MODULE 5 Flashcards
What were the most likely early cellular processes on Earth?
Hyperthermophilic anaerobic, chemolithotrophic/anaerobic respiration (abundance of Fe, along with S and H2, carbon from prebiotic compounds or CO2) or anoxygenic phototrophs (S and H2S present)
Explain the strengths and limitations of using 16S rRNA for phylogenetic analyses.
Strengths: universal presence in all organisms, functionally constant, long enough to be statistically significant, compares organisms based on same criteria, relatively easy to extract, amplify, sequence & align
Limitations: single gene, assumes overall mutation rates are similar between species
Explain the endosymbiotic hypothesis? What evidence strongly backs the hypothesis?
Explains the development of major organelles in eukaryotes: mitochondria from an aerobic bacterium and chloroplasts came from a phototrophic bacterium which developed stable symbiotic relationships within the cytoplasm of primitive eukaryotic cells. Bacterial ribosomes and 16S rRNA sequences.
Why are size and shape often less useful in characterising prokaryotic species than eukaryotic microbial species?
There is a much wider range of shapes and sizes in eukaryotic microbes, often quite distinctive for related organisms. Prokaryotes often they look the same under a microscope even unrelated species.
One of the advantages of some newly developed rapid identification tools is that pure cultures aren’t needed. Why is a pure culture necessary for biochemical tests such as the Enterotube, but not for DNA probes?
Biochemical tests assess metabolic activity of bacteria using different substrates. If cultures are not pure, you wouldn’t know which bacterium in a mixture was responsible for any positive results. Whereas DNA probes can detect the presence of specific a nucleotide sequence in one type of bacteria in a mixture.
Why is the study of extremophiles useful when looking at the possibility of life elsewhere?
The conditions on other planets or moons will be extreme by our standards, most like the habitats of extremophiles on Earth.
What are the possibilities for how life originated on Earth?
Most likely an accumulation of prebiotic compounds, formed under the conditions on Earth at the time, over hundreds of millions of year.
Regarding trends in genomics, how would you interpret the finding of a large genome in (a) a newly discovered bacteria that was an intracellular parasite, (b) a deeply branching Achaea from a hydrothermal vent?
Both with scepticism! An intracellular parasite is able to use some functions of the host cell so doesn’t need as many genes; Deeply branching Archaea have changed very little in millions of years and not picked up many new genes.
In Bergey’s manual, the gram positive cocci include the genera Micrococcus and Staphylococcus. The reported G+C content of the genome of Micrococcus is 66-75 mol % and 30-40 mol % for Staphylococcus. Is it possible that these two genera are related?
Very unlikely - they are not closely related. G+C content shows differences only, not the degree of similarity
If a species of microbe were discovered that did not appear to mutate, scientists probably would hypothesize that its lack of mutation would affect existence of ancestors that species. Explain why such an organism would have been detrimental to future life on earth if it developed early in the evolution of life.
Evolution of life is based on adaptation and molecular changes such as mutation. The organism could not adapt to changing conditions and would die out. The line of descent for that organism would end.
What is the major characteristic that distinguishes notable members of phylum Firmicutes, Bacillus and Clostridium, from most other bacteria? What phenotypic characteristic is generally used to distinguish between the two genera?
Endospore formation Oxygen requirements (Bacillus: aerobic or facultative, Clostridium: anaerobic)
What is important about nitrogen fixing bacteria?
Convert atmospheric N2 gas to ammonia, thereby accessing the largest source of nitrogen for organisms to use for growth
Prior to molecular sequencing, Rickettsia and Chlamydia were classified together, now they are in different Phyla. What common characteristic do they share that would have been the main reason for classifying them together?
Intracellular parasites
Staphylococcus aureus is often referred to as “golden Staph” and is one of the best known of all bacteria. Why is this the case?
Yellow pigmented, often part of human normal flora and can cause numerous diseases due to a wide variety of virulence factors e.g. food poisoning, wound infections, many postoperative infections, toxic shock syndrome, scalded skin syndrome, abscesses, meningitis, pneumonia.
It is well recognized that if alien life is to be found it will be most likely microbial. What do we need to look for when assessing the possibility of extraterrestrial life?
Biosignatures – signs of microbial life: e.g. fossils or microbial structures, products of microbial metabolism which can be either distinctive or at levels above expected non-biogenic rates
