Bacteria Under The Microscope – Types, Morphology And Reproduction

Bacteria are similar to archaeans in that they are both prokaryotic cells.

Prokaryotic cells are single-celled organisms that do not have a nucleus membrane or a nuclear envelope as it is often referred to. 

Bacteria are measured in nanometers as they are often incredibly small.

Bacteria Under The Microscope - Types, Morphology And Reproduction

To put nanometers into context, one centimeter is equal to ten million nanometers and so often bacteria would not have a diameter even close to a centimeter in size. 

Due to their small size, bacteria are viewed under incredibly powerful microscopes in order to study the morphology and reproduction cycles of bacteria.

In this piece, we look at the different types of bacteria and how they can range in size and shape, as well as the different morphology and reproduction cycles they follow. 

Microscopy

Microscopy is the technical field of studying and researching samples by viewing them through microscopes in a scientific setting.

These samples are of things that cannot be viewed by the naked eye, hence the need for advanced technology to do so.

Below we look at the steps that are taken to prepare a slide and view a sample under a microscope.

Step 1: Culturing The Bacteria

Before viewing a sample of bacteria under a microscope there are certain steps followed to ensure the sample will give a good visual and so bacteria are grown in culture media to help enhance cell division, which multiples the numbers of bacteria in a sample. 

There are different types of culture media that can be used and researchers and scientists would choose a specific technique depending on the type of bacteria they believe they are looking at.

Some of the cultural media that can be used are listed and briefly described below. 

  • Basal Media: Basal Media tends to be either peptone water or a nutrient broth and these media are used for bacterias that don’t need a special enrichment to thrive and grow. This would be used in the case of Staphylococcus bacteria.
  • Enriched Media: This type of cultural media has the addition of a special component, such as blood, to support the growth of a given bacteria. When looking at Streptococci blood is added to favor the growth of this bacteria.
  • Selective Media: This type of media was first developed by Lowenstein and so it is often referred to as the Lowenstein-Jensen media. This type of cultural media can stop certain bacteria from growing while encouraging others at the same time. It is typically used for the culture of different types of Mycobacterium.
  • Transport Media: Transport media is used when a sample is being preserved. This media helps to stop the overgrowing of a certain bacteria before it is transported to its final destination, which in most cases would be a laboratory. This media is also called the Amies Transport Media. This media is known for preserving and prolonging bacteria.

Step 2: Preparing The Sample Slides

Once the bacteria have been cultured and multiplied the next step is to prepare the slides that will be used when viewing the samples through a microscope.

There are certain requirements necessary for this step, these requirements include equipment that would be found in most major laboratories around the world.

They include a Bunsen Burner, Compound Microscope, Inoculating Loop, Glass Slide for the microscope, a dropper, distilled water, and a wax marking pencil to label the sample.

Once these tools have been gathered and set up a sample would then be retrieved of the cultured bacteria that will be viewed under the microscope. 

Next is the smearing process. Each piece of equipment mentioned above is used in this six-step process. Find these steps outlined below:

  • The wax marking pencil is used to draw a circle in the center of the clean glass slide. This is where the smear of the cultured bacteria will be placed and highlight where the researchers should look when viewing through the microscope.
  • Next, the inoculating loop is flamed using a bunsen burner before placing a drop of the distilled water in the center of the circle on the glass slide. If the media being used is a nutrient broth then distilled water is not necessary for this process.
  • The inoculating loop is passed through a flame from a bunsen burner again and this is left to cool before a small amount of the surface of the cultured bacteria is scooped out. To prevent contamination the tips of the collecting tube should be passed through a flame before it is covered with the lid. 
  • The sample of the bacteria is next mixed gently with the drop of water on the water slide and this creates the smear.
  • The slide is now left to completely dry on a drying rack, to prevent accidentally knocking it over in which case you would need to restart the entire process thus far.
  • Lastly, the glass slide with the smear is passed over a bunsen burner flame a number of times. This helps to enhance the stain that is a result of the fully dried smear, making the bacteria more visible under the microscope.

Step 3: Bacteria Staining Process

The next step in preparing a sample of cultured bacteria to be viewed under a microscope is the bacteria staining procedure.

This is done to enhance the differences in the shapes and sizes of bacteria within a sample. 

There are three different types of stains that are used, these are:

  • Crystal Violet
  • Methylene Blue
  • Safranin

One of these stains is used to cover the smear on a glass slide that has been previously prepared. The slide is placed on a staining rack and using a dropper the sample is covered with one of the above stains for 60 seconds.

Once this step has been completed there are only three final steps that prepare the sample for viewing. 

  1. A gentle stream of water is run along the slide to remove any additional or excess stain
  2. Using an absorbent paper, any excess water of stain is then wiped from the edges of the slide
  3. The slide is next placed on the microscope stage and is viewed starting with low power. If vision is obscured or not clear an immersion oil can be added before reviewing the slide under a higher power on the microscope

Observation Of The Slide Under The Microscope

Observation Of The Slide Under The Microscope

When observing bacteria under a microscope there are two specific elements that are heavily documented and researched, being the size and shape of the bacteria.

All bacteria are typically put into a different category or family depending on their shape and how they stain.

The shape of bacteria is referred to as their morphology and how they stain is classed within two different categories, being gram-positive bacteria and gram-negative bacteria. 

