Chemotactic responses of the rumen bacterial community towards the daidzein flavonoid

Mónica M Galicia-Jiménez,Rafael Rojas-Herrera,Carlos Sandoval-Castro,Silvia E Murialdo,Héctor Magaña-Sevilla

doi:10.1016/j.livsci.2014.05.022

Abstract

Chemotaxis is a mechanism which involves bacterial mobilization to find nutrients or escape from harmful environments. Although ruminal fermentation processes and its by-products are well-known, rumen bacterial chemotaxis has received no attention. Daidzein is one of the common metabolites in plants and has chemotactic effects on soil bacteria that colonize the plants. There are several tests to assess bacterial chemotaxis, but none focused on anaerobic microorganisms as rumen bacteria. We standardized a chemotaxis assay for rumen bacteria by modifying a well-known aerobic capillary method by combining it with technology commonly used for measuring in vitro gas production. Parallel assays were included for studying daidzein isoflavone as a possible attractant and the effect of different chemoattractants (sterile rumen fluid, cellulose and daidzein) on ruminal bacterial consortium was tested. Daidzein showed 3 phylotypes (phylotypes 1, 3 and 4); phylotype 3 was also present in the rumen fluid and cellulose, phylotype 1 (present only in daidzein) was identified as a microorganism closely related to Ruminococcus albus 7. A better understanding of the mechanisms underlying rumen microbial fermentation can lead to a proper manipulation in order to create probiotic cultures for cattle, which could act beneficially on the intestinal flora of the individual.

Highlights

The rumen is a highly dynamic environment, and none of the changes are permanent within the influence due to microbial species which are found in the rumen, since each species has an affinity for a substrate and / or fermentation byproducts (Church, 1974; Janssen and Kirs, 2008)
The response of bacteria to daidzein was greater than the response to cellulose, supporting the hypothesis that when fodder is chewed by the ruminant it releases daidzein which can attract rumen bacteria towards feed particles for attachment and subsequent degradation
This chemotaxis assay was not designed for the study of anaerobic bacterial consortia, some modification have been developed for different purposes (Bharat et al, 2004)

Summary

Introduction

The rumen is a highly dynamic environment, and none of the changes are permanent within the influence due to microbial species (bacteria, archaea, fungi and protozoa) which are found in the rumen, since each species has an affinity for a substrate and / or fermentation byproducts (Church, 1974; Janssen and Kirs, 2008). Recent studies have shown that extracts of plants containing secondary metabolites (i.e. saponins, tannins and essential oils) can modify rumen microbial population. It is not clear how these metabolites affect rumen bacteria populations and ruminant production efficiency. Daidzein can stimulate the growth of some rumen bacteria and lactobacilli in the intestine of piglets (Yu et al, 2004), and may have stimulating effects on rumen microbial fermentation, suggesting an interaction between rumen microorganisms and this isoflavonoid (Mao et al, 2007). We included parallel assays for studying the isoflavone daidzein as a possible attractant and looked through the profile fingerprints of Denaturing Gradient Gel Electrophoresis (DGGE) the effect of different chemoattractants (sterile rumen fluid, cellulose and daidzein) on ruminal bacterial consortium

Objectives

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Discussion

Conclusion