No abstract

The presence of phytase activity was demonstrated in 26 strains of rabbit cecal bacteria. In 25 strains a low phytase activity, 0.10-0.62 micromol phosphate released per min per mg protein, was found. High activity (2.61 micromol/min per mg protein) was found in the strain PP2 identified as Enterococcus hirae. Phytase activity was cell-associated, being higher in the cell extract than in the cell walls. Extracellular phytase activity and cell-associated phosphatase activity were not detected. Phytase activity was optimal around pH 5.0, which is below the physiological cecal pH range. The K (m) determined using the Lineweaver-Burk plot was 0.19 micromol/mL. Cations Fe(3+), Cu(2+) and Zn(2+) at 0.5 mmol/L decreased phytase activity in sonicated cells of E. hirae by 99.4, 90.7 and 96.5 %, respectively. In contrast, Mg(2+) increased activity by 11.0 %. Characteristics of E. hirae phytase (pH optimum, K (m), cation sensitivity) were similar to those of other bacterial phytases reported in the literature. Other bacteria with a high phytase activity may be present in the rabbit cecum but remain to be identified.

Five 11-week-old rabbits, fed a commercial granulated feed, were slaughtered and cecal starch-degrading bacteria enumerated; total concentration of cultivable bacteria utilizing starch averaged 5.5 x 10(10) CFU/g. The activity and cellular localization of amylases was determined in 9 bacteria identified as Actinomyces israeli (strains AA2 and AD4), Bacteroides spp. (strain AA3), Dichelobacter nodosus (strain AA4), Mitsuokella multiacidus (strain AA6), Eubacterium spp. (strains AA7 and AB2), Clostridium spp. (strains AD1 and AA5). Four strains (AA3, AA4, AA5, AD4) produced extracellular amylases with an activity of 26-35 micromol of reducing sugars per h per mg of protein; in five strains (AA2, AA6, AA7, AB2, AD1) amylases were membrane-bound with an activity of 14-18 micromol of reducing sugars per h per mg of protein. All strains exhibited a low intracellular amylolytic activity. The pH optimum of amylases was 6.8-7.0. In strains producing extracellular amylases a substantial loss of viscosity was observed during incubations of cultivation supernatant with starch, similar to viscosity reduction in starch solutions treated with alpha-amylase; this indicates an endo-type (random cleavage) of extracellular amylase reaction in the bacteria under study. No strain possessed glucoamylase activity.