[Microbiology] Re: Hydrocarbon eating microbes

Lesley Robertson l.a.robertson at tnw.tudelft.nl
Mon Feb 27 04:55:58 EST 2006

"Gman" <Ghainke at aol.com> wrote in message 
news:1140229345.302654.264420 at o13g2000cwo.googlegroups.com...
> Hello all.I am NOT a biologist but have been fooling with Geochemistry,
> searching for oil by examining changes in surface soil over oil
> reservoirs.(Iodine, etc..)
> Phillips Petroleum came up with a way of culturing soil samples to
> identify soils that contain bacteria that eat hydrocarbons, the idea
> being that these colonies would be elevated over suspected oil seeps.
> I think their method cultured the soil in Butanol, and then they would
> count the populations after about 1 week of incubation.
> I have never cultured bread mold, let alone hydrocarbon eating
> bacteria!!
> Does anyone have the ability to put such a procedure in terms I can
> understand??

The technique is known as the enrichment or elective culture (invented here 
in sunny Delft by our Professor Beijerinck). The basis is simple - if you 
want a bug that can grow on chemical A at a given temperature and acidity, 
it makes sense to provide chemical A and those conditions, and not just use 
general purpose culturing conditions. Thus, when I wanted a bug that could 
use sulphide and nitrate, I provided a medium containing those things plus 
mineral salts, but no organics or oxygen. That meant that the bugs that 
require organic compounds or oxygen couldn't get going, and my target bugs 
were favoured. of course, you don't get a pure culture as there's always 
something that can grow off metabolic products or dead target bugs, but it 
does cut the screeening down. We use continuous cultures to speed up the 
process, otherwise you have to sub-culture at least 5 times. It also helps 
if you start with an inoculum likely to contain the bugs you want (my 
favourite source of incoculum for this sort of thing is soil from near the 
oil refineries at Europort). Another example: When my 1st years are required 
to isolate nitrogen fixing bugs, they use a medium that contains no nitrogen 
comounds and an inoculum from our botanic garden which has never had 
fertilisers applied. Since the nitrogen fixers require low amounts of 
oxygen, they use flasks with a large surface area and no shaking.
It works in the other direction: None of our students use media likely to 
favour pathogens such as blood agar, and we tend to work at room temperature 
or above 42C for the same reason - the bugs that like human body temps will 
be at a disadvantage.
Lesley Robertson

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