Figure 8. Growth of acetogen isolate G3.2a in acetogen medium under 200 kPa of a H2:CO2 (80:20) gas mixture plus (triangles) or minus (circles) 2.5 mM glucose.
discussion A preliminary batch culture experiment demonstrated that citrate plus phosphate was a better buffer system than MES for the isolation of acetogenic bacteria from ruminal contents. However, when the citrate plus phosphate was used as buffer in continuous culture, citrate utilizing bacteria were selected (data not reported). Therefore, MES was utilized as the buffer system for isolation of acetogenic bacteria in continuous culture. In many beef operations, monensin is used to manipulate rumen fermentations; therefore, monensin was included in the medium used to isolate acetogens. A preliminary study was performed to determine the minimum inhibitory concentration (MIC) of monensin on acetogenic bacteria that had been previously isolated by our lab. Both gram positive acetogens, strain A10 and strain 3H, were insenstive to the highest concentration of monensin tested
(60 μM). This concentration of monensin is higher than the concentration (3 to 5 μM) normally found in the rumen (Russell and Strobel, 1989). Our results, thus indicated that monensin may not inhibit some acetogens. The second experiment on the isolation of acetogenic bacteria resulted in the isolation of ten potential acetogenic strains from each of the four growth vessels utilized. Post-isolation studies were conducted to determine the ability of these strains to grow on a H2:CO2 gas mixture and to produce acetate. A total of eight isolates were identified as acetogenic bacteria. After further studies comparing growth and acetate production on H2:CO2 versus N2:CO2 gas mixtures, three of the eight isolates were selected for further study because of their greater H2 utilization and acetate production. The three isolates chosen were strains G1.4b, from growth vessel one; G2.4a, from growth vessel 2; G3.2a, from growth vessel 3. Of these three isolates, G3.2a had higher growth and produced more acetate than the other two.
Agric. Food Anal. Bacteriol. • AFABjournal.com • Vol. 3, Issue 2 - 2013
141