Culture of soil bacteria - (Jul/16/2009 )

I am now involving a study regarding soil bacteria. Is it compulsory for me to do serial dilutions for the soil sample before pouring the aliquot onto the agar medium? And what is the difference between mixing the soil sample with Phosphate Buffer Saline (PBS) instead of using sterile distilled water? Thanks.

QQ_lin on Jul 16 2009, 03:28 PM said:

You do not really need to make a dilution, it all depends on how many cells you have in your sample.
You could make a dilution and plate out every dilution and see till what dilution you still have a good growth on your plates.

I you have almost no cells in your sample, then you do not want to dilute.

And PBS could favor your cells(its isotonic), but all depends on what cells you have.
You could try one sample with PBS and another one with distilled water. If both works out the same then simply use the cheapest one.

pbs - lucozade for cells

Pito's resonse was a good one but Lucozade? PBS is hardly an energy drink. The idea is that it offers isotonic stability to cells that might otherwise by prone to lyse under hypotonic conditions. There's no sugar or signficant additonal nutrients.

Gratuitous comparison to Lucozade aside, what do you want to understand about the microbes in the soil sample? Total culturable count? Many of the bacterial species in sopil won't grow well or at all in culture and fungal biomass is not correctly estimated by culture counts.

didnt lucozade sell itself as being isotonic? or is that the wrong drink?

Dominic on Jul 17 2009, 02:22 PM said:

I think it depends on what "kind" you buy because Lucozade Hydro Active is not isotonic but hypotonic.

Why do you come up with this Lucozade anyway?
Is it cheaper to buy then to make some PBS?

Lucozade includes sugar syrup and other substrate whereas PBS will only offer dilute salt.

Ingredients in Lucozade
Carbonated Water, Glucose Syrup (26%), Citric Acid, Lactic Acid, Flavourings (including Caffeine), Preservatives (Sodium Benzoate, Sodium Bisulphate), Antioxidant (Ascorbic Acid), Colour (Sunset Yellow).

But back to the initial question - soil itself will offer more solutes than the little in PBS and what would be the purpose of buffering in dilution?
Stil - as pito said - try it both ways.

Really thanks for your reply, Pito and also the others. I really appreciate it. Actually I want to see what types of bacteria colonies that I can get from the soil sample that I collected from different areas so that I can do isolation for those that I am interested in.

QQ_lin on Jul 18 2009, 05:13 PM said:

If that is the case, then do not dilute.
See what you get first and then you can start thinking about making dilutions etc..

I'm with pito of this. Try direct cultivation - you may otherwise miss some of the bugs that require cofactors (e.g. terragens factor).