Learn to be an independent learner !!

1. Learn to be an independent learner !!

2. LECTURE 20: Microbial Growth In NaturalEnvironments; Biofilm and Quorum Sensing Microbiology and Virology; 3 Credit hours Atta-ur-Rahman School of Applied Biosciences (ASAB) National University of Sciences and Technology (NUST)

3. Biofilm Formation Planktonic Loosely Bound EPS secreting

4. Biofilm Definition • Biofilms are communities of microorganisms in a matrix that joins them together onto living or inert substrates • Biofilms are surface attached communities of bacteria, encased in an extracellular matrix of secreted • proteins, • carbohydrates, • and/or DNA,

5. Biofilm Formation

6. Biofilm Formation

7. Biofilm Formation

8. Biofilm Formation

9. Biofilm Formation Steps • Biofilms can form on virtually any surface, once it has been conditioned by proteins and other molecules present in the environment • Microbes reversibly attach to the conditioned surface and eventually begin releasing polysaccharides, proteins, and DNA • As the biofilm thickens and matures, the microbes reproduce and secrete additional polymers • The end result is a complex, dynamic community of microorganisms.

10. Biofilm Formation

11. Microbial Interaction in Biofilm • The microbes interact in a variety of ways. • For instance, the waste products of one microbe may be the energy source for another microbe. • Finally, the presence of DNA in the extracellular slime can be taken up by members of the biofilm community. • Thus genes can be transferred from one cell (or species) to another.

12. Antimicrobial compound and Biofilm • In the biofilm, microbes are protected from numerous harmful agents such as UV light, antibiotics, and other antimicrobial agents. • This is due in part to the extracellular matrix in which they are embedded. • The resistance of biofilm cells to antimicrobial agents has serious consequences. • When biofilms form on a medical device such as a hip implant, they are difficult to kill and can cause serious illness. • Often the only way to treat patients in this situation is by removing the implant. • Another problem with biofilms is that cells are regularly sloughed off.

13. Continous shedding of bacteria from Biofilm

14. Quorum Sensing

15. Cell-Cell Communication Within Microbial Populations • Previously microbiologists used to think of bacterial populations as collections of individual cells growing and behaving independently. • But about 30 years ago, it was discovered that the marine luminescent bacterium Vibrio fischeri controls its ability to glow by producing a small, diffusible substance called auto-inducer (acyl homoserine lactone).

16. Euprymnascolopes (Hawaiian bobtail squid)

17. Euprymnascolopes and Vibrio fischeri • The bacteria are housed within epithelial cavities, of this light organ, encouraged to produce light through bacteria regulated quorum sensing and oxygen provided by the squid.  • The squid uses this light organ in counter illumination, a technique that camouflages the squid within the environment.  • Since the squid is active at night, the light from the moon and stars can penetrate the shallow water and illuminate the squid’s presence to its prey or predators.  • Through sensors on the squid’s back, the squid is able to match the amount of ambient light by manipulating the amount of light given off by the light organ with its ink sac.  • Thus, the squid does not have a shadow. Every morning, the squid expels about 90% of the bacteria from the light organ, allowing a fresh culture for the remaining bacteria to flourish in as the squid buries itself in the sand for the day.

18. G (-ve) Bacteria and SQ • Pseudomonas aeruginosause AHLs to regulate the expression of virulence factors • The plant pathogens Agrobacterium tumefaciens will not infect a host plant and Erwiniacarotorvorawill not produce antibiotics without AHL signaling

19. G (+ve) Bacteria and SQ • Gram positive bacteria usually exchange short peptides called oligopeptidesinstead of autoinducer like molecules. • Enterococcus faecalis, whose oligopeptide signal is used to determine the best time to conjugate (transfer genes). • Oligopeptide communication by Staphylococcus aureusand Bacillus subtilisis used to trigger the uptake of DNA from the environment. • The soil microbe Streptomyces griseusproduces a gamma-butyrolactone known as A-factor. • This small molecule regulates both morphological differentiation and the production of the antibiotic streptomycin.

20. Learn to be an independent learner !!