Bacteriovorax VS Vibrio: Predator-prey interactions at the microscopic scale

The importance of predator-prey interactions is well established for most macroscopic organisms; however, only a few studies have looked at the influence that bacterial prey has on the community structure of its predator. The most studied bacterial obligate predators are the Bdellovibrio and like organisms (BALOs), which include several bacterial genera. BALOs prey on many gram negative bacteria, serving as both a food source and a growth and multiplication chamber. 

This study focused on the predator Bacteriovorax, a group of BALOs ubiquitous in the salt-water environment. In fact, Chen et al. wanted to investigate how the community structure of Bacteriovorax varies in response to two different preys, Vibrio vulnificus and Vibrio parahaemolyticus. Laboratory microcosms, containing water samples from different locations and a suspension of either V. vulnificus or V. parahaemolyticus, were used to monitor the prey abundance and the Bacteriovorax composition. However, since Bacteriovorax require the presence of their prey to be able to grow and to be cultured, techniques involving pure cultures cannot be used. Instead, the comparative analysis of 16 rRNA sequences has been found useful in the identification and detection of specific Bacteriovorax phylogenetic clusters or operational taxonomic units (OTUs). 

In each case the addition of prey resulted in a thousand fold increase of Bacteriovorax. However, the predator composition varied significantly depending on the prey present in the sample: the predominant Bacteriovorax OTU’s in the V. vulnificus sample were Cluster IX and X, whereas no single OTU dominated in the V. parahaemolyticus sample, where a high diversity of OTUs was observed. These results were narrowed down in a further experiment, where prey abundance (V. vulnificus or V. parahaemolyticus) was monitored in presence of either Cluster IX or Cluster IV Bacteriovorax. Chen et al. showed that Cluster IX preyed on both species, whereas predation of Cluster IV was found significantly higher for V. parahaemolyticus than for V. vulnificus. It was deduced that Cluster IX has the properties of a specialist as exclusive efficient predator on V. vulnificus as well as acting as generalist for having similar feeding efficiency on other prey such as V. parahaemolyticus, which overall makes Cluster IX qualify as versatilist. 

Chen et al. have showed successfully that predator-prey interactions and the resulting selective pressures shape community structure and diversity even at a microbial scale. Furthermore, they propose that more studies should aim to characterise the predatory patterns (specialist, generalist, versatilist) of bacterial predator for “a greater comprehension and appreciation for the diversity of predation among all organisms”.  However, although I appreciate that this study is one of the first in this field, I question the applicability of their findings in the natural environment, where the presence of numerous different prey species, physical parameters such as temperature and light availability, and predation on BALOs themselves will most certainly limit the predictability of ecosystem changes considerably. Therefor further research, notably with a wider range of prey species, is necessary to get a more general picture of the predatory patterns in Bacteriovorax.

Chen, H., Athar, R., Zheng, G., Williams, H.N., 2011. Prey bacteria shape the community structure of their predators. The ISME journal, 5(8), pp.1314–1322.
Available at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3146273/pdf/ismej20114a.pdf