Robust new research published in the journal Nature Communications is demonstrating how a particular species of gut bacteria can directly improve long-term memory in bumblebees. The study found a bacterial metabolite can improve cognitive function in the bees, offering compelling insights into the relationship between the microbiome and the brain.
Bees, like humans, host complex populations of bacteria in their gut. And just like us these bacterial populations influence general health. Relatively speaking, however, a bee gut microbiome is significantly smaller and less complex than a human gut microbiome, making them a useful model to study how specific bacteria can influence health and behavior.
“The bee hindgut (ileum and rectum) has the highest abundance of bacteria and is dominated by five core bacterial species clades (phylotypes Snodgrassella alvi, Gilliamella apicola, Lactobacillus Firm-4, Lactobacillus Firm-5, and Bifidobacterium species),” the researchers explain in the new study. “Each bacterial species within this core group are thought to be symbiotic and possess distinct metabolic functions linked to mutualistic interactions with the host, as well as biofilm formation, and carbohydrate breakdown.”
The researchers first set out to measure individual memory performance in a number of bees. To do this, a memory test was developed where the bees were let loose in an enclosed environment containing 10 different colored artificial flowers. Five of the colors signaled flowers with a sweet solution and the other five colors were linked with a bitter solution.
The bees were trained to discriminate between the sweet and bitter flowers through five short foraging trips. They were then confined to their nest for three days before being let loose again, with their movements tracked to measure how well they remembered which flowers were sweet and which were undesirable.
The researchers then sampled the insects' gut microbiome to determine any correlation between certain species of gut bacteria and better memory performance. One species, known as Lactobacillus apis, quickly stood out. Those bees with more of this bacteria in their gut performed much better on the memory test.
To home in on whether this relationship between bacteria and memory was causal, the researchers fed groups of bees different bacteria. One group received Lactobacillus apis, and two other groups received common species of gut bacteria not linked with cognition. Those bees consuming the Lactobacillus apis supplements did display significant improvements in memory performance compared to the others.
“Our results suggest not only that the natural variation in the amount of a specific gut bacterium effects memory, but also show a causal link – that by adding the same bacterial species to a bee’s diet can enhance their memories,” explains lead author on the study, Li Li.
So how exactly could bacteria be influencing a bee’s memory?
The researchers discovered Lactobacillus apis plays a role in a metabolic pathway mediated by a group of molecules known as glycerophospholipids. The more of this particular bacteria in the bee hindgut, the more circulating glycerophospholipids were detected. And, when the researchers supplemented bees directly with a particular type of glycerophospholipid they detected the same level of memory improvement seen when bees were fed Lactobacillus apis.
In humans, glycerophospholipids are an important part of healthy neural membranes. Glycerophospholipid supplementation in humans has been proposed as a possible way to maintain cerebral structural integrity as a person ages.
“Glycerophospholipid supplementation has been found to improve cognitive function, reduce factors linked to cognitive decline, and benefit cerebral structure in humans, rats and mice,” the researchers note in the study. “Glycerophospholipid degradation can also produce second messengers such as diacylglycerol and arachidonic acid, which are important for synaptic plasticity and cognition.”
The researchers intriguingly hypothesize the evolutionary origins of this bacteria-mediated memory enhancement in bees. It is suggested that the bacteria could be increasing its own fitness by promoting the cognitive ability of its host.
“Bumblebee workers with better cognitive abilities should survive longer and bring back more food to the colony, thereby increasing the number of bacteria deposited in the nest and to nestmates,” the researchers speculate in the study. “As a result, the bacteria then have a greater chance of being taken up by the virgin queens in the later stages of the colony’s life, and increase their chances of being passed on to the next generation of bumblebees.”
The new study ultimately offers one of the most thorough descriptions of a gut-brain relationship enhancing memory in an organism published to date. Corresponding author on the study Wei Zhao also indicates the findings could be applicable to humans.
“It’s amazing to find out the specific memory-enhancing bacteria species,” says Zhao. “The results further validate our belief that we may improve our cognitive ability via the regulation of gut microbiota.”
The new study was published in the journal Nature Communications.
Source: Queen Mary University of London