Topic 2 BIO 205

what did robert koch do

developed agar plates for culture techniques

generation time

the time it takes for a population of cells to double

varies by species and is influenced growth conditions

the steps binary fission

1. cell gets longer and DNA replicates

2. DNA is moved into each future daughter cell and cross wall forms

3. cells divide into two and separate

equation used to calculate number of bacterial cells after a certain amount of time

Nt=N0×2^n

Nt- number of cells at a given time in minutes

N0- intitial number of cells in a population

n= number of generations

extracellular polymeric substances

mixtures of hydrophilic polymers including polysaccharides, DNA, and protein that are secreted by microbial cells as part of biofilm formation

biofilm

polymer encased community of microorganisms

-most bacterial infections involve biofilms.

-microbes within biofilms often resist antibiotics and the body’s immune system

-microbes in biofilms can also be helpful (ex. bioremediation)

development of a biofilm

1.planktonic bacteria move to surface and adhere

2.bacteria multiply and produces extracellular polymeric substance

3.other bacteria may attach to EPS and grow

4.cells communicate and create channels in the EPS that allow nutrients and waste products to pass

5.some cells detach and move to other surfaces to create additional biofilms

describe positive and negative interactions of mixed microbial communities

-helpful: aid in growth of species that otherwise couldn’t survive (metabolic waste of one organism is nutrients for another)

-negative: may compete for nutrients, synthesizing toxic compounds that inhibit competitors (contact dependent growth inhibition=certain gram-negative bacteria can insert needle like structure into competing bacteria cells, injecting toxic compounds)