Characterization of a new virulent phage ϕMC1 specific to Microbulbifer strain CMC-5.

Microbulbifer strain CMC-5, isolated from decomposing seaweeds degrades agar, alginate, carrageenan, chitin, carboxymethyl cellulose and xylan. Using bacterial strain CMC-5 as host, a novel virulent phage, designated ϕMC1 was isolated from the coast of Goa, India. Although ϕMC1 demonstrated cross infectivity with type species of Microbulbifer such as M. agarolyticus JAMBA3T and M. celer KCTC 12973T, it did not infect M. mangrovi KCTC 23483T, M. salipalidus JCM 11542T, M. elongatus DSM 6810T and M. hydrolyticus IRE-31T. The one step growth experiment of ϕMC1 infecting bacterial strain CMC-5 at a multiplicity of infection of 0.1, revealed a latent period of 60 min and a burst size of 180. TEM analysis of ϕMC1 indicated it to be a tailless phage with an icosahedral head having a diameter of 60 ± 1.42 nm. The ds DNA of ϕMC1 was restricted by EcoRI, HindIII and SmaI whereas HaeIII, BamHI, PstI, NotI did not cleave the DNA. The molecular size of ϕMC1 DNA was analyzed by restriction digestion as well as pulsed field gel electrophoresis and was estimated at 48.5 kb. The phage infectivity was adversely affected by organic solvents demonstrating the presence of a lipid membrane. The inhibition of ϕMC1 infectivity by EDTA was abolished by addition of Ca and Mg salts.

Genomic analysis of cold-active Colwelliaphage 9A and psychrophilic phage-host interactions.

The 104 kb genome of cold-active bacteriophage 9A, which replicates in the marine psychrophilic gamma-proteobacterium Colwellia psychrerythraea strain 34H (between -12 and 8 °C), was sequenced and analyzed to investigate elements of molecular adaptation to low temperature and phage-host interactions in the cold. Most characterized ORFs indicated closest similarity to gamma-proteobacteria and their phages, though no single module provided definitive phylogenetic grouping. A subset of primary structural features linked to psychrophily suggested that the majority of annotated phage proteins were not psychrophilic; those that were, primarily serve phage-specific functions and may also contribute to 9A's restricted temperature range for replication as compared to host. Comparative analyses suggest ribonucleotide reductase genes were acquired laterally from host. Neither restriction modification nor the CRISPR-Cas system appeared to be the predominant phage defense mechanism of Cp34H or other cold-adapted bacteria; we hypothesize that psychrophilic hosts rely more on the use of extracellular polymeric material to block cell surface receptors recognized by phages. The relative dearth of evidence for genome-specific defenses, genetic transfer events or auxiliary metabolic genes suggest that the 9A-Cp34H system may be less tightly coupled than are other genomically characterized marine phage-host systems, with possible implications for phage specificity under different environmental conditions.

Isolation and characterization of marine psychrophilic phage-host systems from Arctic sea ice.

Phage-host systems from extreme cold environments have rarely been surveyed. This study is concerned with the isolation and characterization of three different phage-host systems from Arctic sea ice and melt pond samples collected north-west of Svalbard (Arctic). On the basis of 16S rDNA sequences, the three bacterial phage hosts exhibited the greatest similarity to the species Shewanella frigidimarina (96.0%), Flavobacterium hibernum (94.0%), and Colwellia psychrerythraea (98.4%), respectively. The host bacteria are psychrophilic with good growth at 0 degrees C, resulting in a rapid formation of visible colonies at this temperature. The phages showed an even more pronounced adaptation to cold temperatures than the bacteria, with growth maxima below 14 degrees C and good plaque formation at 0 degrees C. Transmission electron microscopy (TEM) examinations revealed that the bacteriophages belonged to the tailed, double-stranded DNA phage families Siphoviridae and Myoviridae. All three phages were host-specific.