Prokaryotes

What is the study of microorganisms and their interaction with each other and their environment.

Microbial Ecology

The Prokaryotes

Organisms whose nucleus, respiratory, and
photosynthetic machinery were not separate from cytoplasm by membranes; where nuclear division occurred by fission rather than mitosis; and whose cell walls contained mucopeptide

Bacteria

Single celled
• 1-10 μm
• High surface area to volume ratio
• Many shapes

Bacterial shapes are

Not fixed, can change in size and chape over time
- Often in response to environmental conditions

Gram - bacteria

has an external lipid membrane “on top” of its peptidoglycan layer in the cell wall
- Peptidoglycan layer is thinner (5-10% of total cell wall)

Gram + bacteria

does not have an external membrane
- Peptidoglycan layer is thicker (90% of total cell wall)

How many chromosomes do bacteria have?

Usually, just one chromosome
- Not contained in a separate compartment (unlike eukaryotes)

How numerous in the environment?

4-6 × 10^30 cells total

How many bacteria can fit on a soil particle?

soil is solid and highly heterogenous and thus the space available for microbes to inhabit is limited.
- Space for organisms to grown on the surface plays a large role in our determination of the number and diversity or organisms in soil

The surface area paradox –
New Revelations

Much larger surface area is covered by microbes because their effective size is much larger than gas molecules

Lag Phase in Bacterial Growth

Growth rate essentially zero
- Adaptation of population to new conditions
- Cells need time to make mRNA and proteins to respond to new env.
- Low cell density slows nutrient uptake and sharing between organisms
- Transitions to exponential phase after population doubles

Exponential Phase in Bacterial Growth

Two terms to describe:
- Generation time: time needed for cell doubling
- Specific growth rate: maximum growth rate that can be achieved under specific conditions present

Rarely ever reach max growth rate because environmental conditions not ideal

Stationary phase in Bacterial Growth

No net growth: death = life
- Nutrients/substrate becomes limiting, microbes
harvest nutrients from dead neighbors
(endogenous metabolism)
- Waste products build up and inhibit cell growth
or are toxic to cells
- Eventually, more cells are dying that being
produced – enter death phase
- Because recycling of cell components from dead neighbors isn’t 100% efficient

Death phase in Bacterial Growth

Net loss of culturable cells
- Often exponential

Driven by loss of substrate, predation, viral infection

The Monod equation

determine specific growth rate

Lag phase can be much longer if

- Very small numbers of population that can use substrate
- Populations may be dormant or injured
- Generation times longer because not “ideal” conditions
- Population may not exist – requiring mutation, gene transfer, or invasion by external population

Bacterial switch between

exponential and stationary phase

Archaea

highly abundant in soils and other environments
- Often associated with “extreme” environments
archaea often have unique adaptations that
are less common in bacteria and fung

Archaeal cell wall

1. Contains pseudomurein instead of peptidoglycan
2. Has external “S-layer” of glycoproteins
• Can be used as a taxonomic trait