Abstract
Monensin is an ionophore for monovalent cations, which is frequently used to prevent ketosis and to enhance performance in dairy cows. Studies have shown the rumen bacteria Prevotella bryantii B14 being less affected by monensin. The present study aimed to reveal more information about the respective molecular mechanisms in P. bryantii, as there is still a lack of knowledge about defense mechanisms against monensin. Cell growth experiments applying increasing concentrations of monensin and incubations up to 72 h were done. Harvested cells were used for label-free quantitative proteomics, enzyme activity measurements, quantification of intracellular sodium and extracellular glucose concentrations and fluorescence microscopy. Our findings confirmed an active cell growth and fermentation activity of P. bryantii B14 despite monensin concentrations up to 60 µM. An elevated abundance and activity of the Na+-translocating NADH:quinone oxidoreductase counteracted sodium influx caused by monensin. Cell membranes and extracellular polysaccharides were highly influenced by monensin indicated by a reduced number of outer membrane proteins, an increased number of certain glucoside hydrolases and an elevated concentration of extracellular glucose. Thus, a reconstruction of extracellular polysaccharides in P. bryantii in response to monensin is proposed, which is expected to have a negative impact on the substrate binding capacities of this rumen bacterium.
Highlights
The prudent use of antibiotics in livestock farming is a crucial aspect for health of a dense stock
Monensin and its derivates were originally isolated from the soil bacteria Streptomyces cinnamonensis, which synthesizes the compound via the precursor butyrate and isobutyrate [9,10,11]
A self-intoxication by monensin is prevented due to the anti-isobutyrate factor (AIB), which allows S. cinnamonensis to resist monensin, and toxic concentrations of short-chain fatty acids (SCFAs) [12]. Several rumen microorganisms such as Selenomonas ruminantium and Methanobacterium ruminantium appeared to be insensitive towards monensin, while Fibrobacter succinogenes, Bacteroidetes succinogenes, Prevotella ruminicola and Bacteroidetes ruminicola showed a retarded growth in the presence of monensin [5,13]
Summary
The prudent use of antibiotics in livestock farming is a crucial aspect for health of a dense stock. The application of monensin as a growth promotor in livestock farming became restricted to therapeutic interventions since 1996 in Denmark, 1999 in Switzerland and 2006 in the European Union [2,3,4]. A self-intoxication by monensin is prevented due to the anti-isobutyrate factor (AIB), which allows S. cinnamonensis to resist monensin, and toxic concentrations of short-chain fatty acids (SCFAs) [12]. Several rumen microorganisms such as Selenomonas ruminantium and Methanobacterium ruminantium appeared to be insensitive towards monensin, while Fibrobacter succinogenes, Bacteroidetes succinogenes, Prevotella ruminicola and Bacteroidetes ruminicola showed a retarded growth in the presence of monensin [5,13]. Monensin cell binding can be reduced by TRIS-EDTA washing, as it was shown for mixed ruminal bacteria [21]
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