Article

Interactions between Entodinium caudatum and an amino acid-fermenting bacterial consortium: Fermentation characteristics and protozoal population in vitro

Tansol Park1,2, Zhongtang Yu2,*
Author Information & Copyright
1Chung-Ang University, Anseong-si 17546, Korea.
2The Ohio State University, Columbus 43210, United States.
*Corresponding Author: Zhongtang Yu, The Ohio State University, Columbus 43210, United States. Phone: 1-614-292-3057. E-mail: yu.226@osu.edu.

© Copyright 2022 Korean Society of Animal Science and Technology. This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Ruminal protozoa, especially entodiniomorphs, engulf other members of the rumen microbiome in large numbers; and they release oligopeptides and amino acids, which can be fermented to ammonia and volatile fatty acids (VFAs) by amino acid-fermenting bacteria (AAFB). Studies using defaunated (protozoa-free) sheep have demonstrated that ruminal protozoa considerably increase intraruminal nitrogen recycling but decrease nitrogen utilization efficiency in ruminants. However, direct interactions between ruminal protozoa and AAFB have not been demonstrated because of their inability to establish axenic cultures of any ruminal protozoan. Thus, this study was performed to evaluate the interaction between <italic>Entodinium caudatum</italic>, which is the most predominant rumen ciliate species, and an AAFB consortium in terms of feed degradation and ammonia production along with the microbial population shift of select bacterial species (<italic>Prevotella ruminicola</italic>, <italic>Clostridium aminophilum</italic>, and <italic>Peptostreptococcus anaerobius</italic>). From an <italic>Ent. caudatum</italic> culture that had been maintained by daily feeding and transfers every 3 or 4 days, the bacteria and methanogens loosely associated with <italic>Ent. caudatum</italic> cells were removed by filtration and washing. An AAFB consortium was established by repeated transfers and enrichment with casamino acids as the sole substrate. The cultures of <italic>Ent. caudatum</italic> alone (Ec) and AAFB alone (AAFB) and the co-culture of <italic>Ent. caudatum</italic> and AAFB (Ec+AAFB) were set up in three replicates and incubated at 39°C for 72 h. The digestibility of dry matter (DM) and fiber (NDF), VFA profiles, ammonia concentrations, pH, and microscopic counts of <italic>Ent. caudatum</italic> were compared among the three cultures. The co-culture of AAFB and <italic>Ent. caudatum </italic>enhanced DM degradation, VFA production, and <italic>Ent. caudatum</italic> cell counts; conversely, it decreased acetate: propionate ratio although the total bacterial abundance was similar between Ec and the Ec+AAFB co-culture after 24 h incubation. The ammonia production and relative abundance of <italic>C. aminophilum</italic> and <italic>P. anaerobius</italic> did not differ between AAFB alone and the Ec+AAFB co-culture. Our results indicate that <italic>Ent. caudatum</italic> and AAFB could have a mutualistic interaction that benefited each other, but their interactions were complex and might not increase ammoniagenesis. Further research should examine how such interactions affect the population dynamics of AAFB.

Keywords: Amino acid-fermenting bacteria; Co-culture; Entodinium caudatum; Intraruminal nitrogen recycling; Mutualistic interaction