Some Nutritional Requirements of Bovine Rumen Bacteria

During the course of nutritional investigations of bacteria from the bovine rumen, it has become evident that rumen fluid is an indispensable constituent of any medium used to cultivate maximum total numbers of these bacteria.The rumen fluid requirements of pure cultures of rumen bacteria have been noted by Hungate (10) and Bryant (2) and indirectly by Burroughs et al. (4).In this laboratory, Doetsch et al. (5) also have reported that bacteria cannot be cultured from higher dilutions of normal rumen fluid if rumen fluid is omitted from a standard medium used for making counts.The purpose of this work was ~o obtain information that would reveal the nature of the essentiality of rumen fluid.Such information, although concerned more directly with the metabolism and physiology of the bacteria within the rumen, would also have important implications with respect to the nutrition of the animal itself, since cow and bacteria are so intimately related.Rumen fluid is a mixture of bacteria, protozoa, plant fragments, soil, and many chemical compounds, both substrates and end products, in aqueous solution and suspension.In order to eliminate inconsistencies that might arise from using such variable material, experiments were devised that might reveal the function of rumen fluid in the stimulation of bacterial growth.This was attempted by looking for better defined and more readily available materials capable of the same stimulation.The ultimate objective was an approximate characterization and possible isolation of the active principles. EXPERIMENTALAssay procedure.The following experimental plan was employed.A sample of rumen fluid was obtained, and one portion was used immediately to prepare a standard rumen fluid agar medium.With some modifications (5) this medium is essentially the same as that of Hungate (10) and will be referred to throughout this paper as the standard medium.Another portion of the rumen fluid sample was subjected to various treatments and extractions in an attempt to effect an isolation of the active principles.These preparations then were used in the standard medium in place of fresh rumen fluid.In addition, still other lots of the standard medium were made, omitting rumen fluid entirely, and in its place using many of the nitrogenous sources and stimulatory extracts which are employed in the cultivation of nutritionally