Module 7: Microbial Genomics (Variability) Flashcards

1
Q

Comparative Genomics

A

The study of evolutionary relationships among organisms based upon DNA sequence (using genomic tools)

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2
Q

Comparative Genomics provides insights into (5):

A

1) Phylogeny of all life

2) Relationships between species

3) Fundamental processes influencing microbial diversity and evolution

4) Differences between strains of a species

5) Identification of genes for virulence + pathogenicity

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3
Q

Homologs

A

A gene that has a common evolutionary descent (same ancestral gene) to another gene (Evolutionarily linked genes)

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4
Q

Duplication Events

A

Types of mutations in which a region of DNA containing a gene is replicated

== 2 copies of the same gene occur within the genome at once!

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5
Q

Paralogs

A

Homologs that arose from a duplication event of an ancestral gene WITHIN a lineage

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6
Q

How are paralogs able to form from duplication events?

A

Because when two of the same gene exist within the genome, only ONE must carry out its original function for a given cell to survive

–> As such, one of the copies is “free” to evolve a new function

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7
Q

Paralog Families

A

Genes (paralogs) with a similar function but have different substrates they act upon and thus different specific products

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8
Q

What is an example of a paralog family?

A

ABC transporters

–> All of them have a similar function/are same KIND of protein but each will allow for the transport of different molecules

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9
Q

Orthologs

A

Homologs (related genes) that have evolved from the same ancestor and have the SAME function in TWO DIFFERENT species

–> Became separated via speciation!

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10
Q

What genes of two species genomes are assumed to be orthologs?

How do we truly test for orthologs?

A

Genes in 2 genomes with HIGH levels of sequence similarity

True test = whether or not the 2 genes have the same function!

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11
Q

What is an example of paralogs vs example of orthologs (with dehydrogenases)?

A

Paralogs = Malate dehydrogenase + Lactate dehydrogenase in the SAME genome!

(Many cells have multiple dehydrogenases that act upon different substrates as a result of evolution from duplication event)

Orthologs = Malate dehydrogenase + malate dehydrogenase in two different species genomes!

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12
Q

Horizontal Gene Transfer

A

HGT

== Sharing of genetic info by microbes

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13
Q

Why are genomes considered as “mosaics”?

A

Because current genomes have arisen via both evolutionary changes and horizontal gene transfers

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14
Q

What is a main piece of evidence that HGT may have occurred between species?

A

G-C Content (% GC)

(Genomic Base Pair Composition)

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15
Q

Genomic Base Pair Composition

A

The ratio or proportion of A-T and G-C base pairs out of the total number of base pairs

(An indicator that a gene or genomic region may have been transferred via HGT)

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16
Q

% GC

(GC content)

A

The % of the total # of base pairs that are GC in the entire genome

17
Q

Why can GC content be used to determine if HGT may have occurred between 2 species?

A

Because GC content is typically unique per genome + does not vary much WITHIN a singe genome

(= any region of a genome that has a different GC content than the majority of the genome is likely not from the organism)

18
Q

Examples of GC content values for E.coli, Streptomyces, and S. cerivisiae

A

E. coli = 50% GC

Streptomyces = 72% GC

S. cerivisiae = 38% GC

19
Q

Genes/regions exhibiting a significant difference in GC content could indicate…

A

Genes/regions exhibiting a significant difference in GC content could indicate that the specific gene had a distinct evolutionary history from the rest of the genome (and as such was likely transferred)

20
Q

If Strain A (50% GC) and Strain B (70% GC) both have GENE X (and their versions of this gene have a similar sequence) BUT gene X in Strain B has GC content = 50%. What does this suggest?

A

Suggests that:
1) Gene X has a distinct evolutionary history == likely not from this organism == Likely a transferred gene!

2) Gene X was likely transferred to Strain B from Strain A!

21
Q

Other than GC content, what other pieces of evidence are there for HGT events?

A

1) Differences in nucleotide pair patterns

2) Differences in codon usage patterns

3) Presence of repetitive sequences

4) Gene phylogeny

(When evolutionary relationship predicted by SSU rRNA + DNA sequence are NOT matching)

22
Q

What is a limitation of predicted HGT with GC content analysis?

A

It may lead to a lack of recognition of HGT occurring between genomes with similar GC content

–> GC content does NOT need to be anomolous in order for HGT to occur

23
Q

GC content does NOT need to be ________________ for HGT to occur

In actuality…

A

–> GC content does NOT need to be anomolous in order for HGT to occur

In actuality, HGT is most successful between genomes with similar GC contents!

24
Q

Genomic Islands

A

DNA segments of >10-200 Kb that are transferred from one species to another

25
Q

What are genomic islands typically associated with?

A

1) tRNA genes
2) Transposable elements
3) Plasmids/bacteriophages

26
Q

How were genomic islands discovered?

(What was observed?)

A

They were discovered during comparisons of sequences of related microbes

== Observed many large regions of DNA that were completely present in one of the related species while completely absent in the other

–> Suggests transfer of DNA!

27
Q

A single genome sequence does NOT exist for microbe species because…

A

Extensive HGT = highly variable genome!

28
Q

Metagenomics

A

Process by which DNA is extracted directly from microbial communities and analyzed as a composite mixture

–> Application of genomic tools for study of microbial communities

29
Q

What are metagenomic methods typically used for?

A

To study the genomes + features of UNCULTIVATED microbes

30
Q

What are some limitations of metagenomics?

A

1) Targets only a SUBSET of a microbial community (too big of a task to analyze each independent genome in a collected culture)

2) Does not lend itself to confident predictions (of the uncultivated microbes being studied)

3) Does not provide info on microbial interactions (within the community being analyzed)

31
Q

In what way do metagenomics NOT lend to “confident predictions”?

A

For uncultivated microbes, their DNA sequences (collected via metagenomics) is not enough to produce predictions about their physical features

32
Q

What are benefits of metagenomics? (2)

A

1) Functional Metagenomics (study of gene functions within a metagenomic library)

(Leads to…)

2) Discovery of novel enzymes (many of which have applications in biotech)

33
Q

Functional Metagenomics

A

Experimental approach for studying gene function, starting from the extracted DNA of mixed microbial populations

–> Clones in the metagenomic library are SCREENED for specific enzymatic functions or proteins produced!

34
Q

What is Single-Cell Genomics and FACS?

A

Single-Cell Genomics = Field that studies the unique characteristics and genome of individual cells

FACS = Fluorescently Activated Cell Sorting

–> A method (used in single-cell genomics) that can be used to recover individual uncultivated cells to amplify and sequence their genomes

35
Q

For what microbes is FACS utilized?

A

For microbes detected via only single genes!

36
Q

Define Metatranscriptomics + Metaproteomics

A

Metatranscriptomics = DIRECT analysis of RNA from the environment (no cloning)

Metaproteomics = Analysis of environmental proteins DIRECTLY (no cloning)