Chapter 4 Prokaryotic growth

steps to biofilm formation

1. Planktonic bacteria move to the surface and adhere. 2. Bacteria multiply and produce extracellular polymeric substances (EPS). 3. Other bacteria may attach to the EPS and grow. 4. Cellus communicate and create channels in the EPS that allow nutrients and waste products topass. 5. Some cells detach and then move to other surfaces to create additional biofilms.

example of use of formula used to calculate cell replication 10 cells of food borne pathogen sits for 4 hours and has a generation time of 20 minutes.

4 hours/ 20minutes = 12 generations 10 x 2^12 = 40,960

Complex medium

A culture medium that contains protein digests, extracts, or other ingredients that vary in their chemical composition.

Colony

A single prokaryotic cell, supplied with the right nutrients and conditions,will multiply on the solid medium in a limited area to form this distinct mass of cells.

Binary fission

After a cell has increased in size and doubled its components,it divides. The increase in cell numbers is exponential.

Batch cultures or closed systems

Bacteria and Archaea grown either on agar plates, tubes, or flasks of broth. Closed systems because nutrients are not renewed,nor are wastes removed.

At the end of the exponential (log phase) phase what processes do the cells perform?

Begin sporulation to create endospores. If they cannot, they still alter their activities to prepare for starvation conditions.

Obligate anaerobes

Cannot multiply if O2 is present. Large intestine- clostridium botulinum.

Autotrophs convert inorganic carbon to an organic form by what process?

Carbon fixation.

Autotrophs play a critical role in the cycling of what in the environment?

Carbon.

Organisms growing in O2 also produce what enzyme?

Catalase.

Colony growth

Cells at the edge of the colony may grow exponentially with less competition for O2 and nutrients. Those in the center may be in the death phase with rapidly depleting available O2 and nutrients due to competition. Cells between the two extremes may be in the stationary phase.

Growth Curve

Characterized by five distinct stages. 1. lag phase 2. exponential or log phase 3. stationary phase 4. death phase 5.phase of prolonged decline.

Major elements

Chemical elements that make up cell constituents. Include; carbon, oxygen, hydrogen, nitrogen, sulfur, phosphorus, potassium, magnesium, calcium, and iron.

Glucose salts

Chemically defined medium. Used in laboratory experiments to study nutritional requirements of bacteria. Not selective or differential.

Nutrient agar

Complex medium used for routine laboratory work. Supports the growth of a variety of nonfastidious bacteria. Not selective or differential.

Blood agar

Complex medium used routinely in clinical labs. Differential because colonies of hemolytic organisms are surrounded by a zone of red blood cell clearing. Not selective.

Chocolate agar

Complex medium used to culture fastidious bacteria, particularly those found in clinical specimens. Not selective or differential.

MacConkey agar

Complex medium used to isolate gram negative rods that typically reside in the intestine. Selective because bile salts and dyes inhibit Gram-positive organisms and gram negative cocci. Differential because the pH indicator turns pink-red when the sugar in the medium, lactose,is fermented.

Secondary metabolites

Compounds that begin accumulating at this stage are made for purposes other than growth.

Nitrogen fixation

Converting nitrogen gas to ammonia and then incorporating that into cellular material.

Catalase

Converts hydrogen peroxide into O2 and water.

Cells begin to die due to too much of their own waste accumulating at what phase in the growth curve?

Death phase

Phase of prolonged decline

Few cells survive using nutrients from the dead ones to survive at least for a short time longer. Few progeny better equipped for survival can grow. This dynamic process generates successive waves of slightly modified populations, each more fit to survive than the previous ones.

Temperature and food preservation

Freezing can preserve food, but wont kill the microbes on it prior. Refrigeration temperatures (approximately 4 C)slow spoilage.

Why can some prokaryotes withstand very high temperatures but most cannot?

General rules says, proteins from thermophiles are not denatured at high temperatures. This thermostability is due to the amino acid sequence of the protein.

Robert Koch

Greatest contributor to methods of cultivating bacteria. Primarily interested in identifying disease causing bacteria. Fannie Hess, the wife of an associate of Koch suggested using agar.

