To better understand how L. hongkongensis adapts to human body and freshwater habitat temperatures at the molecular level, the types and quantities of proteins expressed in L. hongkongensis HLHK9 cultured at 37uC and 20uC were compared. Since initial 2D gel electrophoresis analysis of L. hongkongensis HLHK9 proteins under a broad range of pI and molecular weight conditions revealed that the majority of the proteins reside on the weakly acidic to neutral portion, with a minority on the weak basic portion, consistent with the median pI value of 6.63 calculated for all putative proteins in the genome of L. hongkongensis HLHK9, we therefore focused on IPG strips of pH 4-7 and 7-10. Comparison of the 2D gel electrophoresis patterns from L. hongkongensis HLHK9 cells grown at 20uC and 37uC revealed 12 differentially expressed protein spots, with 7 being more highly expressed at 20uC than at 37uC and 5 being more highly expressed at 37uC than at 20uC (Table 2, Figure 3 ). The identified proteins were involved in various functions (Table 2 ). Of note, spot 8 [N-acetyl-L-glutamate kinase (NAGK)-37, encoded by argB-37] was up-regulated at 37uC, whereas spot 1 (NAGK-20, encoded by argB-20), was upregulated at 20uC (Figures 3, 4A and 4B ). These two homologous copies of argB encode two isoenzymes of NAGK [NAGK-20 (LHK_02829) and NAGK-37 (LHK_02337)], which catalyze the second step of the arginine biosynthesis pathway.