Proboscis Monkeys

The stomach of proboscis monkeys (Nasalis larvatus) has four chambers. The first of the four chambers, called the foregut, is the largest; thus the monkeys are pot-bellied. The contents in the foregut are regulated to a neutral pH of 7; hence, the monkey’s stomach harbors a varying amount of gut bacteria. These symbiotic bacteria are used by proboscis monkeys to ferment the plant fiber that is non-digested to generate energy in the form of short-chain fatty acids; this process is called foregut fermentation. Additionally, symbiotic bacteria decompose the substances that are harmful and toxic during digestion, which is beneficial to the proboscis monkeys. In a study, biochemical analyses showed that this novel bacterium has a high ability to break down various sugars contained in the natural diet consumed by proboscis monkeys. Complex, chambered stomach of proboscis monkeys is composed of a host of bacteria that aid in breaking down the plant material consumed by the monkeys. This process is similar to that seen in domestic cows. Proboscis monkeys chew their cud before the bacteria present in their gut help in further breakdown of the food consumed. The cell walls of the plant consumed contain cellulose, which is broken down by the specific bacteria. Aside from the mechanical breakdown of plant material when the monkeys chew their cud, these bacteria are maintained in the gut of the monkeys to further break down the food consumed. This process allows the monkeys to increase the nutritional value obtained from their diet containing low nutrition.

Proboscis monkey Photo of a proboscis monkey

Discovery of Lactobacillus nasalidis

A research group including Sayaka Tsuchida and Nami Hashido, both from the Chubu University, in collaboration with Yokohama Zoo and the Faculty of Environmental Earth Science of Hokkaido University, discovered a novel species of lactic acid bacteria from a proboscis monkey raised in Yokohama Zoo, Japan. This bacterium was named Lactobacillus nasalidis. This new species of the  bacterium was officially recognized by the International Committee on Systematics of Prokaryotes. Lactobacillus nasalidis is found in the foregut of proboscis monkeys regardless of whether the monkeys are raised in captivity or are living in the wild. Because of their peculiar digestive system, proboscis monkeys are raised only in Yokohama Zoo.

Lactobacillus nasalidis   Lactobacillus nasalidis                                          SEM image of Lactobacillus nasalidis

The bacterial cells on MRS agar are shown to have a rod shape and rounded end of 1µm width with variable lengths in the range of 3–6µm. These bacteria are Gram-stain-positive, anaerobic, and non-motile. The bacterial colonies on MRS agar exhibit a diameter of 1–2 mm; they are convex, white in color, disc-shaped, and smooth  after 48h at 37°C under anaerobic conditions. These bacteria are homofermentative and produce only d-lactic acid. The bacterial growth does not occur in 6.5–10% NaCl. It occurs at a pH of 4.0–10 with positive production of ammonia from l-arginine.

Lactobacillus nasalidis1

 Schematic of Lactobacillus nasalidis


  • These bacteria have a high ability to decompose the plant material consumed by the proboscis monkeys. 
  • Absorption and digestion of food in proboscis monkeys are greatly aided by this novel lactic acid bacterium. 
  • It has been speculated that these bacteria provide an essential ability in proboscis monkeys.

Ramya Kasinathan


Tags: Lactobacillus nasalidis

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