Air has more bacterial species than we thought it did.

New research has shown that we truly live in a sea of bacteria: the air we breathe.

Writing in PNAS, scientists reported on a 17-week study of bacterial populations over two US cities, Austin and San Antonio. They designed and built a 'DNA chip', naming it the PhyloChip, capable of detecting just under 9000 bacterial orders, i.e., all known bacterial types. (An order is a mid-level rank used in our biological taxonomy system). With the PhyloChip in hand, they then collected dailysamples near environmental monitoring stations in Austin and San Antonio, and analyzed which bacteria are found.

The results? Firstly, they were able to detect 1800 types of bacteria using the chip. This kind of diversity is usually associated with soil samples which we have long known contain a myriad of bacterial populations. Another question is whether background bacterial populations vary between cities, or whether there is a 'regional fingerprint'. Austin and San Antonio were chosen because they have similar population densities, elevation and topography, and they are only about 100 kilometers apart. After taking into account these common characteristics, the researchers found that the two cities shared a similar microbial composition.

Another finding is that the time of the year during the 17-week testing period was the most significant source of variation in bacterial population, followed by atmospheric conditions. For example, warmer and dryer conditions led to increased amounts of spore-forming bacteria. In essence, the geographical location was not a major source of variation, and the variation could be predicted. This means that if we determine a bacterial census, it will have to account for this kind of variation.

So why do this? Many reasons. Firstly, we don't know what's out there, and this is a great technology to answer questions about air-borne bacterial populations. Another aspect is bioterrorism: if we set up a network of bacterial detectors, we need to calibrate them to the already-present background 'noise' to avoid false alarms. Also, if we have a natural outbreak of an air-borne bacterial disease, we can use this technique to track its progress and hopefully implement better public health policies.

All in all, it's a great step forward that opens a new avenues of study.

Technorati Tags: air, bacteria, gene chip, dna chip, PhyloChip, bioterrorism