Is polyethylene glycol innocuous to the rumen bacterial community? A preliminary in vitro study
Polyethylene glycol (PEG) is a polymer that is widely used in nutritional studies examining the effect of tannins on ruminal fermentation. There is no information however on its potential effect on the structure of the rumen bacterial community. Therefore, the aim herein was to investigate its effect on rumen bacterial profile, using an in vitro batch culture experiment with three substrates (alfalfa hay, maize grain, and a combination of both) to simulate three different rumen environments, treated with or without PEG. Rumen fluid was collected from four cannulated sheep and pooled to inoculate the cultures, which were run at 39°C for 22 h. At the end of the incubation, samples were immediately frozen for microbial DNA extraction. Terminal restriction fragment length polymorphism analysis of 16S rRNA genes revealed that, although there was a high similarity in the fragments detected in the cultures with or without PEG, their relative abundances suggested that PEG might induce some changes in the bacterial community structure when a starch-rich substrate (e.g. maize) is assayed. Furthermore, the relative frequency of some abundant fragments, such as one compatible with bacteria of the phylum Bacteroidetes detected with the enzyme HhaI, and another that may match microorganisms of the genus Ruminococcus obtained with the enzyme MspI, was increased when PEG was added to maize-supplied microbial cultures. These results suggest that the use of PEG in batch cultures may not be as innocuous to rumen bacterial populations as previously described regarding ruminal fermentation, and might be relevant to studies using this polymer to examine the effect of tannins on rumen microbiota.