Fig. 4. Proposed pathway between intestinal glycerophospholipid production and memory enhancement.

Based on our metagenomic and metabolomic analyses, we suggest that increased levels of L. apis (and other Firm-5 species which similarly contain many genes for the PTS sugar transport pathway) will cause increased sugar metabolism, which will lead to the production of more glycerophospholipids. These glycerophospholipids are then transported into the hindgut and are rapidly secreted into the haemolymph (perhaps helped by an increase in mGlu2 receptors). They are transported to the brain via the bee’s open circulatory system, with attached metabolites, leading to improved structure and function of neural and synaptic membranes, thereby promoting better memory. Purple shapes: genes that positively correlated with long-term memory; rectangles: genes found in all three analyses (analyses based on genes mapped to the whole gut microbiota, Firm-5 and L. apis); Ovals: genes found in whole gut microbiota and Firm-5 analyses; Rounded rectangles: remaining memory-correlated genes; Grey shapes: genes which did not correlate with long-term memory; Blue arrows: sugar metabolism; Red arrows: glycerophospholipid metabolism; Purple arrows: the increase or decrease of metabolites after L. apis supplementation.