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Does Fermentation Enhance Beverage Safety? Kombucha's Resistance to Microbial Invasion Suggests a Protective Role.
Gissel Marquez Alcaraz, Shrinath Narayanan, Joe Alcock, Jessica D Ayers, Cristina Baciu, Hanna L Berman, Robert R Dunn, Angelo Fortunato, Alexander May, Carlo C Maley, Jessica Siegel, Bryan Yavari, Athena Aktipis
bioRxiv : the preprint server for biology·2025
Does fermentation enhance the safety of beverages? This study investigates kombucha's resilience to microbial invasion from human hands. Kombucha, an ancient fermented tea, relies on a biofilm known as a symbiotic community of bacteria and yeast (SCOBY) and a starter culture to ferment sweet tea, producing various metabolites including gluconic acid, acetic acid, ethanol, and carbon dioxide. While fermented foods have been historically associated with potential health benefits, direct evidence comparing the prevalence of human pathogens in fermented versus non-fermented beverages has been lacking. To address this, we conducted a citizen science experiment at Arizona State University, introducing swabs from people's palms into both kombucha and a sweet tea control. Over 30 days, we monitored the bacterial and fungal composition using 16S and ITS rRNA sequencing. Our findings reveal that kombucha maintained a relatively stable microbial profile and physical appearance, with a typical SCOBY biofilm developing. In stark contrast, the sweet tea experienced a dramatic change in microbial composition and was visibly compromised by rapidly growing microorganisms. Importantly, this suggests that the complex microbial ecosystem of kombucha can limit the growth of foreign microbes introduced from human hands. Given that human pathogens were absent from the kombucha while present in the tea samples, our results indicate that the antimicrobial properties of fermentation byproducts and the physical barrier of the SCOBY may contribute to this resilience. Further research is warranted to fully elucidate the mechanisms underlying kombucha's resistance to microbial invasion.
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View paper →Parental investment without kin recognition: Simple conditional rules for parent-offspring behavior.
C Athena Aktipis, Eduardo Fernandez-Duque
Behavioral ecology and sociobiology·2010
Species differ widely with regard to parental investment strategies and mechanisms underlying those strategies. The passing of benefits to likely offspring can be instantiated with a number of different computational and behavioral systems. We report results from an agent-based model in which offspring maintain proximity with parents and parents transmit benefits to offspring without the capacity of either parent or offspring to 'recognize' one another. Instead, parents follow a simple rule to emit benefits after reproducing and offspring follow a simple rule of moving in the direction of positive benefit gradients. This model differs from previous models of spatial kin-based altruism in that individuals are modeled as having different behavioral rules at different life stages and benefits are transmitted unidirectionally from parents to offspring. High rates of correctly directed parental investment occur when mobility and sociality are low and parental investment occurs over a short period of time. We suggest that strategies based on recognition and bonding/attachment might serve to increase rates of correctly directed parental investment under parameters that are shown here to otherwise lead to high rates of misdirected and wasted parental investment.
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