Rapid Screening of Cultural Parameters for Extracellular Halophilic Glutaminase Production from Tetragenococcus Muriaticus FF5302 using the Plackett-Burman’s Experimental Design

The Plackett-Burman’s experiemental design was used to efficiently select the key cultural parameters for the production of halophilic glutaminase by moderating halophilic bacterium Tetragenococcus muriaticus FF5302. Eleven variables were selected, which involved glutamine, peptone, yeast extract, glucose, fructose, KCl, MgSO4, NaCl, temperature, pH, and inoculum size, to identify the most significant variables affecting halophilic glutaminase production in 12 experimental trials. The results of the statistical analyses demonstrated that glutamine, pH, and temperature had significant effects on halophilic glutaminase production. The maximum halophilic glutaminase activity of 199.27 U mL-1 was observed after 120 h of fermentation. After Plackett-Burman’s design experiments, the glutaminase activity was found to be 2.28 folds increase compared to basal conditions. Thus, the cultivation of T. muriaticus FF5302 under the optimal condition could enhance the production of halophilic glutaminase enzyme effectively.

Assessment of the Distribution and Safety of Tetragenococcus muriaticus for Potential Application in the Preparation of Chinese Grasshopper Sub Shrimp Paste

The bacterial profiles of 63 grasshopper sub shrimp paste samples collected from seven typical regions around the Bohai Sea were investigated by high-throughput sequencing. Tetragenococcus muriaticus was found to be the prevailing species present in all the samples, and the presence of T. muriaticus also weakly correlated with the histamine content in the samples. Six T. muriaticus strains with low biogenic amine (BA)-producing ability and deficient in histamine production were identified and subjected to safety assessment. All six strains displayed weak resistance to fifteen known antibiotics as based on the Enterococcus breakpoint values. None of the strains exhibited hemolytic activity or biofilm formation. All strains exhibited were able to grow on MRS agar containing 21% NaCl and expressed amine oxidase and strain-specific proteases and lipases. Most of the strains exhibited acid production at 18% NaCl. Moreover, three of the strains (designated as SG, TS, and QH) with histamine degradation ability were inoculated into separate shrimp paste samples to determine their effect on BA accumulation. The results indicated that the addition of T. muriaticus to shrimp pastes not only led to a significant reduction of BA content in the pastes but also improved the flavor of the pastes. Consequently, these strains may be used as potential candidates for controlling the content of histamine in fermented foods.

Draft Genome Sequences of Tetragenococcus muriaticus Strains 3MR10-3 and PMC-11-5 Isolated from Thai Fish Sauce during Natural Fermentation

ABSTRACT Tetragenococcus muriaticus strains 3MR10-3 and PMC-11-5 are homofermentative halophilic lactic acid bacteria isolated from Thai fish sauce during natural fermentation. Their draft genomes were sequenced. Our interest in these organisms is related to their impact on fish sauce flavor and their high osmotolerance.

Biochemical and genetic evidence for the transfer of Enterococcus solitarius Collins et al. 1989 to the genus Tetragenococcus as Tetragenococcus solitarius comb. nov.

Phylogenetic analysis of 16S rRNA gene sequences revealed that Enterococcus solitarius is not a member of the genus Enterococcus, but is related to species of the genus Tetragenococcus. On a phylogenetic tree, E. solitarius clustered with Tetragenococcus halophilus and Tetragenococcus muriaticus, with which it showed the highest 16S rRNA gene sequence similarity level (about 94 %). Phenotypic studies indicated that E. solitarius was also unable to produce acid from lactose, providing further evidence of its affiliation to the genus Tetragenococcus. DNA hybridization studies indicated that E. solitarius was clearly a separate species, different from T. halophilus and T. muriaticus (reassociation levels of about 23 and 54 %, respectively). As suggested in previous studies, E. solitarius is closely related to but clearly distinct from T. halophilus. Based upon properties that taxonomically distinguish it from species of the genus Enterococcus, it is proposed that E. solitarius be transferred to the genus Tetragenococcus and reclassified as Tetragenococcus solitarius comb. nov. (type strain, 885/78T=ATCC 49428T=CCUG 29293T=CIP 103330T=DSM 5634T=JCM 8736T=LMG 12890T=NCTC 12193T).