Review:: The Nodule Microbiome: N2 Fixing Rhizobia Do Not Live Alone

This paper is a review of the Microbiome associated with nitrogen fixing nodules on plants (mostly legumes).  It was written in 2017.

https://apsjournals.apsnet.org/doi/full/10.1094/PBIOMES-12-16-0019-RVW

This a a freely available article, no money needs to be spent to read this.

Within a nodule (so this does NOT include honey locust, which does not form nodules when fixing nitrogen), there are other bacteria present other than the "primary bacteria" that is tabulated (and is known to fix nitrogen).  There are also differences in the fungi present in the plant not in the nodule, and in the nodule.  It is believed that at least part of the difference in fungi, is to bring the other minerals (other stuff?) that is needed in fixing nitrogen.  Original sources in this review go back to (at least) 1888.

It is not exciting reading.  My guess is that a bit more than 1/3 of the article is references (it is a review).

There are lots of references to chemistry in the root/plant, but there are also references to the structure of the root (cells).

As I thought, I didn't see any mention of honey locust in this article.

But, bacteria, fungi and roots are all involved in fixing nitrogen.  And perhaps trying to tie in honey locust, will point to new knowledge.

Interesting read.

This isn’t exclusively about N2 Fixers, but is fascinating.

Review: Endophytic microbes and their potential applications in crop management

https://onlinelibrary.wiley.com/doi/10.1002/ps.5527

Wayne Mackenzie wrote:

This isn’t exclusively about N2 Fixers, but is fascinating.

Review: Endophytic microbes and their potential applications in crop management

https://onlinelibrary.wiley.com/doi/10.1002/ps.5527

Along these lines, a turning point in our understanding of disease resistance in crops, IMHO,.....just being published in Science magazine.  A gene from a wild relative of wheat was bred into domestic wheat to provide resistance to Fusarium head blight (aka 'wheat scab').  Turns out the gene actually is not originally from a plant source, but from a fungus that was an endophyte of that wild relative.  Through time, and with the close association of the endophytic fungus and the plant, the gene became "horizontally transferred" from the fungal genome to the plant genome!

The original research article is still behind a paywall (I think), but the synopsis of the article is here:  https://www.sciencemag.org/news/2020/04/how-gene-grass-living-fungus-could-save-wheat-crops-worldwide#

Before I ran into this review on N2 fixing bacteria not living alone, a couple of other articles had caught my eye.

I am trained in materials science, but among other things I have done a fair amount of nuclear chemistry (analytic or otherwise).

The second one was from Quora (?), where someone was asking if Yeast Agar Mannitol was the best gel for culturing nitrogen fixing nodules.  The first couple of comments came out, and then there a series of comments acknowledging those first commenters.  If those first couple of commenters were so good, why the need to post a comment?

I can appreciate the need to sterilize the outside of the root.  The first suggestions were something like 10 v/o bleach (sodium hypochlorite).  I have no doubt that it would sterilize the outside of the root at some concentration, but if I was to pick a bleach I  think hydrogen peroxide might be more benign (not drive unwanted reactions).  But in the reading I had done, I thought bench ethanol (192 proof or something) was probably the best.

But, before I had run across this question, I had run into some article which mentioned that some of the components that end up in a nitrogen fixing nodule are reversibly incorporated and some are irreversibly incorporated.  I am guessing, that all the bacteria that we normally associated with nitrogen fixing, are reversibly incorporated (which means they can be cultured).  But, since there are other components in the mix, the resulting culture cannot be as effective/efficient/something as the one which they "exposed" in working on that nodule.  Because there was no way to get the irrevresibly incorporated components into the culture.  But for people doing the culturing, they are going into this situation expecting that there is a single, culturable component which can be harvested from the nodule.  So, even if they are able to extract N culturable components, they are only looking to save one of them.  Hence they likely through the rest out.  Even if they cultured all of them (and there are probably things they have caputred in culture, which don't need to be there), how are they going to identify and then culture all the components which are irreversibly incorporated in the nodule?