Metabolic Perturbations Caused by the Over-Expression of mcr-1 in Escherichia coli

Abstract

Rapid dissemination of the plasmid-born polymyxin resistance gene mcr-1 poses a critical medical challenge. MCR-1 expression is tightly controlled and imposes a fitness cost on the bacteria. We used growth studies and metabolomics to examine growth and metabolic changes within E. coli TOP10 at 8 and 24 h in response to different levels of expression of mcr-1 . Induction of mcr-1 greatly increased expression at 8 h and markedly reduced bacterial growth; membrane disruption and cell lysis were evident at this time. At 24 h, the expression of mcr-1 dramatically declined with restored growth and membrane integrity, indicating regulation of mcr-1 expression in bacteria to maintain membrane homeostasis. Intermediates of peptide and lipid biosynthesis were the most commonly affected metabolites when mcr-1 was overexpressed in E. coli . Cell wall biosynthesis was dramatically affected with the accumulation of lipids including fatty acids, glycerophospholipids and lysophosphatidylethanolamines, especially at 8 h. In contrast, levels of intermediate metabolites of peptides, amino sugars, carbohydrates and nucleotide metabolism and secondary metabolites significantly decreased. Moreover, the over-expression of mcr-1 resulted in a prolonged reduction in intermediates associated with pentose phosphate pathway and pantothenate and CoA biosynthesis. These findings indicate that over-expression of mcr-1 results in global metabolic perturbations that mainly involve disruption to the bacterial membrane, pentose phosphate pathway as well as pantothenate and CoA biosynthesis.

A ProQ/FinO family protein involved in plasmid copy number control favours fitness of bacteria carryingmcr-1-bearing IncI2 plasmids

“…Consistent with the results of the previous studies that overexpression of mcr-1 impairs viability ( 38 , 39 ), and that mcr-1 is generally found in low-copy plasmids ( 40 ), our results suggest that maintaining the mcr-1 plasmid at a low copy number is essential for the fitness of the host bacteria. Furthermore, PcnR maintains a balance between the mcr-1 expression level and bacterial fitness by reducing the copy number of the IncI2 plasmid pHNSHP45 to ensure appropriate expression levels of mcr-1 .…”

“…Although the acquisition of antimicrobial resistance by mutation or HGT is often associated with a fitness cost, bacterial evolution to reduce the cost of resistance contributes to the persistence of resistance in pathogens ( 6 ). High-level expression of mcr-1 has previously been shown to influence bacterial fitness by impairing the growth rate and membrane structural integrity of the host bacteria ( 38 , 39 ). It is likely that maintaining a modest expression level of mcr-1 by a low copy number plasmid plays a key role in the persistence of mcr-1 plasmids in bacterial populations.…”

Impact of mcr-1 on the Development of High Level Colistin Resistance in Klebsiella pneumoniae and Escherichia coli

“…To test this hypothesis, we compared the growth rates of mcr-1 -positive and mcr-1 -negative strains with those of their relevant HLCR mutants and found that HLCR mutants derived from mcr-1 -negative strains exhibited almost no fitness cost, while HLCR mutants of mcr-1 -positive strains showed an evident fitness cost. Previous studies have shown that the fitness cost attributed to chromosomal mutations or the acquisition of wild-type mcr-1 -harboring plasmids seemed to be insignificant ( Cannatelli et al, 2015 ; Wu et al, 2018 ); however, increased expression of mcr-1 could impose a significant fitness burden on host bacteria ( Yang et al, 2017 ; Liu et al, 2020 ). Our results demonstrated that the coexistence of chromosomal mutations and mcr-1 was disadvantageous for K. pneumoniae , which might partly explain the lack of clinical strains with both chromosomal mutations and mcr-1 ( Nang et al, 2018 ).…”

Biophysical Impact of Lipid A Modification Caused by Mobile Colistin Resistance Gene on Bacterial Outer Membranes

“…The mcr genes confer polymyxin resistance by encoding a phosphoethanolamine (pEtN) transferase enzyme (e.g., MCR-1, an inner-membrane (IM)-anchored protein) that catalyzes the addition of pEtN onto a phosphate at the N -acetylglucosamine headgroup of lipid A in the outer membrane (OM; Figure a). , However, this modification usually comes at a cost to the bacterium with the growth rate of mcr-1 positive transformants often substantially lower than that of non-MCR parents. − Additionally, changes in cellular morphology and global metabolic perturbations mainly involving disruption to the bacterial membrane have also been reported with mcr-1 expression. , These results indicate that the acquisition of mcr genes is a “poisoned chalice” for bacteria that protects them from polymyxins but simultaneously has a fitness cost. However, the mechanism(s) by which modification of lipid A with pEtN results in negative consequences for the bacterium are unknown.…”

“…As the expression of mcr is known to induce morphological changes in bacteria, , the influence of different proportions (0–75%) of pEtN-modified lipid A (i.e., lipid A-pEtN) on the morphology of biomimetic bacterial OMs was first investigated. The different proportions of lipid A-pEtN represent different extents of mcr expression.…”