RESUMEN
Although the multiplication of bacteriophages (phages) has a substantial impact on the biosphere, comparatively little is known about how the external environment affects phage production. Here we report that sub-lethal concentrations of certain antibiotics can substantially stimulate the host bacterial cell's production of some virulent phage. For example, a low dosage of cefotaxime, a cephalosporin, increased an uropathogenic Escherichia coli strain's production of the phage PhiMFP by more than 7-fold. We name this phenomenon Phage-Antibiotic Synergy (PAS). A related effect was observed in diverse host-phage systems, including the T4-like phages, with beta-lactam and quinolone antibiotics, as well as mitomycin C. A common characteristic of these antibiotics is that they inhibit bacterial cell division and trigger the SOS system. We therefore examined the PAS effect within the context of the bacterial SOS and filamentation responses. We found that the PAS effect appears SOS-independent and is primarily a consequence of cellular filamentation; it is mimicked by cells that constitutively filament. The fact that completely unrelated phages manifest this phenomenon suggests that it confers an important and general advantage to the phages.
Asunto(s)
Antibacterianos/farmacología , Bacteriófagos/crecimiento & desarrollo , Quinolonas/farmacología , beta-Lactamas/farmacología , ADN Bacteriano , Escherichia coli/efectos de los fármacos , Escherichia coli/genética , Escherichia coli/crecimiento & desarrollo , Proteínas Virales/genética , Proteínas Virales/metabolismoRESUMEN
Among the most numerous objects in the biosphere, phages show enormous diversity in morphology and genetic content. We have sequenced 7 T4-like phages and compared their genome architecture. All seven phages share a core genome with T4 that is interrupted by several hyperplastic regions (HPRs) where most of their divergence occurs. The core primarily includes homologues of essential T4 genes, such as the virion structure and DNA replication genes. In contrast, the HPRs contain mostly novel genes of unknown function and origin. A few of the HPR genes that can be assigned putative functions, such as a series of novel Internal Proteins, are implicated in phage adaptation to the host. Thus, the T4-like genome appears to be partitioned into discrete segments that fulfil different functions and behave differently in evolution. Such partitioning may be critical for these large and complex phages to maintain their flexibility, while simultaneously allowing them to conserve their highly successful virion design and mode of replication.
Asunto(s)
Bacteriófago T4/genética , Variación Genética , Genoma Viral/genética , Sintenía , Fagos T/genética , Secuencia de Aminoácidos , Secuencia de Bases , ADN Viral/genética , Evolución Molecular , Orden Génico , Genes Virales , Datos de Secuencia Molecular , Análisis de Secuencia de ADNRESUMEN
Tailed bacteriophages are the most abundant biological entities in marine environments. However, most of these marine phages are uncharacterized because few of their hosts have been cultivated. To learn more about such phages, we designed a set of degenerate PCR primers for phage T4 g23, which encodes the major capsid protein in all of the T4-type phages, an important family of the tailed phage. These primers were used to amplify g23-related sequences from diverse marine environments (fjords and bays of British Columbia, the eastern Gulf of Mexico, and the western Arctic Ocean) revealing a remarkable level of molecular diversity, which in some cases was correlated with morphological variation of the virions. Phylogenetic analysis showed that although some of these sequences were closely related to well studied subgroups of the T4-type phage, such as the T-evens, the majority of them belong to five previously uncharacterized subgroups. These data indicate that the host range of T4-type phages is much broader than previously imagined and that the laboratory isolate T4 belongs to a phage family that is extraordinarily widespread and diverse in the biosphere.
Asunto(s)
Bacteriófago T4/genética , Bacteriófago T4/aislamiento & purificación , Secuencia de Aminoácidos , Secuencia de Bases , Proteínas de la Cápside/genética , ADN Viral/genética , ADN Viral/aislamiento & purificación , Evolución Molecular , Variación Genética , Datos de Secuencia Molecular , Filogenia , Reacción en Cadena de la Polimerasa , Agua de Mar/virología , Homología de Secuencia de AminoácidoRESUMEN
RB49 is a virulent bacteriophage that infects Escherichia coli. Its virion morphology is indistinguishable from the well-known T-even phage T4, but DNA hybridization indicated that it was phylogenetically distant from T4 and thus it was classified as a pseudo-T-even phage. To further characterize RB49, we randomly sequenced small fragments corresponding to about 20% of the approximately 170-kb genome. Most of these nucleotide sequences lacked sufficient homology to T4 to be detected in an NCBI BlastN analysis. However, when translated, about 70% of them encoded proteins with homology to T4 proteins. Among these sequences were the numerous components of the virion and the phage DNA replication apparatus. Mapping the RB49 genes revealed that many of them had the same relative order found in the T4 genome. The complete nucleotide sequence was determined for the two regions of RB49 genome that contain most of the genes involved in DNA replication. This sequencing revealed that RB49 has homologues of all the essential T4 replication genes, but, as expected, their sequences diverged considerably from their T4 homologues. Many of the nonessential T4 genes are absent from RB49 and have been replaced by unknown sequences. The intergenic sequences of RB49 are less conserved than the coding sequences, and in at least some cases, RB49 has evolved alternative regulatory strategies. For example, an analysis of transcription in RB49 revealed a simpler pattern of regulation than in T4, with only two, rather than three, classes of temporally controlled promoters. These results indicate that RB49 and T4 have diverged substantially from their last common ancestor. The different T4-type phages appear to contain a set of common genes that can be exploited differently, by means of plasticity in the regulatory sequences and the precise choice of a large group of facultative genes.