Biofilms of the phylloplane Flashcards
the below ground habitate colonised by microbes is called the….
rhizosphere
the aerial habitate colonized by microbed is called the…
phyllosphere
what is the phylloplane?
the leaf surface
(where microbes live)
what are the inhabitants of the phylloplane called?
epiphytes
what is the approximate terrestrial leaf surface area?
~640 million sq km
what hostile fluctuating environmnetal stresses do phylloplanes face?
UV, temp, dessication
what are the two most abundant species on leaves of perennial rye (Lolium perenne)?
Pseudomonas fluorescens 20.12%
Xanthomonas campestris 19.64%
what are the most abundant species on leaves of olive (Olea europea)
Pseudomonas syringae 51.0%
Xanthomonas campestris 6.7%
what fresh produce is E.coli O157:H7 found on?
apple juice, bean sprouts, cabbage, celery, coriander, cress, lettuce
what fresh produce is salmonella found on ?
Aubergine, bean sprouts, celery, cabbage, cauliflower, fennel, lettuce, orange juice, spinach, spring onions, strawberries, tomato, watermelon
what fresh produce is Campylobacter spp found on?
Lettuce, mushrooms, potatoes, parsley, pepper, spinach, spring onions, watercress
what fresh produce is Listeria monocytogenes found on?
Aubergine, bean sprouts, cabbage, cucumber, lettuce, mushrooms, potatoes, radishes, tomato
what fresh produce is shigella found on?
Celery, lettuce, melon, parsley
give some examples of pathogen vehicles onto the leaf surface
- compost
- irrigation water
- feral pig/pigeons
what are the disadvantages to ex situ sample preparation and culture recovery methods
- Non-culturable species and strains exist
- Sub-lethally stressed cells may not grow within a given incubation period, or indeed at all.
- Accuracy depends on efficient recovery from the sample being tested – SAMPLE PREPARATION IS VERY IMPORTANT – the Pulsifier
what microscope is used for in situ detection?
EDICEF microscopy
what leaf structures can be seen in EDIC microscopy?
epidermal cells
stroma
leaf vein cells
what is the stroma?
air pore for diffusion of gases in and out of leaf
what the function of leaf vein cells?
transport of water and nutrients
why does chlorine end up in salad washing processes?
Salad production occurs on the east side of the UK, which is sunny and dry and thus the production process requires lots of water. to minimise water usage the companies recycle the water and add chlorine to it to keep it clean
what are GFP bacteria
how are they useful?
strains of bacteria engineered to produce Green Fluorescent Protein
- This makes each bacterial cell fluoresce bright green when viewed using fluorescence microscopy
- These bacteria can be tracked and counted wherever they colonise, and are a very useful tool across microbiology
describe the localisation of bacteria on leaves after innoculation
- Immediately after inoculation: many bacteria in cell margins but also well spread over leaf surface
- Within 2 hours: bacteria predominantly present at cell margins and within stomatal apertures
give some potential attachments mechanisms of bacteria to the phylloplane
Flagellum
Pilli
Hydrogen bonding
Ionic bonding
Cellulose
how can you tell the difference between pilli and fimbriae
Pilli tend to be the longer ones in fewer numbers and the fimbrae are shorter and more numerous
give example of salmonella attachment mutants
- Δcrl and ΔcsgB (curli (fimbrei) specific gene) mutant strains partly lacking curli fimbriae
- ΔrpoS and ΔcrlΔcsgB mutant strains lacking curli fimbriae
- ΔflhC mutant strains lacking flagella
what is the difference in attachment of curli fimbriae mutants to abiotic and biotic surfaces
When you do these experiments with plastic wells (abiotic) then the knockout mutants do their jobs, affenting attachment and biofilm formation,
however when you do it on real world surface (leaf) then the mutants don’t affect growth that significantly
which salmonella mutant showed reduced attachment to the phylloplane?
flhC mutant
(lacking flagella)
what important genetic regions were identified through ID attachment defective transposon mutants?
- intergenic region between agfB (also called csgB) - the surface-exposed aggregative fimbria (curli) nucleator,
- agfD (csgD), a transcriptional regulator of the LuxR superfamily (quorum sensing),
- and rpoS, the stationary-phase sigma factor.
Both AgfD and RpoS have been reported to regulate curli and cellulose production and RpoS regulates other adhesins such as pili.
how do mutations of the agfA curli subunit and agfB differentially affect attachment to plant tissues?
The agfA (csgA) mutation was not reduced in ability to attach to or colonize alfalfa sprouts,
whereas the agfB (csgB) mutation was reduced.
* Thus, agfB (csgB) alone can play a role in attachment of S. enterica to plant tissue: thin aggregative fimbriae
what is BapA and how does it affect attachment?
BapA: Biofilm associated protein
interacts with calcium to facilitate binding
what is the functional consequences of csgD interaction with adrA
intiates cellulose formation
how does RpoS controll production of cellulose and cyclic di gmp
rpos controls the expression of cgsd which activates expression of adrA
AdrA is part of control of cellulose production and controls cylic di gmp
what are the benefits to bacteria seeking refuge in cell margins and stoma?
- These refuges are less hostile in terms of water availability and protection from solar irradiation, sanitisers and washing/detachment methods
