emes 446 midterm 1

microorganism

traditionally defined as an organism that is too small to be seen clearly with the naked eye (usually smaller 1 millimeter in diameter)

• includes viruses, bacteria, many algae, fungi, and protozoa

EXCEPTION: bacterium thiomargarita

thiomargarita (bacterium)

• isolated off the coast of Namibia in seafloor sediment

• grows in strands of single cells

• approx. 1 mm in diameter (3 million times the volume of an average bacterial cell)

• visible to the naked eye

important events in microbiology

• 1676- Leeuwenhoek discovers “animalcules” (the FATHER of microbio)

• 1953- Watson and Crick propose the double helix structure for DNA

• 1977- escherichia coli genome sequenced

• 2003- first human genome sequence was completed

antonj van leeuwenhoek

• father of micrbio

• dutch, born in 1632

• known for building the first microscope

• 1674- discovers the alga Spirogyra

• 1677- first to observe spermatozoa

• 1683- discovered bacteria in dental tartar

• 1702- discovered diatoms in water

1674- discovery of alga Spirogyra

this event has been considered by some to be the simultaneous births of the fields of microbiology, protistology, and phycology

1677- the first to observe spermatazoa

leeuwenhoek originally thought these were parasites in the genitalia

1683- discovered bacteria in dental tartar

leewenhoek’s first “sample” was his own dental tartar, and later when he was in his 80’s and his teeth fell out, he would study the bacteria in the roots

1702- diatoms in fresh water

now we know diatoms in the ocean produce 20% of the oxygen that we breath

the spontaneous generation hypothesis

• the hypothesis that some vital force contained in or given to organic matter can create living organism from inanimate objects

• was widely held belief throughout the middle ages

• a common example was maggots arising on mean that been left in the open

• Redi thought maggots arose on meat because flies laid their eggs on meat, which hatched into maggots

redi’s experiment

• challenged the “spontaneous generation” hypothesis

• maggots grew on meat in unsealed jar, did not grow on sealed jar, and grew on the gauze-covered jar (but not directly on the meat)

cell theory

• all living things are composed of cells

• cells are the basic unit of structure and function in living things

one-gene-one-enzyme hypothesis

states that one gene results in the production of one enzyme

the genetic code

• a set of rules by which information encoded in genetic material (DNA or RNA sequences) is translated into proteins (amino acid sequences) by living cells

• 61 “sense” codons encode for 20 different amino acids (>100 amino acids in nature)

• 3 “nonsense” or “stop” codons terminate translation when the protein is complete

**most living organisms use the same “universal code” to synthesize proteins

symbiosis

greek for “living together”

• first used by german mycologist Heinrich Anton de Bary in 1879

• de Bary defines symbiosis as “the living together of unlike organisms”

• symbiotic relationships are close and often long-term interactions

Lichens

• the FIRST described symbiosis

• 2 partners: a single FUNGI and single PHOTOSYNTHETIC partner (cyanobacteria (protists with chloroplasts) or algae (bacteria with chlorophyll- related to chloroplasts))

• partners together form structure that individual symbionts cannot make

• fungal hyphae protect photosynthetic partner from environ. hazards (desication)

• photosynthetic partners provides fungi with fixed carbon

• a long-term relationship (estimates at 400 million years)

mutualism

A has positive effect on B

B has a positive effect on A

OBLIGATORY

• an obligatory relationship where there is some reciprocal benefit to both interacting partners

• partners often will not survive if separated

cooperation

A has positive effect on B

B has a positive effect on A

NOT OBLIGATORY

commensalism

A has a positive effect on B

“no effect” of B to A

predation

one organism eating another

parasitism

parasite going into host to get benefits

amensalism

A uses up resources to exclude B

EXPLOITATIVE COMPETITION

interference competition

A directly inhibits/kills B

symbiont

the microbe

host

the larger organism

ectosymbiont

symbiont is on the surface of the host

endosymbiont

symbiont within the host

• can be intracellular (within host cell) or extracellular (in body cavities but not intracellular)

holobiont

when there is more than one symbiont, this group of organisms (host and all its microbial symbionts) is sometimes called a “holobiont” Ex. corals

microbiome

when there are multiple microbial symbionts within a host

aposymbiotic

a host that is without its symbiotic partner

• can potentially be seen in nature

horizontal transmission

cyclic occurrence of aposymbiotic and symbiotic phases in the host’s life cycle

• symbiont has a facultative life style consisting of the host-associated and the free-living phases

• the free-living population serves as the inoculum for the symbiosis

examples- soybean, bobtail squid, vestimentiferan tubeworm

vertical transmission

transfers symbiont directly from parent to offspring

• no aposymbiotic stage (symbiosis is permanent)

• symbiont transmission occurs (most often) through the eggs because eggs have more space and nutrients

examples- hermaphroditic bryzoan, hermaphroditic earthworm

pros/cons of horizontal transmission

pros

• more opportunities to evolve (symbiont)

• increase fitness as needed (host)

pros/cons of vertical transmission

pros

• host do not have to compete for symbionts

• most common for obligatory mutualisms

cons

• 
  

pea aphid and the Buchnera aphidicola

host- pea aphid

symbiont- intracellular endosymbiont Buchnera)

transmission mode- maternal vertical transmissions

obligatory mutualism

• pea aphid feeds on plant phloem sap that is deficient in essential aminod acids

• Buchnera lives inside aphid and aids in synthesis of these amino acids

• Buchnera is transferred to offspring through mat. vert. trans.

• pea aphid has many secondary symbionts, but Buchnera is its primary symbiont showing that symbiosis are not typically monospecific (one bacterium one host)

history of B. aphidicola Mutualism

• lost approx. 86% of genome during adaptation to endosymbiotic life

• genome has remained highly stable (little change) over the last 50 million years