Virus isolation studies suggest short-term variations in abundance in natural cyanophage populations of the Indian Ocean

Abstract

and a.d.millard@warwick.ac.uk Cyanophage abundance has been shown to £uctuate over long timescales and with depth, but little is known about how it varies over short timescales. Previous short-term studies have relied on counting total virus numbers and therefore the phages which infect cyanobacteria cannot be distinguished from the total count.In this study, an isolation-based approach was used to determine cyanophage abundance from water samples collected over a depth pro¢le for a 24 h period from the Indian Ocean. Samples were used to infect Synechococcus sp. WH7803 and the number of plaque forming units (pfu) at each time point and depth were counted. At 10 m phage numbers were similar for most time-points, but there was a distinct peak in abundance at 0100 hours. Phage numbers were lower at 25 m and 50 m and did not show such strong temporal variation. No phages were found below this depth. Therefore, we conclude that only the abundance of phages in surface waters showed a clear temporal pattern over a short timescale. Fifty phages from a range of depths and time points were isolated and puri¢ed. The molecular diversity of these phages was estimated using a section of the phage-encoded psbD gene and the results from a phylogenetic analysis do not suggest that phages from the deeper waters form a distinct subgroup.

Ribonucleotide reductases reveal novel viral diversity and predict biological and ecological features of unknown marine viruses

“…2C). Diel patterns in cyanophage abundance have been observed previously (29). However, the dynamics of generalist and specialist phage populations over these cycles is unknown.…”

Bacteriophage predation regulates microbial abundance and diversity in a full-scale bioreactor treating industrial wastewater

“…Although these methods work well for comparing total bacteria and total phage numbers in a given environment, they provide no data regarding specific phage-host interactions. For that purpose, one must isolate and study specific phagehost systems, as was done in this study and in a small number of other studies covering shorter time periods (Hantula et al, 1991;Comeau et al, 2005;Clokie et al, 2006). As phage abundance depends on the concentration of its specific host, it is preferable to isolate strains that are sufficiently dominant in the studied environment.…”

The diversity of cyanomyovirus populations along a North–South Atlantic Ocean transect

“…Therefore, a range of potentially influential factors could be investigated that might influence myoviral community structure and diversity. Cyanophages are subject to many external influences in the oceans, all of which may have an impact on their diversity: for example, host resistance/susceptibility (Waterbury and Valois, 1993), host abundance (Suttle and Chan, 1994), host starvation (Middelboe, 2000), ultraviolet degradation (Noble and Fuhrman, 1997), mixing (Murray and Jackson, 1993) and diurnal cycles (Clokie et al, 2006). However, this study that utilised a single 'snapshot' sampling approach that is characteristic of oceanic research cruises, revealed no significant correlations between cyanomyoviruses and any other measured parameter or combination of parameters.…”

“…Crucially, our study assessed host and viral diversity simultaneously-samples that were discrete in both time and space. A further factor that may help to explain the lack of correlation is that in surface waters, viral turnover rates are variable, in the order of hours (Bettarel et al, 2002;Clokie et al, 2006) to a few days (Parada et al, 2008). For these reasons, it may be unreasonable to expect that a single snapshot will reveal infection dynamics.…”