Originally published in Plant Healer Quarterly

When teaching about endophytes at the Good Medicine Confluence this past May, someone wanted to know about Cannabis endophytes. I didn’t know anything about that topic other than that all plants tested thus far have endophytes.  I decided to look into it some more, and here we go with an up-to-date view….. 

Endophytes 101

In case you missed the class and accompanying essays…a quick review. 

Endophytes are fungi and bacteria that live inside of plants (hence, endo “inside” and phyte “plant”).  They either live packed in between or within the plant’s cells. This distinguishes them from epiphytes, which live on the surface of the plant. 

Endophytes have been hitching a ride in plants for a very long time. They may have jumped on board shortly after plants appeared on the planet, based on evolutionary data and the fossil record.  This long association implies that plants and endophytes have, possibly to a large extent, directed each others’ evolution.  Indeed, the genes of a plant’s resident endophytes provide the plant with a larger toolbox for dealing with changing conditions.  

As an example…   A Pine tree and its descendants may take a long time to accrue beneficial mutations in their genes…not quickly enough to survive, say, an infestation by a parasitic beetle.  But, the more rapid response of the Pine’s individual endophytes as well as the endophyte population structure as a whole may provide the means for an individual tree to adapt better to changing conditions. This means that the tree will be around to pass its own genes on, but also to pass on at least some of its endophytes. (Endophytes are found in seeds as well as in other plant parts, and in the surrounding soil, and may even spread via spores).  Same idea with us and our microbiome:  We essentially get some of the benefits of “our” microbial genes.

Along these lines, endophytes may benefit the host plant in several ways. For instance, endophytes may produce metabolites that deter grazing by insects or animals. Or, may protect the plant against infection by pathogenic microbes.  Some endophytes enhance plant development and/or growth, or may inhibit the growth of the plant’s competitors. 

However, endophytes don’t simply show up at the plant’s door and say “Hey, how ‘bout we come on board and help you out?”.  In fact, some endophytes may be parasitic, taking from the plant but not giving much back in return.  In any event, the endophyte gets a home along with nutrients. This arrangement is similar to ours with our resident flora…not all of the bugs in our microbiome are necessarily to our benefit, though many are.

Cohabitation of endophytes and plants is relevant to us as herbalists.  More specifically, some of what we call “plant medicine” is actually plant and endophyte medicine, or even largely endophyte medicine.  Why is this?  Because endophytes influence the secondary metabolites (the “medicine”) present in a plant.  Some endophytes do this by stimulating the plant to increase synthesis of a particular plant metabolite. This is seen with the synthesis of Echinacea’s anti-inflammatory alkylamides (1, 2). Others trigger the plant to produce a chemical that wouldn’t be there in the absence of the endophyte (eg. resveratrol in Douglass Firs) (3).

Weirdly enough, sometimes both the endophyte and plant make the same chemical (for example, paclitaxol in the case of the Yew tree and its endophytes (3). Finally, some endophytes generate compounds that the plant itself doesn’t make (so cool!). For instance, endophytes in Guduchi make inhibitors of xanathine oxidase, which is involved in uric acid production (Guduchi is used for gout…)(4).  

On to Cannabis

Does it really need an introduction?  

Cannabis is getting a lot of attention for its medicinal properties beyond its psychoactive effects.The medicinal chemistry of Cannabis is super interesting.  The secondary metabolites number over 400, including cannabinoids, terpenoids, flavonoids and lignans that have a wide range of activities. Many Cannabis constituents — terpenes such as ?-myrcene and limonene, for example — are also found in a slew of other medicinal plants. 

Cannabinoids as a chemical class were originally identified in Cannabis (no duh). Technically speaking, cannabinoids are “terpenophenolic” compounds, with terpenes consisting of isoprenyl units.  Chemicals in the pytocannabinoid family are relatively limited in nature, but are found in a number of plants beyond Cannabis. Helichrysum umbraculiserum, from Africa, is reported to contain cannabigerol (CBG) and its precursor acid form CBGa, along with  other chemically-related compounds (5). CBG is the precursor to other cannabinoids such as cannabidiol (CBD), tetrahydrocannabinol (THC), cannabinol (CBN) and the rest of the 3-lettered collection.  That said, the other cannabinoids aren’t found in Helichrysum, so it may lack the necessary enzymes for conversion.    Metabolites structurally related (but not identical) to CBG, CBD, THC, and cannabichromene (CBC) are synthesized variously by Rodadendron, Liverwort, American Licorice and other plants, and even in a fungus, Cylindrocarpon olidum (5). 

