A review of: De Corte, D. et al (2010) Links between viral and prokaryotic communities throughout the water column in the (sub)tropical Atlantic Ocean, The ISME Journal, 4, 1431-1442.
Marine viruses have a number of important roles within ocean processes; this paper investigates the effects of viruses on the abundance, production and diversity of prokaryotes, with a particular focus on changes in the relation between these two micro-organisms throughout the water column.
The (sub)tropical Atlantic Ocean was the chosen study site. Samples were taken from 37 stations from the epi- to the abyssopelagic layer (from depths of approximately 100 to 7000 m). Flow cytometry was used to determine prokaryotic and viral abundance, and viral, archaeal and bacterial community composition were analysed using randomly amplified polymorphic DNA-PCR (RAPD-PCR), terminal restriction fragment length polymorphism (T-RFLP) and automated ribosomal intergenic spacer analysis (ARISA), respectively. Heterotrophic prokaryotic activity and viral production were also measured.
Results showed that viral abundance was significantly related to both prokaryotic abundance and heterotrophic activity; all decreased with depth with prokaryotic abundance decreasing exponentially. The virus-to-prokaryote abundance ratio saw a linear increase with depth. The authors inferred that the viral abundance decreases at a lesser extent than prokaryotic abundance because viruses take longer to decay in deeper waters than in near-surface waters.
Two types of viral production were analysed; lytic viral production decreased linearly with depth whereas lysogenic viral production showed no clear trend. It is suggested that a shift from a lytic life cycle to a lysogenic life cycle could occur as a result of a decrease in host abundance, although the authors point out that the lack of a pattern in lysogenic viral production indicates inconsistent virus-prokaryote interactions in deep waters.
A total of 24 operational taxonomic units (OTUs) were determined in the viral community, with a cluster found in the bathy- abyssopelagic layer. Within the bacterial community a total of 142 OTUs were found with clusters at the epi- mesopelagic and bathy- abyssopelagic layers. Ten OTUs on the 16s rDNA level were found within the archaeal community, with clusters at the meso- upper bathypelagic and bathy-abyssopelagic layer.
Covariance was seen between the number of OTUs of archaea and viruses. Both initially decreased with depth, remaining constant from the mesopelagic to a depth of 3000 - 4000m, before decreasing again. In contrast the number of bacterial OTUs increased twofold between depths of 3000 – 5200m. This could be because different methods were used to identify the numbers of OTUs, but the authors suggest it is more likely that viruses at these depths have a wider host range than viruses nearer the surface.
Previous studies on interactions between viruses and prokaryotes have mainly taken place in surface waters. This paper, although not very extensive, details many results and observations. The general conclusion reached is that the deep Atlantic is more heterogeneous than previously thought. The strong link between viral abundance and heterotrophic activity observed within both surface and deeper waters suggests that dynamic systems are found throughout the water column, from the lower epi- to the abyssopelagic layer.
1 comment:
Hi Helen
I know the authors found no trend in lysogenic viral production and depth but I can see that a switch to this viral cycle in responce to low cell numbers would be best for survival. I guess there is no sense in continuing to multiply if your going to use up the last few cells. Best to lie dormant until cells are more plentiful.
Post a Comment