Pediococcus pentosaceus are Gram-positive, facultatively anaerobic, non-motile and non-spore-forming, members of the industrially important lactic acid bacteria. Like other lactic acid bacteria, P. pentosaceus are acid tolerant, cannot synthesize porphyrins, and possess a strictly fermentative metabolism with lactic acid as the major metabolic end product (Axelsson, 1998; Garvie, 1986). Phylogenetically Pediococcus and Lactobacillus form a super-cluster that can be divided in to two sub-clusters, all species of Pediococcus fall within the Lactobacillus casei Pediococcus sub-cluster. Morphologically, pediococci (cocci; 0.6-1.0 mm in diameter) and lactobacilli (rods) are distinct. The formation of tetrads via cell division in two perpendicular directions in a single plane is a distinctive characteristic of pediococci. Pediococcus can be described as the only acidophilic, homofermentative, lactic acid bacteria that divide alternatively in two perpendicular directions to form tetrads (Simpson and Taguchi, 1995). Lactic acid is produced from hexose sugars via the Embden-Meyerhof pathway and from pentoses by the 6-phosphogluconate/phosphoketolase pathway (Axelsson, 1998). P. pentosaceus grow at 40 but not 50oC, between pH 4.5 an 8.0, in 9-10% NaCl, hydrolyzes arginine, can utilize maltose and some strains produce a pseudo-catalase (Garvie, 1986, Simpson and Taguchi, 1995).
Strains of P. pentosaceus have been reported to contain between three and five resident plasmids (Graham and McKay, 1985). Plasmid-linked traits include the ability to ferment raffinose, melibiose, and sucrose, as well as, the production of bacteriocins (Daeschel and Klaenhammer, 1985;Gonzalez and Kunka, 1986). Plasmids can be conjugally transferred between Pediococcus and Enterococcus, Streptococcus, or Lactococcus (Gonzalez and Kunka, 1983). Electroporation has been utilized to introduce plasmids into pediococci, including P. pentosaceus (Kim et al, 1992; Caldwell, 1996).