Subject(s)
Bacteria/genetics , Beta vulgaris/microbiology , Food Preservation/methods , Industrial Microbiology/methods , Oligonucleotide Array Sequence Analysis/methods , Sucrose/metabolism , Bacteria/growth & development , Beta vulgaris/chemistry , Colony Count, Microbial/methods , DNA, Bacterial/chemistry , DNA, Bacterial/genetics , Food Microbiology , Hydrogen-Ion Concentration , Kinetics , Osmolar Concentration , Population Dynamics , Species Specificity , Time FactorsABSTRACT
Tetragenococcus halophilus is known to flourish in extreme salt environments. Recently, this halophilic bacterium also appeared as the dominant microflora during storage of sugar thick juice, an intermediate product of beet sugar production. Although T. halophilus can cause degradation of thick juice, dominance of this bacterium does not always result in degradation. In this study T. halophilus strains from high-salt and high-sugar environments, and in particular from degraded and non-degraded thick juice, were compared in detail. Both physiological and genetic characterization using Biolog, repetitive PCR fingerprinting (rep-PCR) and random amplified polymorphic DNA (RAPD) technology, revealed clear differences between T. halophilus strains isolated from salt- and sugar-rich environments. However, no strain pattern could be specifically and systematically associated with degraded or non-degraded thick juice. Remarkably, halophilic T. halophilus strains were not able to grow in sugar thick juice. Irrespective of the differences between the strains from high-salt or high-sugar environments, DNA-DNA hybridization grouped all strains within the species T. halophilus, except one isolate from sugar thick juice that showed different physiological and genetic characteristics, and that may represent a new species of Tetragenococcus.
Subject(s)
Food Microbiology , Gram-Positive Cocci/genetics , Gram-Positive Cocci/metabolism , Sodium Chloride/metabolism , Sucrose/metabolism , Beta vulgaris/microbiology , DNA Fingerprinting , DNA, Bacterial/genetics , Genes, Bacterial , Genes, rRNA , Nucleic Acid Hybridization , Phylogeny , Polymerase Chain Reaction , RNA, Ribosomal, 16S/genetics , Random Amplified Polymorphic DNA TechniqueABSTRACT
The diversity of the bacterial population in sugar thick juice, an intermediate product in the production of beet sugar, which exhibits an extreme, osmophilic environment with a water activity value (a(w)) less than 0.86, was assessed with both culture-dependent and -independent 16S ribosomal RNA (rRNA) gene-based analyses. In comparison with previous studies, the number of different thick juice bacterial species increased from 29 to 72. Remarkably, a limited, gram-positive, culturable flora, encompassing species of Bacillus, Staphylococcus and mainly Tetragenococcus dominated thick juice during storage, while a more heterogeneous and unculturable fraction of Acinetobacter, Sporolactobacillus and Thermus species could be detected in freshly produced thick juice. Notably, almost all bacteria detected in the thick juice were also detected in the air, emphasising the importance of further investigation and assessment of strategies to reduce (air) contamination during processing and storage. The discovery of the contamination source may be used for the development of management strategies for thick juice degradation resulting from microbial activity.
Subject(s)
Air Microbiology , Bacteria/isolation & purification , Food Contamination/analysis , Food Preservation/methods , Industrial Microbiology/methods , Sucrose/metabolism , Bacteria/growth & development , Beta vulgaris/chemistry , Colony Count, Microbial/methods , DNA, Bacterial/chemistry , DNA, Bacterial/genetics , Food Handling/methods , Food Microbiology , Gene Library , Osmolar Concentration , RNA, Ribosomal, 16S/genetics , Species Specificity , Temperature , Time FactorsABSTRACT
The industrial storage of sugar thick juice was simulated on a laboratory scale. Terminal Restriction Fragment Length Polymorphism (T-RFLP) analysis and the application of Clone Libraries in parallel with classical microbiology were used to study the bacterial diversity and all revealed a dominance (>99%) of Tetragenococcus halophilus during storage. The degradation of thick juice correlated with the appearance of L-lactic acid and high concentrations of T. halophilus. In addition, pure cultures of T. halophilus induced degradation of sterile thick juice. A specific PCR was developed to detect T. halophilus and industrial thick juice samples from Belgium, Germany and France all contained T. halophilus, suggesting a consistent association of this organism with thick juice. T. halophilus has been known only as a halophile thus far, and this report is the first to show an association of this organism with a sugar-rich environment.