"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
