Phytase activity of anaerobic ruminal bacteria

This study investigated phytase activity—the ability to release phosphate from phytate, the predominant phosphorus form in grains and legumes—among 334 strains of 22 anaerobic ruminal bacterial species. Phytase activity was demonstrated in strains of Selenomonas ruminantium, Megasphaera elsdenii, Prevotella ruminicola, Mitsuokella multiacidus, and Treponema species. The activity was particularly prevalent in S. ruminantium, with over 96% of tested strains showing measurable activity. Activity levels varied considerably among positive strains, ranging from minimal to 703 nmol phosphate released per milliliter of culture. Notably, the phytase activity was exclusively cell-associated and did not require phytate for induction, appearing in medium containing high phosphate concentrations (~14 mM). Rumen fluid fractions from steers fed grain-based diets showed greater phytase activity than those on forage alone, suggesting activity increases with dietary phytate levels. The findings indicate ruminal bacteria could be a promising commercial source of highly active phytase enzyme.

Key findings

• Selenomonas ruminantium strains exhibited the highest phytase activity (up to 703 U/ml), with over 96% of tested strains being positive, making them the dominant phytase-producing bacteria in the rumen
• Phytase activity was located exclusively on bacterial cells and was not released into the supernatant, regardless of high phosphate levels in growth media (~14 mM)
• Five bacterial species demonstrated phytase activity: Selenomonas ruminantium, Megasphaera elsdenii, Prevotella ruminicola, Mitsuokella multiacidus, and Treponema species
• Ruminal phytase activity increased substantially on high-grain diets compared to hay-only diets, correlating with higher dietary phytate levels in cereal grains
• Ruminal bacterial phytase activity levels compare favorably with commercially important phytases from Aspergillus and Bacillus species, suggesting potential for commercial development