Genome of potential bacterial factory sequenced

A collaboration of American researchers have completed the genome sequence of Azotobacter vinelandii, paving the way for new applications in biotechnology, including the possible use of the bacteria as a 'factory' for the production of other proteins, in particular those that may be damaged by the presence of oxygen.

The work will also help advance research on A. vinelandii's role as a model study organism for investigation of nitrogen fixation and other biochemical processes.

A. vinelandii lives in soil and has the ability to convert nitrogen from the atmosphere into ammonia via bacterial enzymes called nitrogenases. Nitrogen fixation is essential for life since different nitrogen-containing molecules are used to produce DNA and the amino acids that are the building blocks of proteins.

For most bacteria, the nitrogenase enzymes involved in nitrogen fixation are very susceptible to destruction by oxygen. A. vinelandii is one of the few bacteria that can fix nitrogen in the presence of oxygen, using three distinct nitrogenase systems.

The work of the Azotobacter vinelandii genome project team identifies unique features of the A. vinelandii's genome that explain how the bacteria is involved in oxygen-sensitive reactions such as nitrogen fixation, while maintaining strictly aerobic metabolism.

A. vinelandii has one of the highest respiratory rates of any known bacterium and has the capacity to maintain low levels of cytoplasmic oxygen through a process called respiratory protection.

The sequence of the bacteria's genome allowed the team of researchers to identify the genes involved in respiration, including those responsible for respiratory protection.

Genome analysis helped pinpoint the chromosomal location of the three known oxygen-sensitive nitrogenases, as well as the genes that code for other oxygen-sensitive enzymes such as carbon-monoxide dehydrogenase and a formate dehydrogenase.

The sequence also provided important information on the genes that code for alginate, a polymer that further protects the organism from excess oxygen by forming a physical barrier around the bacterium.

"A. vinelandii is an attractive model organism for biochemical studies because of its ability to produce high yields of quality enzymes," said lead author, João Setubal, associate professor at the Virginia Bioinformatics Institute and the Department of Computer Science at Virginia Tech.

"The findings in this study provide new prospects for the wider application of this bacterium as a factory for the production and characterization of oxygen-sensitive proteins through the use of genetic approaches to achieve high-level protein expression."

According to Ray Dixon, project lead in Molecular Biology at the John Innes Centre in the United Kingdom, "The international collaboration created by the Azotobacter genome project was an integral part of the discovery of these unexpected anaerobic processes in A. vinelandii, which confirmed the importance of this organism as a host for the expression and purification of oxygen-sensitive enzymes."

The work will also provide more information about the unique biosynthetic pathways involved in the bacteria's ability to adapt its metabolism to diverse sources of nutrients.

For example, if no carbon source is present, A. vinelandii will undergo a differentiation process, forming cysts that are resistant to desiccation and other chemical and physical challenges.

A. vinelandii belongs to the Pseudomonadaceae family. The completion of the A. vinelandii genome will serve as an essential phylogenetic anchor point for comparative genomics work with other systems.

The research is published in the Journal of Bacteriology.