Leucaena rumen inoculum - composition and activity along the supply chain

Summary

​For the past 20 years a fermentor-grown inoculum containing Synergistes jonesii has been produced and supplied to the beef industry as an oral rumen drench to protect cattle from Leucaena toxicity. The aim of the current study was to define the bacterial composition of the inoculum, determine if there had been major changes in inoculum composition over the last 20 years and to determine the survivability of S. jonesii along the supply chain. 16S rRNA gene amplicon sequencing showed that the inoculum contains an estimated 300-400 bacterial species (taxa) and these are predominated by commensal, rumen bacteria of the Bacteriodes and Firmicutes phyla. Significant, albeit, small changes in the overall bacterial composition were seen in batches produced between 1999 and 2012. However, it was determined that there was one strain of S. jonesii present in the inoculum and  no changes in the levels of this strain of S. jonesii in the inoculum over the 20 years of production. Viable cell counts of S. jonesii in the inoculum showed that thawing followed by storage at 4 °C for 30 hours decreased viability from 1.1 x105 to 9.4 x104 colony forming units (CFU's) which represents 0.05 ± 34 % log10fold change. These results were consistent with experiments performed using pure cultures of S. jonesii which showed a slightly higher 0.21 ± 18 % log10fold decrease in viability. Additionally, supply chain conditions tested had no effect on the ability of pure cultures to resume DHP degradation.  These findings suggest that reductions in S. jonesii viability due to conditions along the supply chain are unlikely to impact on the overall ability of the inoculum to establish and maintain its activity in vivo.