Introducing microbes
Micro-organisms (or microbes for short) play a very important role in our lives. Some microbes cause disease but the majority are completely harmless. In fact we couldn’t live without them, but they could live without us.
These microscopic organisms play a key role in maintaining life on earth, fixing gases and breaking down dead plant and animal matter into simpler substances that are used at the beginning of the food chain. Biotechnologists can also exploit the activities of microbes to benefit humans, such as in the production of medicines, enzymes and food. They are also used to breakdown sewage and other toxic wastes into safe matter. This process is called bioremediation.
Microbes are very small living organisms, so small that most of them are invisible. The majority can only be seen with a microscope, which magnifies their image so we can see them. In fact microbes are so tiny you would find over a million in a teaspoon of soil. They make up more than 60 % of the Earth’s living matter and scientists estimate that 2-3 billion species share the planet with us.
Micro-organisms occur in an amazing variety of shapes and sizes and they are divided into one of 6 groups:
Bacteria
More than just pathogens - can be friend or foe.
More information
Viruses
Smallest of all the microbes but are they alive?
More information
Fungi
More than just mushrooms.
Protozoa
Microbes with a taste for poo and so much more.
More information
Algae
Microbial powerhouses essential for life.
More information
Archaea
First found existing on the edge of life.
More information
Bacteria are single celled microbes. The cell structure is simpler than that of other organisms as there is no nucleus or membrane bound organelles. Instead their control centre containing the genetic information is contained in a single loop of DNA. Some bacteria have an extra circle of genetic material called a plasmid. The plasmid often contains genes that give the bacterium some advantage over other bacteria. For example it may contain a gene that makes the bacterium resistant to a certain antibiotic.
Bacteria are classified into 5 groups according to their basic shapes: spherical (cocci), rod (bacilli), spiral (spirilla), comma (vibrios) or corkscrew (spirochaetes). They can exist as single cells, in pairs, chains or clusters.
The different bacterial shapes
© Jamie Symonds Medium RareMore information
A typical bacterial cell
© Jamie Symonds Medium RareMore information
Antibiotic resistance
Artwork of bacterial cells becoming resistant to antibiotics. This resistance is acquired from a donor cell's plasmid (circular unit of deoxyribonucleic acid, DNA), which has resistance seen at upper left (red/yellow, red is resistance). Viral transmission involves a virus (pink, lower left) obtaining a resistant gene, and passing it to a bacterial cell that incorporates it into its plasmid. Bacterial cells also acquire segments of DNA released from dead cells (upper left). Mutations (not seen) may also occur, which may be antibiotic resistant and thus allow the bacteria to survive and reproduce.
ترجمة
© Bryson Biomedical Illustrations / Custom Medical Stock Photo / Science Photo LibraryMore information
Bacillus anthracis spores
This bacterium causes anthrax in farm animals and less commonly in humans. Spores can survive for many years and are resistant to extremes of heat, cold and drying.
© NIBSC / Science Photo LibraryMore information
Reproduction through Binary Fission
One becomes two ... two becomes four ... four becomes eight
This means in 8 hours, the number of bacteria will have risen to a colossal 16,777216!More information
Other bacteria
The different bacterial shapes
A typical bacterial cell
Antibiotic resistance
Bacillus anthracis spores
Binary Fission-
Bacteria are found in every habitat on Earth: soil, rock, oceans and even arctic snow. Some live in or on other organisms including plants and animals including humans. There are approximately 10 times as many bacterial cells as human cells in the human body. A lot of these bacterial cells are found lining the digestive system. Some bacteria live in the soil or on dead plant matter where they play an important role in the cycling of nutrients. Some types cause food spoilage and crop damage but others are incredibly useful in the production of fermented foods such as yoghurt and soy sauce. Relatively few bacteria are parasites or pathogens that cause disease in animals and plants.
How do bacteria reproduce?
Bacteria reproduce by binary fission. In this process the bacterium, which is a single cell, divides into two identical daughter cells. Binary fission begins when the DNA of the bacterium divides into two (replicates). The bacterial cell then elongates and splits into two daughter cells each with identical DNA to the parent cell. Each daughter cell is a clone of the parent cell.
When conditions are favourable such as the right temperature and nutrients are available, some bacteria likeEscherichia coli can divide every 20 minutes. This means that in just 7 hours one bacterium can generate 2,097,152 bacteria. After one more hour the number of bacteria will have risen to a colossal 16,777,216. That’s why we can quickly become ill when pathogenic microbes invade our bodies.
