Histamine or scombrotoxin fish poisoning is caused by ingestion of bacterially produced histamine in fish. Histamine-producing bacteria generally contain the histidine decarboxylase gene. However, some strains of Photobacterium phosphoreum are known to produce significant levels of histamine, although the histidine decarboxylase gene in these strains has not been recognized. The objective of this study was to investigate a previously unidentified mechanism of histamine production by P. phosphoreum. We identified a protein with histidine decarboxylase (HDC) activity comparable to activity of the pyridoxal-5-phosphate (PLP) dependent HDC from P. kishitanii and M. morganii. The newly identified protein (HDC2) in P. phosphoreum and P. kishitanii strains, was approximately 2× longer than the HDC protein from other gram-negative bacteria and had 12% similarity to previously identified HDCs. In addition, the hdc2 gene cluster in P. phosphoreum was identical to the hdc gene cluster in P. kishitanii. HDC2 had optimal activity at 20–35 °C, at pH 4, and was not affected by 0–8% NaCl concentrations. Compared to the hdc gene from P. kishitanii, expression of the hdc2 gene was constitutive and not affected by pH or excess histidine. This newly identified protein explains possible mechanisms of histamine production in P. phosphoreum. Characterization of this protein will help in designing control measures to prevent or reduce histamine production in fish.

摄入鱼中细菌产生的组胺会导致组胺或毒素中毒。产生组胺的细菌通常含有组氨酸脱羧酶基因。然而，尽管尚未认识到某些菌株中的组氨酸脱羧酶基因，但已知某些发光细菌的菌株会产生大量的组胺。这项研究的目的是研究以前不清楚的磷产生组胺的机制。我们确定了一种具有组氨酸脱羧酶（HDC）活性的蛋白质，其与可从P. kishitanii和M. morganii依赖于吡ido醛5磷酸（PLP）的HDC的活性相当。在新发现的蛋白（HDC2）发光菌和P. kishitanii菌株比其他革兰氏阴性细菌的HDC蛋白长约2倍，并且与以前鉴定的HDC具有12％的相似性。此外，在HDC2基因簇发光菌是相同的在HDC基因簇P. kishitanii。HDC2在20–35°C，pH 4下具有最佳活性，并且不受0–8％NaCl浓度的影响。与基希氏假单胞菌的hdc基因相比，hdc2基因的表达是组成性的，不受pH值或过量组氨酸的影响。这种新近鉴定的蛋白质解释了在磷中产生组胺的可能机制。该蛋白的表征将有助于设计预防措施，以预防或减少鱼类中的组胺产生。