BIO 3124 4 - Bacterial Growth and Environmental Influences

Microbes can grow at different speeds depending on...?

Where they live, nutrition, and niche-specific physical parameters like temperature and pH.

Like all living things, microorganisms need what to grow?

water, carbon sources, and energy

Bacteria have been able to find and metabolize a wide assortment of food sources due to?

the remarkable plasticity of microbial genomes

Plasticity of microbial genomes refers to what?

The genetic material of bacteria is very flexible allowing them to survive in all types of environments. They can gain, lose add or rearrange genes easily.

Essential nutrients

nutrients that must be supplied from the environment

Macronutrients

- nutrients needed in large amounts

- major elements in cell macromolecules (DNA, protein, etc.)

- C, O, H, N, P, S

- cations necessary for protein function

- Mg2+, Ca2+, Fe2+, K+

Micronutrients

trace elements necessary for enzyme function (Co, Cu, Mn, Zn)

How microbes build biomass

all of earth's life-forms are based on carbon, which they acquire in different ways.

Autotrophs

Fix inorganic carbon (CO2) into organic molecules

- make their own carbon source

Heterotrophs

Use preformed organic molecules

- rely on others

Energy source prefixes

Photo-

Chemo-

Phototroph

light absorption captures energy

Chemotroph

chemical reactions yield energy

Electron source prefixes

Litho-

Organo-

Lithotroph

inorganic molecules donate electrons

Organotroph

organic molecules donate electrons

Membrane selective permeability is achieved in three ways

1. Substrate-specific carrier proteins, or permeases

2. Dedicated nutrient-binding proteins that patrol the periplasmic space

3. Membrane-spanning protein channels or pores

Before membrane transporters can uptake nutrients what must occur?

the nutrients must cross the peptidoglycan layer

How do nutrients cross the peptidoglycan layer?

Bacteria secrete enzymes that break down 'food' into small enough pieces so they can cross the peptidoglycan layer.

Passive transport

movement down a concentration gradient, requires no energy

Types of passive transport

diffusion, osmosis, facilitated diffusion (channel or carrier-mediated)

Active transport

Movement against a concentration gradient, requires energy. Carried out by membrane proteins often referred to as pumps.

Normal growth conditions

- sea level

- 20°C-40°C

- near neutral pH

- 0.9% salt

- ample nutrients

Any ecological niche outside of the normal growth conditions is called, ____________ and organisms inhabiting them are called _______________.

extreme, extremophiles

the earliest microbes probably thrived in what type of environment?

In extreme environments. As the earth's environment slowly changed to its current state, some ancient extremophiles adapted. Those who couldn't adapt remained in extreme niches.

cardinal temperatures

the minimum, optimum, and maximum temperatures at which an organism grows

Optimum temperature

temp at which the microbe grows most rapidly

Range of cardinal temperatures for most microbes is...?

< 40℃

Temperature changes concentrations of what in water?

gas and mineral concentration

Why is temperature important in survival?

temperature affects every aspect of function. It affects membrane fluidity, enzyme structure and function, DNA and RNA stability.

Psychrophiles

Prefer cold temperatures

- 0-20℃

what type of microbes are responsible for refrigerated food spoilage?

psychrophiles

Mesophiles

prefer moderate temperatures

- 30-40℃

- most microbes we interact with

Thermophiles

prefer high temperatures

- 55-60℃ (max 70℃)

Hyperthermophiles

prefer very high temperatures

- 80-100℃

- inhabit hot springs

sea level pressure

1 atm = 0.101MPa

Barosensitive microbes

organisms that die as pressure increases

Barophiles/piezophiles

organisms adapted to grow at very high pressures

- up to (1,000 atm)

Barotolerant microbes

organisms that grow well over the range of 1-50 MPa (1-500atm), but their growth falls off thereafter.

