The ISME Journal (2013) 7, 1069–1079 & 2013 International Society for Microbial Ecology All rights reserved 1751-7362/13 www.nature.com/ismej ORIGINAL ARTICLE Exploring the bovine rumen bacterial community from birth to adulthood Elie Jami1,2, Adi Israel1, Assaf Kotser1 and Itzhak Mizrahi1 1Department of Ruminant Sciences, Institute of Animal Science, Agricultural Research Organization, Bet-Dagan, Israel and 2Department of Molecular Microbiology and Biotechnology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat-Aviv, Israel The mammalian gut microbiota is essential in shaping many of its host’s functional attributes. One such microbiota resides in the bovine digestive tract in a compartment termed as the rumen. The rumen microbiota is necessary for the proper physiological development of the rumen and for the animal’s ability to digest and convert plant mass into food products, making it highly significant to humans. The establishment of this microbial population and the changes occurring with the host’s age are important for understanding this key microbial community. Despite its importance, little information about colonization of the microbial populations in newborn animals, and the gradual changes occurring thereafter, exists. Here, we characterized the overall bovine ruminal bacterial populations of five age groups, from 1-day-old calves to 2-year-old cows. We describe the changes occurring in the rumen ecosystem after birth, reflected by a decline in aerobic and facultative anaerobic taxa and an increase in anaerobic ones. Some rumen bacteria that are essential for mature rumen function could be detected as early as 1 day after birth, long before the rumen is active or even before ingestion of plant material occurs. The diversity and within-group similarity increased with age, suggesting a more diverse but homogeneous and specific mature community, compared with the more heterogeneous and less diverse primary community. In addition, a convergence toward a mature bacterial arrangement with age was observed. These findings have also been reported for human gut microbiota, suggesting that similar forces drive the establishment of gut microbiotas in these two distinct mammalian digestive systems. The ISME Journal (2013) 7, 1069–1079; doi:10.1038/ismej.2013.2; published online 21 February 2013 Subject Category: Microbial population and community ecology Keywords: gut colonization; gut microbiota; microbial ecology; microbiome; rumen microbiology Introduction millions of years to allow efficient digestion of plant materials (Mackie, 2002). This system’s effective- Relationships between gut bacterial communities ness is conferred by its design, which prolongs and and their mammalian hosts have been shown in maximizes plant biomass exposure to specialized recent years to have an important role in the host’s microorganisms that degrade the plant fibers, while well being and proper function (Ley et al., 2008; providing stable and favorable conditions for their Zilber-Rosenberg and Rosenberg, 2008). A classic growth. During the first weeks of life, when the example of these relationships is found in the first animals are still suckling milk, the rumen is not compartment of the digestive tract of ruminants— functional: the suckled milk does not pass through it the rumen, where plant digestion enables the due to closure of the esophageal groove by reflex conversion of plant fibers into chemical com- action (Van Soest, 1994). Its relative proportions are pounds, which are subsequently absorbed and considerably smaller than in the adult and some of digested by the animal (Mackie 2002). This process its functional components, such as the rumen wall is of extreme importance to mankind as it enables villi, which serve for absorption of nutritional utilization of the solar energy stored in plant fibers components, have not yet developed (Van Soest, via their conversion into food products, such as milk 1994). The changes in the structural and physiolo- and meat. The digestive strategy, architecture and gical properties of the rumen with age are linked to physiology of this system have evolved for over the development of the rumen microorganisms, as their fermentation products are important for the development of the rumen wall villi (Klein et al., Correspondence: I Mizrahi, Department of Ruminant Sciences, 1987; Beharka et al., 1998). Early research into the Agricultural Research Organization, P.O. Box 6, Bet-Dagan 50250, emergence of microbial communities in the rumen Israel. E-mail: [email protected] of newborn animals revealed rapid colonization of Received 3 July 2012; revised 5 December 2012; accepted 6 the rumen by aerobic and facultative anaerobic December 2012; published online 21 February 2013 microbial taxa close to birth, which decreased Rumen bacterial colonization E Jami et al 1070 gradually to a constant level at between 6 and handling by cooling on ice has been reported not 8 weeks of age, being gradually replaced by to affect the samples or their subsequent analyses exclusively anaerobic taxa (Bryant et al., 1958; (Wu et al., 2010). The samples were centrifuged at Fonty et al., 1987; Minato et al., 1992). Interestingly, 10 000 g and the pellet was dissolved in extraction bacteria with cellulolytic capabilities appeared in buffer (100 mM Tris-HCl, 10 mM ethylenediaminete- 3–5-day-old animals, becoming abundant in 2-3- traacetic acid (EDTA), 0.15 M NaCl; pH 8.0); 1 g of week-olds (Fonty et al., 1987; Minato et al., 1992). pellet was dissolved in 4 ml of buffer and incubated However, those studies used classical culture-based at 4 1C for 1 h, as chilling has been shown to microbiology methods, which describe only a small maximize the release of particle-associated bacteria fraction of the total bacterial populations (Janssen, from ruminal contents (Dehority and Grubb, 1980). 