Can a Bacterium works as Electronic switch? Fact File 43

Yes it is possible. The Halobacterium salinarium can be used as a Bioswitch.The bacterial protein Bacteriorhodopsin from Halobacterium salinarium has created great interest among scientists to produce bio-logic gates functioning similar to semiconductor logic gates. It is a bacterial species living in the salt marshy lakes of California. These bacteria can survive at very high temperature of 150 degree Fahrenheit or more and in high salt concentration around six times higher than the sea water. These bacteria have a light sensitive protein called Bacteriorhodopsin (bR) in their cell membrane. This protein exhibits unusual properties of structural changes when exposed to different wavelengths of light. This property of the Bacteriorhodopsin is exploited to create molecular switches.

The Molecular switches increase the possibility of fast random access and transportability of datas in Multimedia systems. If these are used in computers, appreciable amount of size reduction, fast memory access, mass storage of datas etc can be achieved. The ability of Biomolecule to work as switching devices in computers is a major area of research in the present day with the invention of some bacterial proteins which functions exactly similar to the electronic switches.

Bacteriorhodopsin is the light sensitive, heat stable protein present in Halobacterium salinarium. The bR absorbs different wavelengths of light and changes its structure into different forms. For example when it absorbs Red light, its structure changes into one form and retains the structure. When it absorbs Green light, another structure is formed. Thus by exposing to Red and Green lights, it is possible to change the structure of bR exactly similar to the semiconductor logic gates giving high and low outputs in varying voltages.

The light induced switching between the bR and K forms of Bacteriorhodopsin can be exploited to create molecular switches that work much faster than the semiconductor gates. The conversion of bR and K forms shows a speed of a few trillionth of a second. The bR chips can be created using a number of bR molecules in a 3D fashion. These chips can have high speed and high density capabilities.

Read and Write operations can also be done using different colors of Laser beams. The entire data processing, retrieval, data storage etc can be done in a milli second. The bR Arrays can be arranged to form bR Cubes that functions as Photosensitive Molecular switches. When light passes through these cubes, they senses 1 and 0 states and give corresponding outputs. The cubes detect the luminescent power of light and convert it into corresponding electrical outputs.

It is possible to create Molecular biochips using the Hybrid technology. It combines both biomolecules and semiconductor materials to create the biochips. Several biomolecules such as DNA, Proteins etc have been experimented in hybrid technology.

About Bacteriorhodopsin (bR)

The Thermal and photochemical characteristics of bR makes it as a good choice to create molecular switches. The bR also has specific Optical properties suitable to create Optical memories. Walther Stockenius of California University and Dicter Osterhelf of Maxplanck Institute of Biochemistry first noted the unusual light sensing properties of Bacteriorhodopsin.

Photo cycle of Bacteriorhodopsin

The energy absorbing material in the Bacteriorhodopsin is called as Chromophore that absorbs the incident light energy and triggers a series of photochemical changes. These changes cause alteration in the optical and electrical characteristics of bR. The photochemical change of bR at different wavelengths light is

1. Green light changes the initial structure bR to K form

2. K form then relaxes into M form and then into O form

3. Red light changes O form into P form

4. P form then relaxes to become a stable Q form

5. Blue light changes the stable Q form into initial bR form again.

So any two forms of the bR can be compared to the binary codes 1 and 0 and the 1 and 0 states of logic gates.