Use of endogenous bacteriocins to manipulate the rumen microbial ecology

Summary

Ionophore antibiotics, such as monensin, are used routinely in the meat and livestock industry to improve animal health and growth. They are used particularly in feedlots, which are a growing feature of the industry. There is significant consumer concern regarding the use of antibiotics and their role in the emergence of drug resistant pathogens.
Bacteriocins produced by the rumen bacterium Streptococcus bovis were pursued as a possible source of endogenous antibacterial agents which could supplant the use of antibiotics in the cattle industry. Bacteriocins have the potential to project the same benefits as antibiotics without the negative impact on public perception, human health, animal health, and environmental concerns.
The chosen bacteriocin-producing S. bovis isolate (Sb15) was found to have a spectrum of activity similar to that of monensin. Methods for improving the consistency and levels of bacteriocin production were developed. A protocol for quantifying the concentration of bacteriocin was developed and used to verify that the level of activity of the bacteriocin produced by the wild-type isolate is equivalent to that of the commercially produced bacteriocin nisin. The bacteriocin’s thermostability, resistance to proteases and activity spectrum marks it as being suitable for use in manipulating the rumen environment. Sequencing of the purified protein indicated that it was essentially identical to the well-characterised HC5 bacteriocin; however several amino acid residues could not be resolved and so the level of identity cannot be fully determined.
The fact that the identified bacteriocin is near-identical to HC5 reduces the attractiveness of this project to large agrichemical companies, who otherwise would see broader applications for the bacteriocin. Since the use of HC5 is not patented, however, it does not prevent its local development for the feedlot industry.
An economic evaluation confirmed a priori assumptions that batch fermentation with
a wild-type strain would not be competitive compared to monensin. However, bacteriocin production from S. bovis fermentation on sugar mill streams can be competitive, if

1. The specific productivity is increased 5-fold through strain engineering;

2. The final biomass density is increased 10-fold by implementing a fed batch process with lactic acid removal using electrodialysis; and

3. The production is greater than 100 tonnes per annum

Attempts to enhance bacteriocin production through random mutagenesis failed due to a lack of a technique for effectively evaluating a large number of clones and/or techniques for enriching for superior clones. Industrial-style robotics-based screening and/or rational strain engineering will be required to generate superior strains. The potential of using eletrodialysis on whole broth was confirmed, though a full scale REED system and fed batch optimisation is required to establish, if a 10-fold improvement is feasible.
With a lengthy research phase ahead, the project was deemed inappropriate for the CRC SIIB to continue pursuing. However, the use of bacteriocins should still be considered a viable strategy for MLA to realise the aim of phasing out antibiotics use from animal production. Alternative production options, such as using bacteriocin producing bacteria as silage inoculants, may overcome production cost issues.