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Types of Symbiotic Relationships
Type Population A Population B
Mutualism Benefitted Benefitted
Amensalism Harmed Unaffected
Commensalism Benefitted Unaffected
Neutralism Unaffected Unaffected
Parasitism Benefitted Harmed

When two species benefit from each other, the symbiosis is called mutualism (or syntropy, or crossfeeding). For example, humans have a mutualistic relationship with the bacterium Bacteroides thetaiotetraiotamicron , which lives in the intestinal tract. B. thetaiotetraiotamicron digests complex polysaccharide plant materials that human digestive enzymes cannot break down, converting them into monosaccharides that can be absorbed by human cells. Humans also have a mutualistic relationship with certain strains of Escherichia coli , another bacterium found in the gut. E. coli relies on intestinal contents for nutrients, and humans derive certain vitamins from E. coli, particularly vitamin K, which is required for the formation of blood clotting factors. (This is only true for some strains of E. coli , however. Other strains are pathogenic and do not have a mutualistic relationship with humans.)

A type of symbiosis in which one population harms another but remains unaffected itself is called amensalism . In the case of bacteria, some amensalist species produce bactericidal substances that kill other species of bacteria. For example, the bacterium Lucilia sericata produces a protein that destroys Staphylococcus aureus , a bacterium commonly found on the surface of the human skin. Too much handwashing can affect this relationship and lead to S. aureus diseases and transmission.

In another type of symbiosis, called commensalism , one organism benefits while the other is unaffected. This occurs when the bacterium Staphylococcus epidermidis uses the dead cells of the human skin as nutrients. Billions of these bacteria live on our skin, but in most cases (especially when our immune system is healthy), we do not react to them in any way.

If neither of the symbiotic organisms is affected in any way, we call this type of symbiosis neutralism . An example of neutralism is the coexistence of metabolically active (vegetating) bacteria and endospores (dormant, metabolically passive bacteria). For example, the bacterium Bacillus anthracis typically forms endospores in soil when conditions are unfavorable. If the soil is warmed and enriched with nutrients, some endospores germinate and remain in symbiosis with other endospores that have not germinated.

A type of symbiosis in which one organism benefits while harming the other is called parasitism . The relationship between humans and many pathogenic prokaryotes can be characterized as parasitic because these organisms invade the body, producing toxic substances or infectious diseases that cause harm. Diseases such as tetanus, diphtheria, pertussis, tuberculosis, and leprosy all arise from interactions between bacteria and humans.

Scientists have coined the term microbiome to refer to all prokaryotic and eukaryotic microorganisms that are associated with a certain organism. Within the human microbiome , there are resident microbiota and transient microbiota . The resident microbiota consists of microorganisms that constantly live in or on our bodies. The term transient microbiota refers to microorganisms that are only temporarily found in the human body, and these may include pathogenic microorganisms. Hygiene and diet can alter both the resident and transient microbiota.

Questions & Answers

what is fermentation example ?
Sonal Reply
is proceess in which an agent couses of an oganic substances breakdown into simpler substance,especially in aneorobic breakdown of suger into alcohol.
Okashat
is it better to study microbiology and then medicine it makes no difference to go directly to medicine?
Jessee Reply
Dray's mathdme cell wall konse color k hote he
Jinal Reply
what is dray's mathdme cell wall
Prabhat
I confused. please help me
Karen
just confused
Raj
l don't understand it please explain it for me.
Karen Reply
epitopes are present on the surface of
Rohit Reply
at the tip of variable region on the antibody...where antigen and antibody binding sites combine...
Fiza
The term that is used refer to moving microbes under a microscope are referred to as?
Lee Reply
Members of the genus Neisseria cause which of the folowing human diseases?
Farah Reply
genital infections
Kamaluddeen
gonorrhoea
sandip
gonorrhoea
Jessee
4. Which of the following specimens should not be refrigerated? a. Urine b. Urogenital swab
Zahraa Reply
urine
Muuse
urine
Agatha
Urine
Tean
urine
Yasser
Urine
Ebtehal
urine
anamika
urine
Puja
urine
Inemesit
urine
Samuel
Urine
Muhammad
Details about McConkey agar
Muhammad
urine
SK
urine
what is bacteria
anamika Reply
a member of large number of unicellular microorganism which have cell wall but lack of cell organelles an oranised nucleus including somewhat can cause disease
Sukhdeep
Bacteria are usually composed of one cell onl to that are neither plants nor animals, microscopic, that may cause diseases or may be beneficial(in gut)... it depends upon their weapons. Nearly all animal life is dependent on Bacteria for their survival
Fiza
thanks
anamika
what factor make bacteria colony large and how could we sterlise it in large scale
fatty
nutrient concentration temp gaseous conc ph ion or salt concentration mositure condition factors contribute to make large colony. by autoclaving we will sterilize bactetia
Sukhdeep
Colony is actually visible growth of Bacteria that is as a result of suitable environment for growth i.e optimal conditions for growth, temperature, moisture etc. there're many methods to get rid of bacteria. If We stop giving them optimal conditions for living Bacteria will die soon .
Fiza
what's the difference between an antigen and a pathogen?
Pathogens are organisms that cause disease in other organisms whereas Antigen is a part of a pathogen that triggers the immune response..
Rajat
so it is the antigen that dendritic cells present to the T cells and not the pathogen itself?
no no antigen are the west product or part of the pathogen. in such case bacteria it self fight with over immune response & in another case bacteria release antigens
vasava
& other antigen like pollan grain, dust particles etc.....
vasava
pathogen are microbes that can infect the body and causw illness....antigens are the part of pathogens that alert the body to an infection
Sukhdeep
antigen is a part of blood and pathogen is foreign particle which causes diseases
Yogyata
antigen could be non microorganism.... where as pathogen is mixroorganism
tadesse
Thanks
Karen
a pathogen is a disease causing organism while an antigen is a protein in the white blood cells which combats pathogens.
Jessee
what type of widal test
sobhit Reply
this test determine for typhoid in this test if H,O antigen are present that indicate the positive test bac. are salmonella typhy
vasava
what h.o denotes
Iqra
o: body of bacteria, h: flagellate
Explain Mould
Chinenye Reply
Explain mycoses and it's classification
Chinenye
why do we have hiccups?
Manisha Reply
shakey diaphragm
Curlisse
The antibody binding site is formed primarily by:
Asalla Reply
How many types of MICROORGANISMS do we have?
Hope Reply
Hello friends
Hope
microorganisms are divided into seven type Bacteria archaea protozoa algae fungi virus and multicellular animal parasites
Raj
Practice MCQ 3

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Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
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