Abstract
We identified two poplar (Populus sp.)-associated microbes, the fungus, Mortierella elongata strain AG77, and the bacterium, Burkholderia strain BT03, that mutually promote each other’s growth. Using culture assays in concert with a novel microfluidic device to generate time-lapse videos, we found growth specific media differing in pH and pre-conditioned by microbial growth led to increased fungal and bacterial growth rates. Coupling microfluidics and comparative metabolomics data results indicated that observed microbial growth stimulation involves metabolic exchange during two ordered events. The first is an emission of fungal metabolites, including organic acids used or modified by bacteria. A second signal of unknown nature is produced by bacteria which increases fungal growth rates. We find this symbiosis is initiated in part by metabolic exchange involving fungal organic acids.
Highlights
Fungi and bacteria regularly co-occur, and engage in symbioses that affect many facets of human health and life (Hogan and Kolter, 2002; Frey-Klett et al, 2011; Labbé et al, 2014; Wolfe and Dutton, 2014; Deveau et al, 2018)
Microbial growth rate assays were performed with two beneficial Populus root associates, Burkholderia strain BT03 and M. elongata strain AG77 (Table 1)
The radial growth rate of M. elongata on P20 plates increased from 3.00 ± 0.43 mm/day in mono-culture to 4.38 ± 0.74 mm/day when co-cultured with Burkholderia (p = 7.099e-04 Student’s t-tests) (Figure 1A)
Summary
Fungi and bacteria regularly co-occur, and engage in symbioses that affect many facets of human health and life (Hogan and Kolter, 2002; Frey-Klett et al, 2011; Labbé et al, 2014; Wolfe and Dutton, 2014; Deveau et al, 2018). Bacterial–fungal interactions (BFIs) frequently occur in the rhizosphere, or vicinity of actively growing plant roots, and sometimes stimulate each other’s growth and benefit plant health (Frey-Klett et al, 2007; Shakya et al, 2013; Deveau et al, 2018). Many bacterial–fungal symbioses are documented, details of the interactions preceding these symbioses remain elusive, and the signals involved uncharacterized. To understand how symbiotic relationships are established and maintained, we need to understand the dynamics and conditionality of how bacteria and fungi produce, transmit, receive, and interpret signals from one another (Putnoky et al, 1988; Isack and Reyer, 1989; Gagnon and Ibrahim, 1998; Nadal and Paszkowski, 2013)
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