SURVIVAL OF THE RECOMBINANT BACTEROIDES THETAIOTAOMICRON STRAIN BTX IN IN VITRO RUMEN INCUBATIONS

Authors: Cotta, Michael; Whitehead, Terence; Rasmussen, Mark

Submitted to: Journal Of Applied Bacteriology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/28/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Microbial fermentation in the forestomach (rumen) of ruminant livestock (sheep, cattle, goats, etc.) enables these animals to live on diets composed largely of fibrous plant materials. Although this confers an advantage to these animals and allows them to convert inexpensive feeds into high quality animal products, the use of plant components is often incomplete. As a result, higher quality and more costly feeds are added to diets to meet the nutrient demands required by modern livestock production systems. Efforts to improve the use of the fiber portion of animal diets has centered on physical and chemical treatments of feed materials. An alternative to this approach would be to modify the activities of the microorganisms themselves to increase their capacity for digestion of these materials. The bacterium, Bacteroides thetaiotaomicron strain BTX, was developed for this purpose. Strain BTX produces high levels of a digestive enzyme that may help breakdown plants. The current studies were conducted to test whether strain BTX could survive if added to rumen-like cultures in the laboratory. Our results demonstrated strain BTX could grow under rumen simulating conditions, if additional nutrients were provided for its growth. The information obtained will be helpful to further the development of this strain as a rumen additive.

Technical Abstract: The survival of Bacteroides thetaiotaomicron strain BTX under rumen simulating conditions was studied. Strain BTX is a recombinant variant of strain 5482 engineered for the production of high levels of xylanase, an enzyme important in the degradation of hemicellulose. Strain BTX was not inhibited by compounds present in rumen fluid, and it grew well in media containing rumen fluid (up to 75%) or high concentrations of volatile fatty acids (total concentration, 100 mM). The ability of strain BTX to compete with other microorganisms under rumen-like conditions was studied in in vitro incubations of rumen contents. These experiments employed a consecutive batch culture (CBC) system consisting of alfalfa suspended in a rumen fluid buffer inoculated with blended rumen contents and maintained by transfers (10%, v/v) at 48 h intervals. CBC cultures contained a diversity of microbial morphotypes and accumulated fermentation products in rumen-like proportions. When added alone, the number of BTX cells were maintained for only a few hours and then declined precipitously until undetectable after 48 h. If CBC cultures were also supplemented with chondroitin sulfate, strain BTX grew and the pattern of its population generally followed that of the total population of ruminal bacteria in these cultures. When transferred into fresh CBC cultures containing chondroitin sulfate, BTX was again able to grow and increase in numbers, but to a diminished degree. Although BTX was able to survive and maintain itself in chondroitin sulfate supplemented cultures, this was at a very low level (10**5 per ml). The potential for manipulation of rumen function by inoculation with recombinant bacteria is discussed.