Microbio Lab quiz 3

How do chemoautotrophic organisms obtain their nutrients?

can produce their own food/nutrients from inorganic carbon and energy sources

How do chemoheterotrophic organisms obtain their nutrients?

depend on the environment to provide nutrients

what does it mean to say that microbes are ubiquitous?

they appear to be present everywhere

what are most animal associated prokaryotes found?

on the skin on and in the GI tract

what are biofilms?

thin, complex layers of bacteria

can be composed of one species but often is made of variety of different species, including other microbes such as fungi

what is an organism that uses inorganic compounds as a carbon source (CO2)?

autotrophs

what are organisms that use organic compounds as a carbon source (ex. glucose)?

heterotrophs

what are organisms that use light as an energy source?

photoautotrophs or photoheterotrophs (depending on their carbon source)

what are organisms that use inorganic compounds as their energy source?

chemoautotrophs

what are organism that use organic compounds as their energy source

chemoheterotrophs

what else is present in biofilms other than the microbes?

a dense matrix of polysaccharides, proteins, DNA, inorganic components, and channels for transportation of nutrients

how do microbes within a biofilm communicate with one another?

quorum sensing

what happens to biofilms if nutrients become scarce?

microbes will detach and move away as single cells (planktonic cells) in order to find another nutrient-rich location in which to settle

where can biofilms be found?

in nature, human beings, or as biofilm infections (acquired from medical devices or otherwise)

why are biofilms beneficial to microbes?

dense structure makes it difficult to destroy them, allowing for antibiotics resistance and escaping of the host’s immune defenses

what microbes are often seen in biofilms?

Gram - positive (S. aureus) and Gram - negative (E. coli and P. aeruginosa) bacteria and Candida albicans (fungus)

for the plate containing the sample swabbed from the environment (3-1), why did we incubate at a lower temp?

Environmental microbes are adapted to cooler conditions (room temp, 30 degree), not body temp (37 degree)

For the plate containing the sample swabbed from the environment (3-1), why use TSA (and not MM1)?

TSA supports the growth of a wide variety of unknown environmental microbes, while MM1 would be too restrictive

For the plate containing the sample swabbed from the environment (3-1), why did we tape it shut?

prevent contamination, ensure accurate results and maintain safety by containing unknown microbes

what does it mean if nothing grew on the plate of microbes sampled from the environment? Does it mean the surface you sampled was sterile?

No, area could have been recently disinfected, the microbes could require different conditions in order to properly cultivate (more incubation time, more specific nutrients, incubation at a different temp, etc.)

what 2 bacterial species were present in the simulated soil sample?

bacillus subtilis (larger colonies) Micrococcus luteus (smaller, more yellow in color)

How can E.coli grown aerobically/anaerobically?

can grow in both conditions, facultative anaerobe (prefers aerobic conditions but can grow in anaerobic conditions)

how can M. luteus grow aerobically/anaerobically?

only grow aerobically. obligate anaerobe

what is an aerotolerant anaerobe?

a microbe that does not use oxygen, but can survive around it

what is nitrate reduction?

many enteric facultative anaerobes use nitrate as a terminal electron acceptor when oxygen is not available, in this process nitrate (NO3-) is reduced to either nitrite (NO2-) or ammonia (NH3)

what is denitrification?

many soil bacteria use Nitrate (NO3-) as a terminal electron acceptor, which results in the reduction of nitrate to nitrogen gas (N2). In this process other gaseous forms of nitrogen are also formed- nitric oxide (NO) and Nitrous oxide (N2O)

what does the sulfanillic acid and napthylamine do?

checks if nitrite is present in the nitrate broth ( whether or not nitrate reduction occured)

How do you interpret the results of nitrate broth after the addition of sulfanillic acid and napthylamine?

red- nitrate was reduced to nitrite (positive result for nitrate reduction)
no color change- no nitrate reduction or nitrate was reduced further (to ammonia or nitrogen gas)

how do you interpret the results of a nitrate broth that is negative for sulfanillic acid and napthylamine (remained yellow) after the addition of zinc?

if the tube turns red after zinc:

• nitrate was still there

• bacteria did not reduce nitrate (overall negative result)

if there is no color change after zinc and no air bubbles in Durham tube

bacteria reduced the nitrate beyond nitrite to nitrogen gas (denitrification)

How does E. hoshinae react in nitrate broth?

reduce nitrate to nitrite

how does B. subtilis react in nitrate broth?