Cannabis and endophytes

Now, we’re finally getting to the point of the article!  Cannabis has both fungal and bacterial endophytes, with microbial species and population structure varying based on cultivar (and also both  “hemp” and “marijuana”), growth region, growth stage and plant part (6, 7). 

Multiple fungal species from Aspergillus, Penicillium, Chaetomium, Alternaria and others have been isolated from Cannabis, mainly from cultivated plants though not entirely (8-11), and the bacteria genera isolated include Bacillus, Staphylococcus, Pseudomonas, Acinetobacter, Enterobacter, Pantonea and others.  (7, 11,12).  Endophytes live in the leaves, petioles, twigs, buds and roots (6, 10, 12). 

Endophytes and cannabinoid production

Aside from someone asking me about Cannabis endophytes at the Good Medicine Confluence, the other reason I embarked on this article was to nerd out on how endophytes influence cannabinoid production. 

And……..not.   Not that endophytes don’t influence the presence of cannabinoids in Cannabis. There simply are no published reports documenting this that I’ve found via either Medline, Ovid or Google Scholar databases.  Plenty of research groups have speculated that endophytes do, indeed, influence cannabinoid production.  But, again, no actual reports, as yet, that I know of.  Disappointing!  But  I’m going to out on a limb and guess that more than one research group is working on this and that reports will likely come out over the next year or so, so stay tuned.  

I’m not sure if the issue is in technical challenges?  Cannabis endophytes have been identified starting not quite a decade ago….     To truly nail how the endophytes associated with a particular plant species, the plant actually has to be grown under sterile conditions and then inoculated with the endophytes. (This has been done, for instance, with Echinacea where plants were grown in lab conditions from seeds sterilized of all microbes.)   I wonder if there is some difficulty in doing this with Cannabis for some reason not immediately obvious to me, having no experience in growing it…. 

Endophytes and plant growth

OK, so I struck out on the endophyte-cannabinoid thing.  Next was looking into how endophytes may influence Cannabis growth, given that endophytes are known to improve the growth, and hence, yield, of other medicinal plants.  And, again, not a hell of a lot of work’s been published on this as yet.  What I could find:

There is a study from China reporting increased production of Hemp fiber in response to 6 Cannabis endophytes, including fungi in the Fusarium and Chaetomium genera, though I couldn’t access anything but the abstract and, thus couldn’t look at the methods or actual data (13).   

Endophytes isolated from Cannabis cultivars have been found to produce, when grown in culture, metabolites that when added to other plants increases growth. For example, endophytes from wild Cannabis increased the growth of canola (rapeseed) and increased the plants’ resistance against various types of stressors  enhance the growth of canola and also protect against various stress-inducing factors  (14).  Similarly, inoculation of rice plants with the Cannabis-derived endophytic fungus, Bipolaris sp. CSL-1 improved plant growth and chlorophyll content by producing 2 classes of plant hormone while also stimulating production of plant hormones by the plants (15). 

Flipping this approach around, microbe(s) not isolated from Cannabis increased were able to increase Cannabis plant height, stem basal area and bud size (16). Yield of product was increased by 16.5%  No idea what the bugs actually were, apparently it’s proprietary (“Mammoth P™”)(16).

All of this implies that the native endophytes in Cannabis may improve its growth, but, again, this hasn’t yet been demonstrated, to my knowledge. (At least I haven’t seen it in the research databases I’ve searched.)  Will put money on this data coming out soon as well.  

Endophyte-mediated protection from Cannabis pathogens

Finally, an area where there is a bit more information!  Cannabis endophytes may have a role in protecting the plant from pathogenic microbes.  The battle of the bugs, as it were. Which isn’t particularly surprising…this has been seen for other plants, and our microbiome does the same for us. 

