유산균의 분류 및 보존관리

The lactic acid bacteria are Gram-positive, non spore-forming, catalase-negative, of nonaerobic habit but aerotolerant, fastioius, acid-tolerant, nonrespiring cocci or rods, which produce lactic acid as a major sole end product of the fermentation of sugar. They consist of more than 20 genera including Aerococcus, Alloiococcus, Carnobacterium, Dolosigranulum, Enterococcus, Globicatella, Lactobacillus, Lactococcus, Lactosphaera, Leuconostoc, Oenococcus, Pediococcus, Streptococcus, Tetragenococcus, Vagococcus, Weissella, and etc. It is difficult to differentiate lactic acid bacteria based on physiological and biochemical characteristics because they grow on the same selection medium, MRS medium and have similar characteristics in traditional taxonomic test. Today, we have the means to examine macromolecules of the cell such as nucleic acids, believed to be more accurate in defining relationships and phylogenetic positions. Fortunately, nature has provided us with different kinds of nucleic acids for different types of taxonomic studies. Close relations (at species and subspecies level) can be determined with DNA-DNA homology studies. Based on analysis of 16S rRNA sequence for lactic acid bacteria, new genera have been reported and some species have transferred to other genera. With this technique, a clearer picture of the phylogeny of lactic acid bacteria is emerging. It is difficult to do long-term preservation of lactic acid bacteria because of their weak viability. We usually use the methods of lyophilization and cryopreservation with skim milk for long-term preservation of lactic acid bacteria.