Localization of Lactococcus lactis ssp lactis bv diacetylactis in alginate gel beads affects biomass density and synthesis of several enzymes involved in lactose and citrate metabolism

Abstract

Lactococcus lactis ssp lactis bv diacetylactis, immobilized in calcium alginate beads, was grown in synthetic medium in a continuous flow reactor. Cell distribution inside the gel, as well as the activity of various enzymes, was measured after 30 h of operation. The included biomass tended to concentrate at the periphery of the bead along a section of radius about 100 ~m long. ATPase activity was maximal in this zone. The activity of NADH oxidase, alcohol dehydrogenase, diacetyl reductase and acetoin reductase, which are repressed in the presence of citrate, were higher in the deeper zones than at the surface of the beads. This result shows that only the peripheral zone of the bead is responsible for the bioconversion of citrate into flavour compounds (diacetyl and acetoin).

pH-controlled cell release and biomass distribution of alginate-immobilized Lactococcus lactis subsp. lactis

“…Biomass concentrations of 70 g dry weight l –1 were measured in layers with an approximate thickness of 150 μm adjacent to the surface of the beads. These values are somewhat less than those reported by Cachon and colleagues (Cachon and Divies 1993; Cachon et al. 1995) in studying L. lactis subsp.…”

“…The analyses of biomass distribution within calcium alginate beads were performed as described by Cachon and Divies (1993). Assays of biomass concentration inside gel beads were performed by dissolution of alginate beads in a 1% solution of sodium citrate (pH 6·0).…”

“…In gel beads containing immobilized growing bacteria the situation becomes complex as the growing bacteria are exposed to different local environments throughout the gel beads. (Cachon and Divies 1993) demonstrated that, after 50 h of continuous fermentation of immobilized Lactococcus lactis subsp. lactis in calcium alginate beads, 95% of the biomass is located near the surface of the bead.…”

Unexpected distribution of immobilized microorganisms within alginate beads

“…Bacteria and spore percentages at the periphery of alginate-gel beads were f5-fold higher than at the center of those beads (a result which holds for the dried beads as well). This fluctuation, although significant, had never been recognized or reported (as the cells' initial state) upon examination by optical or scanning electron microscope or by cell counting (absorbance or plate count) techniques (Bandhyopadhyay et al, 1999;Basu and Baldwin, 2000;Cachon and Divies, 1993;Kikuchi et al, 1993; Klinken- Muyima and Cloete, 1995;Quiros et al, 1996). In these cases, the nonhomogeneous distribution was reported after immersing the cells in a growth medium following their immobilization.…”

“…It has always been assumed that after the entrapment of the cells they are distributed homogeneously in the beads that entrap them as well. In fact, many references emphasize this initial state of homogeneous distribution (Bandhyopadhyay et al, 1999;Basu and Baldwin, 2000;Cachon and Divies, 1993;Kikuchi et al, 1993;Klinkenberg et al, 2001;Muyima and Cloete, 1995;Quiros et al, 1996), which is taken for granted. Here we show that with some immobilization procedures this a priori assumption is not correct: cell distribution in the beads depends on bead formation, rather than the type of entrapped microorganism.…”