How Yeast and Bacteria Alter Nectar Characteristics Anthony Schmitt Abstract Plant - Pollinator Relationships Are Based Off a Binary Reward System
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Volume 1: Spring 2014: pp. 19-29. R E V I E W The invisible communities of nectar: How yeast and bacteria alter nectar characteristics Anthony Schmitt Abstract Plant - pollinator relationships are based off a binary reward system. Plants present pollinators with nectar as an energetic reward, while pollinators transfer genetic material to help plants achieve full reproductive success. The constituents of nectar play a crucial role in facilitating this mutual relationship. A new area of research is emerging that may change the way biologists view this binary system; it may no longer be a two-way interaction. Microorganisms - yeasts and bacteria - have been found to inhabit nectars across a wide geographic range and across a large range of plant species. These microorganisms change the characteristics of nectar in such a way to can alter pollinator behavior. For example, yeasts and bacteria can modify the sugar composition and concentration of nectar. Sugars in nectar are a chief reward for pollinator visitation. This review examines the new field of research presented by these microbes by breaking down changes in nectar as a result of microbial communities. The implications presented by these findings may significantly change the way biologists view plant-pollinator interactions as research continues to develop. *Biology Department, University of Minnesota Duluth *Writing Studies Department, University of Minnesota Duluth Introduction facilitating co-evolution (Cronk and Ojeda Understanding the interactions of species 2008). It was long believed that the plant- within a community is important in pollinator system was a binary relationship. expanding our ecological and evolutionary However, new studies are finding a new knowledge, especially when two species factor in this relationship. rely on each other for reproductive The chemistry of nectar is understood to success. Many plants rely on the mutual have an important role in the plant-pollinator relationship between themselves and their binary system. Constituents attract and pollinators in order to produce a maximum deter specific organisms to help facilitate seed set. There are many ways that plant pollination in a way that will maximize species attract the pollinators that help fecundity (Adler 2000; Heil 2011). Although some constituents, such as H O , is thought plants achieve reproductive success. A 2 2 few examples include flower morphology, to sterilize nectar by killing off microbes (Adler 2000; Carter et al. 2007; Carter and Corresponding flower placement, flower color and scent. Thornburg 2004), but some microbes are Author: Perhaps the most important attractant is the still present in nectar. Anthony Schmitt production and enticement of nectar within It has long been known that [email protected] flowers. Nectar is a major energetic reward plants present to their pollinators in order to microorganisms, such as yeasts, inhabit help facilitate this desired interaction. The floral nectars (Sandhu and Waraich 1985), specificity of this system can be important in but their role was never closely examined. However, new research indicates that The Duluth Journal of Undergraduate Biology 119 R E V I E W Volume 1: Spring 2014 microorganisms are emerging as a source of pollinators. In his review, Heil (2011) of variation in the characteristics of nectar wrote that nectars rich in sucrose generally and therefore may have a significant role in attract hummingbirds, butterflies, moths, the plant-pollinator relationship. Microbial long-tongued bees, and ants whereas nectars community structure and ecology, in rich in hexose (glucose and fructose) attract general, is a field that is largely unexplored short – tongued bees and flies. Amino acids and research in this area may be beneficial have been reported to be more attractive to understanding the ecology of nature on a to insects rather than bird pollinators since wide spectrum (Furhman 2009). birds may be able to gain essential nutrients This review aims to present the current from other sources (Gonzalez-Teuber and knowledge of how yeasts and bacteria Heil 2009; Heil 2011). Some components shift nectar characteristics. Additionally, are thought to be specifically for defending the review will briefly discuss the potential against microbial infection and some are impact microorganisms may have on plant thought to be toxic to organisms that may – pollinator interactions. The purpose of this harm the plant (Adler 2000; Carter et al. paper is to bring awareness to this emerging 2007; Carter and Thornburg 2004). All the ecological niche within nectars that may different components within nectar provide hold larger