Snodgrassella alvi lives in the gut of honey bees and other corbiculate (
pollen-basket) bees. Strains comparable in genome were found in all subsequently studied species of the genera
Apis (n=6) and
Bombus (n=8) and in 9 out of 13 studied species of
stingless bees (
Meliponini); it is not detected in other species and outside their hosts. It is a keystone species in the honeybee gut and dominates this microbiome together with seven other species, some of which have not yet been finally identified:
Lactobacillus spp. Firm-4,
Lactobacillus spp. Firm-5 (phylum Firmicutes),
Bifidobacterium spp. (phylum
Actinobacteria),
Gilliamella apicola,
Frischella perrara,
Bartonella apis, and Alpha 2.1 (phylum
Proteobacteria). Together, these species represent 95% of the intestinal bacteria.
Snodgrassella alvi,
Gilliamella apicola, and
Frischella perrara are considered species-specific keystone species.
Snodgrassella alvi and the gammaproteobacterium
Gilliamella apicola dominate the area of the
ileum and colonize the inner wall of the intestine there. Only a few bacteria exist in the anterior region of the intestine, while
Frischella perrara dominates the short region of the pylorus and is found almost exclusively there. In the rectum,
Lactobacillus strains and
Bifidobacterium are predominant. The transmission of the microbiome and especially of key species occurs in
social insects within the hive via the transmission of saliva and food. Bee
larvae and young
workers are almost devoid of gut bacteria in their first days of life and acquire their normal gut microbial flora orally only later through social interactions with other workers and by transmission between individuals within a hive during mutual food transfer (
trophallaxis) in their first days outside the
combs and at the beginning of their life in the colony. The protective effect of the natural bacterial composition has been demonstrated, among other things, against pathogens such as the protozoa
Crithidia bombi or
Nosema bombi, which infect various bumblebee species and lead to potentially fatal infections. However, excessive colonization of the bee gut by
Snodgrassella alvi is likely to disrupt the gut flora and increase susceptibility to infection by the
trypanosome Lotmaria passim.
Interaction with Gilliamella apicola Within the bee gut, the two dominant species
Gilliamella apicola and
Snodgrassella alvi occupy different areas of the gut and different metabolic niches. Together, they form a biofilm on the inner gut wall, where the colonies of
Snodgrassella alvi sit directly on the gut wall and the colonies of
Gilliamella apicola cover them.
Gilliamella apicola is a bacterium that breaks down sugars and produces
carboxylic acids (saccharolytic fermenter), while
Snodgrassella alvi oxidizes carboxylic acids. In the gut, they form a metabolic resource-sharing network in which each species benefits from the properties of the other.
Gilliamella apicola appropriately converts simple
carbohydrates (sugars) into energy through
glycolysis and passes the leftover molecules to
Snodgrassella alvi, which has and uses the genes necessary for the
Krebs cycle but cannot perform glycolysis. Both species also have numerous genes and proteins that enable intestinal colonization and interactions between bacterial cells. However, in a second study, they found that there was a shift in
genotypes in
Gilliamella apicola in favor of
antibiotic-resistant cells, resulting in a reduction in genetic diversity, while genetic diversity in
Snodgrassella alvi was not affected. However, resistance of some strains of
Snodgrassella alvi to glyphosate has also been described. The team modified the bacteria to produce labeled double-stranded RNA (
dsRNA) through an incorporated plasmid. The dsRNA module can be targeted to interfere with specific bee genes as well as key virus and mite genes. In the laboratory, gene expression of the selected region could be blocked for at least 15 days when the modified bacteria established in the bee gut and continuously expressed the dsRNA. As an effect, the survival of varroa mites on the bees was reduced as well as the transmission and infection with
deformed wing virus was inhibited. == Taxonomy ==