What question did this study set out to answer?

The study aims to isolate and characterize novel phage satellites in Mycobacteriaceae, specifically focusing on their induction of prophage excision.

April 12, 2026Open Access

A novel phage satellite class induces prophage excision in Mycolicibacterium aichiense

Key Points

The study aims to isolate and characterize novel phage satellites in Mycobacteriaceae, specifically focusing on their induction of prophage excision.
Isolated phage satellites from Mycobacteriaceae.
Conducted genomic sequencing on thirteen isolates to determine genomic characteristics.
Used Virus Intergenomic Distance Calculator (VIRIDIC) to analyze nucleotide similarity and gene content.
Employed transmission electron microscopy to visualize morphological features.
Identified EPIPs as the first phage satellites from Mycobacteriaceae with approximately 83.3% nucleotide similarity.
Categorized EPIPs into distinct groups based on VIRIDIC similarity scores and gene content.
Observed that EPIPs lack capsid proteins and tail proteins, implying they hijack the helper phage HerbertWM for replication.
Noted that EPIPs have highly flexible tails and smaller capsids compared to HerbertWM.

Abstract

Phage satellites are mobile genetic elements that parasitize a helper phage to complete their life cycle. While phage satellites are widespread in diverse bacterial hosts, none have yet been isolated in Mycobacteriaceae . Here, we report the first phage satellites isolated and characterized in Mycobacteriaceae , Extracellular Prophage-Inducing Particles (EPIPs). EPIPs induce a helper phage—HerbertWM, a Mycolicibacterium aichiense prophage—upon infection. Genomic sequencing of thirteen isolates revealed a genome size of ∼11 kb and ∼83.3% nucleotide similarity calculated using Virus Intergenomic Distance Calculator (VIRIDIC). Although gene content and synteny were broadly conserved across the isolates, the EPIPs were categorized into distinct groups based on VIRIDIC similarity scores, gene content, and synteny. Notably, EPIPs lack capsid proteins, tail proteins, and holins, suggesting EPIPs hijack the machinery of HerbertWM to replicate, assemble, and lyse the host. Furthermore, the unique gene content of EPIPs compared to other phage satellites, particularly the presence of a tape measure protein and absence of antirepressors, suggests they are distinct from other phage satellite classes. Transmission electron microscopy of EPIPs reveals that they not only feature smaller capsids compared to HerbertWM, but that they feature highly flexible tails of variable length. Additionally, greater EPIP protein similarity to proteins in bacteria as opposed to free phage proteins suggests a functional or evolutionary relationship may exist. The nucleotide similarity, synteny, and unique gene content of EPIPs suggest EPIPs are a distinct class of phage satellites that induce Mycobacteriaceae prophages. • EPIPs are the first phage satellites experimentally isolated from Mycobacteriaceae • EPIPS share 58.1%-99.8% sequence identity, with conserved gene content and synteny • Despite lacking canonical antirepressors, EPIPs induce a prophage, HerbertWM • EPIPs have longer, more varied tails and smaller capsids than prophage HerbertWM • Gene content of EPIPs is distinct from that of other phage satellite classes

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Qian et al. (Wed,) studied this question.

synapsesocial.com/papers/69db365c4fe01fead37c489e https://doi.org/https://doi.org/10.1016/j.virol.2026.110911

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