Yeast–Bacterium Interactions: The Next Frontier in Nectar Research

Abstract

Beyond its role as reward for pollinators, floral nectar also provides habitat for specialized and opportunistic yeasts and bacteria. These microbes modify nectar chemistry, often altering mutualistic relationships between plants and pollinators in ways that we are only beginning to understand. Many studies on this multi-partite system have focused on either yeasts or bacteria without consideration of yeast-bacterium interactions, but recent evidence suggests that such interactions drive the assembly of nectar microbial communities and its consequences for pollination. Unexplored potential mechanisms of yeast-bacterium interactions include the formation of physical complexes, nutritional interactions, antibiosis, signaling-based interactions, and horizontal gene transfer. We argue that studying these mechanisms can elucidate how nectar microbial communities are established and affect plant fitness via pollinators.

Towards a better understanding of the role of nectar-inhabiting yeasts in plant–animal interactions

“…Additionally, the yeast communities associated to specific floral structures of M. polymorpha showed differences in species richness and phylogenetic diversity, both of which were higher for stamina and styles than for nectar [29]. Such microhabitat-dependent variation in species richness may be due not only to the large morphological and physiological differences occurring within flowers, but also to the filtering effect of microbial diversity exerted by specific floral microhabitats such as floral nectar [19,29,[45][46][47].…”

“…Most studies on the flower-insect-microbe system to date have focused on yeasts, and it is only recently that also bacteria have been studied in this regard [9, 10, 13, 66-68, 74, 77-80]. Nevertheless, very limited attention has been given to potential fungal-bacterial interactions, even when recent evidence suggests that such interactions drive the assembly of nectar microbial communities and might affect plant-animal interplays [45]. The limited information currently available on the potential interactions taking place between flower-inhabiting fungi and bacteria mostly came from the analysis of co-occurrence patterns of nectar yeasts and bacteria [20], and the study of microcosms mimicking floral nectar [81].…”

“…), antibiosis, signaling-based interactions (e.g. quorum sensing), and horizontal gene transfer between fungal and bacterial cells [45].…”

Evidence for the plant recruitment of beneficial microbes to suppress soil-borne pathogen

“…Plants have been subject to selective pressures from pathogens, pests, and undesirable soil (e.g., nutrient deficient) and weather (e.g., drought) conditions since their evolutionary origin (Chakraborty & Newton, 2011;. Assemblages of host-specific microbiomes in the rhizosphere, root endosphere and other niches, such as the phyllosphere (leaf) and anthosphere (flower) have been reported (Edwards et al, 2015;Álvarez-Pérez et al, 2019;Grady et al, 2019). Emerging evidence indicates that these microbial symbionts, rather than merely acting as tenants, intimately interact with plants and influence their immune systems and multiple processes of plant growth and development .…”

Nectar Microbial Diversity and Changes Associated with Environmental Exposure

“…Despite the range of strategies to prevent microbial colonisation of nectar, the evidence shows that floral nectar contains several species of highly adapted yeast and fungal communities [12,16,33,34] with the ability to alter the amino acid and sugar composition of the nectar [16,21,35]. Bacteria have previously been isolated, cultured and identified in a small number of floral nectar studies [36,26,37].…”