Both Gram-positive and Gram-negative bacteria commonly have a surface layer called an S-layer. In Gram-positive bacteria, the S-layer is attached to the peptidoglycan layer. Gram-negative bacteria's S-layer is attached directly to the outer membrane). Specific to Gram-positive bacteria is the presence of teichoic acids in the cell wall
However, there are cases where the color may appear yellowish, sometimes referred to as âyellow spermâ or âyellow semenâ. The cause of yellow sperm is uncertain but it is believed that it can be caused by infection, or foods which are rich in sulfur such as garlic and onions.Another possible cause for yellow semen could be the natural thickening of semen; especially if you have not ejaculated for quite some time.he cause of yellow sperm is uncertain but it is believed that it can be caused by infection, or foods which are rich in sulfur such as garlic and onions.
Causes of yellow semen. There are various factors that can cause changes in the color of your semen. A manâs age is one of the factors here. As men get older, they notice that the color of their semen is not as whitish as it used to be.ormally, semen is whitish to a light gray in color. It is usually quite thick but tends to liquefy within 20 to 30 minutes. Changes in its appearance or color are usually temporary and not often a cause for concern.