Recombinant Escherichia coli O6:K15:H31 Spermidine export protein MdtI (mdtI)

Introduction to Recombinant Escherichia coli O6:K15:H31 Spermidine Export Protein MdtI (mdtI)

Escherichia coli ( E. coli) is a diverse group of bacteria, with some strains being harmless and others causing disease . Uropathogenic E. coli (UPEC) strain 536 (O6:K15:H31) is a well-studied strain known for causing urinary tract infections . This strain carries several pathogenicity islands (PAIs), which are distinct DNA regions encoding virulence factors .

Spermidine is a polyamine essential for cell growth, and its levels within cells are tightly regulated . The mdtI gene encodes a spermidine export protein, MdtI, which is part of the MdtJI complex . This complex catalyzes the excretion of spermidine from the cell, maintaining proper spermidine levels .

Function and Mechanism of MdtI

The MdtJI complex, which includes MdtI, is crucial for recovering from the toxicity caused by overaccumulation of spermidine . MdtI belongs to the small multidrug resistance (SMR) family of drug exporters . The expression of the mdtJI mRNA is increased by spermidine, indicating a regulatory response to spermidine levels .

Key functions of MdtI:

• Spermidine Excretion: MdtI, in complex with MdtJ, catalyzes the excretion of spermidine at neutral pH .

• Regulation of Spermidine Levels: By exporting spermidine, MdtI helps maintain optimal intracellular concentrations of this polyamine .

• Reversal of Toxicity: Overaccumulation of spermidine can be toxic to cells; MdtI helps alleviate this toxicity by exporting excess spermidine .

Experimental Evidence and Research Findings

The function of MdtI has been confirmed through several experiments:

• Cell Viability Assays: Introducing the mdtJI gene into E. coli strains deficient in spermidine acetyltransferase (which metabolizes spermidine) increased cell viability in the presence of excess spermidine .

• Spermidine Content Measurement: When mdtJI was transformed into E. coli, the accumulation of spermidine was greatly diminished, which correlated with the recovery of cell viability .

• Excretion Assays: Excretion of radio-labeled spermidine was observed in cells transformed with mdtJI, confirming its role in spermidine export .

Table 1 summarizes the impact of MdtJI on spermidine accumulation and cell viability.

Table 1: Impact of MdtJI on Spermidine Accumulation and Cell Viability

Specific amino acid residues in MdtI are crucial for its function. It was found that Glu 5, Glu 19, Asp 60, Trp 68, and Trp 81 in MdtI are involved in the excretion activity of MdtJI .

Role in Multidrug Resistance

MdtI is part of a multidrug resistance protein complex, suggesting its broader role in exporting toxic compounds from the cell . The MdtJI complex belongs to the SMR family, which includes proteins known for conferring resistance to multiple drugs .

Genetic and Genomic Context

The mdtI gene is often found alongside mdtJ, forming an operon that is co-regulated . These genes are located on the bacterial chromosome and may be part of pathogenicity islands in certain UPEC strains . The presence of PAIs can contribute to the virulence and adaptability of E. coli strains .

Potential Applications and Further Research

Understanding the function and regulation of MdtI has potential applications in several areas:

• Antimicrobial Development: Targeting spermidine export could be a strategy to enhance the efficacy of certain antibiotics or develop new antibacterial agents.

• Understanding Bacterial Virulence: MdtI contributes to the survival and virulence of E. coli strains by managing intracellular spermidine levels and conferring multidrug resistance.

• Biotechnology: MdtI could be used in engineered strains to control spermidine levels, which can be important in various biotechnological applications .