectively downregulating iron uptake 33 transporters. Our results suggest that the ability to counteract diverse antibiotic-induced 34 stresses promotes high-level antibiotic tolerance and highlight the complex responses 35 elicited by antibiotics in addition to their primary mechanism of action. 36 37 by either developing the ability to grow in their presence (antibiotic resistance, ABR) or 49 to simply stay alive in their presence for extended time periods (antibiotic 50 tolerance/persistence) [3][4][5][6][7][8] . While the mechanisms and consequences of ABR are 51 relatively well-established, antibiotic tolerance remains poorly understood, limiting our 52 ability to develop antibiotic adjuvants that increase the efficacy of existing drugs. 53 54The -lactam antibiotics (penicillins, cephalosporins, carbapenems, cephamycins and 55 monobactams) are highly potent bactericidal agents. Their typically lethal action results 56 from their ability to simultaneously inhibit multiple targets (i.e, the transpeptidase 57 domain of multiple penicillin-binding proteins [PBPs]), which ultimately causes bacterial 58 cells to deplete essential cell wall precursors and self-destruct through the activity of 59 endogenous, cell wall lytic enzymes ('autolysins'; endopeptidases, amidases and lytic 60 transglycosylases) 9-12 . However, we and others have recently shown that many 61 clinically significant Gram-negative pathogens are remarkably -lactam tolerant. The 62 cholera pathogen Vibrio cholerae, the opportunistic pathogen Pseudomonas aeruginosa 63 and clinical isolates of Enterobacteriaceae all survive treatment with -lactam antibiotics 64 (including the "last resort" agent meropenem) by forming non-dividing, cell wall deficient 65 spheroplasts 11,13,14 . Upon...

Adaptive laboratory evolution (ALE) is used to find causal mutations that underlie improved strain performance under the applied selection pressure. ALE studies have revealed that mutator populations tend to outcompete their non-mutator counterparts following the evolutionary trajectory. Among them, mutS- inactivated mutator cells, characterize d by a dysfunctional methyl-mismatch repair system, are frequently found in ALE experiments. Here, we examined mutS inactivation as an approach to facilitate ALE of Escherichia coli. The wild-type E. coli MG1655 and mutS knock-out derivative (Δ mutS ) were evolved in parallel for 800 generations on lactate or glycerol minimal media in a serial-transfer experiment. Whole-genome re-sequencing of each lineage at 100-generation intervals revealed that (1) mutations emerge rapidly in the Δ mutS compared to in the wild-type strain; (2) mutations were more than fourfold higher in the Δ mutS strain at the end-point populations compared to the wild-type strain; and (3) a significant number of random mutations accumulated in the Δ mutS strains. We then measured the fitness of the end-point populations on an array of non-adaptive carbon sources. Interestingly, collateral fitness increases on non-adaptive carbon sources were more pronounced in the Δ mutS strains than the parental strain. Fitness measurement of single mutants revealed that the collateral fitness increase seen in the mutator lineages can be attributed to a pool of random mutations. Together, this study demonstrates that short-term mutator ALE extensively expands possible genotype space, resulting in versatile bacteria with elevated fitness levels across various carbon sources.

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Staphylococcus aureus infection is a rising public health care threat. S. aureus is believed to have elaborate regulatory networks that orchestrate its virulence. Despite its importance, the systematic understanding of the transcriptional landscape of S. aureus is limited. Here, we describe the primary transcriptome landscape of an epidemic USA300 isolate of community-acquired methicillin-resistant S. aureus. We experimentally determined 1,861 transcription start sites with their principal promoter elements, including well-conserved -35 and -10 elements and weakly conserved -16 element and 5′ untranslated regions containing AG-rich Shine-Dalgarno sequence. In addition, we identified 225 genes whose transcription was initiated from multiple transcription start sites, suggesting potential regulatory functions at transcription level. Along with the transcription unit architecture derived by integrating the primary transcriptome analysis with operon prediction, the measurement of differential gene expression revealed the regulatory framework of the virulence regulator Agr, the SarA-family transcriptional regulators, and β-lactam resistance regulators. Interestingly, we observed a complex interplay between virulence regulation, β-lactam resistance, and metabolism, suggesting a possible tradeoff between pathogenesis and drug resistance in the USA300 strain. Our results provide platform resource for the location of transcription initiation and an in-depth understanding of transcriptional regulation of pathogenesis, virulence, and antibiotic resistance in S. aureus.