I think not only the rhizobic bacteria, but may bacteria can fix atmospheric nitrogen under favourable conditions, since it is a nutrient needed by them. The media for their growth may or may not contain nitrogen, but the atmosphere should be favourable for their growth which is needed.

Dear Rabiul,

Rhizosphere is the store house of a diverse range of bacterial population. Nitrogen fixers are one of them.Nitrogen fixing bacteria are both symbiotic and free-living. Of course, rhizosphere bacteria can fix atmospheric nitrogen in nitrogen free medium. There are lots of examples for it. The previous answer stated by Ms. Asha is absolutely correct.

Searching some related literature's would be very much helpful for you to understand the entire matter.

Good luck

Dear Rabiul,

Unlike the Mycorrhizal symbiosis, legume plants establish a mutualistic symbiosis with bacteria belonging to various genera, including Rhizobium, Bradyrhizobium, Mesorhizobium, Sinorhizobium, or Azorhizobium, depending on the legume species. Eg. Mesorhizobium loti colonize Lotus sp. But not Medicago sp.

Differentiated bacteria called “bacteroids” fix the atmospheric nitrogen but not the bacteria. This transition happens only during symbiosis or symbiotic organs ‘nodules’. Therefore I assume that rhizobia may not fix N on artificial media. And I also doubt that bacteria may not grow in nitrogen free media in first place.

Cheers

Yes I completely agree with Dr. Manoj for host specificity of rhizobia.

However, there are several reports indicated that rhizobia also fix nitrogen under ex-planta ( under this condition the substrate of nitogenase would be Acetylene rather than nitrogen, since the substrate of nitrogenase is triple bond structure) (reference attached).

Therefore, in contrary of  Dr. Manoj,  rhizobia also fix nitrogen under artificial condition.

Thank you very much all of them (Asha Tom, Sosanka PROTIM Sandilya, Manoj Kumar Arthikala,Upendra Kumar).

• The fact that some of the Bradyrhizobium spp. isolated from sugarcane as endophytes showed nitrogenase activity in vitro 
• Please refer Luc Felicianus Marie Rouws et al 2014

 Environmental Microbiology Reports (2014) 6(4), 354–363 doi:10.1111/1758-2229.12122

Bender et al (1986) report shared by Upendra indeed show the Acetylene Reduction by free-living rhzobium bacteria, good one. Are there any recent work on this? 

Based on actual figures & Ecology of nitrogen-fixing bacteria the N fixation rate in symbiosis is 100-400 kg N/ha/y, where as 2-10 kg N/ha/y,free-living bacteria.

Dear Manoj,

We are currently handling the project on BNF in rice. So far we generated lot more data on nitrogen fixing endophytes and yet to publish. Like legumes, it is somewhat tricky to quantify BNF in rice and one possible alternative to use indirect methods. There is no available formula to convert ARA into KgN/ha/year.

Moreover, we are discussing here whether free living rhizobia are able to fix nitrogen under artificial condition or not... and answer is yes for sure...obviously in low concentration.. but once one can simulate the condition definitely  the conc. may increase.

Cheers

Upendra 

Upendra, Your project sounds interesting and my best wishes for your project. I look forward for your published work. 

cheers

Manoj

Only free nitrogen fixing rhizobia

Rhizobia bacteria can fix nitrogen and can growth on nitrogen free media.

Pham Van Toan

Thank you very much Ramachandran Muthukumrasamy, Manoj Kumar Arthikala, Upendra Kumar, Clement Ncho, Toan Pham.

I isolated some diazotrophic bacteria on a nitrogen-free medium. One of the bacteria is Rhizobium sp.

Thanks for answer Yurnaliza Yurnaliza, i want to know which rhizobia bacteria you isolate from nitrogen free media that are you genus identification yes or not. and which method you utilize this procedure please tell me.