THE UNSEEN LIFE OF RIVERS: Mysterious aquatic microorganisms
Author: Jovana Kostić-Vuković
Keywords: microorganisms, bacteria, viruses, fungi, protozoa, algae, periphyton
Short intro: In this article, you will learn something about the smallest living systems on the planet and the communities they form and their important roles in aquatic ecosystems. Since these organisms could be seen only with the help of the microscope, we call them microorganisms.
1. MICROORGANISMS
Most living organisms like plants, animals, and humans are visible to the naked eye. Still, the world around us is teeming with living creatures which could not be seen by the naked eye. Since they require a microscope to be seen, these organisms are called microorganisms.
Most microorganisms are unicellular and require magnifying instruments to be seen. However, some unicellular microbes could be seen by the naked eye (example: Thiomargarita namibiensis), while there are some multicellular organisms that are microscopic. Also, colonies of some microorganisms could be seen by the naked eye.
Thiomargarita namibiensis (Schulz et al., 1999)
Colonies of different types of bacteria and fungi (www.schaechter.asmblog.org)
Microorganisms are found in each of the three domains of life: Bacteria, Archaea, and Eukarya.
Three domains of life: Bacteria, Archaea, and Eukarya (www.ib.bioninja.com.au)
Microorganisms within the domains Bacteria and Archaea are prokaryotes (their cells lack a nucleus), while the one in the domain Eukarya are eukaryotes (their cells have a nucleus). Some microorganisms, such as viruses, does not have cellular organization and do not fall within any of the three domains (www.courses.lumenlearning.com).
Different groups of microorganisms under microscope
Microorganisms are present in large quantities everywhere, and some of them can survive extreme physical and chemical conditions. Many microorganisms play foundational roles in aquatic ecosystems, capturing the sun’s energy through photosynthesis and, through their role in decomposition, releasing nutrients stored in organic tissue.
1.1 Prokaryotic Microorganisms
1.1.1 Bacteria and Archaea
Bacteria and archaea could be found everywhere! They are at this very moment present on your skin, nose, and teeth. Some other could be found in soil, water, and air. Some specific „strong“ bacteria and many archaea live in the environments where none of us could survive, such are hot springs in Yellowstone National park in America, where water reaches the boiling temperature, or inside the ice on Antarctica.
Yellowstone National park (www.yellowstonepark.com) and Antartic ice (Baron Reznik/Flickr (CC BY-NC-SA 2.0))
Bacteria and archaea are single-celled organisms and they are considered as one of the first inhabitants on the Earth. Ancient bacteria filled Earth’s atmosphere with oxygen over millions of years, allowing oxygen-breathing life to exist.
Bacteria are natural and vital members of all aquatic communities, and are the foundation of lake and stream ecology—without them, the natural water worlds would not be possible. In rivers and streams, many of the bacteria wash in from the surrounding land, and their abundance can increase dramatically after a rainfall. Typically bacteria are present in the millions per milliliter, and in the hundreds of millions per milliliter in productive or polluted waters. Under suitable conditions bacteria will reproduce rapidly, by simple division, producing very large numbers in a short period of time.
Bacteria can be found suspended in the water, associated with decaying material (such as dead wood or leaves), or coating the surface of rocks, stones, and sand grains as part of the biofilm (the slippery coating on hard surfaces in rivers). They can make up a large fraction of the living material in aquatic systems.
Bacteria display the greatest range in metabolic ability of any group of organisms. There are both autotrophic and heterotrophic bacteria. Heterotrophic bacteria are a crucial link in the decomposition of organic matter and the cycling of nutrients in aquatic systems. Autotrophic bacteria, predominantly cyanobacteria, are primary producers in aquatic systems.
Even though bacteria have a bad reputation, most are completely harmless, or even helpful! They help us digest our food and fight off some illnesses. Bacteria are used in recycling and clean-up of environmental disasters like oil spills. Our world would not be able to survive without bacteria.
In the past, it was thought that Archaea represent an unusual group of bacteria and they were classified as Archaebacteria. When it was shown that Archaea have an independent evolutionary history and numerous differences from other forms of life, they were classified as a separate domain in the three-domain system. Archaea were first believed to inhabit only extreme environments, such as hot springs with boiling water, Antartic frigid deserts, very salty lakes, and environments with high or low pH. However, today it is known that they have much wider distribution, inhabiting non-extreme marine waters, soils, freshwaters, and even our skin (Gribaldo & Brochier-Armanet, 2006).
1.1.1.1 The size and the shape of bacteria and archaea
It is difficult to distinguish between Archaea and Bacteria on the basis of their morphology since they generally have similar size and shape. They can take on different shapes, but the most common are cocci-shaped that look like spheres or ovals, rod-shaped called bacilli, and spiral-shaped called spirilla. However, some archaea may have very interesting shapes, such as the Haloquadratum walsbyi with flat, square-shaped cells.
