PERIPHYTON: CHARACTERISTICS, MORPHOLOGY, COMPONENTS, GROWTH - BIOLOGY - 2025

The periphyton, known by some as biofilm can be defined as a set of microorganisms that form a kind of lining of or is anchored to various substrates. The microorganisms that make up the periphyton are held together thanks to the presence of the extracellular matrix that they secrete.

Due to the great diversity of microorganisms in the periphyton, it can be found in all types of habitats, even in the most adverse climatic conditions, such as glaciers and even hot springs.

Periphyton. Source: Everglades NPS from Homestead, Florida, United States

From an ecological point of view, the periphyton is very important, since it fulfills various functions in ecosystems, among which its capacity as an indicator of pollution levels stands out.

General characteristics

The periphyton is a complex, woven network that is generally attached to some type of substrate submerged in water. Likewise, given that the organisms that comprise it tend to reproduce exponentially, the periphyton has a rapid growth. This is so because in the medium there are the necessary nutrients for the microorganisms to develop optimally.

Similarly, one of the most notable characteristics of periphition is that the organisms that make it up secrete a kind of extracellular matrix with a gelatinous consistency that holds them together and anchored to each other and to the substrate.

The periphyton is composed of a wide variety of microorganisms such as bacteria, protozoa, and algae. Each of these contributes its particular properties and characteristics for the periphyton to thrive, develop and prevail.

Morphology

Morphologically, the periphyton is observed as a thin carpet that covers the different surfaces found in the waters. It is made up of a wide range of microorganisms of different types, such as algae, bacteria, fungi and protozoa that secrete a polysaccharide matrix in which they are compacted.

Although the periphyton is found covering a wide variety of substrates, new research seems to suggest that it is found mainly on plants.

Some specialists describe it as a kind of grass, whose thickness can vary according to the ecosystem in which it is found. The texture of the periphyton is quite smooth, even classified as slug by some specialists. The predominant color is green, thus betraying the abundance of photosynthetic organisms in its composition.

Components

The components of the periphyton are quite varied, mainly members of the monera and protista kingdoms.

Organisms of the Monera kingdom

The amount of bacteria present in the periphyton is very abundant. Of course, bacterial species are not standard, rather they depend on the ecosystem in which it is found.

However, taking into account various studies in which the periphyton of various areas throughout the world have been characterized, it can be established that the prokaryotic genera present in it with greater frequency are the following:

• Enterobacter sp: made up of anaerobic bacteria that are mainly decomposers of organic matter. They also carry out the fermentation process through which they metabolize carbohydrates, and also under aerobic conditions they are capable of oxidizing a great variety of substrates. Some are also recognized human pathogens.
• Pseudomonas sp: are gram-negative bacillus-shaped bacteria that mainly thrive in oxygen-rich environments. They are catalase positive organisms, so they can degrade hydrogen peroxide. Thanks to metabolic diversity, they have the ability to colonize a wide range of environments, making it possible to find them as components of periphyton in many ecosystems.
• Citrobacter sp: group made up of bacillary bacteria that have an aerobic metabolism. They are gram negative and are capable of fermenting some carbohydrates such as lactose. They are common inhabitants of water and soil, which is why they are regular components of the periphyton.
• Other bacterial types: other bacterial genera that have been found as components of the periphyton in a multitude of environments are Chromobacterium sp, Acinetobacter sp, Stenotrophomonas sp and Klebsiella sp, among others.
• Cyanobacteria: These are generally known as blue-green algae. They have pigments such as chlorophyll inside their cells, so some can photosynthesize. They are also capable of using atmospheric nitrogen as a source of this element.

