Chapter 9

Question 1

What is microbial growth?

Answer 1

Microbial growth refers to an increase in number of cells rather than an increase in cell size.

Question 2

Define binary fission.

Answer 2

Binary fission is when prokaryotic cells, such as bacteria, replicate through a type of simple cell division.

Question 3

What would the generation time be for an organism that goes through five generations in
150 minutes?

Answer 3

30 Generation time= growth time/# of generations

Question 4

Name and describe the 4 phases of bacterial growth in a closed batch system.

Answer 4

There are four distinct phases of the growth curve: lag, exponential (log), stationary, and death.

Question 5

How does oxygen impact microbial growth?

Answer 5

Bacteria and many microorganisms are very sensitive to oxygen concentrations. Some will only grow in its presence and are called obligate aerobes. Facultative aerobes will grow either aerobically or in the absence of oxygen (anaerobic conditions), but they generally do better with oxygen.

Question 6

Describe the 5 categories of bacteria based on their use of oxygen?

Answer 6

Obligate aerobe, microaerophile, facultative anaerobe, aerotolerant anaerobe, or obligate anaerobe

Question 7

What techniques may be used to grow anaerobic microbes?

Answer 7

Agar, incubated flask

Question 8

How does pH impact growth?

Answer 8

Each curve has an optimal pH and extreme pH values at which growth is much reduced. Most bacteria are neutrophiles and grow best at near-neutral pH (center curve). Acidophiles have optimal growth at pH values near 3 and alkaliphiles have optimal growth at pH values above 9.

Question 9

How does temperature affect growth?

Answer 9

In general, at low temperatures, microbes grow slower. At higher temperatures, microbes grow more quickly.

Question 10

Name the classes of microbes according to their temperature preferences.

Answer 10

Psychrophiles grow best in the temperature range of 0–15 °C whereas psychrotrophs thrive between 4°C and 25 °C. Mesophiles grow best at moderate temperatures in the range of 20 °C to about 45 °C. Pathogens are usually mesophiles. Thermophiles and hyperthemophiles are adapted to life at temperatures above 50 °C.

Question 11

What is a biofilm and how does it form?

Answer 11

A biofilm is an assemblage of microbial cells that is irreversibly associated (not removed by gentle rinsing) with a surface and enclosed in a matrix of primarily polysaccharide material.

Question 12

What is the matrix of a biofilm composed of?

Answer 12

Hydrated extracellular polymeric substances of mostly polysaccharides, but also proteins, nucleic acids, lipids

Question 13

What is the role of quorum sensing in a biofilm?

Answer 13

Bacteria use quorum sensing to coordinate certain behaviors such as biofilm formation.

Question 14

Aerobes

Answer 14

Microbes that have evolved to use oxygen in their metabolic pathways; usually have enzymes to detoxify ROS (reactive oxygen species) so that they can safely use oxygen in their metabolism.

Question 15

Aerotolerant anaerobes

Answer 15

Organisms that tolerate atmospheric oxygen, even though they do not use it in their metabolic processes. Like aerobes, these microbes have ways to deactivate ROS (reactive oxygen
species).

Question 16

Facultative anaerobes

Answer 16

Group of microbes that spans both aerobic and anaerobic environments; can use oxygen for their metabolism, but if needed, they can perform anaerobic metabolism when oxygen is absent.

Question 17

Generation time

Answer 17

The time it takes for a particular species of cell to divide.

Question 18

Growth media

Answer 18

Mixtures of nutrients that support organismal growth in an artificial setting.

Question 19

Lag phase

Answer 19

First phase of a standard bacterial growth curve; occurs while bacterial cells adjust to their new environment; during this phase, cells alter their gene expression in response to their new setting; population growth is not usually seen in this phase.

Question 20

Exponential

Answer 20

Describes a type of growth in which one cell begets two, the two yield four, those four become eight, and so on. Microbes replicate as fast as they can.