------------------
2/3The bacterium, which is a single cell, divides into two identical daughter cells. Each daughter cell is a clone of the parent cell. Under ideal conditions such as the right temperature and nutrients are available, some bacteria such as Escherichia coli can divide every 20 minutes
Survival mechanism
Some bacteria can form endospores. These are dormant structures, which are extremely resistant to hostile physical and chemical conditions such as heat, UV radiation and disinfectants. This makes destroying them very difficult. Many endospore-producing bacteria are nasty pathogens, for example Bacillus anthracis is the cause of anthrax.-----
الفيروسات
أصغر من جميع الميكروبات ولكن هل هم على قيد الحياة؟
Viruses
Viruses are the smallest of all the microbes. They are said to be so small that 500 million rhinoviruses (which cause the common cold) could fit on to the head of a pin. They are unique because they are only alive and able to multiply inside the cells of other living things. The cell they multiply in is called the host cell.
A virus is made up of a core of genetic material, either DNA or RNA, surrounded by a protective coat called a capsid which is made up of protein. Sometimes the capsid is surrounded by an additional spikey coat called the envelope. Viruses are capable of latching onto host cells and getting inside them.
Computer artwork of a typical virus particle which is icosahedral in shape.
The virus consists of a core of RNA (ribonucleic acid, green) enclosed in a capsid, or protein coat (blue spheres). Surrounding the capsid is a glycoprotein envelope (pink and green). Inserted in the envelope are surface proteins (orange spheres), which help the virus attach to its host cell.
© NIBSC / Science Photo LibraryMore information
Tobacco mosaic virus which is helical in shape.
© Centre For Bioimaging, Rothamsted Research / Science Photo LibraryMore information
T2 bacteriophage viruses (orange) attacking an Escherichia coli bacterium.
Each phage consists of a large DNA- containing head and a tail composed of a tube-like central sheath with several fibres.
© Lee D. Simon / Science Photo LibraryMore information
AIDS virus (red/green) budding from the surface of a white blood cell.
© Eye Of Science / Science Photo LibraryMore information
Herpes simplex virus infection.
A section through a cell being destroyed by herpes simplex virus infection. At centre is a large cluster of viral capsids (protein coats, red) which the cell has produced at the direction of the virus's genetic material.
© Dr Linda Stannard, Uct / Science Photo LibraryMore information
Other viruses
Computer artwork of a typical virus particle
Tobacco mosaic virus which is helical in shape
T2 viruses attacking an E-coli bacterium
AIDS virus budding from a white blood cell
Herpes simplex virus infection-
Viruses only exist to make more viruses. The virus particle attaches to the host cell before penetrating it. The virus then uses the host cell’s machinery to replicate its own genetic material. Once replication has been completed the virus particles leave the host by either budding or bursting out of the cell (lysis).
Budding
As the newly formed viral particle pushes against the host cell’s plasma membrane a portion adheres to it. The plasma membrane envelops the virus and becomes the viral envelope. The virus is released from the cell. This process slowly uses up the host’s cell membrane and usually leads to cell death.
Lysis
The virus particles burst out of the host cell into the extracellular space resulting in the death of the host cell. Once the virus has escaped from the host cell it is ready to enter a new cell and multiply.
الفطريات
Fungi
Fungi can be single celled or very complex multicellular organisms. They are found in just about any habitat but most live on the land, mainly in soil or on plant material rather than in sea or fresh water. A group called the decomposers grow in the soil or on dead plant matter where they play an important role in the cycling of carbon and other elements. Some are parasites of plants causing diseases such as mildews, rusts, scabs or canker. In crops fungal diseases can lead to significant monetary loss for the farmer. A very small number of fungi cause diseases in animals. In humans these include skin diseases such as athletes’ foot, ringworm and thrush.
How a mycelium is formed and how spores are distributed
© Jamie Symonds Medium RareMore information
The yeast Saccharomyces cerevisiae.
Budding yeast Saccharomyces cerevisiae. Scars yellow can be seen on the surface. It is used in the production of beer, wine and bread.
© Eye Of Science / Science Photo LibraryMore information
Macroscopic filamentous Fly agaric fungus (Amanita)
© Simon Fraser / Science Photo LibraryMore information
Multicellular filamentous mould.
Rhizopus nigricans growing on bread left in a moist plastic bag for 7 days. Tangled mycelium are visible as well as sporangia bearing spores.
© Gregory Dimijian / Science Photo LibraryMore information
Honey mushroom fungus
The largest organism in the world, when measured by area, is the Honey mushroom fungus, Armillaria.
