Genome sequences of 31 mycobacteriophages isolated on Mycobacterium smegmatis mc2155 at room temperature.

We report the genome sequences of 31 mycobacteriophages isolated on Mycobacterium smegmatis mc2155 at room temperature. The genomes add to the diversity of Clusters A, B, C, G, and K. Collectively, the genomes include 70 novel protein-coding genes that have no close relatives among the actinobacteriophages.

Genome Sequences of Subcluster M2 Mycobacteriophages Estes and Aziz.

Estes and Aziz are mycobacteriophages that were isolated on Mycolicibacterium smegmatis mc2155 at room temperature from soil samples collected in Spokane, WA. Their genome sequences are 83,601 and 83,412 bp long, respectively, and they are members of subcluster M2. Each contains 21 tRNA genes and short conserved repeats characteristic of cluster M phages.

Genome Sequences of Cluster K Mycobacteriophages DrHayes, Urkel, and SamuelLPlaqson.

Mycobacteriophages DrHayes, Urkel, and SamuelLPlaqson were isolated from soil samples in Spokane, WA, using Mycobacterium smegmatis mc2155 grown at room temperature. The three genomes differ by only a few nucleotides, are 60,526 bp long, have 97 predicted protein-coding genes and one tRNA gene, and are members of subcluster K1.

Prophage-mediated defence against viral attack and viral counter-defence.

Temperate phages are common, and prophages are abundant residents of sequenced bacterial genomes. Mycobacteriophages are viruses that infect mycobacterial hosts including Mycobacterium tuberculosis and Mycobacterium smegmatis, encompass substantial genetic diversity and are commonly temperate. Characterization of ten Cluster N temperate mycobacteriophages revealed at least five distinct prophage-expressed viral defence systems that interfere with the infection of lytic and temperate phages that are either closely related (homotypic defence) or unrelated (heterotypic defence) to the prophage. Target specificity is unpredictable, ranging from a single target phage to one-third of those tested. The defence systems include a single-subunit restriction system, a heterotypic exclusion system and a predicted (p)ppGpp synthetase, which blocks lytic phage growth, promotes bacterial survival and enables efficient lysogeny. The predicted (p)ppGpp synthetase coded by the Phrann prophage defends against phage Tweety infection, but Tweety codes for a tetrapeptide repeat protein, gp54, which acts as a highly effective counter-defence system. Prophage-mediated viral defence offers an efficient mechanism for bacterial success in host-virus dynamics, and counter-defence promotes phage co-evolution.

Evidence for karyogamy and exchange of genetic material in the binucleate intestinal parasite Giardia intestinalis.

The diplomonad parasite Giardia intestinalis contains two functionally equivalent nuclei that are inherited independently during mitosis. Although presumed to be asexual, Giardia has low levels of allelic heterozygosity, indicating that the two nuclear genomes may exchange genetic material. Fluorescence in situ hybridization performed with probes to an episomal plasmid suggests that plasmids are transferred between nuclei in the cyst, and transmission electron micrographs demonstrate fusion between cyst nuclei. Green fluorescent protein fusions of giardial homologs of meiosis-specific genes localized to the nuclei of cysts, but not the vegetative trophozoite. These data suggest that the fusion of nuclei, or karyogamy, and subsequently somatic homologous recombination facilitated by the meiosis gene homologs, occur in the giardial cyst.

Cell cycle synchrony in Giardia intestinalis cultures achieved by using nocodazole and aphidicolin.

Giardia intestinalis is a ubiquitous intestinal protozoan parasite and has been proposed to represent the earliest diverging lineage of extant eukaryotes. Despite the importance of Giardia as a model organism, research on Giardia has been hampered by an inability to achieve cell cycle synchrony for in vitro cultures. This report details successful methods for attaining cell cycle synchrony in Giardia cultures. The research presented here demonstrates reversible cell cycle arrest in G(1)/S and G(2)/M with aphidicolin and nocodazole, respectively. Following synchronization, cells were able to recover completely from drug treatment and remained viable and maintained synchronous growth for 6 h. These techniques were used to synchronize Giardia cultures to increase the percentages of mitotic spindles in the cultures. This method of synchronization will enhance our ability to study cell cycle-dependent processes in G. intestinalis.