A new bacterial endosymbiotic relationship in Kluyveromyces marxianus isolated from the mezcal fermentation process

In Mexico, agave has a significant cultural and economic impact via its use as a raw material for producing fermented drinks. The agave plant grows in arid and nitrogen-deficient soil where it associates with fungi and bacteria to meet nutrient demands, particularly under extreme conditions of fungal growth; this community of microorganisms is called the microbiome. In the microbiome, aromatic volatile synthesis activates the defense response, resistance to abiotic stress, and plant growth. These aromatic volatiles also impact the organoleptic characteristics of fermented beverages and are produced by microorganisms during agave fermentation. This research presents the behavior of K. marxianus cultivated in the presence of extreme and deficient nitrogen concentrations. In addition, a new biological relationship between K. marxianus ITD0090 from mezcal fermen-tation and Bacillus tequilensis ITD-UANL-01 is reported, confirmed by fluorescence microscopy and intracellular recovery. Our results also reveal that B. tequilensis ITD-UANL-01 is a nitrogen-fixing bacterium that provides assimilable nitrogen to K. marxianus under nitrogen starvation conditions. This phenomenon allows for 144 h of viability without nitrogen. Furthermore, this is the first report of an endosymbiont of K. marxianus ITD0090 in fermentation.