Histidine decarboxylases and their role in accumulation of histamine in tuna and dried saury

Abstract

Histamine-producing bacteria (HPB) such as Photobacterium phosphoreum and Raoultella planticola possess histidine decarboxylase (HDC), which converts histidine into histamine. Histamine fish poisoning (HFP) is attributable to the ingestion of fish containing high levels of histamine produced by HPB. Because freezing greatly decreases the histamine-producing ability of HPB, especially of P. phosphoreum, it has been speculated that HFP is caused by HDC itself from HPB cells autolyzing during frozen storage, even when HPB survive frozen storage. Here we constructed recombinant HDCs of P. phosphoreum, Photobacterium damselae, R. planticola, and Morganella morganii and investigated the ability of HDCs to produce sufficient histamine to cause HFP. To elucidate the character of these HDCs, we examined the specific activity of each recombinant HDC at various temperatures, pH levels, and NaCl concentrations. Further, we also investigated the stability of each HDC under different conditions (in reaction buffer, tuna, and dried saury) at various temperatures. P. damselae HDC readily produced sufficient histamine to cause HFP in fish samples. We consider that if HDC is implicated as an independent cause of HFP in frozen-thawed fish, the most likely causative agent is HDC of P. damselae.

FIG. 1.

Amino acid sequences of HDCs of P. phosphoreum NBRC 13896 and YS4-7, P. damselae JCM 8969, R. planticola ATCC 43176, and M. morganii JCM 1672. Symbols: *, residues common to P. phosphoreum NBRC 13896; +, the lysine at residue 232 that binds PLP.

FIG. 2.

Results of sodium dodecyl sulfate-polyacrylamide gel electrophoresis of crude and purified preparations of HDC of P. phosphoreum NBRC 13896 (lanes 1 and 6) and YS4-7 (lanes 2 and 7), P. damselae JCM 8968 (lanes 3 and 8), R. planticola ATCC 43176 (lanes 4 and 9), and M. morganii JCM 1672 (lanes 5 and 10). Lanes 1 to 5 represent crude cell extracts from induced cultures, and lanes 6 to 10 represent the purified enzymes.

FIG. 3.

Temporal changes in the relative percentages of the specific activities of HDC at −20, 4, 20, 30, and 40°C. Symbols: •, P. phosphoreum NBRC 13896; ▪, P. phosphoreum YS4-7; ▴, P. damselae JCM 8968; ×, R. planticola ATCC 43176; +, M. morganii JCM 1672.

FIG. 4.

Histamine accumulation in tuna and dried saury samples by the HDCs of P. phosphoreum NBRC 13896, P. damselae JCM 8968, and R. planticola ATCC 43176 at 4, 20, and 30°C. Symbols: ○, P. phosphoreum NBRC 13896 in tuna; □, P. damselae JCM 8968 in tuna; ▵, R. planticola ATCC 43176 in tuna; ×, control in tuna; •, P. phosphoreum NBRC 13896 in dried saury; ▪, P. damselae JCM 8968 in dried saury; ▴, R. planticola ATCC 43176 in dried saury; +, control in dried saury.

FIG. 5.

Histamine accumulation in tuna and dried saury samples at −20°C and after incubation for 2 h at 20°C, followed by storage at −20°C by the HDC of P. phosphoreum NBRC 13896, P. damselae JCM 8968, and R. planticola ATCC 43176. ○, P. phosphoreum NBRC 13896 at −20°C; □, P. damselae JCM 8968 at −20°C; ▵, R. planticola ATCC 43176 at −20°C; ×, control at −20°C; •, P. phosphoreum NBRC 13896 after incubation; ▪, P. damselae JCM 8968 after incubation; ▴, R. planticola ATCC 43176 after incubation.