The most common shapes of bacterial cells (www.biologyblock4.pbworks.com) and cell of Haloquadratum walsbyi (www.microbestiary.org)
The bacterial or archaeal cell is very small and typically ranges in size from about 0,2 – 2 micrometers (µm) in diameter for bacteria, and 0,5-4 µm for archaea. One µm is equal to one-millionth of a meter and is so small that hundreds of bacteria can fit into a space the size of the period at the end of this sentence.
Even though each bacterium weighs less than a quadrillionth of a gram, the weight of all bacteria in the world is roughly one billion tons (a gigaton). This is about equal to the weight of all plants on Earth. In other words, the biomass (mass of living organisms) of bacteria roughly equals the weight of 50 million blue whales.
1.1.1.2 How do bacteria and archaea reproduce?
Bacteria and archaea reproduce quite differently from plants and animals. The most common form of their reproduction is called binary fission, where a single cell splits into two identical daughter cells.
Binary fission (printscreen www.youtube.com/watch?v=f-ldPgEfAHI)
This is an example of asexual reproduction because the genetic material of the offspring comes from one parent. They can also reproduce asexually by budding and fragmentation. Bacterial populations can grow very rapidly, doubling in size as quickly as every 20 minutes.
1.2 Eukaryotic microorganisms
1.2.1 Fungi
Fungi occur as single cells, and in filaments called hyphae. Most aquatic fungi are microscopic. Fungi are heterotrophic, and, like heterotrophic bacteria, obtain their nutrition by secreting exoenzymes into their immediate environment, which break compounds down into simpler substances the fungi can absorb. Fungi are critical to the decomposition of plant matter in aquatic systems because they are among the few organisms that can break down certain plant structural compounds such as cellulose and lignin.
Variuos types of fungi (www.collective-evolution.com, www.videoblocks.com)
1.2.2 Protozoa
Protozoa are microscopic, single-celled organisms that sometimes group together into colonies. There are both autotrophic and heterotrophic types of protozoa. Unlike bacteria and fungi, which absorb dissolved organic compounds from their environment, heterotrophic protozoa (such as the amoebas and Paramecium) consume other organisms such as algae, bacteria, or other protists. Together with other microorganisms, protozoa make up the biofilm coating sediments and hard surfaces on riverbeds, though some protozoa are free-swimming, and some are parasites.
Protozoa (www.deviantart.com)
1.2.3 Algae and Phytoplankton
Algae vary in size from microscopic to large colonies that can be considered macrophytes.
Different Algae (Leliaert et al., 2012)
Several types of algae, including phytoplankton, have an important role in supplying the energy at the very base of many aquatic food webs. Phytoplankton represents small, microscopic algae that live in the open water. Phytoplankton is generally more abundant in lakes than rivers, and are absent from fast-flowing streams, or where the rate at which the plants are washed downstream is greater than the rate at which they reproduce. Damming a river leads to still-water conditions more suitable for phytoplankton, and nuisance algal blooms may develop in reservoirs. Inputs of nutrients, including nitrogen and phosphorus, can also lead to algal blooms.
Phytoplankton is a direct food source for many zooplankton and some fish. Phytoplankton varies in their requirements for nutrients, light, and other conditions. Waterbodies support a complex mixture of phytoplankton that can change markedly with environmental conditions. In rivers containing significant amounts of phytoplankton, the concentration of algal cells is generally highest when flows are lowest, while elevated suspended sediment loads during high flows can lead to reduced light and thus photosynthesis. Some phytoplankton can cause taste and odor problems in water, and anoxic conditions that can kill fish (www.ramp-alberta.org/river/ecology/life/microorganisms.aspx).
1.3 Periphyton and Biofilm
Periphyton represents a mixture of autotrophic and heterotrophic microorganisms embedded in a matrix of organic detritus. It covers all submerged surfaces, including bottom sediment, rocks, submerged leaves, branches, and macrophytes. The term periphyton refers to a layer consisting mainly of algae, but the entire assemblage of layers is often called a biofilm. The blue-green algae in periphyton are primary producers which give periphyton a green color. Periphyton is the most important primary producers in the streams. When primary producers are eaten, they pass on the energy they collected from the sun to other organisms, known as consumers, that can’t make energy from the sun. Consumers of periphyton are snails, frogs, aquatic insects, and fish. Without periphyton, the food web of the freshwater would collapse. Periphyton also represents a home for numerous small organisms. If you take a piece of periphyton and observe it, you may find small worms, insects, or eggs on its surface or inside. Biofilm can also be important in absorbing or breaking down chemical contaminants.