Anyone who’s grown Cannabis knows it’s susceptible to infection by a wide variety of pathogenic microbes, including the fungi Botrytis cinerea (brown rot); Trichothecium roseum (a big problem in greenhouse-raised plants); Penicillium species (bud rot); Fusarium species (leaf and stem wilt) and even a protist, Phythium (root rot) (17, 18). 

Cannabis is also susceptible to mold and powdery mildew (17, 18). It’s been said by a Hemp expert named Dewey in the early 1900s that hemp has no enemies, but it turns out to be not so accurate…particularly in the green house. 

Studies done in culture have shown that Cannabis endophytes have activity against the 2 major Cannabis pathogens I just mentioned, Botrytis and Trichothecium (19) and against a passel of other plant pathogens (10, 20). One way Cannabis endophytes inhibit other microbes is by producing anti-microbial metabolites toxic or otherwise inhibitory to them.  

An even sneakier way Cannabis endophytes out compete pathogenic bugs is by rendering the pathogens harmless (21). This is accomplished by inactivating the pathogen’s virulence factors…the very things that make them a pathogen to the plant.  More specifically, some endophytic bacteria of Cannabis appear to disrupt quorum sensing by Cannabis pathogens (21), in a process known as “quorum quenching”.  Quorum sensing is a way that single celled organisms such as bacteria can behave somewhat like a multicellular organism by sending out chemical signals that regulate, as a group, activities such as replication, virulence, biofilm generation and antibiotic resistance.  This is good news for the plant. Keep in mind that it’s not that the resident endophytes are being nice to the plant, they’re simply protecting their home and meal ticket.

Is the presence of endophytes in Cannabis a risk factor for us?

While endophytes, by definition, don’t cause disease in their host plant, you may have noticed that some of the same genera that are Cannabis endophytes are also Cannabis pathogens.  Just to make things confusing, some Cannabis endophytes may be pathogenic to us.    

For example, representatives from the Aspergillus genus are endophytes in Cannabis (and other plants), and there are a number of cases where immunocompromised folks smoking Cannabis have developed dangerous lung infections with the fungus (22, 23). In some cases resulting in fatalities. There is also an immunocompetent person who developed aspergillosis after smoking Cannabis (23).   

Other fungal species, such as Fusarium, found in Cannabis can produce a variety of mycotoxins (22, 23).  Potentially toxic (to us) fungi native to Cannabis flowers include not just Apergillus, but also species in the Penicillium genus such as P. citrinium and P. paxilli  (23). Though this study didn’t distinguish endophytes from those fungi residing on the surface of the plant. 

To be clear, this issue isn’t limited to Cannabis…many food crops harbor endophytes that may not be great for us (24), so while the topic of plant endophytes and their benefits for our plant medicine is fascinating, it’s not entirely sunshine and roses for us.   

A handful of remaining questions on cannabis endophytes…

  1. Do Cannabis endophytes impact the synthesis of secondary metabolites such as cannabinoids, terpenoids, flavonoids and such in Cannabis?

Presumably the answer is “of course they do”.  Just waiting on the studies looking at this…. 

2.  Are there endophytes in Cannabis capable of synthesizing cannabinoids, and if so, are they able to do this in culture outside of the plant?  

While many of us herbalists prefer crude extracts, you know that some company somewhere is looking at this, either for pharmaceuticalization of individual cannabinoids and using them as source material for the generation of other cannabinoids.  

3. How much is the regional and strain variation in Cannabis chemistry impacted by their particular collection of endophytes?

It’s known that the endophyte populations of a particular plant species do vary based on region. For example, endophyte diversity is higher in equatorial regions compared to temperate regions.  This variation in endophyte species and population structure seen in different regions may be one of the reasons the medicine from a plant varies regionally. 

4.  Can Cannabis endophytes isolated from the wild and inoculated into cultivated strains to improve yield and cut down on resource utilization?

This is a question that almost certainly being looked at as well.  We know that in other medicinal plants, certain endophytes improve factors such as plant growth, resistance to pathogens and other stress and increased yield of medicinally-relevant metabolites.  Likely this will be the case for Cannabis as well. 

So, there it is. Cannabis endophytes in nutshell. To be continued as more research comes out…


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