implications in the important some type of function, which leads to the role pollinators have with plant fecundity. central purpose of this review. Microbes, such as yeasts, use nectar as a habitat and are Nectar chemical composition is interacting with the varying characteristics important for plant-pollinator that allow nectar to provide its ecological facilitation role in plant reproduction. The chemistry of nectar and its relation to Yeasts in Nectar pollinators has been extensively reviewed (for instance see reviews by Gonzalez- The approach to studying yeasts, and other Teuber and Heil 2009; Heil 2011). To fully microbiota, in nectar has resulted in two core understand all the components regarding fields of research. Recent studies support the function of nectar, some background the assertion that yeasts are present in flower information on nectar chemistry may be nectars across a wide range of plants species useful. It is well established that nectar is in separate plant communities. These mainly a solution of water and sugars (Baker studies provide evidence that nectar-living and Baker, 1983), although other constituents yeasts are geographically wide spread. including amino acids, proteins, lipids, Additionally, other recently published alkaloids and several other compounds studies support the notion that yeasts have have also been found in nectars (Baker and the ability to modify nectar chemistry. Baker 1983; Gonzalez-Teuber and Heil Nectar robber 2009). Some nectar compounds are thought Yeasts are common in nectar Organisms who to attract beneficial species (Brandenburg In order to establish the importance of consume a flowers et al. 2009), while some, such as alkaloids, yeasts in nectar, recent studies examined nectar generally by drilling a hole in the are thought to deter harmful species, such whether or not there was support for the corolla. Nectar robbers as nectar robbers. The concentration and postulate that yeasts are found throughout generally do not abundance of certain components that make a wide variety of plant nectars. Herrera et provide any benefit to up a flower’s nectar chemistry is believed to al. (2009) performed a quantitative survey the plant. be strongly correlated to plant – pollinator across two continents that helped establish mutualism. the wide-ranging occurrence of yeasts in the Sugars and free amino acids are nectar of insect-pollinated plants. understood to be important for the attraction Yeast communities were frequently The Duluth Journal of Undergraduate Biology 20 Invisible communities in nectar R E V I E W Volume 1: Spring 2014 established throughout floral nectars in species (Herrera et al. 2010). This may the species and flowers surveyed reaching be due to the nature of nectar as a rather high densities within these nectars (Herrera hostile environment to yeasts (Adler 2000; et al. 2009). The study examined plant Carter and Thornburg 2004). The hostile communities from two separate continents environment may allow yeast species with and three different locations with different osmotolerance and resistance to secondary habitat variations (see study for further compounds found in nectar to have an explanation)– Donana (south-western advantage over other yeast species (Herrera Spain), Cazorla (south-eastern Spain) and et al. 2010). Yucatan (eastern Mexico). Overall, nectar Pozo et al. (2011) tested the osmophilic from 44 plant families and 130 plant species tolerance of nectar-living yeast species were examined. In Donana 31.8% of flowers by testing their growth response (positive contained yeasts, 42.3% of Cazorla flowers or negative response) in solutions of Metschnikowia contained yeasts, and 54.4% of flowers in 50% glucose in order to classify them as reukaufii Yucatan contained yeasts (Herrera et al. osmophilic species versus non – osmophilic A nectar living yeast 2009). Herrera et al. (2009) also found that species. There was a higher frequency of species that is found yeast cell densities of 104 cells mm-3 were osmophilic yeast species (35.5% of plant in the nectar of almost all plant species that quite common. It should be noted that other species surveyed) when compared to non – have been surveyed so studies have found that yeasts can reach osmophilic yeast species (4.8% of the plant far. It is a fungus part higher densities within nectar (de Vega et species surveyed). of the Ascomycota al. 2009), but generally densities were close As mentioned earlier, M. reukaufii has phylum and the to what was found in this survey (Brysch- been found in high densities across all the Metschnikowiaceae family. Herzberg, 2004; Herrera et al. 2009; de studies reviewed and may be a species Vega et al. 2009 and Belisle et al. 2011). with specialized traits to allow it to thrive DNA methylation Since yeasts are found in rather high in nectar. Once source of this nectar niche- The