Social Behaviour in Microbes Flashcards
Name some types of social behavior
- Complex communication and decision making
- Bullying - bacteria have been observed to bully each other
- Cheating- microbes can be observed to take nutrients out of the system without doing any work
- ### Helping others - ants making a bridge for other ants, themselves getting washed away.
- ### Suicide
- ### Aggression - microbes can show aggression, detect enemies
- ### Families helping each other
- Selfish gene -
Bacteria will help each other if they are the same family, but not if they are from different families
Book ‘selfish gene’ – much of biology is designed to protect the genetic makeup of a particular organism.
- African Lion cubs
What is the difference between gram-negative and gram-positive bacteria?
Danish scientist Hans Christian Gram devised a method to differentiate two types of bacteria based on the structural differences in their cell walls. In his test, bacteria that retain the crystal violet dye do so because of a thick layer of peptidoglycan and are called Gram-positive bacteria. In contrast, Gram-negative bacteria do not retain the violet dye and are colored red or pink. Compared with Gram-positive bacteria, Gram-negative bacteria are more resistant against antibodies because of their impenetrable cell wall. These bacteria have a wide variety of applications ranging from medical treatment to industrial use and Swiss cheese production.
Talk about the evolution of social behavior
- ##### These behaviours are not unique to man, or even to complex animals
- ##### All can be observed in bacteria and even viruses (maybe not in viruses - Grant has not found any concrete examples.
- ##### During evolution, the advantages of working together quickly became clear and led to a selective advantage
- ##### Social networks began in bacteria
What are the benefits of forming a biofilm?
Motile cells settling forming a biofilm in the image.
Biofilm – example of group behavior in bacteria. One they have become attached to a surface they’ll differentiate and start producing matrix polymers (polysaccharides ect). Bind together and start working as a social group of organisms.
The function being protecting them with a big layer of cells, creating chemical buffering against changes in the PH in the main water body. Also producing a permanent more stable pH, and attracting more nutrients.
If the bacteria want to leave the biofilm they can disperse the biofilms with extracellular enzymes or other biological agents.
Give four concrete examples of predation and how social behavior in bacteria can lead to the absorption of nutrients through predation.
- Phagocytosis of a eukaryotic cell
- Cell invasion of prey by swimming Bdellovibro bacteriovorus cells. They burrow through the outer walls and secrete hydrolytic enzymes, obtaining energy for growth and division before lysing the prey cell host to complete the predatory cycle.
- Releasing of far-ranging antibiotic secondary metabolites by Streptomyces coelicolor (blue, filamentous cells) results in lysis of sensitive bacteria. The bacterium also secretes hydrolytic exoenzymes that could be involved in deriving a nutritional benefit from lysed neighbors.
- Predation by Myxacoccus xanthus (orange cells) utilizes enzymes and secondary metabolites are secreted, but the specific roles of each for this contract-based killing mechanism unknown.
Find another example from wider reading?
What similarities do social behaviours have between bacteria and animals?
Examples of convergent evolution.
What is Quorum sensing?
The discovery that bacteria are able to communicate with each other changed our general perception of many single, simple organisms inhabiting our world. Instead of language, bacteria use signalling molecules which are released into the environment. As well as releasing the signalling molecules, bacteria are also able to measure the number (concentration) of the molecules within a population. Nowadays we use the term ‘Quorum Sensing’ (QS) to describe the phenomenon whereby the accumulation of signalling molecules enable a single cell to sense the number of bacteria (cell density). In the natural environment, there are many different bacteria living together which use various classes of signalling molecules. As they employ different languages they cannot necessarily talk to all other bacteria. Today, several quorum sensing systems are intensively studied in various organisms such as marine bacteria and several pathogenic bacteria.
Why is quorum sensing important?
QS enables bacteria to co-ordinate their behavior. As environmental conditions often change rapidly, bacteria need to respond quickly in order to survive. These responses include adaptation to availability of nutrients, defense against other microorganisms which may compete for the same nutrients and the avoidance of toxic compounds potentially dangerous for the bacteria. It is very important for pathogenic bacteria during infection of a host (e.g. humans, other animals or plants) to co-ordinate their virulence in order to escape the immune response of the host in order to be able to establish a successful infection.
Give a gram-positive example of a bacteria that use quorum sensing from Grant.
Gram-positive bacteria
Peptides
Density-dependent
Eg Staphylococcus aureus
In staphylococci, the ability to sense the bacterial cell density, or quorum, and to respond with genetic adaptations is due to one main system, which is called accessory gene regulator (Agr). The extracellular signal of Agr is a post-translationally modified peptide containing a thiolactone structure. Under conditions of high cell density, Agr is responsible for the increased expression of many toxins and degradative exoenzymes, and decreased expression of several colonization factors. This regulation is important for the timing of virulence factor expression during infection and the development of acute disease, while low activity of Agr is associated with chronic staphylococcal infections, such as those involving biofilm formation. Accordingly, drugs inhibiting Agr are being evaluated for their capacity to control acute forms of S. aureus infection.
Give a gram-negative example of a bacteria that use quorum sensing from Grant.
Gram-negative - bacteria
Small molecules such as AHLs
Density-dependent
Many examples including Vibrio fischeri
What components does quorum sensing involve in gram-negative organisms?
Quorum sensing in gram-negative organisms involves two regulatory
components: the transcriptional activator protein (R protein) and the AI
molecule produced by the autoinducer synthase.
What molecule do bacteria sense when detecting the density of surrounding organisms?
- Ammonia (Nijland et al Bacterial Olfaction)
- Ammonia signalling induces biofilm formation
- Bernier et al showed that ammonia also induces antibiotic resistance
- Work into whether hospitals should let in more fresh air to reduce the antibiotic resistance of bacteria in hospitals.
Describe how the paper Bacterial Olfaction produced by one of Grants PHD students shows that bacteria can respond to ammonia in a similar manner of olfaction as higher organisms.
Bacillus licheniformis
On microtitre plates, the bacterium closest to another culture of bacteria produced a biofilm (pigmented pellicle).
What is the purpose of bacterial lactonase in plants?
Bacterial lactonase protects plants by breaking down the Bacillus enzyme, and breaking down AHLs
Transgenic tobacco and potato
INfected with Erwinia Carotovora.
Conclusions
Microbes display a surprising array of complex social behaviors
The molecular mechanisms of some of these have been elucidated – examples include QS and Olfaction
Knowledge of these systems suggests ways to combat microbes by preventing their ability to communicate.
Bacteria have already thought of that !
