Zebrafish develop rapidly and prolifically, making them a great model species for studying host-microbe interactions. They have transparent vertebrate and remain germ-free until they hatch. (I can’t help wondering if lionfish hunt zebrafish, but I doubt it.) Karen Guillemin from the University of Oregon brings us two stories of microbial-secreted proteins influencing host biology in zebrafish.
The first story was of pancreas development in zebrafish. A protein (BefA) produced by bacterial strains in zebrafish promote pancreas development, including bacterial strains that have homologues in the human microbiome. Further analysis found this to be a new and unique protein. The second story was of intestinal inflammation. Different resident bacteria can have different effects on the inflammation in the intestine, and one, Aeromonas, secretes an uncharacterized protein (AimA) that reduces intestinal neutrophils. Doing so increases Aeromonas survival in the gut. However, double mutations of this protein led to fish deaths, showing that a lack of AimA in the system was important for fish survival. Intestinal neutrophils respond to resident bacteria, but it has been difficult to separate the benefit to the microbe from the benefit to the host – absence of the AimA protein is detrimental to both.
An important question regarding these discoveries is whether microbial secreted proteins are serving as cues or as signals. Guillemin believes that BefA, promoting pancreas development, serves as a cue, while AimA, which affects inflammation, serves as a signal. Understanding the role of these proteins both to the host and to the microbe will be an important consideration for future research.