Periphyton on rock surface (www.hiveminer.com) and under microscope (www.phycotech.com)
Viruses
Viruses are thought to be in a grey zone between living and non-living entities. They are obligate intracellular parasites, which means they can not live and replicate outside of the host cell. The ability for replication classifies them as living entities. However, since they do not have cellular organization and cannot survive outside the host cell, they are considered non-living. Host cells of viruses are found in all three domains of life (Bacteria, Archaea, and Eukarya), which means there are viruses of bacteria, archaea, plant, fungi, protozoa and animal cells. Viral particle is called virion and it is built of genetic material (DNA or RNA) surrounded by a protein coat called a capsid. Sometimes a virus can have additional layers borrowed from a host cell. In freshwater ecosystem viruses and their impact on host cells (bacteria, fungi, plants, and animals) have recently begun to be explored.
www.orbitbiotech.com
Conclusion
Microorganisms are wide spread and important members in all ecosystems. Autotrophic microorganisms, such are some bacteria (cyanobacteria) and algae supply aquatic ecosystems with the oxygen they produce in the process of photosynthesis. They can take inorganic substances and with the help of the sun transform them into organic nourishment. Thus, autotrophs are primary producers at the base of all food chains. Heterotrophic microorganisms, such are bacteria and fungi have an irreplaceable role in aquatic ecosystems for decomposition of complex organic matter into simple ones that will be later used by autotrophs in the production of organic matter. In the next article „Roles of aquatic microorganisms in the recycling of matter,“ you will learn more about these heterotrophic organisms – naturally born recyclers.
References:
http://mocomi.com/microorganisms/
Schulz, H. N., Brinkhoff, T., Ferdelman, T. G., Mariné, M. H., Teske, A., Jørgensen, B. B. (1999). Dense populations of a giant sulfur bacterium in Namibian shelf sediments. Science, 284(5413), 493-495.
https://courses.lumenlearning.com/microbiology/chapter/types-of-microorganisms/
Baron Reznik/Flickr (CC BY-NC-SA 2.0)
Gribaldo, S., Brochier-Armanet, C. (2006). The origin and evolution of Archaea: a state of the art. Philosophical Transactions of the Royal Society of London B: Biological Sciences, 361(1470), 1007-1022.
http://biologyblock4.pbworks.com/w/page/51845180/Kingdom%20Monera%20%28Bacteria%20and%20Viruses%29
http://microbestiary.org/portfolio-item/haloquadratum-walsbyi/
http://www.teachoceanscience.net/
https://www.youtube.com/watch?v=f-ldPgEfAHI
https://www.deviantart.com/paleoaeolos/art/Protozoa-47313031
Leliaert, F., Smith, D. R., Moreau, H., Herron, M. D., Verbruggen, H., Delwiche, C. F., De Clerck, O. (2012). Phylogeny and molecular evolution of the green algae. Critical Reviews in Plant Sciences, 31(1), 1-46.
www.ramp-alberta.org/river/ecology/life/microorganisms.aspx
https://hiveminer.com/Tags/periphyton%2Csampling
https://www.phycotech.com/Services/Periphyton
Glossary:
Colony – two or more conspecific individuals living in close association with one another. Cells in colony are often derived from a single parent cell and thus represent cluster of identical cells (clones).
Photosynthesis – process by which green plants and some other organisms use sunlight to synthesize organic nutrients from carbon dioxide and water, releasing oxygen as a by-product.
Budding – a form of asexual reproduction in which a new individual develops from some generative anatomical point of the parent organism.
Fragmentation – a form of asexual reproduction in which a parent organism breaks into fragments, each capable of growing independently into a new organism.
Hyphae – comprised of hypha, the long filamentous branches found in fungi and actinobacteria.
Macrophyte – a macroscopic plant, commonly used to descibe aquatic plant, that is large enough to be visible to the naked eye.
Phytoplankton – a type of microscopic plankton capable of photosynthesis found in oceans, seas, and freshwater, and an essential component of aquatic ecosystems.
Detritus – waste or debris of any kind.
DNA – deoxyribonucleic acid, a self-replicating material present in all living organisms, and a carrier of genetic information.
RNA – ribonucleic acid, complex compound of high molecular weight that functions in cellular protein synthesis and replaces DNA as a carrier of genetic information in some viruses.
Further readings:
Schulz, H. N., Brinkhoff, T., Ferdelman, T. G., Mariné, M. H., Teske, A., Jørgensen, B. B. (1999). Dense populations of a giant sulfur bacterium in Namibian shelf sediments. Science, 284(5413), 493-495.
http://www.biology.arizona.edu/cell_bio/tutorials/pev/main.html
http://encyclopedia.kids.net.au/page/ar/Archaea
https://academickids.com/encyclopedia/index.php/Archaea
https://www.ducksters.com/science/bacteria.php
https://easyscienceforkids.com/bacteria-good-guy-or-bad-guy/
https://easyscienceforkids.com/all-about-fungi/
https://www.kidsdiscover.com/teacherresources/fungi/
https://kidsbiology.com/biology-basics/fungi-kingdom/
https://www.factmonster.com/dk/encyclopedia/nature/fungi
https://kids.kiddle.co/Protozoa
https://easyscienceforkids.com/protists/
http://encyclopedia.kids.net.au/page/pr/Protozoa
https://kids.britannica.com/kids/article/algae/352729
https://academickids.com/encyclopedia/index.php/Algae
http://encyclopedia.kids.net.au/page/al/Algae
https://www.ducksters.com/science/biology/viruses.php
https://kidsbiology.com/biology-basics/what-is-a-virus/
https://www.neok12.com/Microorganisms.htm
https://www.amnh.org/explore/ology/microbiology/microbes-coloring-book-scavenger-hunt/online-coloring-bacteria
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