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CHEMICAL COMMUNICATION
Using chemical signals, bacteria guide certain algae, which are seeking a spot in which to grow, to a favorable location. The green seaweed Enteromorpha reproduces by releasing zoospores that swim away from the parent plant in search of a surface to attach to and form a new mature plant. The zoospores attach to surfaces colonized by biofilm-forming bacteria--but only if those bacteria secrete one of three homoserine lactones: N-hexanoylhomoserine lactone, N-(3-hydroxyhexanoyl)homoserine lactone, or N-(3-oxodecanoyl)homoserine lactone. Absent these lactones, zoospore attachment is greatly reduced.
According to Joint, before settling in a location, Enteromorpha zoospores first test the surface--a rock or a ship's hull. If it is not optimal, they try somewhere else. "Once a zoospore makes the final attachment, it is irreversible. The adhesive it releases is extremely strong. It is in the seaweed's interest to make sure it attaches to the best possible surface," he explains. Through the lactones, bacteria signal a prime location. It is not known what the bacteria get in return for this service. However, the response of zoospores to the compounds is also tied to the existence of concentration gradients--the closer the favorable location, the higher the lactone concentration. Dumping lactones into seawater covering the biofilms of lactone-producing bacteria removes that natural gradient, discouraging zoospore attachment, the researchers find. Disrupting the chemical signaling could be a means to control Enteromorpha colonies, they suggest. |
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