Interactions Between Bacillus Spp., Pseudomonas Spp. and Cannabis sativa Promote Plant Growth

Abstract

Plant growth-promoting rhizobacteria (PGPR) deploy several mechanisms to improve plant health, growth and yield. The aim of this study was to evaluate the efficacy of two Pseudomonas spp. strains and three Bacillus spp. strains used as single treatments and in consortia to improve the yield of Cannabis sativa and characterize the impact of these treatments on the diversity, structure and functions of the rhizosphere microbiome. Herein, we demonstrate a significant C. sativa yield increase up to 70% when inoculated with three different Pseudomonas spp./Bacillus spp. consortia but not with single inoculation treatments. This growth-promoting effect was observed in two different commercial soil substrates commonly used to grow cannabis: Promix and Canna coco. Marker-based genomic analysis highlighted Bacillus spp. as the main modulator of the rhizosphere microbiome diversity and Pseudomonas spp. as being strongly associated with plant growth promotion. We describe an increase abundance of predicted PGPR metabolic pathways linked with growth-promoting interactions in C. sativa.

Exploiting Beneficial Pseudomonas spp. for Cannabis Production

“…In this context, since cannabis phytochemicals possess welldocumented antimicrobial properties (Ali et al, 2012), they may act as repellents or chemotaxis molecules that potentially inhibit or favor the colonization of bacteria in the vicinity of the roots and/or in the phyllosphere (Comeau et al, 2020). Accordingly, factors like cannabis cultivar and/or developmental stage have been reported to affect the microbiome composition within root tissues (Winston et al, 2014;Comeau et al, 2020), while soil characteristics and cropping practices also exert a preponderant influence on rhizosphere communities (Winston et al, 2014;Perea, 2019;Barnett et al, 2020;Comeau et al, 2021). Based on the ubiquity of Pseudomonas spp.…”

“…Pioneering assays of microbial inoculants in cannabis, using P. putida, P. protegens, Pseudomonas synxantha and Pseudomonas simiae among other PGPR microorganisms, have already successfully increased several indicators of biomass and fiber yield, such as total plant weight and/or stem length, diameter, and weight (Jin et al, 2014;Conant et al, 2017;Pagnani et al, 2018;Balthazar et al, 2020;Comeau et al, 2021;Kakabouki et al, 2021a,b). Further studies are needed to assess the full agronomic potentials of this promising avenue with indicators considering fiber quality, such as internode length and bast fiber content (Jin et al, 2014), fiber width (Müssig and Amaducci, 2018), pectin and lignin content reduction and fiber decortication efficiency (Petit et al, 2020).…”

“…Additional studies reported positive effects of Pseudomonas spp. inoculants on hemp growth but without investigating the underlying mechanisms (Balthazar et al, 2020;Comeau et al, 2021).…”

“…Two main strategies are usually distinguished when selecting beneficial microorganisms for plant inoculation and microbiome engineering: the bottom-up or synthetic approach which pieces together candidates exhibiting desired traits from an extensive pool gathered from various sources, and the topdown or stepwise approach, which starts from a complex existing microbial community and identifies its keystone players (Tabacchioni et al, 2021). In cannabis, bottom-up studies seem undeniably promising given the recent results obtained with existing PGPR strains (Citterio et al, 2005;Jin et al, 2014;Pagnani et al, 2018;Comeau et al, 2021), biocontrol agents (Balthazar et al, 2020(Balthazar et al, , 2021, or commercialized bioproducts (Gonsior et al, 2004;Conant et al, 2017;Kakabouki et al, 2021a,b;Punja, 2021;Punja and Ni, 2021;Scott and Punja, 2021), thus paving the way for future work with existing Pseudomonasbased bioproducts that are already registered for cereals, fruit trees, and greenhouse vegetables (Fischer et al, 2013;Khan et al, 2016). On the other hand, several top-down studies have also started to examine the potential of harnessing cannabis microbiome residents to improve pathogen control (Gautam et al, 2013;Kusari et al, 2013;Qadri et al, 2013;Scott et al, 2018;, salinity tolerance (Afzal et al, 2015), soil phytoremediation (Liste and Prutz, 2006;Iqbal et al, 2018), cannabinoid production , and fiber retting process (Di Candilo et al, 2010;Ribeiro et al, 2015;Liu et al, 2017;Law et al, 2020).…”

“…In this context, innovative holistic approaches have also been proposed, such as the design of synthetic microbial communities (SynComs, e.g., complex consortia mimicking microbiome functions, interaction networks and/or phylogenetic profiles) (Paredes et al, 2018;de Souza et al, 2020), core-microbiome therapy (e.g., transfer of an artificially cultivated microbiome from a healthy plant to a diseased one, like performed in clinical gastroenterology) (Gopal et al, 2013), prebiotic approaches (e.g., molecules stimulating the bioactivity of the resident microbiome and the growth of beneficial organisms) (Massart et al, 2015;Tabacchioni et al, 2021), or combination with helper strains (e.g., bacteria without beneficial properties by themselves but enhancing the efficacy of co-inoculated partners) (Massart et al, 2015;Berninger et al, 2018). In cannabis, several Pseudomonas strains in consortia with Bacillus strains promoted hemp growth significantly more than the corresponding single-strain inoculants (Comeau et al, 2021), but did not improve ISR elicitation against Botrytis gray mold disease (Balthazar et al, 2020). Other bacterial consortia also significantly promoted hemp growth and/or retting process, but comparisons with single-strain inoculants were not investigated (Di Candilo et al, 2010;Conant et al, 2017;Pagnani et al, 2018).…”