September 13 is Hans Christian Joachim Gram’s birthday. Gram was a Danish doctor and bacteriologist best known for inventing the Gram staining technique in microbiology.
Gram staining is a technique used to identify bacteria into two different groups, Gram-positive and Gram-negative. First, a sample of bacteria affixed to a microscope slide and treated with crystal-violet stain, a common dye in histology. This turns all of the bacterial cells a bright purple color. The slide is then washed with iodine to fix the purple color. Then the slide is washed again with an organic solvent such as acetone or alcohol. Some cells will remain stained purple. The bacterial cells that stay purple are called Gram-positive. The cells of Gram-positive bacteria contain a compound called peptidoglycan that absorbs the stain and thick cell walls to resist the penetration of the solvent.
The cells that did not retain the purple coloring are Gram-negative. Their cells walls are thinner than Gram positive and the solvent can wash away any of the purple stain. Gram found he could treat the sample again with a counterstain of fuchsine or safranin. This would turn the Gram negative cells a bright pink making them easier to distinguish from Gram positive under a microscope.
Gram staining is a good first test when attempting to identify a strain of bacteria. When combined with shape identification, growth media, and aerobic or anaerobic is often enough to identify a particular bacteria.
Notable Science Events for September 13
2004 – Luis Ernesto Miramontes died.
Miramontes was a Mexican chemist who first synthesized the compound norethindrone. Norethindrone would be the basis for progestin, the first oral contraceptive. It can also be used to treat premenstrual and menopausal syndromes.
He also published papers and held patents for a wide range of studies including organic chemistry, petrochemistry, atmospheric chemistry, and pharmaceutical chemistry.
1949 – August Krogh died.
Krogh was a Danish physiologist who was awarded the 1920 Nobel Prize in Medicine for his discovery on how the body regulates the flow of blood through capillaries in skeletal muscle tissue.
He is also known for the Krogh principle that describes that for large numbers of problems, there will be some animal of choice that will make them most conveniently studied.
1912 – Horace Welcome Babcock was born.
Babcock was an American astronomer who made several improvements to optical instruments used in astronomy. One invention was the magnetograph which took continuous measurements of the Sun’s magnetic field. His measurements of the magnetic strength of sunspots showed the magnetic poles of the Sun switched places in 1955 and back again in 1958. He used this technique to measure the magnetic fields of stars and discovered some stars are magnetically variable.
1887 – Lavoslav Stjepan Ružička was born.
Ružička was a Swiss-Hungarian biochemist who was awarded half the 1939 Nobel Prize in Chemistry for his work on polymethylenes or cyclic alkanes and terpenes. He worked in the perfume industry investigating the compounds that make up the scent from musk deer and civet cats.
He also investigated and determined the structure of the sex hormones androsterone and testosterone.
1886 – Robert Robinson was born.
Robinson was an English chemist who was awarded the 1947 Nobel Prize in Chemistry for his work on plant alkaloids. He investigated the chemical reactions that produce alkaloids and discovered the structures of morphine and strychnine. His work and theories on the nature and structures of organic compounds helped in the synthesis of penicillin and other anti-malarial drugs.