 | ||||
Gram Positive Bacteria
Gram+ Bacterial Cell Wall Structure
from Science Prof Online
| ||||||
VIRTUAL CLASSROOMS
| ||||||
Science Prof Online (SPO) is a FREE science education website. Donations are key in helping us continue to provide this FREE resource.
Please help!
(This donation link uses PayPal on a secure connection.)
Nearly all types of bacteria have a cell wall containing structural chemical components that are unique to bacterial cells. The rigid structure of the bacterial cell wall is due to securely linked peptidoglycan monomers that surround the cytoplasmic membrane, giving the prokaryotic bacterial cell shape and protection.
Gram-positive Cell Wall
From the peptidoglycan inwards all bacterial cells are very similar. Going further out, the bacterial world divides into two major classes: Gram positive (Gram +) and Gram negative (Gram -).
In Gram-positive cells, peptidoglycan makes up as much as 90% of the thick cell wall; more than 20 layers of peptidoglycan stacked together. These layers are the outermost cell wall structure of Gram + cells, whereas in Gram negative cells, the thinner peptidoglycan component is covered by an external lipopolysaccharide (LPS) membrane.
The Gram Stain
Once scientists understood that infectious disease was caused by microorganisms (Germ Theory), it was imperative to find a way to view bacteria and other microbes; because in addition to being minute, most bacteria colorless.
In the 1800’s, Christian Gram, a Danish bacteriologist, developed a technique for staining bacteria that is still widely used today. The Gram stain protocol involves the application of a series of dyes that leaves some bacteria purple (Gram +) and others pink (Gram -). This differential staining not only colors the bacteria, but the specific stain reaction distinguishes between two meaningful categories of bacteria based on the differences in their cell wall structure.
After this staining procedure, Gram + cells appear purple; their thick layers of peptidoglycan having retained the primary stain, crystal violet. Because Gram negative cells have a very thin layer of peptidoglycan layer, these cells do not retain the purple primary stain. At the end of the Gram staining procedure, Gram-negative cells retain the secondary stain, safanin, and appear pink.
Gram Positive Bacteria
Gram+ bacteria are extremely diverse. Some are pathogens, others normal flora that is beneficial to our body. There are important groups that live in the soil and are vital to the cycling of nutrients, and yet other types of Gram+ bacteria that are used to manufacture antibiotics.
Sources
Bauman, R. (2005) Microbiology.
Park Talaro, K. (2008) Foundations in Microbiology.
Article Summary: Most bacteria have one of two types of cell walls. Here are the features of the Gram-positive bacterial cell wall that distinguish it from Gram-.
Gram-positive Bacteria
This article originally appeared on Suite101 online magazine.
Page last updated: 2/13/2012
| ||||
You have free access to a large collection of materials used in a college-level introductory microbiology course. The Virtual Microbiology Classroom provides a wide range of free educational resources including PowerPoint Lectures, Study Guides, Review Questions and Practice Test Questions.
S. epi written in Staphylococcus epidermidis, a gram-positive bacteria.
SCIENCE PHOTOS
