Exploring the Prokaryotic Community Associated With the Rumen Ciliate Protozoa Population.

Bar Levy,Elie Jami

doi:10.3389/fmicb.2018.02526

Bar Levy, Elie Jami

Open Access

https://doi.org/10.3389/fmicb.2018.02526

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Abstract

Ciliate protozoa are an integral part of the rumen microbiome and were found to exert a large effect on the rumen ecosystem itself as well as their host animal physiology. Part of these effects have been attributed to their ability to harbor a diverse ecto- and endo-symbiotic community of prokaryotic cells. Studies on the relationship between the protozoa population and their associated prokaryotic community in the rumen mainly focused on the methanogens, revealing that protozoa play a major role in enhancing methanogenesis potential. In contrast, little is known about the composition and function of the bacteria associated with rumen protozoa and the extent of this association. In this study, we characterize the prokaryotic communities associated with different protozoa populations and compare their structure to the free-living prokaryotic population residing in the cow rumen. We show that the overall protozoa associated prokaryotic community structure differs significantly compared to the free-living community in terms of richness and composition. The methanogens proportion was significantly higher in all protozoa populations compared to the free-living fraction, while the Lachnospiraceae was the most prevalent bacterial family in the protozoa associated bacterial communities. Several taxa not detected or detected in extremely low abundance in the free-living community were enriched in the protozoa associated bacterial community. These include members of the Endomicrobia class, previously identified as protozoa symbionts in the termite gut. Our results show that rumen protozoa harbor prokaryotic communities that are compositionally different from their surroundings, which may be the result of specific tropism between the prokaryotic community and protozoa.

Highlights

Ciliate protozoa are a diverse group of eukaryotic microorganisms, ubiquitous across many environments and are known to live in close association with their surrounding prokaryotic community (Dziallas et al, 2012; Newbold et al, 2015)
This analysis revealed that the methanogens/bacteria ratio within the protozoa fractions is significantly higher compared to the ratio found in the free-living fraction (Wilcoxon rank sum, P < 0.05; Figure 1A)
The free-living prokaryotic community had 0.8% archaea, relative to bacteria which was significantly lower than the protozoa associated samples (Wilcoxon rank sum, P < 0.01; Figure 1)

Summary

Introduction

Ciliate protozoa are a diverse group of eukaryotic microorganisms, ubiquitous across many environments and are known to live in close association with their surrounding prokaryotic community (Dziallas et al, 2012; Newbold et al, 2015). Rumen Protozoa/Prokarya Association their hosting cell (Gast et al, 2009). Protozoa associated prokaryotes were shown to serve as electron sinks through nitrogen fixation, acetogenesis or methanogenesis (Yamada et al, 1997; Ohkuma et al, 2015; Tai et al, 2016), provide defense against predators (Vannini et al, 2003; Görtz, 2006; Montagnes et al, 2008) or serve as nutrition for the hosting cell (Gast et al, 2009; Dziallas et al, 2012; Williams and Coleman, 2012). Protozoa are commonly observed to harbor intracellular and extracellular prokaryotic cells, part of which, thought to be engaged in a symbiotic relationship with the hosting cell (Fenchel and Finlay, 1992; Finlay et al, 1994; Lloyd et al, 1996; Hackstein and Vogels, 1997)

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