Influence of Infected Cell Growth State on Bacteriophage Reactivation Levels

Abstract

Reactivation of UV-C-inactivated Pseudomonas aeruginosa bacteriophages D3C3, F116, G101, and UNL-1 was quantified in host cells infected during the exponential phase, during the stationary phase, and after starvation (1 day, 1 and 5 weeks) under conditions designed to detect dark repair and photoreactivation. Our experiments revealed that while the photoreactivation capacity of stationary-phase or starved cells remained about the same as that of exponential-phase cells, in some cases their capacity to support dark repair of UV-inactivated bacteriophages increased over 10-fold. This enhanced reactivation capacity was correlated with the ca. 30-fold-greater UV-C resistance of P. aeruginosa host cells that were in the stationary phase or exposed to starvation conditions prior to irradiation. The dark repair capacity of P. aeruginosa cells that were infected while they were starved for prolonged periods depended on the bacteriophage examined. For bacteriophage D3C3 this dark repair capacity declined with prolonged starvation, while for bacteriophage G101 the dark repair capacity continued to increase when cells were starved for 24 h or 1 week prior to infection. For G101, the reactivation potentials were 16-, 18-, 10-, and 3-fold at starvation intervals of 1 day, 1 week, 5 weeks, and 1.5 years, respectively. Exclusive use of exponential-phase cells to quantify bacteriophage reactivation should detect only a fraction of the true phage reactivation potential.Numerous studies have demonstrated that significant numbers of viruses exist throughout the biosphere (3, 23, 29). For instance, bacteriophages are estimated to account for ca. 1% of the dissolved organic carbon in the open ocean (3). This relative abundance raises the question whether these bacteriophages merely persist or are functional and infective or whether, as found for the cyanophages (15), both possibilities are correct. We are interested in suitable methods for studying phage dynamics in aquatic ecosystems, i.e., suitable methods for monitoring the numbers and types of phages present over time. In this regard, there should be a dynamic equilibrium between the production of new phages following infection and the disappearance of phages, usually from one of three primary causes (21, 28): (i) consumption by grazing protozoans; (ii) attachment to labile colloids; and (iii) inactivation by UV radiation. Accurate estimates of the infective phage potential of a given sample or environment must take into consideration both the extent of the solar UV damage to the phage population and the availability of suitable bacterial hosts which could repair the damaged phage DNA.Previously, we addressed the question of phage reproductive potential in changing ecosystems by looking at the prevalence of broad-host-range bacteriophages able to infect multiple bacterial species, including Sphaerotilus natans, Escherichia coli, and Pseudomonas aeruginosa (11). It is probable that any UVdamaged broad-host-range bacteriophages are capable of undergoing reactivation in several dif...

Degree of ultraviolet radiation damage and repair capabilities are related to G+C content in marine vibriophages

“…2). It might also explain the apparent lack of dark repair in the Weinbauer et al (1997) and Wilhelm et al (1998b) (Palit et al 1983), Pseudomonas aeruginosa (Kadavy et al 2000). We also detected different levels of repair in different viruses (vp6, vp1, vp11, and vp12) that infect the same host (Fig.…”

“…Based on the argument that some lethal solar damage other than dimers (UVA-induced lesions) is less effectively dark repaired than 254 nm UV damage (Harm 1980) and some wavelengths of UVA inhibit excision repair (Turner & Eisenstark 1984), our methods could overestimate the amount of excision possible. Conversely, Kadavy et al (2000) have found that starved or stationary-phase hosts (modeling bacteria in the environment) have increased dark repair, perhaps due to stress response. Their data suggest that experiments done with exponential-phase cells (like this study) would underestimate the amount of excision repair possible.…”

Virus-infected bacteria in oligotrophic open waters of the East Sea, Korea

“…Our observation of FVIB in oligotrophic seawaters is, perhaps, not surprising because even starved bacteria are known to be infected by bacteriophages and subject to lysis (Schrader et al 1997, Kadavy et al 2000. This raises the question as to why viral infection rates are so low in the Mediterranean.…”

“…The presence of different FVIB in the 2 environments might also be due to the presence of different virus-host systems. For instance, it has been shown that UVdamaged bacteriophages can be reactivated by repair mechanisms of host cells (Weinbauer et al 1997, Kadavy et al 2000, but this process varies among host-virus systems (Schrader et al 1997, Kadavy et al 2000. Further, different microbial communities could vary in their relative repair capabilities and thus influence the propagation of viruses.…”

Quantifying Substrate Uptake by Individual Cells of Marine Bacterioplankton by Catalyzed Reporter Deposition Fluorescence In Situ Hybridization Combined with Microautoradiography

“…The range of activity levels within a given bacterial population might be wide or might be narrow, with similar levels of activity in all the active cells. As the activity level likely influences a number of key ecological features, such as viral infection (13,14) and flagellate grazing (9), this kind of information about specific bacterioplankton populations is essential for a more in-depth understanding of the ecology of specific phylotypes. Thus, to obtain metabolic rate estimates on a single-cell level, we quantified the halo area obtained by MICRO-CARD-FISH using image analysis.…”