Polyamines and linear DNA mediate bacterial threat assessment of bacteriophage infection.

Monitoring the extracellular environment for danger signals is a critical aspect of cellular survival. However, the danger signals released by dying bacteria and the mechanisms bacteria use for threat assessment remain largely unexplored. Here, we show that lysis of Pseudomonas aeruginosa cells releases polyamines that are subsequently taken up by surviving cells via a mechanism that relies on Gac/Rsm signaling. While intracellular polyamines spike in surviving cells, the duration of this spike varies according to the infection status of the cell. In bacteriophage-infected cells, intracellular polyamines are maintained at high levels, which inhibits replication of the bacteriophage genome. Many bacteriophages package linear DNA genomes and linear DNA is sufficient to trigger intracellular polyamine accumulation, suggesting that linear DNA is sensed as a second danger signal. Collectively, these results demonstrate how polyamines released by dying cells together with linear DNA allow P. aeruginosa to make threat assessments of cellular injury.

Ribosomal-processing cysteine protease homolog modulates Streptococcus mutans glucan production and interkingdom interactions.

Glucan-dependent biofilm formation is a crucial process in the establishment of Streptococcus mutans as a cariogenic oral microbe. The process of glucan formation has been investigated in great detail, with glycosyltransferases GtfB, GtfC, and GtfD shown to be indispensable for the synthesis of glucans from sucrose. Glucan production can be visualized during biofilm formation through fluorescent labeling, and its abundance, as well as the effect of glucans on general biofilm architecture, is a common phenotype to study S. mutans virulence regulation. Here, we describe an entirely new phenotype associated with glucan production, caused by a mutation in the open reading frame SMU_848, which is located in an operon encoding ribosome-associated proteins. This mutation led to the excess production and accumulation of glucan-containing droplets on the surface of biofilms formed on agar plates after prolonged incubation. While not characterized in S. mutans, SMU_848 shows homology to the phage-related ribosomal protease Prp, essential in cleaving off the N-terminal extension of ribosomal protein L27 for functional ribosome assembly in Staphylococcus aureus. We present a further characterization of SMU_848/Prp, demonstrating that the deletion of this gene leads to significant changes in S. mutans gtfBC expression. Surprisingly, it also profoundly impacts the interkingdom interaction between S. mutans and Candida albicans, a relevant dual-species interaction implicated in severe early childhood caries. The presented data support a potential broader role for SMU_848/Prp, possibly extending its functionality beyond the ribosomal network to influence important ecological processes. IMPORTANCE: Streptococcus mutans is an important member of the oral biofilm and is implicated in the initiation of caries. One of the main virulence mechanisms is the glucan-dependent formation of biofilms. We identified a new player in the regulation of glucan production, SMU_848, which is part of an operon that also encodes for ribosomal proteins L27 and L21. A mutation in SMU_848, which encodes a phage-related ribosomal protease Prp, leads to a significant accumulation of glucan-containing droplets on S. mutans biofilms, a previously unknown phenotype. Further investigations expanded our knowledge about the role of SMU_848 beyond its role in glucan production, including significant involvement in interkingdom interactions, thus potentially playing a global role in the virulence regulation of S. mutans.

Complete Genome Sequence of the N4-like Pseudomonas aeruginosa Bacteriophage vB_PaeP_CMS1.

vB_PaeP_CMS1 is a lytic bacteriophage that infects Pseudomonas aeruginosa. Whole-genome sequencing revealed that vB_PaeP_CMS1 has a linear double-stranded DNA (dsDNA) genome composed of 72,673 bp, with a GC content of 54.9%, that harbors 92 predicted open reading frames, with the greatest genome homology to members of the family Podoviridae, genus Litunavirus.