© Michael P. Gadomski / Science Photo LibraryMore information
Other fungi
How a mycelium is formed
The yeastSaccharomyces cerevisiae
Amanita
Multicellular filamentous mould
Honey mushroom fungus-
Types of fungi
Fungi are subdivided on the basis of their life cycles, the presence or structure of their fruiting body and the arrangement of and type of spores (reproductive or distributional cells) they produce.
The three major groups of fungi are:
multicellular filamentous moulds
macroscopic filamentous fungi that form large fruiting bodies. Sometimes the group is referred to as ‘mushrooms’, but the mushroom is just the part of the fungus we see above ground which is also known as the fruiting body.
single celled microscopic yeasts
Multicellular filamentous moulds
Moulds are made up of very fine threads (hyphae). Hyphae grow at the tip and divide repeatedly along their length creating long and branching chains. The hyphae keep growing and intertwining until they form a network of threads called a mycelium. Digestive enzymes are secreted from the hyphal tip. These enzymes break down the organic matter found in the soil into smaller molecules which are used by the fungus as food.
Some of the hyphal branches grow into the air and spores form on these aerial branches. Spores are specialized structures with a protective coat that shields them from harsh environmental conditions such as drying out and high temperatures. They are so small that between 500 – 1000 could fit on a pin head.
Spores are similar to seeds as they enable the fungus to reproduce. Wind, rain or insects spread spores. They eventually land in new habitats and if conditions are right, they start to grow and produce new hyphae. As fungi can’t move they use spores to find a new environment where there are fewer competing organisms.
Macroscopic filamentous fungi
Macroscopic filamentous fungi also grow by producing a mycelium below ground. They differ from moulds because they produce visible fruiting bodies (commonly known as mushrooms or toadstools) that hold the spores. The fruiting body is made up of tightly packed hyphae which divide to produce the different parts of the fungal structure, for example the cap and the stem. Gills underneath the cap are covered with spores and a 10 cm diameter cap can produce up to 100 million spores per hour.
Yeasts
Yeasts are small, lemon-shaped single cells that are about the same size as red blood cells. They multiply by budding a daughter cell off from the original parent cell. Scars can be seen on the surface of the yeast cell where buds have broken off. Yeasts such as Saccharomyces, play an important role in the production of bread and in brewing. Yeasts are also one of the most widely used model organisms for genetic studies, for example in cancer research. Other species of yeast such as Candida are opportunistic pathogens and cause infections in individuals who do not have a healthy immune system.
الترجمة
البروتوزوا
Protozoa
Protozoa are single celled organisms. They come in many different shapes and sizes ranging from an Amoeba which can change its shape to Paramecium with its fixed shape and complex structure. They live in a wide variety of moist habitats including fresh water, marine environments and the soil.
Amoeba proteus protozoa
These are freshwater single-celled microbes that feed on bacteria and smaller protozoa. They use pseudopodia (cytoplasmic extensions) to engulf their food and for locomotion.
© Steve Gschmeissner / Science Photo LibraryMore information
The test (shell) of the British formaminiferan, Elphidium crispum.
Foraminifera are single-celled protozoa which construct and inhabit shells. The shells are usually divided into chambers which are added during growth. These shells are made of calcium carbonate but some are made from sand and even silica.
© Power And Syred / Science Photo LibraryMore information
An illustration of the protozoan Trypanosoma brucei.
This illustration depicts Trypanosoma brucei moving past human red blood cells in the blood. It is motile and has a single flagellum for locomotion.
Vorticella ciliate in compost heap.
Vorticella is bell- shaped with a contractile stalk (bottom) to anchor itself to the surface. It has a flattened top with a mouth surrounded by a wreath of cilia (tiny hair-like projections). By beating these cilia the organism causes the water to swirl like water down a plug hole which draws bacteria into its mouth.
© Eye Of Science / Science Photo LibraryMore information
Paramecium a protozoan
This single-celled organism lives in freshwater habitats. It is covered in cilia, short hair-like structures used for swimming and for wafting food into its groove-like mouth (centre).
© Power And Syred / Science Photo LibraryMore information
Other protozoa
Amoeba proteusprotozoa
The test of the British formaminiferan
An illustration of the protozoanTrypanosoma brucei
Vorticella ciliate in compost heap
Paramecium a protozoan-
Some are parasitic, which means they live in other plants and animals including humans, where they cause disease.Plasmodium, for example, causes malaria. They are motile and can move by:
Cilia - tiny hair like structures that cover the outside of the microbe. They beat in a regular continuous pattern like flexible oars.
Flagella - long thread-like structures that extend from the cell surface. The flagella move in a whip-like motion that produces waves that propel the microbe around.
Amoeboid movement - the organism moves by sending out pseudopodia, temporary protrusions that fill with cytoplasm that flows from the body of the cell.
