AUTOLYSIS: CAUSES, PHASES AND CONSEQUENCES - BIOLOGY - 2025

The autolysis is a process by which cells are enzymatically digested by the action of its own enzymes. It literally means that the mechanisms that lead to its own lysis (death) are triggered in a cell.

This process of "self-degradation" has been observed during the normal course of growth and development of bacteria and fungi. However, many scientific texts establish that it is typical of "dying" cells or "wounded" or "injured" cells.

Representative diagram of the cellular structure of a yeast (Source: Frankie Robertson using Inkscape, own work. Via Wikimedia Commons)

Autolysis also occurs in animal and plant tissues, but some authors describe this process as the non-bacterial “self-decomposition” that occurs after cell death.

This process was described by Salkowski, in 1890, as an enzymatic process of self-digestion, but it was in 1900 that Jacobi coined the term autolysis. Today it is known that the enzymes in charge of this process are not "by-products" of lysis, but are the same enzymes that participate in cellular processes.

Given its importance for the industry, the most thoroughly reviewed autolytic process is the one that takes place in yeasts, especially those used during the fermentation processes of alcoholic beverages (wine and beer) and in the bakery.

Autolytic derivatives of yeast are commonly used in the formulation of culture media, as they represent a good source of amino acids and other nutrients.

Causes of autolysis

Autolysis can occur in response to a number of factors. In unicellular organisms (microorganisms) this phenomenon responds to many environmental conditions such as temperature, pH, oxygen concentration, composition of the medium, the amount of nutrients, the presence of toxic substances, etc.

During the fermentation of wine or beer, for example, the autolysis of yeasts occurs in response to the decrease in the nutritional components of the fermenting liquid, as well as to the considerable increase in the concentration of ethanol, which is one of the products of your metabolism.

In humans it has been shown that autolytic processes can be triggered by prolonged surgical interventions or medical procedures, especially during endoscopic submucosal dissections.

In addition, in many animals autolysis occurs in places where there are wounds or lacerations and fulfills the function of eliminating damaged tissue during healing

In some plant tissues, autolysis functions in growth and development, as well as in the transport of water and gases through the xylem ducts, which takes place thanks to the degradation of the protoplasts (membrane + cytosol) of the tracheids; occurs, then, in response to stimuli typical of plant development.

On the other hand, certain species of filamentous fungi can undergo autolysis of their cells in response to some antibiotics or toxic substances applied to the surrounding environment.

Phases

The autolytic process that will be described below is the one that takes place in yeasts, however, it can be extrapolated to any microorganism or any group of cells in a plant or animal tissue.

Cell death

Every autolytic process begins with the death of the cell in question. The initial phenomenon has to do with the alteration of the cellular membranous systems, especially when it comes to eukaryotic organisms, which allows their digestive enzymes to come into contact with the components that will be degraded.

The enzymes that participate in the autolytic event are responsible for degrading their substrates into smaller fragments. For example, proteases or peptidases "cut" almost any type of protein, releasing peptides or amino acids.

Nucleases, on the other hand, degrade nucleic acids such as DNA or RNA, fragmenting them and releasing nucleosides, mononucleotides, and polynucleotides. There are other enzymes responsible for the digestion of some components of the cell wall, usually glucanases (in yeast).

Commonly, what results from cell lysis and digestion is known as autolysate, which is released to the surrounding environment through breaks in the yeast cell wall, where digestion can continue. The concentration of the degraded cellular components usually produces something known as yeast extract.

Yeast autolysis can be divided into two processes

- The degradation of cellular components by "lytic" enzymes, especially proteinases and peptidases (proteolysis, proteolytic enzymes).

- The degradation of the cell wall, which allows true cell lysis or rupture and the release of the autolysate.

Yeasts have vacuoles that house most of the proteolytic enzymes of these cells. When such a cell dies, then these enzymes come into contact with its substrates and degrade them. In other eukaryotic animal cells these enzymes are contained in lysosomes.

Glucanases and some proteinases participate in the degradation of the components of the yeast cell wall, causing the opening or formation of "pores", which promote the release of the degradation products of internal lytic enzymes.

Consequences

The main consequences of autolytic events are evident, since a cell that self-kills dies and disappears, leaving different fractions of its constituent molecules in the process.

Some authors consider that autolysis in certain organs leads to internal "liquefaction" which, consequently, can cause atrophies or morphological deformations of the same.

For the food industry

This process can also occur in many foods, especially of animal origin, which generally implies the non-bacterial decomposition of their muscle tissues and the release of a large amount of peptides, amino acids, phosphate groups, carbohydrates, etc., which represents an ecological opportunity for the colonization of decomposing bacteria.

Another negative consequence of autolytic processes is exemplified in cheese production, where the autolysis of "starter" bacteria, belonging to the Lactococcus lactis species, has important implications in the development of the flavor of these dairy derivatives.

In some scientific texts related to the production of alcoholic beverages, the contradiction may be faced that for some authors it is a beneficial process and for others not, although this depends, essentially, on the type of drink in question.

Some wine producers consider that autolytic processes allow the release of many beneficial internal components of yeast, which have a significant influence on the sensory properties and biological stability of this liquid.

Yeast extracts have multiple uses in the production of meat derivatives (sausages), soups, sauces and other sandwiches.

Photograph of yeast extract concentrate (Source: SKopp via Wikimedia Commons)

Since the death of millions of yeasts in a culture in liquid medium represents the release of a large amount of amino acids, sugars, vitamins and other micronutrients, lysates are not only used as "enhancers" of the color and flavor of food, but are also used for the formulation of experimental growth media.

References

1. Dernby, KG (1920). A study on autolysis of animal tissues. Studies from the Rockefeller Institute for Medical Research, 32, 359.
2. Dharmadhikari, M. (2011). Yeast autolysis.
3. Escamez, S., & Tuominen, H. (2017). Contribution of cellular autolysis to tissue functions during plant development. Current opinion in plant biology, 35, 124-130.
4. Hyun, JJ, Chun, HJ, Keum, B., Seo, YS, Kim, YS, Jeen, YT,… & Chae, YS (2012). Autolysis: a plausible finding suggestive of long ESD procedure time. Surgical Laparoscopy Endoscopy & Percutaneous Techniques, 22 (2), e115-e117.
5. Mukundan, MK, Antony, PD, & Nair, MR (1986). A review on autolysis in fish. Fisheries Research, 4 (3-4), 259-269.
6. Rogers, AA, Rippon, MG, Atkin, L., Ousey, K., & Independent Wound Care Consultant, UK Autolysis: mechanisms of action in the removal of devitalised tissue in wounds.
7. White, S., McIntyre, M., Berry, DR, & McNeil, B. (2002). The autolysis of industrial filamentous fungi. Critical reviews in biotechnology, 22 (1), 1-14.