Pediococcus

Of the approved species of Pediococcus (Garvie, 1986b; Weiss, 1992), only four have been isolated from wines; P. damnosus, P. parvulus, P. inopinatus, and P. pentosaceus (Davis et al., 1986a; 1986b; Edwards and Jensen, 1992). Several researchers previously reported isolation of P. cerevisiae from wines (Maret and Sozzi, 1977; 1979; Costello et al., 1983; Lafon-Lafourcade et al., 1983b; Fleet et al., 1984). The species is now considered invalid because it represents at least two species including P. damnosus and P. pen-tosaceus (Garvie, 1974; Raccach, 1987). P. damnosus and P. parvulus appear to be more commonly found in wines than the other species.

Pediococci are characterized as being Gram-positive, nonmotile, catalase-negative, and aerobic to microaerophilic bacteria (Garvie, 1986b; Pilone et al., 1991; Weiss, 1992). Members of this genus are

Figure 2.3. Pediococcus damnosus as viewed with phase-contrast microscopy at a magnification of 1000x. Photograph provided with the kind permission of WineBugs LLC.

homofermentative (Section 2.4.1), with glucose converted to either l- or dl-lactate (Garvie, 1986b). Under glucose limitation, Pasteris and Strasser de Saad (2005) noted that a strain of P. pentosaceus degraded glycerol to pyruvate, the latter being further metabolized to either acetate or diacetyl or 2,3-butanediol through "active-acetaldehyde" (Section 2.4.5). Growing cultures commonly possess the ability to form l-lactate from l-malic acid (Raccach, 1987; Edwards and Jensen, 1992). Pediococci are chemoorgano-trophs and require complex growth factor and amino acid requirements. In addition, these are the only lactic acid bacteria that divide in two planes, which results in the formation of pairs, tetrads or large clumps of spherical cells as shown in Fig. 2.3 (Garvie, 1986b; Axelsson, 1998). Characteristics for three species of Pediococcus are listed in Table 2.2.

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