Significance of lysogeny for the metabolism of Desulfovibrio spp. strains isolated from aquatic environments of Georgia.

AIMS: Sulphate-reducing bacteria (SRB) are ecologically important group of anaerobic micro-organisms that can reduce sulphate to form hydrogen sulphide-a toxic gas causing iron corrosion on metal surfaces. In this work, SRB strains were isolated from aquatic environments in the country of Georgia to determine their lysogenicity and the role of temperate phages in host metabolism. METHODS AND RESULTS: SRB strains were isolated in samples from the Black Sea coast of Georgia. Based on their genetic, cytological and physiological properties of bacteria, 10 Georgian isolates were assigned to the genus Desulfovibrio. Temperate bacteriophages were induced from three out of ten strains by UV-exposure. Comparison of metal (Fe and Cr) reduction and utilization of various carbon sources by the wild-type (lysogenic) bacterial strains and their UV-irradiated counterparts was done. CONCLUSIONS: Temperate phage in the cells of SRB could alter significant functions of bacteria and may have a contribution in the acquisition of different traits by SRB. SIGNIFICANCE AND IMPACT OF THE STUDY: This article pointed to a significant role for temperate bacteriophages in the metabolism and metabolic potential of host strains of SRB, which were first isolated from the aquatic environment of Georgia.

Desulfovibrio alaskensis prophages and their possible involvement in the horizontal transfer of genes by outer membrane vesicles.

Desulfovibrio alaskensis is a Gram-negative bacterial species that belongs to the group of Sulphate Reducing Bacteria (SRB) and presents prophages in genomes, a common characteristic of the genus Desulfovibrio. Genetic material can be transported by outer membrane vesicles, however, no data regarding the production of these vesicles has been reported for D. alaskensis. To verify the expression of D. alaskensis prophages and their involvement with outer membrane vesicles, the DSM16109 strain was used. The DSM16109 strain had three prophages and presented reduced growth after mitomycin C addition when compared to the control culture. This reduction was accompanied by the presence of virus-like particles (VLPs), indicating mitomycin C dependent prophage induction. The increase in the number of cap gene copies and transcriptions of the three prophages was verified in the control sample, however, without the formation of VLPs. Prophage genes were identified in outer membrane vesicles from cultures treated and not treated with mitomycin C. DSM16109 prophages are expressed spontaneously but only in the presence of mitomycin C was it possible to observe VLP formation. Due to the genetic material detection from the prophages within outer membrane vesicles, this property may be related to the horizontal transfer of viral genes.

Screening and characterization of prophages in Desulfovibrio genomes.

Bacteria of the genus Desulfovibrio belong to the group of Sulphate Reducing Bacteria (SRB). SRB generate significant liabilities in the petroleum industry, mainly due to their ability to microbiologically induce corrosion, biofilm formation and H2S production. Bacteriophages are an alternative control method for SRB, whose information for this group of bacteria however, is scarce. The present study developed a workflow for the identification of complete prophages in Desulfovibrio. Poly-lysogenesis was shown to be common in Desulfovibrio. In the 47 genomes analyzed 53 complete prophages were identified. These were classified within the order Caudovirales, with 69.82% belonging to the Myoviridade family. More than half the prophages identified have genes coding for lysozyme or holin. Four of the analyzed bacterial genomes present prophages with identity above 50% in the same strain, whose comparative analysis demonstrated the existence of colinearity between the sequences. Of the 17 closed bacterial genomes analyzed, 6 have the CRISPR-Cas system classified as inactive. The identification of bacterial poly-lysogeny, the proximity between the complete prophages and the possible inactivity of the CRISPR-Cas in closed bacterial genomes analyzed allowed the choice of poly-lysogenic strains with prophages belonging to the Myoviridae family for the isolation of prophages and testing of related strains for subsequent studies.

Bacteriophage lytic to Desulfovibrio aespoeensis isolated from deep groundwater.

Viruses were earlier found to be 10-fold more abundant than prokaryotes in deep granitic groundwater at the Aspö Hard Rock Laboratory (HRL). Using a most probable number (MPN) method, 8-30 000 cells of sulphate-reducing bacteria per ml were found in groundwater from seven boreholes at the Aspö HRL. The content of lytic phages infecting the indigenous bacterium Desulfovibrio aespoeensis in Aspö groundwater was analysed using the MPN technique for phages. In four of 10 boreholes, 0.2-80 phages per ml were found at depths of 342-450 m. Isolates of lytic phages were made from five cultures. Using transmission electron microscopy, these were characterized and found to be in the Podoviridae morphology group. The isolated phages were further analysed regarding host range and were found not to infect five other species of Desulfovibrio or 10 Desulfovibrio isolates with up to 99.9% 16S rRNA gene sequence identity to D. aespoeensis. To further analyse phage-host interactions, using a direct count method, growth of the phages and their host was followed in batch cultures, and the viral burst size was calculated to be approximately 170 phages per lytic event, after a latent period of approximately 70 h. When surviving cells from infected D. aespoeensis batch cultures were inoculated into new cultures and reinfected, immunity to the phages was found. The parasite-prey system found implies that viruses are important for microbial ecosystem diversity and activity, and for microbial numbers in deep subsurface groundwater.

Prophage-like gene transfer agents-novel mechanisms of gene exchange for Methanococcus, Desulfovibrio, Brachyspira, and Rhodobacter species.

Gene transfer agents (GTAs) are novel mechanisms for bacterial gene transfer. They resemble small, tailed bacteriophages in ultrastructure and act like generalized transducing prophages. In contrast to functional prophages, GTAs package random fragments of bacterial genomes and incomplete copies of their own genomes. The packaged DNA content is characteristic of the GTA and ranges in size from 4.4 to 13.6kb. GTAs have been reported in species of Brachyspira, Methanococcus, Desulfovibrio, and Rhodobacter. The best studied GTAs are VSH-1 of the anaerobic, pathogenic spirochete Brachyspira hyodysenteriae and RcGTA of the nonsulfur, purple, photosynthetic bacterium Rhodobacter capsulatus. VSH-1 and RcGTA have likely contributed to the ecology and evolution of these bacteria. The existence of GTAs in phylogenetically diverse bacteria suggests GTAs may be more common in nature than is now appreciated.