Relapsing-fever spirochetes achieve high cell densities (>10(8)/ml) in their host's blood, while
Lyme disease spirochetes do not (<10(5)/ml). This striking contrast in pathogenicity of these two groups of bacteria suggests a fundamental difference in their ability to either exploit or survive in blood. Borrelia hermsii, a
tick-borne relapsing-fever spirochete, contains orthologs to glpQ and glpT, genes that encode
glycerophosphodiester phosphodiesterase (GlpQ) and glycerol-3-phosphate transporter (GlpT), respectively. In other bacteria, GlpQ hydrolyzes deacylated
phospholipids to glycerol-3-phosphate (G3P) while GlpT transports G3P into the cytoplasm.
Enzyme assays on 17 isolates of borreliae demonstrated GlpQ activity in
relapsing-fever spirochetes but not in
Lyme disease spirochetes. Southern blots demonstrated glpQ and glpT in all
relapsing-fever spirochetes but not in the
Lyme disease group. A Lyme disease spirochete, Borrelia burgdorferi, that was transformed with a shuttle vector containing glpTQ from B. hermsii produced active
enzyme, which demonstrated the association of glpQ with the hydrolysis of
phospholipids. Sequence analysis of B. hermsii identified glpF, glpK, and glpA, which encode the
glycerol facilitator,
glycerol kinase, and
glycerol-3-phosphate dehydrogenase, respectively, all of which are present in B. burgdorferi. All spirochetes examined had
gpsA, which encodes the
enzyme that reduces
dihydroxyacetone phosphate (DHAP) to G3P. Consequently, three pathways for the acquisition of G3P exist among borreliae: (i) hydrolysis of deacylated
phospholipids, (ii) reduction of DHAP, and (iii) uptake and phosphorylation of
glycerol. The unique ability of
relapsing-fever spirochetes to hydrolyze
phospholipids may contribute to their higher cell densities in blood than those of
Lyme disease spirochetes.