# Bactericidal membrane attack complex formation initiates at the new pole of E. coli

## TL;DR

The study shows that the immune system's MAC pores attack E. coli at the new bacterial pole, causing damage and stopping cell division.

## Contribution

The study reveals that MAC pores form preferentially at the new pole of E. coli, not randomly.

## Key findings

- MAC pores localize at the new pole of E. coli, causing inner membrane damage.
- C8 and C9 MAC components prefer the new pole, while C3b is randomly distributed.
- An image analysis pipeline confirms the findings in a high-throughput manner.

## Abstract

Human immune protection against bacteria critically depends on activation of the complement system. The direct bacteriolytic activity of complement molecules against Gram-negative bacteria acts via the formation of Membrane Attack Complex (MAC) pores. Bactericidal MAC pores damage the bacterial outer membrane, leading to destabilization of the inner membrane. Although it is well-established that inner membrane damage is crucial for bacterial cell death, the critical event causing MAC-mediated inner membrane damage remains elusive. Here we question whether the bacterial cell envelope possesses vulnerable spots for MAC pores to insert. By following the localization of MAC pores on E. coli over time using fluorescence microscopy, we elucidate that MAC deposition initiates at the new bacterial pole, which induces inner membrane damage and halts bacterial division. MAC components C8 and C9 preferentially localize at new bacterial poles, while C3b localizes randomly on the bacterial surface. This suggests that preferential MAC localization is determined by one of the initial steps of MAC formation. These findings provide valuable information about the interplay between immune components and the Gram-negative cell envelope.

Bactericidal Membrane Attack Complex (MAC) pores preferentially insert at the new pole of E. coli. Preferred localization of MAC components is independent of complement activation, which occurs randomly along the bacterial surface.

The formation of lethal MAC pores does not occur randomly on the surface of E. coli but initiates at the new bacterial pole.MAC deposition at the new pole is sufficient to cause inner membrane damage and can halt bacterial growth.In contrast to MAC components, complement activation product C3b localizes randomly along the bacterial surface.An advanced image analysis pipeline validates the presented microscopy-based findings in a high-throughput manner.

The formation of lethal MAC pores does not occur randomly on the surface of E. coli but initiates at the new bacterial pole.

MAC deposition at the new pole is sufficient to cause inner membrane damage and can halt bacterial growth.

In contrast to MAC components, complement activation product C3b localizes randomly along the bacterial surface.

An advanced image analysis pipeline validates the presented microscopy-based findings in a high-throughput manner.

Bactericidal Membrane Attack Complex (MAC) pores preferentially insert at the new pole of E. coli. Preferred localization of MAC components is independent of complement activation, which occurs randomly along the bacterial surface.