reduce nitrate to ammonia

how does P.dentrificans react in nitrate broth?

reduce nitrate all the way to N2 gas (denitrification)

what is a pH optimum?

the pH at which the organism grows best

what are alkaliphiles?

pH optimum alkaline environment ( less than 9)

what are neutrophiles?

pH optimum 6.5-7.5

what are acidophiles?

pH optimum acidic environment (below 5)

what is E. coli classified as in terms of pH?

neutrophile

what is S. griseus classified as in terms of pH?

neutrophile

what is S. cerevisiae classified as in terms of pH?

acid- tolerant neutrophile

what is osmosis?

the movement of water molecules from an area of high concentration to an low area of concentration

what is an isotonic environment?

equal concentration of solutes exist outside and inside the cell

what is hypertonic environment? and what happens if cells are in one?

higher concentration of solutes exists outside the cell compared to inside the cell- water will be drawn out of the cell and into the solution (can lead to plasmolysis)

what is a hypotonic environment and what happens if cells are in one

lower concentration of solutes exists outside the cell compared to inside the cell- water will be drawn out of the solution and into the cell (can lead to lysis of cells)

what are halophiles?

require salt to grow and can tolerate up to 20% NaCl (2% NaCl inhibits growth of many other bacteria)

what are halotolerant organisms?

tolerate up to 10%- 15% NaCl but do not require salt to grow

what do haloferax volcanii and H, salinarun require

aeration in order to grow well (shaking)

If you have 2 petri dishes with potato slice in them and one is soaked in H2O and the other in 20% NaCl solution, which is more bendy?

potato soaked in 20% NaCl solution is more bendy because water moves out of the cells, cells shrink (plasmolysis), therefor tissue becomes limp, soft, and less flexible

what are the EnteroPluri- Test and API 20E system?

both are expensive
both miss organism that are:

• not in the database

• for which the media is not suitable

what are the differences of the EnteroPluri-Test and the API 20E system?

EnteroPluri- Test: easier to inoculate

API 20E System: harder to inoculate but easier to add chemicals for interpretation

why is it easy to predict that S. epidermidis is halotolerant?

it lives on salty human skin and must tolerate high salt conditions to survive

what does autoclaving do?

use moist heat under pressure, which allows temperatures to be raised above the boiling point of water/aqueous solutions, to sterilize growth media (destroy all contaminating organism, as well as endospores)

what does the addition of UV radiation do?

induces the formation of thymine dimers in DNA, these DNA lesions alter the structure of DNA, and if not repaired, can consequently cause mutations.

what typically happen to thymine dimers formed by UV radiation?

will normally be repaired by a set of “repair enzymes” within the cells

what is the primary cause of melanomas in human?

unrepaired pyrimidine dimers

UV radiation can be used to kill bacteria but what are the drawbacks?

• poor penetration if UV light

• short distance to source is required (15 cm)

• long exposure time

• UV radiation is not equally effective among the bacteria

what is an example of mutualistic relationship?

relationship between Rhizobium (bacteria), and the soybean plant

nodules on soybean roots consist of enlarged plants cells packed with bacteria

what is an example of parasitic relationship?

T4 bacteriophage infecting E. coli cells

which bacterial strain can form a biofilm at the air liquid interface (a pellicle)?

B. subtilis

what is selective media?

only some microbes grow (ex.PIA)

what is selective differential media?

characteristics of both (MacConkey)

what is differential media?

a variety of bacteria may grow but they are visually distinguishable (starch Agar)

how was S. epidermidis affected by high heat?

did not show growth at any point after 2 mins in the hot bath

how were the vegetative cells of B. subtilis affect by high heat

did not show growth at any point after 2 mins in the hot bath

how were the endospores of B. subtilis affected by high heat?

showed growth until after 20 mins in the hot bath

how was S. epidermidis affected by UV radiation?

did not show growth at any point after 0.2 mins exposed to the UV except with a lid on

how were the vegetative cells of B. subtilis affected by UV radiation?

did not show growth at any point after 0.2 mins exposed to the UV except with a lid on

how were the endospores of B. subtilis affected by UV radiation

did not show growth at any point after 1 min exposed to the UV except with a lid on

which bacterial strain is susceptible to T4 bacteriophage E. coli 455 or E.coli 363?

E. coli 363 (plaques present)

what is the difference between the CFU calculating formula and the PFU calculating formula?

the formulas are mathematically the same but:

• CFU counts the growth of bacteria (colonies)

• PFU counts the presence of viruses (plaques)