Week 4: Microbial growth and the microbiome

Microbial growth is described as the change in ______ not in _______

number; size

What are colonies

large number of microbes usually derived from one organism (clone)

What is the process of bacterial cell division called?

binary fission

what are the steps of binary fission?

1. Elongation of cell and DNA duplication

2. Cell wall & plasma membrane increase and start folding inward

3. Formation of cross wall between DNA regions

4. Cells separate into 2 new identical cells

Name the three physical requirements for growth

• Temperature

• pH

• Osmotic pressure

Name the chemical requirements for growth

– Carbon

– Nitrogen, sulfur, and phosphorous

– Trace elements

– Oxygen

– Organic growth factors

differentiate between psychrophiles, mesophiles, thermophiles, and extreme thermophiles

psycrophiles are cold loving (0-15 C)

mesophiles are moderate temp loving (10-47 C)

thermophiles are heat loving (40-70 C)

extreme thermophiles are XTRA heat loving (65-110 C)

what is the “danger zone” in relation to bacterial growth

a temperature ranged (60-100 F and 15-50 C) where bacterial growth is rapid and some may produce toxins

What pH range do most bacteria grow and what are they called?

6.5 - 7.5 pH, neutrophile

Distinguish between acidophiles and alkalinophiles

acidophiles grow in acidic environments (pH lower than 4)

alkalinophiles can grow at high pH

What happens to a bacterial cell when it is placed in a hypertonic solution?

plasmolysis

Differentiate between extreme/obligate halophiles and facultative halophiles

extreme/obligate halophiles require high solute concentrations/high osmotic pressure

facultative halophiles can tolerate high osmotic pressure but don’t require it.

Distinguish between a chemotroph and a photo troph

chemotrophs get their energy by oxidising electron doners

phototrophs get their energy by capturing photons

Distinguish between autotrophs and heterotrophs

autotrophs make complex organic compounds from simpler substances

heterotrophs have to take up nutrients

What is nitrogen used for in bacteria

• Component of proteins, DNA, and ATP

• Most bacteria decompose protein material for the nitrogen source

• Some bacteria use NH4+ or NO3- from organic material

• A few bacteria use N2 in nitrogen fixation

what is sulfer used for in bacteria

• Used in amino acids, thiamine, and biotin

• Most bacteria decompose protein for the sulfur source

• Some bacteria use SO42 or H2S

what is phosphorous used for in bacteria

• Used in DNA, RNA, and ATP

• Found in membranes

• PO43 is a source of phosphorus

What are trace elements

essential inorganic elements that cannot be synthesize and must be supplied

• usually include iron, copper, magnesium etc

• used as enzyme cofactors.

what are organic growth factors?

• Organic compounds obtained from the environment

• Vitamins, amino acids, purines, and pyrimidines

Define the 5 kinds of oxygen requirements in bacterial cells

obligate aerobes - require oxygen

obligate anaerobes - unable to use oxygen and most are harmed by it

facultative anaerobes - can grow via fermentation/anaerobic respiration when O2 is lacking, but prefers O2

aerotolerant anaerobes - can tolerate O2 but don’t use it

micro anaerobes - require oxygen concentrations lower than air

What is hydrogen peroxide, what enzyme is used to neutralize it, and what are the end products?

• a type of toxic oxygen

• it is neutralized by catalase

• the products are H2O and O2

What is a biofilm?

microbial communities that can comprise of many species

How do bacteria communicate in a biofilm?

They use quorum sensing; they secrete an inducer (chemical signal) to attract other bacterial cells

True or false: biofilms are 1000x more resistant than microbicide and are responsible for 70% of human infections

true

define “generation time”

Time required for a cell to divide

How do you calculate the total number of cells?

2^(number of generations)

How are bacterial growth curves represented in graph form

logarithmically

name and describe the 4 phases of the bacterial growth curve

1. Lag:

• reacting to their environment and preparing proteins, enzymes, etc

• increase in cell size and division (but division is slow)

2. Log:

• maximal growth and division and increased metabolic activity

3. Stationary:

• nutrient depletion and metabolic by product building up

• # if new cells = # of dead cells

4. Death:

• whole culture dies slowly and then exponentially

Describe direct cell count (direct method)

a method that physically measures the number of cells in a specific volume of a sample using a microscope or automated counter

describe serial dilutions (direct method)

a step-by-step process of repeatedly diluting a concentrated solution by a constant factor

describe filtration (direct method)

• Solution passed through a filter that collects bacteria

• Filter is transferred to a Petri dish and grows as colonies on the surface

Describe MPN (direct method)

a statistical technique used to estimate the concentration of viable microorganisms in a liquid sample by observing growth patterns across a series of replicated dilution tubes

What other methods can be used to measure cell growth (indirect methods)?

• Turbidity

• Metabolic activity

• Dry weight

What is a superorganism?

multiple organisms that can be considered to function as a single organism

what abiotic factors can impact a microbiome?

O2, pH, moisture, and nutrients

Where in the human body is the biggest microbiome found?

Digestive tract

describe the four phases of early gut colonization

phase 1: sterile gut

• microbes cannot pass the placenta so unborn babies are sterile

phase 2: initial acquisition

• vaginal exit, c-section, feces, and hospital all expose infants to microbes

phase 3: feeding

• breast feeding exposes to more bifidobacteria

• bottle feeding exposes to more diversity; bacterioides and clostridium

phase 4: solid foods

• moving into adult flora as solid foods are introduced

What are some of the main functions of the gut microbiome

• aids in digestion

• fills niches to keep pathogens out

• synthesizes vitamins and helps absorb Ca and Fe

• detoxify poisons/metabolize drugs

• helps form healthy immune system

What is the relationship between our microbiome and our metabolism?

They are directly related and influence each other. Our metabolisms impacts how healthy our microbiome is and our microbiome impacts how well our metabolism runs

Why does fiber promote a healthy microbiome?

fiber allows for a healthy diversity of microbes because it allows for mucosal membrane around intestinal lining, keeping pathogens out of our cells

• low fiber diets can increase risk of infection