Microbes live everywhere, even in the open ocean. They have to compete for survival just like other organisms, but even tiny single-celled bacteria can work together when they must. Biofilms can form tough microbial communities, for example. It also seems that even marine bacteria can clump together when food is scarce. If marine microorganisms are in environments with low levels of nutrients like phosphorous, nitrogen, or iron, they can stick together, even using appendages as tiny as little cilia, which are like miniature antennas on cells, to collect more.
New research reported in the Proceedings of the National Academy of Sciences has found that the beating cilia on clumped marine microbes can generate tiny currents that attract ten times as many nutrients as they would alone. Even if the ocean is extremely turbulent, microbes can stick together and split the important labor, said senior study author John H. Costello of Providence College and the Marine Biological Laboratory, Woods Hole.
"For all conditions but the most radically extreme mixing, these microbial cells live in fluid spaces that are smaller than the eddies caused by ocean mixing," Costello said. "In their world, the surrounding fluid is always viscous and they do not experience turbulent eddies as humans feel them."
In this study, a tool known as Particle Image Velocimetry was used to assess the strength and direction of fluid as it flowed around a marine diatom called Coscinodiscus wailesii both when it was attached to a partner with cilia (Pseudovorticella coscinodisci), and when it was unattached. With the ciliated partner beating, the nutrient flow to the surface of the diatom was four to ten times greater compared to when the diatom was unattached.
Microbes might also move to deeper parts of the marine environment when there are insufficient nutrients. As the microbial cells sink, they're exposed to higher concentrations of nutrients.
"Sinking might work well in low-nutrient conditions where mixing will recirculate the cells back up from the depths to the sunlit layers," noted Costello. "That way, the risk to the diatom of sinking might be countered by the probability of being returned to high-light environments. But in low-mixing conditions, forming consortia with ciliates could be a more favorable solution to low nutrient availability."
Diatoms are can conduct photosynthesis and take carbon dioxide out of the atmosphere. This research helps provides some insight into changes in the ocean and its microbes, which may become increasingly important to climate change.