IbpAB small heat shock proteins are not host factors for bacteriophage {varphi}X174 replication

Bacteriophages exploit host proteins for successful infection. Small heat shock proteins are a universally conserved family of stress-induced molecular chaperones that prevent irreversible aggregation of proteins. Two small heat shock proteins, IbpA and IbpB, are a class of holding modulators or "holdases", which bind partially folded proteins and await ATP-driven folding chaperones for refolding. Bacteriophage {phi}X174 is a small, icosahedral, and non-tailed virus belonging to the Microviridae. During {phi}X174 infection of Escherichia coli C122, IbpA and IbpB were previously found to be the most highly upregulated host proteins, with expression levels comparable to {phi}X174 proteins. In this work, to understand the role of IbpA and IbpB during {phi}X174 infection, we used a hybrid approach of CRISPR interference and genomic knockouts to disrupt the ibpA and ibpB genes. We show that these two proteins do not appear to be necessary for efficient {phi}X174 replication, and moreover, their absence has no effect on {phi}X174 fecundity. ImportanceThe small heat shock proteins (sHsps) are universally conserved family of stress-induced molecular chaperones that prevent irreversible protein aggregation. In E. coli, the IbpA/B sHsps work together, and separately, to bind partially folded proteins and await ATP-driven folding chaperones for refolding. These proteins are highly upregulated during protein overexpression and bacteriophage infection, but their collective role in bacteriophage infection has not been investigated. Here, we show that the ibpA/B genes are dispensable for bacteriophage {phi}X174 infection, and are likely not essential host factors despite their abundance during diverse phage infections. Instead, this work points towards their role as cell wall integrity sensors, similar to the phage shock protein system, in addition to their canonical role as holdases of cytoplasmic protein.