Organisms of the protist kingdom

The members of the protista kingdom that are part of the periphyton are algae and protozoa, among which are:

• Chlorophytas: they are the so-called green algae, with abundant chlorophyll in their cells, which gives them their characteristic green color. Due to the presence of chlorophyll, they are autotrophic organisms, capable of carrying out the photosynthesis process. Its size is variable, and green algae can be observed in the periphyton, both macroscopic and microscopic. Among the genera of green algae found in the periphyton can be mentioned Ulothrix, Chaetophora and Oedogonium, among others.
• Rhodophytas: commonly known as red algae. They are generally multicellular and contain chlorophyll and other pigments, such as carotenoids. The latter contribute to giving it its typical reddish coloration. One of the most commonly found genera of red algae in the periphyton is Hildebrandia.
• Diatoms: they are unicellular algae quite common in marine habitats. They are characterized because their cells are limited by a cell wall made up of hydrated silicon dioxide. They are capable of photosynthesis. The most common diatom genera in the periphyton are Cocconeis, Cymbella and Navicula, among others.

Diatom, regular member of the periphyton. Source: Picturepest

• Protozoa: they are characterized by being eukaryotic microscopic organisms, unicellular and generally heterotrophic. Some have flagella that help them in the process of locomotion. The common protozoan genera in the periphyton are Stentor, Vorticella, Euplotes, and Epistylis, among many others.

Increase

The growth and development of the periphyton is a gradual process that encompasses several stages:

• Contact and anchoring to the surface: it is the initial phase of the formation process of the periphyton. At this stage, the bacteria and other microorganisms that form it begin to establish certain connections with the substrate and anchor themselves to it. Initially, these connections are somewhat weak, but as the number of microorganisms grows, they become stronger.
• Formation of microcolonies: microorganisms that had anchored to the substrate begin to reproduce, mainly asexually through binary fission.
• Communication between molecules and production of the extracellular matrix: through a mechanism known as "quorum sensing" bonds are established between the various cells. Likewise, the production of EPS (extracellular polymeric substances) is increased, which contribute to the microorganisms being closely together.
• Maturation of the periphyton: already at this stage a complex structure begins to develop. Here the organisms that make up the periphyton begin to adapt to aspects such as the availability of oxygen and some nutrients.

Growth stages of the periphyton. Source: Aalexopo

Utility

The periphyton is an element of vital importance in ecosystems, since through it it is possible, for example, to determine the degree of contamination, as well as to clean up polluted waters. In the same way, the periphyton serves as a food source for the fish in the ecosystem in which it is found, so it is also used in aquaculture.

Pollution and water quality indicator

The periphyton has been used in numerous ecosystems as an indicator of pollution levels. This is because there are organisms that have a predilection for certain components that can be considered pollutants.

In this sense, when you want to know the levels of contamination of a site, you can take a sample of the periphyton that has grown there and identify the microorganisms present in it.

By knowing the relationship between some microorganisms of the periphyton and certain pollutants, it can be concluded without a doubt whether an environment is contaminated or not.

Likewise, the periphyton can be used to determine water quality due to its high sensitivity to changes and the rapid response it generates to them.

Ecosystem Cleaner

Various studies have shown that periphyton is an excellent cleaner of ecosystems. This is because the microorganisms that make it up are capable of absorbing and metabolizing certain pollutants, such as some metals such as zinc, cadmium, copper and nickel.

By doing this, they greatly reduce pollution levels in certain places. Its abilities to remove harmful chemicals, as well as to reduce water turbidity, are currently under study.

Fish feed and in the aquaculture industry

The periphyton has been shown to be a food source for some fish that show certain adaptations that allow them to scrape the periphyton from the substrate. Likewise, it has been used in some projects that involve aquaculture in order to be food for fish and mollusks that are raised in this way.

References

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4. Hill, W., Ryon, M., Smith, J. and Marshall, s. (2010). The role of periphyton in mediating the effects of pollution in a stream ecosystem. Environmental Management. 45 (3). 563-76.
5. Rojas, J. (2005). Bacterial diversity in the periphyton in roots of eichornia sp, pistia sp and azolla sp, in an artificial wetland of the Earth University. Viewed at: repositoriotec.tec.ac.cr
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