Unit 17 - Microbial Symbioses with Plants and Animals

What is symbiosis?

Intimate, long-term association between organisms of different species

Define common arrangement

Multicellular eukaryote (host) and microbial partner (symbiont)

What are the three types of symbioses?

• Parasitism

• Commensalism

• Mutualism

Define parasitism

Symbiont lowers fitness

Define commensalism

Microbe has no net impact on host fitness

Define mutualism

symbiont increases host fitness

Define root nodules

N2 fixing “factories” of rhizobia

Root nodules are responsible for what percentage of N2 fixed on Earth?

1/4

Steps of Root Nodule Development (5)

• Recognition and Attachment due to rhicadesin

• Root hair curls, envelops rhizobium cell

• Rhizobium penetrates root hair and multiply through Infection Thread

• Infection grows towards root cell

• Root nodule forms and cycle repeats with cell division

What is an infection thread?

A tube internal to the root hair that allows the bacteria to grow

What does Crown Gall Disease do?

Create tumors of plant tissues with uncontrollable growth

Define Agrobacterium tumefaciens (2)

• Gram Negative Bacteria

• Causative agent of Crown Gall Disease

How does Agrobacterium tumefaciens cause disease?

Transferring a piece of DNA called the T-DNA from a plasmid known as the Ti plasmid

What is inside the Ti plasmid? (3)

• T-DNA

• Opine catabolism genes

• Vir genes

Define T-DNA

Integrated into the host chromosome, the host then synthesizes opines

Define opine catabolism genes

Promotes growth of A. tumefaciens within the tumor

Define vir genes

mediates T-DNA transfer into host

What are opines?

Modified amino acids

How does T-DNA transfer into the host cell? (2)

• Plant wounds release phenolics (aromatic + hydroxyl) which serves as signal of VirA (sensor kinase)

• VirG activates transcription of vir genes which act as the secretion system for T-DNA

T-DNA insertion into the plant genome results in what?

Tumor formation and opine production

Ti plasmids have been mutated to eliminate what?

Virulence factors

What is a bacteriome?

Organ in some insects

What is a glassy-wing sharpshooter?

A xylem feeding insect

Xylem is rich in what and poor in what?

Rich: Carhohydrates

Poor: Proteins/Missing Amino Acids

What is Baumannia cicadellinicola

An endosymbiont within bacteriocytes that helps synthesizes histidine for the glassy-wing sharpshooter

Pholem diet definition

carbohydrate rich, protein poor, 9 missing amino acids including tryptophan

What appears to be an unavoidable outcome from a symbiotic lifestyle

Genome decay

How many Mbp does endoymbionts have

0.14 to 0.80

What is the termite diet

plant material, dung, and humus

Termite gut contains what?

Bacterial symbionts

Higher termites eat what?

Diverse materials

Lower termites eat what?

Wood

Microbes at exterior of the termite gut bacteria respire how?

Respire O2

The interior environment of the termite gut is what? (O2 rich or anoxic)

Anoxic

What occurs in the gut of a termite produces acetate for the host

Fermentation

How many phyla of Bacteria and Archaea are inside higher termite guts?

12 bacteria, few archaea

Define metagenomic analysis

Gene identification by unbiased sequencing

What are the two phytotypes in higher termite metagenomics that can hydrolyze cellulose?

• Spirochaetes

• Fibrobacteres

Define counter-illumination

Bioluminescence directed downwards to avoid detection from below

Define light organ

Contains populations of Vibrio fischeri

What type of bacteria is Vibrio fischeri

Gram negative

Does the Hawaiian bobtail squid hatch with or without bioluminescence?

Without, bacteria acquired later

How does quorum sensing and bioluminescence in hawaiian bobtail squid (3)

• LuxI encodes a synthase for AHL 3-oxo-C6 HSL

• 3-oxo-C6 HSL binds to LuxR which binds to the promoter of LuxI to recruit DNA polymerase

• This leads to more 3-oxo-C6 HSL and the expression of luciferase