Dolphins are able to successfully coordinate their behavior using audio signals. Therefore, the current study tested whether or not belugas can use sound to exchange information in a cooperative task and verified the mechanisms of the transmission of information during trials. The subjects are two male belugas, Nack and Duke. Nack was trained to rotate its body when the experimenter turns a hand in a circular motion (rotation cue) or to take a vertical position on the spot of the pool when the experimenter turned on a light toward the subject (headstand cue). Duke was required to do the same behavior as Nack but was blindfolded. During the test trials, the experimenter presented both cues toward Nack in random order. The result indicated that Nack responded correctly to both cues, and Duke behaved similarly to Nack. Moreover, Nack emitted different sounds in response to the cues, which indicates that Nack spontaneously transmitted information to Duke by emitting sounds, which led Duke to provide correct responses. Although Duke displayed the same behaviors as Nack did despite the lack of training to do so, Duke’s performance was due to learning by hearing sounds instead of training.

BACKGROUND: Production of biofuels from microalgae has been recognized to be a promising route for a sustainable energy supply. However, the microalgae harvesting process is a bottleneck for industrialization because it is energy intensive. Thus, by displaying interactive protein factors on the cell wall, oleaginous microalgae can acquire the auto- and controllable-flocculation function, yielding smarter and energy-efficient harvesting. RESULTS: Towards this goal, we established a cell-surface display system using the oleaginous diatom Fistulifera solaris JPCC DA0580. Putative cell wall proteins, termed frustulins, were identified from the genome information using a homology search. A selected frustulin was subsequently fused with green fluorescent protein (GFP) and a diatom cell-surface display was successfully demonstrated. The antibody-binding assay further confirmed that the displayed GFP could interact with the antibody at the outermost surface of the cells. Moreover, a cell harvesting experiment was carried out using silica-affinity peptide-displaying diatom cells and silica particles where engineered cells attached to the silica particles resulting in immediate sedimentation. CONCLUSION: This is the first report to demonstrate the engineered peptide-mediated harvesting of oleaginous microalgae using a cell-surface display system. Flocculation efficiency based on the silica-affinity peptide-mediated cell harvesting method demonstrated a comparable performance to other flocculation strategies which use either harsh pH conditions or expensive chemical/biological flocculation agents. We propose that our peptide-mediated cell harvest method will be useful for the efficient biofuel production in the future.