Ideonella sakaiensis (plastic-eating bacteria) – An Overview

A new species of the genus Ideonella called Ideonella sakaiensis is a rod-shaped, gram-negative aerobic bacteria. It is also known as a bacterium that consumes plastic. Plastic can serve as a key source of carbon and energy for growth for bacteria that consume it.

With Leo Baekeland’s discovery of Bakelite in 1907, the era of plastics began. The creation of a wide variety of synthetic polymers has led to their widespread use and necessity in both everyday life and, tragically, the environment.

In 2015, there was 5,000 Mt of plastic garbage in landfills and other places. That amount could increase to 12,000 Mt by 2050. Numerous hydrolytic enzymes can hydrolyze the ester bonds that bind the monomers of poly (ethylene terephthalate). Because there are no known enzymes that may directly break their C-C bonds, PET is theoretically more prone to spontaneous deterioration than polyolefin. The genome of I. sakaiensis was sequenced, and this led to the discovery of an enzyme that hydrolyzes PET. The hydrolysis products are discharged into the aqueous environment, and the surface of an amorphous PET film develops pitting that resembles craters. The I. sakaiensis enzyme was given the name PET hydrolase because, when compared to other known PHEs, it displays the highest catalytic preference for PET at ambient temperature (PETase). This bacterium converts PET into CO2 and water, using it as a main source of carbon and energy.

Ideonella sakaiensis Discovery
A group of scientists led by Kohei Oda of Kyoto Institute of Technology and Kenji Miyamoto of Keio University collected 250 samples from a PET-contaminated environment, including sediment, soil, wastewater, and activated sludge close to a plastic bottle recycling facility. PET was introduced into this ecosystem. Using these samples, they searched for microbes that could grow preferentially on low-crystallinity (1.9%) PET film. After being cultivated in a single sediment sample, distinct microbial consortia formed on the PET film, resulting in morphological changes. Ideonella sakaiensis is a species that belongs to the Ideonella genus. The bacteria was given the name Sakai after the Japanese city where it was found.

A collection of microbes in the soil sample, which also contained protozoa and cells that resembled yeast, led to the initial isolation of the bacterium. On the film and in the culture fluid, appendages connecting the cells were visible. There were shorter appendages that may have assisted in delivering secreted enzymes to the film between the cells and the film. The PET film had undergone substantial deterioration and was nearly destroyed after six weeks at 30°C.

Ideonella sakaiensis Classification
Ideonella sakaiensis, a member of the genus Ideonella of the family Comamonadaceae, was discovered to degrade plastic in response to the hunt for a biological system that could degrade plastic waste. In the Betaproteobacteria 16S rRNA phylogeny, members of the Comamonadaceae family are found together in a phylogenetic cluster.

Habitat of Ideonella sakaiensis

• Ideonella sakaiensis can be found in a variety of both natural and artificial environments, and they don’t care if a place is clean or dirty.
• Soil, fresh and groundwater, activated sludge, and water used in industrial processes are a few examples of these ecosystems.
• The physical and physiological traits of the distinct features of the genera vary widely within the species themselves as a result of the large variety of habitats.

Mode of action of Ideonella sakaiensis

PETase enzyme

• PET is broken down by the bacterial enzyme PET hydrolase, or PETase, creating mono (2-hydroxyethyl) terephthalic acid (MHET), a heterodimer consisting of terephthalic acid (TPA) and ethylene glycol (EG).
• PET’s ester bonds are hydrolyzed by I. sakaiensis PETase.
• MHET hydrolase is a different enzyme that is utilized since I. sakaiensis and many other bacteria cannot use TPA but can readily absorb and use ethylene glycol among the products.
• In other words, both chemicals derived from the PET are used by the cell to produce energy and for metabolic functions.
• This system, in particular, ranks among the most effective PET hydrolases known to exist at room temperature in terms of PET breakdown efficiency.
• As carbon is assimilated, it may eventually mineralize into carbon dioxide and be released into the atmosphere.

MHET hydrolase

• The Ideonella sakaiensis genus has another tannase-family enzyme involved in PET metabolism.
• This enzyme hydrolyzes 2-hydroxyethyl terephthalic acid (MHET), the main PET hydrolysis product of PETase, into TPA and EG.
• Due to its strong activity and excellent specificity for mono-(2-hydroxyethyl) terephthalate (MHET), this enzyme was given the name MHET hydrolase (MHETase), but it has a modest hydrolytic effect on bis-(2-hydroxyethyl) TPA (BHET) and a number of other substrates.
• Its composition comprises a lid domain and a hydrolase domain was revealed by the crystal structure.