The effect of condensed tannins from Lotus pedunculatus and Lotus corniculatus on the growth of proteolytic rumen bacteria in vitro and their possible mode of action

Five strains of proteolytic rumen bacteria were treated with condensed tann ins (CT) purified from Lotus pedunculatus and Lotus corniculatus to investi gate their effect on the growth of these bacteria in vitro. Streptococcus b ovis NCFB 2476, Eubacterium sp. C124b, Prevotella bryantii B14, Butyrivibri o fibrisolvens H17c, and Clostridium proteoclasticum B316(T) were tested ag ainst 200, 400, and 600 mug CT.mL(-1) extracted from L. pedunculatus and L. corniculatus. In the absence of CT, all bacterial strains showed typical g rowth and reached maximum optical density (OD) after 6-8 h of incubation in a plant protein medium. Growth of Eubacterium sp., P. bryantii, and B. fib risolvens was inhibited (P < 0.01-0.001) more by the CT from L. pedunculatu s than by the CT from L. corniculatus. All strains continued to grow in the presence of 200 mug.mL(-1) of the CT from L. pedunculatus, but attained si gnificantly (P < 0.05-0.01) lower maximum OD600 values than (minus CT) cont rols, except for S. bovis. At 400 and 600 mug.mL(-1), the addition of CT fr om L. pedunculatus inhibited (P < 0.05-0.001) the growth of all bacterial s trains tested compared with controls. The growth of Eubacterium sp. and P. bryantii was stimulated for the first 4-6 h of incubation (P < 0.001) by 20 0 mug.mL(-1) of CT from L. corniculatus, but then declined leading to a sig nificant difference in OD values compared with the controls. At 400 mug.mL( -1), the CT from L. corniculatus reduced (P < 0.05-0.01) the growth of all strains except S. bovis, while 600 mug.mL(-1) inhibited (P < 0.01-0.001) th e growth of all strains. To study the mechanism of CT action, the degradati on of the large subunit (LSU) of ribulose-1,5-bisphosphate carboxylase/oxyg enase (Rubisco; Fraction 1 Leaf protein) was followed after bacterial cells or Rubisco were preincubated with CT extracted from L. corniculatus and L. pedunculatus. Both preincubations decreased LSU degradation, but they diff ered in their response to polyethylene glycol (PEG) addition. Addition of P EG to CT-Rubisco preincubations negated the effects of CT, while PEG additi on to CT-bacteria preincubations did not. This implies that the CT-bacteria l interaction is stronger than the CT-Rubisco interaction or the interactio n is of a different type. Also, L. pedunculatus CT reduced the degradation of the LSU to a greater extent than the CT from L. corniculatus when preinc ubated with bacteria.