Within batch cultures (closed systems) cells grow and increase and then declines in what characteristic pattern?

Growth curve.

Reactive oxygen species (ROS)

Harmful derivatives by products when organisms use O2 in aerobic respiration. Superoxide and hydrogen peroxide.

Fastidious

Have complicated nutritional requirements. Neisseria.

Prokaryotes that grow in alkaline conditions bring protons where?

In

Aerotolerant anaerobes

Indifferent to O2. Can grow in its presence,but do not harvest energy. Obligate fermenters, because fermentation is their only metabolic option. Streptococcus pyogenes, strep throat.

Plasmolysis

Is cytoplasm dehydrate and shrink from the cell wall. Caused by water diffusion out of the cell due to osmosis.

Anaerobic

Little or no O2 is present.

Extermophiles are what and belong mostly in what domain?

Microbes that live in harsh environments that would kill most other organisms in the domain Archaea.

Halotolerant

Microbes that tolerate high concentrations of salt, up to approximately 10 % NaCl. Staphylococcus.

Formula for cell replication

N0 x 2 ^n = Nt

Most microbes are what?

Neutrophiles

What fixation is unique to prokaryotes?

Nitrogen fixation.

Stock culture

Once pure culture has been obtained, it can be maintained as this. A culture stored for use as an inoculum in later procedures.

Hyperthermophiles

Optimum 70 C or greater. Usually members of the Archaea.

Psychrotrophs

Optimum between 20 C and 30 C, but grow well at lower temperatures. Important cause of spoilage in refrigerated foods.

Mesophiles

Optimum between 25 C and about 45 C. E.coli and most other common bacteria are in this group. Pathogens, adapted to growth in the human body, typically have an optimum between 35 C and 40 C. Mesophiles that inhibit soil, a colder environment, generally have a lower optimum, close to 30 C.

Thermophiles

Optimum between 45 C and 70 C. Organisms commonly live in hot springs and compost heaps.

Temperature requirements for prokaryotes

Optimum is close to the upper limit of the organism's temperature range.

Growth Factor

Organisms grow only if the molecule they cannot produce is available in the surrounding environment. E.coli.

A solid culture medium is contained in what?

Petri dish.

Important limiting nutrients.

Phosphorus and iron

Biofilms

Prokaryotes can live suspended in an aqueous environment,but most attach to surfaces and live in polymer encased communities

How are Stock cultures kept?

Refrigerator on surface of an agar slant. For long term storage, can be frozen at -70 C in a glycerol containing solution that prevents ice crystals.

Plasmolysiscan be caused by what two concentrations?

Salt and sugar.

Primary metabolites

Small molecules made by cells as they multiply.

Virually all organisms that grow in the presence of O2 produce what enzyme?

Superoxide dismutase

Generation time

The time it takes for a population to double in number.

Limiting nutrients

They are available at the lowest concentration relative to need.

Open system or (continuous culture)

To maintain cells in a state of continuous growth, nutrients must be continuously added and waste products removed.

How do you determine if an organism has an O2 requirement?

Use of Shake tube which boils nutrient agar which melts it and drives off the O2. Coll to just above its solidifying temp. Add organism, and gently shake and swirl. Agar medium is allowed to harden and tube is incubated. O2 in the tube is high at the top low at bottom. Cells grow best in area most suitable.

Chemostat

Used to keep microbial cells in a state of continuous growth. Device continually drips fresh medium into a broth culture contained in a chamber. With each drop that enters, an equivalent volume containing cells, wastes,and spend medium leaves through an outlet.

Lag phase

When a dilute culture is transferred into a different medium, the cell number does not immediately increase. They begin synthesizing enzymes required for growth.

Agar

a polysaccharide extracted from marine algae, is used to solidify culture media.

Pure culture

a population descended from a single cell and therefore separated from all other species.

Obligate aerobes

absolute requirement for oxygen. Micrococcus luteus.

