Rumen Microflora: The lengthy history of symbiotic relationships between animals and microbes has influenced th e evolution of animals. Ruminants are great example of it. Ruminants are herbivorous mammals (e.g., cows, goats, sheep, etc.) that have a special gut region before the stomach known as the rumen. It is a chamber for anaerobic digestion. Ruminants are the dominant herbivores on Earth, and because the human food economy is heavily reliant on them, rumen microbiology is of considerable economic significance and importance. Rumen microorganism research has greatly aided our understanding of anaerobic microbial ecosystems, as well as influencing feeding practices and nutritional modelling in ruminants. This topic will go over the relationship between ruminants and microbes. Rumen is an anaerobic digestion chamber of ruminants, so it can only contain anaerobic microbes.
Rumen microbe’s symbiotic interaction: Here I will consider cow as a model animal. In the rumen of cows, bacteria, archaea, protozoa, and fungi coexist. bacteria make up about half of the living organisms but do more than half of the rumen digestive work. They work cooperatively. Cross feeding occurs when one organism breaks down certain carbohydrates and proteins that are used by another. The rumen, reticulum, omasum, and abomasum are the four compartments of the cow. The abomasum is the true stomach of cow.
Bacteria associated with Rumen: There are four types of bacteria work together
1. Fibre digesting or cellulolytic bacteria: Because cows eat gases made up of cellulose, the fibre digester bacteria are present in the rumen. When a cow has acidosis (pH less than 6), the rumen produces less VFA (volatile fatty acid) because the fibre digester cannot produce VFA due to acidosis (volatile fatty acids). Furthermore, a high fat content inhibits the growth of the fibre digester(Madigan et al., 2019). There are several bacteria species in the rumen that can degrade fibre and produce VFA. Viz Ruminococcus albus, Bacteroides succinogenes.
Growth requirements: cellulose, hemicellulose, lignin, pectin etc.
pH: Around 6
By Product: VFA, Hydrogen, carbon dioxide and others by product.
2. Starch and sugar digesting or amylolytic bacteria: A significant portion of the rumen bacterial population is involved in starch and sugar digestion. In general, high-producing dairy cows are fed diets that contain more than 30% starches and sugars, so these bacteria are critical. Even if a cow is fed only straw, the fibre digesters will never constitute more than 25% of the rumen bacterial population. There are several bacterial species in the rumen that can synthesise VFA from starch. For examples Bacteriodes amylophilus, Streptococcus bovis etc.
Growth requirements: starch sugar amino acid also vitamin B ammonia etc.
pH – Around 5.7
Product - lactic acid and VFA
Compared to fibre digesters, starch digesters grow more quickly. Thus, if the ruminant feeds too many grains that include starch, the number of Streptococcus bovis increases and can cause acidosis by reducing the rumen pH from 6 to 5 or less, which results in the ruminant's mortality. lactic acid is more acidic than VFA, despite the fact that some bacteria that break down starch can also make VFA(Madigan et al., 2019). However, it is not enough to for lactic acid to be produced.
3. Lactic acid using bacteria: As was already established, some bacteria, like Streptococcus bovis, create lactic acid, a potent acid. Lactic acid is used by Megasphaera elsdenii to grow. This promotes rumen cleaning and raises rumen pH, which promotes the development of acid resistant fibre digesters(Madigan et al., 2019).
Growth requirements: lactate
Product: VFA
pH: lower than 6.
4. Syntroph: By generating acetate from other VFA, the group of helper bacteria known as Syntroph assists Methanobacter. Example - Syntrohomonas sp.
Growth requirements: hydrogen, VFA etc.
Product: acetate or simple VFA.
Several microbes, rather than bacteria, play an important role in the rumen. Viz -
Rumen Archaea: In order to convert carbon dioxide and hydrogen into methane, archaea are found in the rumen. Rumen protozoa surface is where rumen archaea attach and reside. Example Methanobacterium sp(Madigan et al., 2019).
Growth requirements: hydrogen, carbon dioxide, simple VFA etc.
Product: methane.
pH: 6 or less than 6.
Rumen Protozoa: Protozoa may make up as much as 50% of the total microbial mass in the rumen. However, they play a less important role than the rumen bacteria or archaea. Starch can be stored by rumen protozoa, which might aid in reducing the generation of lactic acid. Some protozoa can coexist as parasites with ruminants. Most protozoa entered the rumen through food. There are several ciliated protozoa found in rumen Entodinium caudatum, Polyplastron sp. Since typical protozoa require oxygen to survive, they cannot exist in the anaerobic environment of the rumen. Therefore, cytochrome is not present in rumen protozoa(Madigan et al., 2019).
Rumen Fungi: Although they are poorly understood, fungi are known to make up up to 8% of the total mass in the rumen. They slowly proliferate and are connected to foot particles. One excellent example of a fungus that can digest fibre is Aspergillus oryzae(Madigan et al., 2019).
Role of different Microbes:
The three different types of microbes produced in the rumen include fungi, bacteria, and protozoa(Page Not Found | Department of Agriculture and Fisheries, Queensland, n.d.).
Different microbes have different digestive roles.
The slow-moving fiber-digesters found on the rumen's fibre mat and the fast-moving bacteria that float around in the rumen fluid in search of easily-digested nutrients like sugars and starches are the two primary categories of rumen microbes.
References:
- Madigan, M., Bender, K., Buckey, D., Sattley, M., & Stahl, D. (2019). Brock biology of microorganisms. In Pearson (Ed.), Brock Biology of Microorganisms.
- Pearson. Page not found | Department of Agriculture and Fisheries, Queensland. (n.d.). Retrieved July 1, 2022, from https://www.daf.qld.gov.au/documents/AnimalIndustries_Dairy/Dairy-1Rumenmicrobes.pdf
- https://en.wikipedia.org/wiki/Rumen#:~:text=The%20rumen%2C%20also%20know n%20as,alimentary%20canal%20of%20ruminant%20animals.
- (https://www.google.com/search?q=fistula+in+cow&tbm=isch&ved=2ahUKEwjiNLr_Nf4AhWAyKACHR4gCQMQ2- cCegQIABAA&oq=fistula+in+cow&gs_lcp=CgNpbWcQA1AAWABgT2gAcAB4AIABAIgB AJIBAJgBAKABAaoBC2d3cy13aXotaW1nwAEB&sclient=img&ei=qQ6_YqKACoCRg8U PnsCkGA&bih=657&biw=1366&).
- (https://www.google.com/search?q=rumen+compartments&rlz=1C1FHFK_enIN970IN97 0&source=lnms&tbm=isch&sa=X&ved=2ahUKEwjv4PLg_df4AhUzRmwGHZqGDPUQ_ AUoAXoECAEQAw&biw=1366&bih=657&dpr=1#imgrc=jz9zkWaXx9Zc7M).
