Scott J. Coutts wrote:
> I must admit that the first thing I thought of was contamination. I
> would incubate an uninoculates plate from the same batch too.
When I streak the bacteria I only streak it at about one fifth of the
total area of the plate. The colonies are showing up in the vicinity of
where I have streaked, up to 1.5 cm away. On the other half of the
plate, away from where I have streaked, no colonies are showing up. So
if it is a contaminant (which we rarely see at our laboratory) it is
dependent on something my new bacteria is producing and will only grow
close to it. Otherwise I would not see this polar effect.
> I assume your loop or wire (if that's what you're using) is not too hot
> when you streak out your bacteria? Otherwise, the media or conditions in
> which you're growing them may not be suitable. Maybe you could try some
> other combinations.
I use a loop of wire yes. When I streak other bacteria I never see the
same strange behaviour, so I don't think it's too hot. Since this is a
new bacteria I'm not sure of it's preferred media. I grow it on LB +
glucose, it grows fine at 30 and 37 degrees, and after one night
incubation I have nice sized colonies. It really seems like the in some
way inhibit each others growth, so that they need a few mm of space
between each colony. I know they inhibit growth of other bacteria, they
are producing some sort of antibiotics.
> Do you dry your plates before using them? Lots of motile bugs will swim
> away from where you streak them (i.e. lots of spirochaetes, Proteus etc)
> but usually they dont swim away to form discrete colonies. But it may be
> possible. You're plate doesnt even have to be actually wet - even if it
> is moist enough they can do it.
I dry the plates at 37 before streaking, so they should be dry. I
thought of this solution, but it just seems too weird that they should
swim for over a cm before proliferating and forming colonies. But at the
moment I have no other explanation... Either long distance swimming or
some way of shooting out spores (even though I couldn't see any spores
through the microscope).
> How much bigger than E. coli are they? Are they bigger, but still
> bacteria sized (rather than yeast or fungus sized).
Difficult to say, I'm not very experienced with the microscope. Some
people at my lab said they looked like Azotobacter vinelandii. At least
double the size of E.coli, I would think. They were unicellular (I could
see someone in the progress of dividing by binary fission) and showed no
signs of differentiation, they all looked the same - slightly bent rods
with polar flagella.
Thank for the input Scott!