Table 1. Divergence in the relevance of the three main trehalose biosynthetic pathways in the viability and pathogenicity of prokaryotes.

	PATHWAY
ORGANISM	OtsAB/TPS-TPP	TreY/Z	TreS
M. tuberculosis [3]	Dominant OtsB2: essential OtsB1: pseudogene Deletion of OtsA leads to reduced virulence in mice	No role in cell viability in vitro and in vivo	Role in prolonged infection
M. bovis [3]	OtsB2 and OtsA are essential enzymes
M. smegmatis [13]	Redundancy between the three pathways: single deletions have no apparent phenotypes, while triple deletions result in growth inhibition at high temperatures
M. leprae [34]	Unique intact pathway	pseudogene	pseudogene
Corynebacterium glutamicum [14], [15]	Contributes to glycolipids synthesis together with the TreYZ pathway	Dominant pathway in osmotic conditions	Contributes to trehalose degradation
E. coli [35]	Sole pathway	none	none
Salmonella enterica [36]	Sole pathway involved in environmental survival but not in virulence)	none	none
Pseudomonas syringae [4]	none	Both pathways are required for trehalose synthesis and depend on each other (the TreS-mediated trehalose synthesis may depend on maltose generated by the TreY/TreZ pathway)