-----------------------
Algae
Algae can exist as single cells, an example of which is Chlamydomonas, or joined together in chains like Spirogyra or made up of many cells, for instance Rhodymenia (red seaweed).
Filaments of the alga Spirogyra
Green algae can make their own food through a process of photosynthesis. They are at the beginning of the food chain and are known as primary producers.
© Eric Grave / Science Photo LibraryMore information
Chlamydomonas.
Chlamydomonas is a unicellular green alga. It is motile and has two tail-like flagella that it uses for locomotion.
© Microfield Scientific Ltd / Science Photo LibraryMore information
Algal blooms lining the shores (light green).(الطحالب بطانة شواطئ (الضوء الأخضر
These blooms occur as a result of a change in the nutrient levels of the river. Contamination by sewage or fertilisers can increase the water's mineral content, which accelerates the growth of all plants, particularly aquatic algae.
A selection of diatoms
Diatoms are single-celled photosynthetic algae. Their cell walls contain a hard substance called silica.
© Steve Gschmeissner / Science Photo LibraryMore information
Dulse (red) seaweed - Rhodymenia palmata
Rhodymenia palmata is an edible alga. Dulse is very popular in Ireland, where it is often mixed with potatoes and butter, adding a salty, savoury bite to fried potato champ.
Other algae
Filaments of the algaSpirogyra
Chlamydomonas
Algal blooms lining the shores
A selection of diatoms
Dulse (red) seaweed-
Most algae live in fresh or sea water where they can either be free-floating (planktonic) or attached to the bottom. Some algae can grow on rocks, soil or vegetation as long as there is enough moisture. A few algae form very close partnerships with fungi to form lichens. Unusual algal habitats are the hairs of the South American Sloth and Polar bears.
All algae contain a pigment called chlorophyll a (other types of chlorophyll such as b, c and / or d may also be present) and they make their own food by photosynthesis. The chlorophyll is contained in the chloroplasts and gives many algae their green appearance. However some algae appear brown, yellow or red because in addition to chlorophylls they have other accessory pigments that camouflage the green colour.
Diatoms a type of algae, are found floating in the phytoplankton of the seas. Their cell walls contain a hard substance called silica. When the diatoms die they sink to the floor. Their soft parts decay and the silica cell wall remains. Over time the pressure of the seawater pushes the silica together to form one large layer. This silica is mined from the seabed, crushed and used in abrasives and polishes such as toothpaste.
Archaea
Archaea can be spherical, rod, spiral, lobed, rectangular or irregular in shape. An unusual flat, square-shaped species that lives in salty pools has also been discovered. Some exist as single cells, others form filaments or clusters. Until the 1970s this group of microbes was classified as bacteria.
Sulfolobus
Sulfolobus is an extremophile that is found in hot springs and thrives in acidic and sulphur-rich environments.
Methanosarcina rumen (green with red cell walls).
Methanosarcina rumen is anaerobic, and is found in places with little or no oxygen. It is a methane- producing organism that digests decaying organic matter. It is found in the rumen of a group of animals called ruminants such as cattle and sheep.
© Eye Of Science / Science Photo LibraryMore information
Staphylothermus marinus
Staphylothermus marinus is an extremophile found in deep ocean hydrothermal vents, thriving on volcanic sulphur and surviving in water temperatures of up to 98°C.
© Wolfgang Baumeister / Science Photo LibraryMore information
Halococcus salifodinae
Halococcus salifodinae is found in water with high concentrations of salt. These high salt concentrations would be deadly to most other forms of life, and so H. salifodinae is also known as an extremophile.
© Eye Of Science / Science Photo LibraryMore information
Methanococcoides burtonii
Methanococcoides burtonii is an extremophile and was discovered in 1992 in Ace Lake, Antarctica, and can survive in temperatures as low as -2.5 °C.
© Dr Keith Wheeler / Science Photo LibraryMore information
Other archaea
Sulfolobus
Methanosarcina rumen
Staphylothermus marinus
Halococcus salifodinae
Methanococcoides burtonii-
Many archaea have been found living in extreme environments, for example at high pressures, salt concentrations or temperatures, and have been nicknamed extremophiles. Their cell wall differs in structure from that of bacteria and is thought to be more stable in extreme conditions, helping to explain why some archaea can live in many of the most hostile environments on Earth.
Examples of archaea habitats are boiling hot springs and geysers such as those found in Yellow Stone Park, USA and ice such as the Artic and Antarctic oceans which remain frozen for most of the year.
ليست هناك تعليقات:
إرسال تعليق