Award: OCE-1948758

Predators are an important factor in Nature’s food chain that supports life on Earth. Generally, peoples thought of predators brings to mind those in the Animal Kingdom such as lions, tigers, wolves, hawks, and sharks among many others. Frequently overlooked is the invisible world of microbes not seen with the naked eye that include bacteria, protists and viruses. Within this world are also predators that play an important role in the cycling of nutrients within the food chain. Some of these predators can be as vicious as tigers or sharks.  Among the microbial predators, the most studied are those within the protists and virus groups. The predatory bacteria are also known to prey on other bacteria, however, very little is known about their overall role in predation in the environment as compared to that of virus or protist predators. This research project was undertaken to learn more about these organisms and uncover the mysteries of their function in the food web, specifically in the marine environment. When organisms die in the oceans and other saltwater environments, as their bodies deteriorate chemicals and nutrients stored with their bodies are released into the surrounding environment. Among those released is dissolved organic matter (DOM).  Much of the DOM would sink to the bottom of the marine water body and be lost to the aquatic food web were it not for bacteria that are the most efficient consumers of DOM. The capture and consumption of the DOM by bacteria preserve this important nutrient material within the food chain. The fate of these bacteria is like that of all organisms. They too will die and their cellular bodies and the DOM within may sink to the bottom and be lost to classical food web.  However, not all bacteria will suffer this fate. Many will fall to victims of predators and be killed by them. Predation by the predators results in a disintegration of the bacteria outer protective wall, known as lysis, that results in the release of internal cellular components including DOM and other nutrients into the environment.  These nutrients will be captured almost immediately by the bacteria in the surrounding environment. Some of these bacteria will be consumed by some protists that will be fed upon by higher forms and ultimately to larger fishes and to the top of the food chain. Beginning with the bacteria capture and consumption of DOM in marine waters, their lysis by predators and the release of their cellular products, including DOM, into the environment that is immediately consumed by the millions of bacteria in the waters is known as the microbial loop because the cycling of DOM and other nutrients is driven by the actions of microbes, bacteria and the predators of bacteria, including viruses and protist.  The microbial loop is a part of the classical food chain. As mentioned previously, the Halobacteriovorax (HBx)species are bacteria that prey upon certain other bacteria and likely play a role in the microbial loop with the viruses and protists. However, very little is known about them. To learn more about them and their role in the microbial loop, we investigated their activities and that of viruses and protists in response to a common prey bacterium, Vibrio parahaemolyticus. We collected coastal water samples from the Apalachicola Bay in northwest Florida.  All predators, viruses, protists and HBx, are natives to marine waters. The waters samples were transported to the laboratory. The samples were equally divided into several flasks and into each was added an equal volume of a suspension of the prey that produced a turbid suspension for the total volumes in the flask. In a time-series study, the predation of each predator on the prey was recorded by measuring the reduction in the optical density (turbidity) at 3-h intervals over a period of five days.  Also, measured by various means was the growth of each of the predators. The results showed which of the predators responded most rapidly to the addition of the prey. The growth of the predators and the predation on the prey allowed the investigators to make this determination. The results showed that the HBx predatory bacterium was competitive with the protists and viruses in predation on the prey. In conclusion, the HBx was found to play an active role in the microbial loop, and for a full understanding of the microbial loop and its contribution to the food chain the activities of the HBx must be considered.  

Last Modified: 02/28/2026
Modified by: Henry Neal Williams