Complete Genome Sequence of Serratia marcescens Podophage Parlo

The power of unbiased phenotypic screens - cellulose as a first receptor for the Schitoviridae phage S6 of Erwinia amylovora

Bacteriophages, host‐dependent replicative non‐cellular entities which significantly shape the microbial genomes and consequently physiological and ecological properties of the microbial populations are exploited to restrict plant, animal and human pathogens. Unravelling of phage characteristics aids the understanding of the basic molecular mechanisms of phage infections which can subsequently lead to the development of rationalized strategies to combat microbial pathogens. In an unbiased screen to investigate the molecular basis of infectivity of the fire blight pathogen Erwinia amylovora by the lytic Schitoviridae phage S6, the biofilm extracellular matrix component cellulose has been identified as a cyclic di‐GMP dependent first receptor required for infection with the phage to possess beta‐1,4‐glucosidases to degrade the exopolysaccharide. This absolute receptor dependency allows maintenance of a phage‐microbe equilibrium with a low bacterial density.

Identification, Characterization, and Genomic Analysis of Novel Serratia Temperate Phages from a Gold Mine

Bacteria of the genus Serratia inhabit a variety of ecological niches like water, soil, and the bodies of animals, and have a wide range of lifestyles. Currently, the complete genome sequences of 25 Serratia phages are available in the NCBI database. All of them were isolated from nutrient-rich environments like sewage, with the use of clinical Serratia strains as hosts. In this study, we identified a novel Serratia myovirus named vB_SspM_BZS1. Both the phage and its host Serratia sp. OS31 were isolated from the same oligotrophic environment, namely, an abandoned gold mine (Zloty Stok, Poland). The BZS1 phage was thoroughly characterized here in terms of its genomics, morphology, and infection kinetics. We also demonstrated that Serratia sp. OS31 was lysogenized by mitomycin-inducible siphovirus vB_SspS_OS31. Comparative analyses revealed that vB_SspM_BZS1 and vB_SspS_OS31 were remote from the known Serratia phages. Moreover, vB_SspM_BZS1 was only distantly related to other viruses. However, we discovered similar prophage sequences in genomes of various bacteria here. Additionally, a protein-based similarity network showed a high diversity of Serratia phages in general, as they were scattered across nineteen different clusters. In summary, this work broadened our knowledge on the diverse relationships of Serratia phages.

Comparative Genomics and Evolutionary Analysis of RNA-Binding Proteins of the CsrA Family in the Genus Pseudomonas

Gene expression is adjusted according to cellular needs through a combination of mechanisms acting at different layers of the flow of genetic information. At the posttranscriptional level, RNA-binding proteins are key factors controlling the fate of nascent and mature mRNAs. Among them, the members of the CsrA family are small dimeric proteins with heterogeneous distribution across the bacterial tree of life, that act as global regulators of gene expression because they recognize characteristic sequence/structural motifs (short hairpins with GGA triplets in the loop) present in hundreds of mRNAs. The regulatory output of CsrA binding to mRNAs is counteracted in most cases by molecular mimic, non-protein coding RNAs that titrate the CsrA dimers away from the target mRNAs. In γ-proteobacteria, the regulatory modules composed by CsrA homologs and the corresponding antagonistic sRNAs, are mastered by two-component systems of the GacS-GacA type, which control the transcription and the abundance of the sRNAs, thus constituting the rather linear cascade Gac-Rsm that responds to environmental or cellular signals to adjust and coordinate the expression of a set of target genes posttranscriptionally. Within the γ-proteobacteria, the genus Pseudomonas has been shown to contain species with different number of active CsrA (RsmA) homologs and of molecular mimic sRNAs. Here, with the help of the increasing availability of genomic data we provide a comprehensive state-of-the-art picture of the remarkable multiplicity of CsrA lineages, including novel yet uncharacterized paralogues, and discuss evolutionary aspects of the CsrA subfamilies of the genus Pseudomonas, and implications of the striking presence of csrA alleles in natural mobile genetic elements (phages and plasmids).

Tackling Intrinsic Antibiotic Resistance in Serratia Marcescens with A Combination of Ampicillin/Sulbactam and Phage SALSA

During the antibiotic crisis, bacteriophages (briefly phages) are increasingly considered as potential antimicrobial pillars for the treatment of infectious diseases. Apart from acquired drug resistance, treatment options are additionally hampered by intrinsic, chromosomal-encoded resistance. For instance, the chromosomal ampC gene encoding for the AmpC-type β-lactamases is typically present in a number of nosocomial pathogens, including S. marcescens. In this study, phage SALSA (vB_SmaP-SALSA), with lytic activity against clinical isolates of S. marcescens, was isolated from effluent. Besides phage characterization, the aim of this study was to evaluate whether a synergistic effect between the antibiotic ampicillin/sulbactam (SAM) and phage can be achieved despite intrinsic drug resistance. Phage SALSA belongs to the Podoviridae family and genome-wide treeing analysis groups this phage within the phylogenetic radiation of T7-like viruses. The genome of Phage SALSA consists of 39,933 bp, which encode for 49 open reading frames. Phage SALSA was able to productively lyse 5 out of 20 clinical isolates (25%). A bacterial challenge with phage alone in liquid medium revealed that an initial strong bacterial decline was followed by bacterial re-growth, indicating the emergence of phage resistance. In contrast, the combination of SAM and phage, together at various concentrations, caused a complete bacterial eradication, confirmed by absorbance measurements and the absence of colony forming units after plating. The data show that it is principally possible to tackle the axiomatic condition of intrinsic drug resistance with a dual antimicrobial approach, which could be extended to other clinically relevant bacteria.