A petri dish is commonly referred to as a plate of that medium for example a nutrient agar plate is called what?

agar plate

Microbial growth is defined as

an increase in the number of cells in a population.

Biofilm formation

begins with planktonic (free floating) prokaryotic cells cells move to a surface and adhere, multiply and release polysaccharides, DNA, and other hydrophilic polymers to which unrelated cells may attach and grow.

Prokaryotes generally multiply by the process of

binary fission

Reactive oxygen species can damage what?

cell components. So cells that grow aerobically must have mechanisms to protect against them.

Exponential Phase (log phase)

cells divide at a constant rate. This is when the generation time is measured.

Examples of trace elements

cobalt, zinc, copper, molybdenum, and manganese.

The medium the cells are gown in, or on, is called a

culture medium.

Microbiologists often group prokaryotes according to what?

energy and carbon sources they utilize.

Bacteria are most sensitive at what phase?

exponential (log phase) Many medications target processes primarily active when bacteria are multiplying.

Meshlike accumulation of these polymers

extracellular polymeric substances (EPS), gives a biofilm its characteristic slimy appearance.

Chemotrophs

extract energy from chemical compounds. Mammalian cells, fungi, and many type of prokaryotes use organic chemicals such as sugars, amino acids,and fatty acids as energy sources.

Facultative anaerobes

grow better if O2 is present, but can also grow without it. They use aerobic respiration if O2 is available, but alternatives if not. Growth is faster with O2 because aerobic respiration yields most ATP. E.coli.

Alkaliphiles

grow optimally at a pH above 8.5.

Acidophiles

grows optimally at a pH below 5.5. Picrophilus.

Superoxide dismutase does what?

inactivates superoxide by converting it to O2 and hydrogen peroxide.

Despite the pH of the external environment, cells maintain a constant what?

internal pH, typically near neutral.

Neutrophiles are what?

live and multiply within the range of pH 5 to pH 8 and have a pH optimum near neutral.

Extreme halophiles

members of Archaea requiring 9 % sodium chloride or more.

Culture medium consists of

nutrients dissolved in water, and can be a liquid broth or a solid gel.

Phototrophs

obtain energy from sunlight. Plant algae, and photosynthetic bacteria.

Psychrophiles

optimum between -5 C and 15 C. Grow in the cold Arctic and Antarctic regions and in lakes fed by glaciers.

Prokaryotes that grow in acidic environments pump

out

Death phase

period when the total number of viable cells in the population decreases as cells die off at a constant rate. (rate of death is slower than cell exponential growth)

Aseptic techniques

procedures that minimize the chance of other organisms being accidentally introduced.

Chemoorganoheterotrophs

referred to as chemoheterotrophs and use organic compounds forboth energy and carbon. By far most common group of microorganism associated with humans and other animals.

Chemolithoautotrophs

referred to simply as chemoautotrophs, use inorganic compounds for energy and derive their carbon from CO2.

Halophiles

require high levels of sodium chloride.

Microaerophiles

require small amounts of O2 (2% to 10%) for aerobic respiration; higher concentrations are inhibitory. Helicobacter pylori.

Trace elements

required in such small amounts that most natural environments, including water, have sufficient levels to support microbial growth.

Streak plate method

simplest and most commonly used technique for isolating prokaryotes. The goal is to reduce the number of cells being spread with each successive series of streaks. By the third set of streaks, cells should be separated enough so that distinct, well isolated colonies will form.

Major environmental factors that influence microbial growth are?

temperature,atmosphere, pH, and water availability.

Photoheterotrophs

use energy of sunlight and derive their carbon from organic compounds.

Autotrophs

use inorganic carbon in the form of carbon dioxide.

Heterotrophs

use organic carbon. An organism deriving its nutritional requirements from complex organic substances. Medically important bacteria are typically heterotrophs.

Photoautotrophs

using the energy of sunlight along with CO2 in the atmosphere to make organic compounds. Cyanobacteria.

All microorganisms require what for growth?

water.

Stationary phase

when cells nutrient levels are too low to sustain growth. Total number of viable cells in the population remains relatively constant, while some die some multiply.