2006). Thus, knowledge of the composition and The suspension was then centrifuged at 500 g for establishment of primary bacterial communities in 15 min at 4 1C to remove ruptured plant particles newborn animals, and rumen composition in gen- while keeping the bacterial cells in suspension. The eral, was limited to only a few cultured species supernatant was then passed through four layers of (Dehority, 2003; Hungate et al., 1964). Recently, a cheesecloth, centrifuged (10 000 g, 25 min, 4 1C) study examining ruminal microbial communities of and the pellets were kept at À 20 1C until DNA pre-ruminant calves—three 14-day-olds and three extraction. 42-day-olds—reported the existence of bacteria and functions found in mature animals (Li et al., 2011). Nevertheless, the identity and composition of the DNA extraction primary rumen bacterial communities acquired DNA extraction was performed as previously shortly after birth, and the changes occurring in described (Stevenson and Weimer, 2007). In brief, these communities at different growth stages of the cells were lysed by bead disruption with phenol animal remain largely unknown, despite their followed by phenol/chloroform DNA extraction. importance for understanding the forces governing The final supernatant was precipitated with 0.6 this microbial ecosystem and its similarities to volume of isopropanol and resuspended overnight others. Therefore, we sought to characterize the in 50–100 ml TE (10 mM Tris-HCl, 1 mM EDTA), composition of rumen bacterial communities in then stored at 4 1C for short-term use, or archived newborn calves and their changes with growth at À 80 1C. stages throughout the animal’s life. We used a robust pyrosequencing approach that provides vast knowl- edge on the bacterial communities, and quantitative 454 bacterial tag-encoded amplicon pyrosequencing real-time PCR for accurate monitoring of selected taxa. and data analyses The Research and Testing Laboratory (Lubbock, TX, USA) performed 454 amplicon pyrosequencing of Materials and methods the ruminal DNA samples, using primers covering the V2 and V3 regions (Gray28F 50-TTTGATC Animal handling and sampling NTGGCTCAG-30 and Gray519r 50-GTNTTACNGC The experimental procedures used in this study GGCKGCTG-30). The tagging and sequencing proto- were approved by the Faculty Animal Policy and col was performed as previously described by Welfare Committee of the Agricultural Research (Dowd et al., 2008). PCR was performed under the Organization Volcani Research Center, and were in following conditions: 94 1C for 3 min followed by 32 accordance with the guidelines of the Israel Council cycles of 94 1C for 30 s, 60 1C for 40 s and 72 1C for for Animal Care. 1 min, and a final elongation step at 72 1C for 5 min. One month prior to sample collection, 2-year-old A secondary PCR was performed for FLX (Roche, (n ¼ 5) and 6-month-old (n ¼ 5) Israeli Holstein cows Nutley, NJ, USA) amplicon sequencing under were fed a diet ad libitum consisting of 70% the same conditions by using specially designed concentrated food, mineral and vitamin mix and fusion primers with different tag sequences 30% roughage (Supplementary Table S1); 2-month- (Supplementary Table S3). Data quality control and old calves (n ¼ 5), just before weaning, were fed milk analyses were mostly performed using the QIIME and a specifically designed solid starter diet pipeline (Caporaso et al., 2011). First, reads were (Supplementary Table S1); newborn calves (n ¼ 6) assigned to their designated rumen sample, then were fed exclusively colostrum. One hour after the length-based filtering (o200 bp was excluded from morning feeding, rumen fluid was extracted via the the analysis) and read-quality filtering was per- mouth using a stomach tube with a rumen vacuum formed. The next step was to align the obtained sampler. Samples were transferred to CO2-contain- sequences to define operational taxonomic units ing centrifuge bottles to maintain anaerobic condi- (OTUs) for eventual taxonomy assignment. The tions and kept on ice for no more than 20 min Uclust method was used to cluster the reads into before processing. Immediately after collection, OTUs (Edgar, 2010). Chimeric OTUs were removed the ruminal samples were processed as previously from the analysis using ChimeraSlayer (Haas et al., described (Stevenson and Weimer, 2007).