lecture 15

Question 1

Surfaces are important microbial habitats because (3)

Answer 1

1) typically offer greater access to nutrients
2) protect from predation
3) cells can remain in favourable habitat

Question 2

Virtually any natural or artificial surface exposed to microbes will be colonized

Answer 2

-plant roots
-soil particles
-microscope slide
catheters/intravenous lines
-industrial pipes

Question 3

Biofilms

Answer 3

Assemblages of bacterial cells attached to a surface and enclosed in an adhesive matrix excreted by the cells
They can contain one or two species, or more commonly many species of bacteria
Biofilms are functional and growing microbial communities and not just cells trapped in a sticky matrix

Question 4

Matrix of biofilms

Answer 4

Mixture of polysaccharides, proteins, and nucleic acids that bind the cells together

Question 5

Biofilms trap

Answer 5

nutrients for microbial growth and help prevent detachment of cells in flowing systems

Question 6

How do biofilms form

Answer 6

Biofilm formation is initiated by attachment of a cell to a surface followed by expression of biofilm-specific genes, and repression of genes for motility
Bacteria sens a suitable surface and this leads to biofilm growth

Question 7

Pseudomonas aeruginosa -notorious biofilm former

Answer 7

Switch from planktonic to biofilm growth is triggered by elevated production levels of small molecule c-di-GMP which initiate production of extracellular polysaccharides, decrease flagellar fctn, prepare cells for cell-cell and cell-surface interactions

Question 8

Quorum sensing

Answer 8

Intraspecies communication which is critical in the development and maintenance of biofilm (leads to increased levels c-di-GMP)

Question 9

Acyl homoserine lactones (AHLs)

Answer 9

Major intracellular signalling molecules
As AHLs accumulate they signal to adjacent cells that the population is enlarging, controls expression of genes involved in biofilm formation

Question 10

Why bacteria form biofilms (3)

Answer 10

1) Self-defense against phagocytosis by protists and immune cells
2) They resist physical forces that sweep away unattached cells and retard the penetration of toxic molecules ex antibio
3) Allows cells to remain in a favorable niche (nutrient rich environment)
4) Allows bacterial cells to live in close association with one another, facilitates cell-cell communication and survival

Question 11

biofilms form on virtually any surface capable of supporting bacterial growth

Answer 11

biofilms are the “default” growth mode for bacteria in natural habitats

Question 12

Biofilms control

Answer 12

Biofilms have been implicated in several medical & dental conditions
Medical implants = ideal for biofilm development

Question 13

Microbial mats

Answer 13

Among the most visible microbial communities
Can be considered as thick biofilms
Have existed for 3.5 billion years

Question 14

Microbial mats are supported by

Answer 14

phototrophic or chemolithotrophic bacteria
Layers composed of species of different microbial guilds - activities are governed by light
Phototrophic mats contain filamentous cyanobacteria

Question 15

Microbial mats can change dramatically within a 24h period as a consequence of..

Answer 15

changing light intensity

Question 16

Chemolithotrophic microbial mats

Answer 16

Most common of them are composed of filamentous sulfur-oxidizing bacteria (SOBs)

Question 17

Chemolithotrophic microbial mats grow on…..

Answer 17

Sediments at the interface between O2 supplied from overlying water & H2S produced by sulfate-reducing bacteria living in the sediment

Question 18

SOB filaments can migrate through

Answer 18

the microbial mat and underlying sediments to optimize the use of e- donor (H2S) and e- acceptor (O2 or nitrate) in cases where they do not overlap in the environment