You can proceed to direct soil suspension (using pyrophosphate that help separating soil particles) , serial dilution and plating on solid medium suitable to the (plant- ?) beneficial bacteria you are looking for (in any case, add cycloheximide to prevent fungal growth). You can also add an initial step of soil microbial extraction by using Nycodenz gradient separation of large quantity of soil through ultracentrifugation (Cf. attach file) or small amount of soil (1g) by adaptation of the protocol to 2ml-microtubes and a bench-centrifuge...

Identification of these bacteria is another matter that may rely on very diverse technics, ranging from culture conditions, biochemical tests, to the use of molecular methods.

Thank you for your valuable information

I agree with Pascal Mirleau

There is no "best method" Anwar. It all depends on your objectives. Any approach of cultivation favours some microorganisms and inhibits the majority of the others. First you need to define your objectives and then you may select an appropriate method by critically reading recent literature on studies with a similar objectives in your favorite peer-reviewed journal.

I do agree with the ealier response. Normally in our lab. we do dilution plating on SEA (soil extract agar). For specifie genus or functional groups we use selective media. Identification the best and simple method is BIOLOG.

As mentioned in earlier replies there is not a "best method" to isolate and "identify" soil bacteria. However, the serial dilution and spread-plate method is a good starting point in order to isolate bacterial colonies from soil. As mentioned by Christoph Tebbe, the choice of the isolation medium is critical and depends on your specific objectives. If your idea is to collect a number of pure cultures from soil and then test single isolates for Plant Growth Promoting characteristics, then you could try with diluted (e.g. 1:10) Tryptic Soy Agar or, as said by Seif Ben Tekaia, with PCA or with R2A agar medium. On the other hand, if you are inetersted in specific microbial groups, e.g. actinomycetes (generally really abundant in all soils), you could use the Actinomycetes Isolation Agar (supplied by different companies) and so on.

Probably, the most rapid method to identify such bacterial isolates is the sequencing of the PCR-amplified 16S rRNA gene. However, as mentioned by Sariah Meon, the Biolog system is a good and fast (culture-dependent) alternative. The only problem is that such a system, which requires the availability of an expensive database and some other Biolog equipements (e.g. turbidimeter, Biolog plate readear), is not so common in microbiological laboratories.

First isolate the bacteria which are closely associated with plants (ex. rhizosphere, rhizoplane) by the methods described earlier by many people here. Then screen them for various plant growth promoting attributes to know their function. Now, you can identify the ones with good PGP activities by using various techniques. There are so many depending upon your access to them.

Good Luck.

First of all every thing depends upon your objective..... the isolation procedure generally people follow to isolated bacteria from soil id by taking soil in sterile bag and then weighing and makings its serial dilution and plating on a suitable medium...... bt u said in your question that u r looking fr beneficial bacteria so u have to be little specific in the terms beneficial in wht terms suppose if you are looking for enzyme producing bacteria then in that case wht sort of enzyme suppose amylase or protease etc...then in that case u have to plate your serial dilution on a particular substrate such as starch agar plate fr amylase or milk agar plate fr protease.......

I should also advice you to check the ph, temp, salinity and other minerals (if possible ) of the soils that you are taking for isolation bz that will help in making medium since you have to make as similar environment as present in that particular niche inorder to isolate maximum organism or bacteria.........

Diluting soil and agitation for an hour and directly plating onto appropriate media may give better results

It is better to use the soil dilution method of rhizosphere of any plant soil which will help you to have beneficial bacteria.and culture them in suitable nutrient media.

Many of soil organisms can't be grown by routine techniques.but some of them can be demonstrated by conventional dilution method: prepare dilutions of the sample and put out them on tryptone-yeast extract agar..

I do not think that there is a "best method for the isolation of bacteria from soil. That will highly depend on your objectives since you may be interested in isolating either the vegetative or the sporulating soil bacteria.

prepare a serial dilution of the soil sample.if you are interested with the sporulating bacteria,heat shock the solution at 80 degrees for15 minutes to kill the vegetative bacteria.This is the  simplest technique that enriches for aerobic spore formers is to pasteurize a diluted soil sample at 80 degrees for 15 minutes, then plate onto nutrient agar and incubate at 37 degrees for 24 hours up to several days. The plates are examined after 24 hours for typical colonies identified as catalase-positive, Gram-positive, endospore-forming rods. Although many species contain sporangia and free spores within 24 hours, some cultures must be incubated 5-7 days before mature sporangia, and the size and shape of the endospore contained therein, can be observed.

We have counts of 10 to the sixth, 10 to the seventh and 10 to the eight with serial dilutions and plating in casein agar (actinomycetes ) and nutrient agar ( agar) further info you can see in the document that we published (https://www.researchgate.net/publication/272565285_INFLUENCIA_DEL_RIEGO_EN_LA_DINMICA_POBLACIONAL_DE_GRUPOS_FUNCIONALES_DE_MICROORGANISMOS_ASOCIADOS_A_LA_RIZSFERA_DE_PALMA_ACEITERA_%28ELAEIS_GUINEENSIS_JACQ%29?ev=prf_pub)

Conference Paper INFLUENCIA DEL RIEGO EN LA DINÁMICA POBLACIONAL DE GRUPOS FU...

Isolation of Bacteria from Soil 

see the attachment files

I hope you will find the answer and the best method for isolation and identification of bacteria from soil.

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.468.2864&rep=rep1&type=pdf

http://www.ableweb.org/volumes/vol-14/6-steubing.pdf

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.468.2864&rep=rep1&type=pdf

http://www.ableweb.org/volumes/vol-14/6-steubing.pdf

Dear Anwar,

If you are looking for beneficial bacteria like lactic acid producing bacteria, please choose lactobacillus MRS broth for isolating those kind of bacteria...

I use molecular tools to determine diversity and identify activities of specific population of soil bacteria. Yes, culturing is limited as microbes especially bacteria live in mutually dependent relationships or communities defining ecosystem-level functions.

It is true what method you use depends on what questions you want to ask?

Good Luck.