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Microbiology Spectrum (2025)

Abstract

Predatory bacteria are a group of organisms that use diverse methods to access nutrients and grow by killing prey bacteria. The predator Bdellovibrio bacteriovorus is capable of preying on a wide range of gram-negative bacteria by invading the periplasmic space, killing, digesting, and ultimately lysing prey cells. B. bacteriovorus, like a phage, replicates at the expense of its host, yet unlike phage defense, there are few characterized mechanisms for bacteria to resist B. bacteriovorus. Previously, we discovered that an extracellular amyloid protein called curli protects Escherichia coli from B. bacteriovorus. Here, we searched for additional modes of B. bacteriovorusresistance and identified a strain within the E. coli Reference (ECOR) collection, ECOR29, that uses a curli-independent mechanism that requires lipopolysaccharide (LPS)-modifying enzymes for defense. Over 30% of the ECOR collection is resistant to B. bacteriovorus. We successfully deleted the gene encoding the major curli subunit in many of these, and only ECOR29 remained resistant. We hypothesized that ECOR29 encoded an alternative resistance mechanism and identified determinants of defense using a forward genetic screen. Our screen revealed critical roles for enzymes that modify LPS, alter the outer membrane, and are homologous to plasmid partitioning systems. Examination of ECOR29 by electron microscopy did not identify overt phenotypes or visible alterations to extracellular structures. We also were unable to identify any secreted factors that impacted B. bacteriovorus viability. Our work demonstrates that E. coli encode curli-independent mechanisms that restrict B. bacteriovorus and expand our understanding of the antipredatory bacteria arm of the bacterial immune system.

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Citation

Sayegh R, Ledvina HE, Whiteley AT.Curli-independent defense against Bdellovibrio bacteriovorus in E. coli. Microbiol Spectr. 0:e00342-25. https://doi.org/10.1128/spectrum.00342-25