Water activity (aw)

the amount of free water in a substance; influenced by solute concentration

The higher the solute concentration, what happens to water activity?

the lower the water activity

As water activity decreases what happens to microbial growth?

it decreases

Water activity measurement

Distilled water aw = 1

All other aw values are between 0 and 1

Bacteria require water activity levels greater than what?

> 0.91

Fungi require water activity levels greater than what?

> 0.86

The higher the water activity of foods, ...

the higher likelihood of spoilage

Food preservation methods reduce microbial growth by?

reducing water activity

- drying

- adding salts

- adding sugar

osmolarity

measure of the number of solute molecules in a solution and is inversely related to water activity

osmophiles

organisms that live in environments high in sugar as solute. Well adapted to osmotic stress

- commonly found in syrups, jams, and honey

Xerophiles

organisms able to grow in very dry environments.

- Don't require high osmolarity

- can tolerate low water activity (lowest aw = 0.61)

Can deserts sustain microbes?

Yes, although deserts during the day aw = 0.1, when it rains and night aw's can reach 0.61 supporting xerophiles

Halophiles

organisms that have specific requirments for NaCl

- optimal [NaCl]: 3-8%

- seawater: aw = 0.98, 3.5% [NaCl]

Halotolerant

organisms that can tolerate some additional dissolved solutes but generally grow best in the absence of the added solute

- can tolerate [NaCl] up to 10%

- ex: skin

Extreme halophiles

organisms that require very high levels (15% to 30%) of NaCl; often unable to grow at lower concentration

Two mechanisms that microbes minimize osmotic stress

1. synthesizing/importing compatible solutes in hypertonic media

2. mechanosensitive channels leaking out solutes in hypotonic media

compatible solutes

small molecules that do not disrupt normal cell function even at high intracellular concentrations

Extreme concentrations of either hydronium or hydroxide ions (OH−) in a solution will?

limit growth

How do bacteria tolerate ranges of pH?

They regulate internal pH to keep enzymes functioning optimally

Optimal internal pH for bacteria

5 - 8.5

Neutralophiles (neutrophiles)

grow at pH 5-8

- include most human pathogens

Acidophiles

grow at pH 0-5

- often chemoautotrophs

Acidophile adaptations

proteins stable in acid

pumps that remove H+

special membranes that are adjusted to stay flexible in low pH

Alkaliphiles

grow at pH 9-11

- found in soda lakes

- used commercially (laundry detergents)

alkaliphile adaptations

- cell surface barrier that sequesters fragile cytoplasmic enzymes away from harsh extracellular pH

- cell wall: acidic polymers and excess of hexoamines

- cell membrane: high levels of diether lipids

- sodium motive force: Na+/H+ antiporter

Na+/H+ antiporter

sodium out, H+ in (keeps internal pH below alkaline pH)

Usually organisms that are an extremophile in one respect are...?

extremophile in another respect

Anaerobes

bacteria that can grow in the absence of oxygen (O2)

Aerobes

Bacteria that require oxygen to grow

In most cases aerobes use ___ as a terminal electron acceptor

oxygen

Aerobic respiration

The process by which cells use oxygen to break down glucose and release energy.

Relies on the electron transport system

aerobic respiration continually produces...?

reactive oxygen species (ROS)

Reactive oxygen species are?

toxic and must be neutralized

Aerobes vs. anaerobes in handling reactive oxygen species

Aerobes have the enzymes to neutralize ROS

Anaerobes lack these enzymes and thus oxygen is toxic to them

reactive oxygen species examples

singlet oxygen, superoxide, hydrogen peroxide, and hydroxyl radicals

Strict aerobes

can only grow in oxygen

Microaerophiles

require oxygen concentrations lower than air (2-10%)

- high [O2] is toxic

Strict anaerobes

die in the least bit of oxygen

- use fermentation to produce energy

Aerotolerant anaerobes

grow in oxygen while retaining a fermentation-based metabolism

- presence of oxygen does not change growth rate

Facultative anaerobes

Can live with or without oxygen, but grow better with it

- possess both the ability for fermentative metabolism and respiration (aerobic and anaerobic)