Below we look at these different focuses when viewing bacteria under the microscope.

Morphology 

As mentioned, the morphology of bacteria refers to their shape. There are several types of bacteria that are grouped together due to their similarities in their shape. 

Coccus Bacteria 

One of the most common shapes is that of the coccus bacteria, which are spherical and are often divided into diplococcus, streptococcus, or staphylococcus groupings.

Diplococcus is when the spherical shapes gather in pairs.

Streptococcus is when the bacteria’s spheres gather in a long chain-like shape and staphylococcus is when the spheres gather in clusters.

You can also find coccus bacterias gathered in groups of eight and can form a cube-like structure.

Bacillus 

Bacillus bacteria appear in a rod-like shape with curved endings at both ends, similar to a pill.

Bacillus bacteria can be found in chain-like structures, which are referred to as streptococcus, or in pairs which are referred to as diplobacillus, but the most common shape of bacillus bacteria is as single cells. 

Spirilla And Vibrio 

Spirilla bacteria are typically an S shape. Vibrio differs from spirilla bacteria as they are more of a comma-like shape. 

Under low-power observation, these bacteria are often confused and that is why if one of these shapes is observed the researcher, scientist or student will adjust the microscope to a higher power to get a clear look to identify what bacteria it actually is. 

Spirilla bacteria also differ from vibrio bacteria as they have flagella on both ends and these flagella enable this bacteria to move in an aquatic environment.

As a result, this bacteria can spread at a faster rate than most other bacteria. 

Vibrio bacteria have a flagellum on one end which allows them to move however not at the same speed as Spirilla and not in aquatic environments.

Other Types

There are three other typical shapes that are observed when viewing bacteria. These are not as common as the bacteria shapes mentioned above but they are worth noting. 

  1. Mycoplasma: This type of bacteria has no cell wall and tends to have a thick sphere-shaped core with elongated cells on either side
  2. Actinomycetes: This bacteria is a branch-like shape
  3. Spirochetes: Spirochete bacteria have a very flexible shape and it tends to move in a corkscrew-like motion. The axial filament allows this bacteria to move in its unique way

Gram-Positive And Gram-Negative Bacteria

As well as their shape, bacteria are also grouped in the way that they appear when they are stained during the staining process. They are viewed to be either gram-positive or gram-negative. 

Gram-Negative 

Bacteria that do not retain the primary stain are referred to as gram-negative. They lose the initial stain, which is applied using Crystal violet, due to their thin Peptidoglycan layer.

They do take on a counterstain which gives them a red-pink coloring when being observed under a microscope.

Salmonella and E Coli would be examples of gram-negative bacteria.

Gram-Positive 

The Peptidoglycan layer would be thicker in gram-positive bacteria and so they are able to retain the initial Crystal violet stain that is applied.

This type of bacteria has a deep blue-purple coloring when observed under the microscope and examples of such bacteria would be Bacillus cereus and Staphylococcus epidermis.

Reproduction Cycle Of Bacteria 

Reproduction of certain bacterias can differ, however for the most part each bacteria share main methods of reproduction, these methods are explained below.

Binary Fission 

Binary fission is the primary method of bacterial reproduction. A cell grows before it separates into two new individual cells.

The genetic make-up of the bacteria is copied between the two cells to ensure that the bacteria’s structure and genetic material remain the same.

Budding 

When scientists and researchers view samples of bacteria under the microscope they can often observe a minor bulging of some cells along the top of the sample.

This bulging is referred to as budding and is a sign of reproduction and proof that the bacteria is multiplying.

Budding involves a new cell forming that is a replica of original cells. When the replica cell grows it eventually breaks off from the parent, or original, cell.

Formation Of Endospheres

Endospheres are similar to asexual reproduction and this only occurs within gram-positive bacteria that are trying to continue to thrive in extreme conditions that could ultimately end the bacteria.

When gram-positive bacteria are put in these conditions a part of the protoplast is transported close to the chromosome and this is then enclosed by a touch cell wall which then forms an endospore.

The endospore helps the cell to survive in these difficult conditions.

When gram-positive cells are kept in more favorable conditions this tough outer wall is broken down which then allows new growth to occur out from the protoplast.

Habitat Of Bacteria 

There are a number of different habitats that you can find bacteria living in and there are different types that can thrive almost anywhere. 

Soil 

The main types of bacteria that can be found in soil are denitrifying bacteria which hold a key role in the conversion of nitrate to nitrogen, which enables plants to thrive.

Actinomycetes can also be found and this bacteria grows as a hyphae and aids the decomposition of substrates in the soil.

Water 

Vibrio bacteria can be found in saltwater and other aquatic environments. This enables them to spread extremely fast, making this type of bacteria potentially dangerous.

Plants 

Plant roots also hold a number of different bacteria, such as Rhizobacteria which exchanges nitrogen fixation and maximizes the number of nutrients in the soil.

Living Hosts

Bacteria such as E Coli live within living hosts, such as in the intestines of living organisms.

This bacteria can help produce Vitamin K2 and stops pathogenic bacteria from growing in the large intestine. 

Final Thoughts

The study of bacteria under the microscope continues to evolve and new morphology and reproduction cycles continue to be discovered.

Jennifer Dawkins