Saccharomyces cerevisiae is one of the most important yeasts in winemaking, the distribution of which is widespread and as a result the origin of which is unknown. What is known is that S. cerevisiae is not an airborne species and therefore requires something else to move it from place to place. Recent research has found that insects, including bees and wasps, are one such vector for S. cerevisiae, but it does not explain all movement of this yeast in nature.
In addition to insects, migratory birds have also been studied for their abilities to transfer microorganisms that can infiltrate the human population. To date, most studies have focused on bacterial transfer by migratory birds, with very little focused on yeasts.
Migratory birds are well known for travelling great distances. They embark on a round-trip journey in the spring and again in the fall; starting at their nesting location, travelling great distances to follow the flow of food resources, andeventually returning back to their nesting location. At times, the birds will need to stop at resting areas if they have deleted their fat stores to a point where they require more before being able to fly further distances.
The purpose of today’s study was to examine the potential of migratory birds in transporting yeasts at great distances (as opposed to the shorter distances – 10km – traveled by insect vectors); to identify the kinds of yeasts present; and to determine how long after ingestion by the birds are the yeasts dispersed into the environment (i.e. when did the birds, ahem…eliminate them….).
Experimental sites were located at known migratory bird stopover points within Sicily during the spring and autumn seasons. This location chosen would capture yeast transporting information from migratory birds travelling from Africa to Europe.
At the stopover point, birds were captured near woody areas just as they were landing. A total of 349 birds were captured. After they were captured, birds were ringed/tagged, identified by species, and measured for subcutaneous fat amount (SFA). Note: when SFA values are between 0 and 1, the fat stores are too low to continue and the bird must stop to refuel.
Yeasts were isolated from the birds’ cloacae (a fancy term for the place waste, urine, and reproductive fluids are eliminated from…). Yeasts were identified using genetic analysis.Results
- Yeasts were found in 32.66% of the birds captured.
- The following bird families were found to have the most yeasts present in their cloacae:
- Genetic analysis identified 125 types of yeasts. Yeasts identified in bird cloacae included the following:
- Aureobasidium pullulans; Candida albicans; Candida glabrata; Candida inconspicua; Candida spp.; Candida stellimalicola; Cryptococcus aureus; Cryptococcus carnescens; Cryptococcus magnus; Debaryomyces hansenii; Hanseniaspora guillrmondii; Metschnikowia pulcherrima; Pichia kudriavzevii; Pichia terricola; Pseudozyma aphidis; Rhodotorula mucilaginosa; Saccharomyces cerevisiae; Sporisorium penniseti
- The yeastspecies most frequently found in migratory bird cloacae were:
- H. guillrmondii – 17.6%
- C. albicans – 16%
- S. cerevisiae – 14.4%
- A. pullulans – 12%
- 72 of the 125 yeast isolates found were associated with known wine-related yeasts. These yeasts include the following:
- A. pullulans; D. hansenii; H. guillrmondii; P. kudriavzevii; P. terricola; M. pulcherrima; R. mucilaginosa; and S. cerevisiae.
- The following bird species were found to have the most yeast biodiversity in their cloacae:
- Garden warbler and subalpine warbler
- S. cerevisiae was found most often in the following bird species:
- Garden warbler, icterine warbler, redstar, whitethroat, subalpine warbler, winchat, and spotted flycatcher.
- For birds with SFA values between 0 and 1 (i.e. time for the birds to stop and refuel), 58.4% of the total yeasts and 63.89% of the wine-related yeasts were isolated.
- The most common wine-related yeasts collected from birds with SFA values between 0 and 1 were A. pullulans at 66.66%, and S. cerevisiae at 66.67%.
- 18 isolates of S. cerevisiae were found.
- Of these, 6 strains were identified.
- 9 of the isolates found were located on Lampedusa island. From these, 3 strains were identified.
- 8 of the isolates found were located on Ustica island. From these, 2 strains were identified.
- The strains found on Lampedusa island were different from the strains found on Ustica island.
- As a result of this, the authors hypothesize that the birds landing on Lampedusa are coming from a different starting point than the birds landing on Ustica.
- The average amount of time for the dispersion of yeast by birds was about 12 hours after initial ingestion.
- This time allows a distance of about 300-350km to be travelled by the birds.
The results of this study show that migratory birds are important players in the distribution and biodiversity of yeasts (both wine yeasts and non-wine yeasts) in the environment in the region of Sicily and that the yeasts were able to survive the entire trip from start to rest stop in the bird’s gastric system. To determine if similar results are found in other regions of the world, the study should be repeated in other migratory bird habitat areas throughout the globe.
The authors also found that the yeast strains in a particular location were more similar to one another than the yeast strains found in a location further away. They suggest this may support the idea that migratory birds contribute to the terroir of an area, since the yeasts they spread in the area are genetically
different from yeasts spread by other birds in a different area, which would then produce slightly different wine in both locations. If the same birds are travelling back and forth to the same locations, theoretically they are dispersing the same yeasts to a particular area over and over again, thus contributing to the uniqueness / terroir of the area.
The authors did not mention this, but I think these results also highlight some of the reasons why conserving migratory bird habitat is very important. Of course, there are many other important reasons why migratory bird habitats should be conserved, most important of which is to ensure their survival, but also to maintain biodiversity of the entire ecosystem they inhabit.
Conserving migratory bird habitat would also effectively allow the maintenance of part of the system that defines terroir, which is further evidence of the complicated nature of ecosystems. It shows that harming this one part of the system (i.e. migratory bird habitats) would have profound consequences for not only biodiversity and migratory bird health survival, but also potentially for the uniqueness that defines each individual wine region throughout the world.
I’d love to hear what you all think! Please feel free to your comments and discussions.
Source: Francesca, N., Canale, D.E., Settanni, L., and Moschetti, G. 2012. Dissemination of wine-related yeasts by migratory birds. Environmental Microbiology Reports 4(1): 105-112.