Fig. 4 Proposed pathway between int

Fig. 4 Proposed pathway between intestinal glycerophospholipid production and memory enhancement. Based on our metagenomic and metabolomicanalyses, we suggest that increased levels of L. apis (and other Firm-5 species which similarly contain many genes for the PTS sugar transport pathway) willcause increased sugar metabolism, which will lead to the production of more glycerophospholipids. These glycerophospholipids are then transported intothe hindgut and are rapidly secreted into the haemolymph (perhaps helped by an increase in mGlu2 receptors). They are transported to the brain via thebee’s open circulatory system, with attached metabolites, leading to improved structure and function of neural and synaptic membranes, therebypromoting better memory. Purple shapes: genes that positively correlated with long-term memory; rectangles: genes found in all three analyses (analysesbased on genes mapped to the whole gut microbiota, Firm-5 and L. apis); Ovals: genes found in whole gut microbiota and Firm-5 analyses; Roundedrectangles: remaining memory-correlated genes; Grey shapes: genes which did not correlate with long-term memory; Blue arrows: sugar metabolism; Redarrows: glycerophospholipid metabolism; Purple arrows: the increase or decrease of metabolites after L. apis supplementation.