Are Yeast Multicellular :Why,How And Detailed Insights And Facts

Are yeast multicellular or not is a very tricky question.Yeast are one of the most economically important fungus having more than 1,500 species all over the world. Let’s try to find out if yeast are multicellular or not?

Yeast are mostly unicellular, evolved from multicellular ancestors. In some cases they can adapt multicellular characteristics or depending on the environmental factors they can switch between unicellular and multicellular life cycle, so we can say that yeast are facultatively multicellular.

In the case of Baker’s yeast or Saccharomyces cerevisiae, it can adapt multicellular characteristics in it by forming colonies or by other mechanisms. Hence we can say that yeast are mostly unicellular but in some cases they are facultatively multicellular.

To know more about Eukaryotes read the article Eukaryotic Cells Examples: Detailed Insights

What is facultative multicellularity?

Facultative means optional so in simple words facultative multicellularity is a condition in which unicellular organisms can be able to achieve multicellular characteristics depending on external factors.

Facultative multicellularity is a condition in which a species which is naturally unicellular, can be able to adapt multicellular characteristics. Some specific environmental factors trigger the unicellular organism for adaptation. In response that unicellular individual becomes a part of the multicellular body. After overcoming that particular obstacle it can revert to its previous unicellular form.

Facultative multicellularity can be present in two different forms, the first one is the simplest way to achieve multicellularity, that is forming a clump by sticking to each other (unicellular cells).The second one is more complex than the first one, cell differentiation.

Examples of facultative multicellularity:

Baker’s Yeast ( saccharomyces cerevisiae) is the most common facultative multicellular.

Are yeast multicellular

Saccharomyces cerevisiae from Wikimedia commons

Causes of facultative multicellularity

When we talk about the causes of facultative multicellularity, then there are some specific environmental factors that trigger an unicellular organism for adaptation. 

Depending on all these factors, an individual unicellular organism changes its gene expressions and adapts multicellular lifestyle for its evolutionary survival. 

  • Structured environment: Structured environment highly influences the facultative multicellularity. Presence of this factor stimulates multicellular metabolic activity by changing the gene expression. Due to that the individual cells start to differentiate into non-dividing forms and make colonies or biofilms.
  • Starvation : Starvation is also an important factor that can trigger facultative multicellularity in unicellular organisms. Starvation or lack of glucose in cells stimulates the cell differentiation process. In this case the diploid organism starts to produce haploid spores (sporulation process). The environmental stress resistance power of these haploid spores are much better than vagitative forms that give the evolutionary benefits to that organism. Due to starvation some organisms like saccharomyces cerevisiae form “pseudohyphal growth” by which they can produce special Q cells (quiescent cells) that give evolutionary benefits to it.
  • Aging: Aging is also a factor for facultative multicellularity. In case of yeast (saccharomyces cerevisiae) after dividing a defined number of times (replicative lifespan or RLS) the mother cells are getting old. Then the metabolic activity and gene expressions are slightly changed. In colonies the cells change from acidic phases to alkaline phases to synchronize better metabolism and communication with each other. Hence the older colonies or biofilms are more resistant than others. 

Importance of facultative multicellularity

Facultative multicellularity gives various evolutionary benefits to those organisms. It makes their lifestyle easier for natural selection. 

  • In some cases where a single celled organism fails, a multicellular group or colonies easily performs all those tasks. 
  • Facultative multicellularity give an organism fitness advantages. Bigger biofilm allows more effective nutrient intake and affects the growth factors positively.
  • Facultative multicellularity also prevents food deficiency related problems. From multicellular yeast cells an enzyme invertase secretes polysaccharide (sucrose) into monosaccharide (glucose and fructose). That’s how the cellular sugar levels maintain and they thrive successfully.
  • The stress resistance power increases. The developing spores or Q cells are more stress resistant than the vagitative forms. In exposure to environmental factors such as starvation or mechanical stress these have more stress tolerance to survive.
  • By achieving multicellularity, the organism also develops an extra protection mechanism. In biofilm colonies the inner cells remain protected by extracellular matrix and surface cells from environmental toxins and external forces. 

Facultative multicellularity in saccharomyces cerevisiae 

The bakers Yeast or Saccharomyces cerevisiae is the best example of facultative multicellular organisms. They achieve multicellular characteristics by both simple cell adhesion to more complex cell differentiation developments. 

  • Cell adhesion : In the most simple way the S. Cerevisiae sticks with each other and performs cellular interactions between them by forming a clump. In other ways through budding a mother forming a daughter cell. After DNA and cytoplasmic division devoid separation they both stay attached with each other and perform a stay together strategy to achieve multicellular characteristics. 
  • Cell differentiation: In complex format the yeast cells interact and perform cell differentiation processes. In this model division of labour is seen. By cell differentiation process they form non-adhesive colonies and biofilms. They achieve multiple evolutionary benefits from it. In this method the yeast cells perform multicellular activities to avoid nutritional deficiencies, develop protection mechanisms and many more. Stress resistance power increases through making biofilms.

To know about eukaryotic cells and bacterial cells read the article on Eukaryotic Cells Vs Bacterial Cells: Detailed Insights

Yeast unicellular characteristics

Yeast are mostly unicellular organisms so they possess several unicellular characteristics in its lifestyle.

  • Simple eukaryotic cell organization. Typically smaller in size approximately 3-4 µm in diameter. Depending on the species variation it can grow upto 40 µm in diameter. 
  • As they are having only a single-cell, the total body is directly exposed to the environment (except colonies).
  • As an unicellular organism, yeast usually reproduce by asexual methods (by budding). A small bud forms in the mother cell, after completing DNA and cytoplasmic division, the bud (daughter cell) separates from the mother cell.
  • Due to absence of proper movement mechanisms yeast cells are normally non-motile ( unable to move).
  • They are usually saprophytic, which means they don’t eat ( metabolism by eating needs multiple cellular mechanisms); they absorb nourishment (unicellularity friendly nutritional method) from other compounds.
  • As an unicellular organism in presence of oxygen yeast undergo cellular respiration convert sugar into carbon dioxide and ATP. 

Are yeast multicellular?

Yeast are naturally unicellular but can be able to adapt multicellular characteristics in presence of advarce situations. They make colonies or biofilms to achieve evolutionary benefits. This condition is called facultative multicellularity.

Through achieving facultative multicellularity they are able to avoid nutritional deficiencies. They develop more complex protection mechanisms and all.

How is yeast unicellular?

Yeast belongs to kingdom fungi. They are normally single-celled organisms. That means it possesses a single cell and performs all its Metabolic activities through it. So, that is why we can say that yeast are unicellular organisms. 

According to a study, yeast are single-celled organisms which evolved from multicellular ancestors. They also possess facultative multicellularity that means they are able to achieve multicellular characteristics.

Are all yeast multicellular?

The answer of this question is very tricky because as we previously discussed all yeasts have only a single eukaryotic cell and possesses it’s Metabolic activities through it. But when the situation is adverse some yeast cells adapt multicellular characteristics, becoming a part of the multicellular body. They form colonies. 

So the answer is most of the yeasts are unicellular and some are facultatively multicellular. 

Baker’s Yeast or Saccharomyces cerevisiae is the best example of facultative multicellular organisms. 

As a whole we can say that yeast are unicellular organisms, having the ability to adapt multicellular characteristics in adverse situations. Which means they are facultatively multicellular. We briefly describe all the possible aspects of facilitative multicellularity. We describe how yeast are multicellular? We also discuss unicellular characteristics of yeast. Hope this article will be helpful to you.

Also Read: