RESUMO
In fish sauce production, microorganisms are associated with the fermentation process; however, the sequential changes in the bacterial communities have never been examined throughout the period of fermentation. In this study, we determined the bacterial floras in a fish sauce mash over 8 months, using three different culture media and 16S rRNA gene clone library analysis. During the first 4 weeks, viable counts of non-halophilic and halophilic bacteria decreased and were dominated by Staphylococcus species. Between 4 and 6 weeks, halophilic and highly halophilic bacterial counts markedly increased from 10(7) to 10(8) cfu/g, and the predominant species changed to Tetragenococcus halophilus. The occurrence of T. halophilus was associated with an increase of lactic acid and a reduction of pH values. In contrast, non-halophilic bacterial counts decreased to 10(6) cfu/g by 6 weeks with Bacillus subtilis as the dominant isolate. Clone library analysis revealed that the dominant bacterial group also changed from Staphylococcus spp. to T. halophilus, and the changes were consistent with those of the floras of halophilic and highly halophilic isolates. This is the first report describing a combination approach of culture and clone library methods for the analysis of bacterial communities in fish sauce mash.
Assuntos
Bactérias/classificação , Bactérias/isolamento & purificação , Biota , Peixes/microbiologia , Microbiologia de Alimentos , Animais , Bactérias/genética , Bactérias/crescimento & desenvolvimento , Carga Bacteriana , DNA Bacteriano/química , DNA Bacteriano/genética , DNA Ribossômico/química , DNA Ribossômico/genética , Fermentação , Concentração de Íons de Hidrogênio , Ácido Láctico/análise , Viabilidade Microbiana , Dados de Sequência Molecular , RNA Ribossômico 16S/genética , Análise de Sequência de DNA , Fatores de TempoRESUMO
Histamine production from histidine in fermented food results in food spoilage, and is harmful to consumers. From fish-miso, we have isolated a new bacterial strain Staphylococcus epidermidis TYH1, which produced histamine under acidic condition in the medium supplemented with glucose. Using oligonucleotides deduced from the histidine decarboxylase gene (hdcA) of Lactobacillus hilgardii, about 14-kbp DNA region of the TYH1 genome was cloned and sequenced. This region contained two putative genes hdcA(TYH1) and hdcP(TYH1) encoding proteins HdcA(TYH1) (310 amino acid residues) and HdcP(TYH1) (495 residues), respectively. Nucleotide sequence around this hdc cluster showed similarity to SCCpbp4 region of S. epidermidis ATCC 12228. Downstream of the cluster, ccrA, ccrB (Type II, respectively) and pbp4 were located. The CcrA and CcrB proteins catalyzed excision of the hdc cluster from the TYH1 chromosome, upon introduction into the TYH1 strain via multicopy plasmid. When hdcA(TYH1) was expressed in Staphylococcus warneri M, histamine was extracellularly accumulated in dependence on exogenous histidine. These results indicate that the gene encoding a histidine decarboxylase resides in a movable genetic element, SCC. This new element is designated as SCChdc.
