Samuel Breselge

Water kefir (WK) is an artisanal fermented beverage made from sugary water, optional fruits and WK grains. WK grains can be reused to start new fermentations. Here we investigate the microbial composition and function of 69 WK grains and their ferments by shotgun metagenomics. A subset of samples was subjected to metabolomic, including volatilomic, analysis. The impact of different fermentation practices on microbial composition and fermentation characteristics was analysed and it was noted that, for example, the common practice of drying water kefir grains significantly reduces microbial diversity and negatively impacts subsequent grain growth. Metagenomic analysis allowed the detection of 96 species within WK, the definition of core genera and the detection of different community states after 48 h of fermentation. A total of 485 bacterial metagenome assembled genomes were obtained and 18 putatively novel species were predicted. Metabolite and volatile analysis show associations between key species with flavour compounds. We show the complex microbial composition of WK and links between fermentation practices, microbes and the fermented product. The results can be used as a foundation for the selection of species for large scale WK production with desired flavour profiles and to guide the regulatory framework for commercial WK production.

Microorganisms are ubiquitous in nature and are central to human, animal, environmental, and planetary health. They play a particularly important role in the food chain and the production of high-quality, safe, and health-promoting foods, especially fermented foods. This important role is not always apparent to members of the public. Here, we describe Kefir4All, a citizen science project designed to provide the general public with an opportunity to expand their awareness, knowledge, and practical skills relating to microbiology, introduced through the medium of producing fermented food, i.e., milk kefir or water kefir. During the course of Kefir4All, 123 citizen scientists, from second-level school and non-school settings, participated in a study to track changes in the microbial composition of kefirs, by performing and recording details of milk kefir or water kefir fermentations they performed in their homes or schools over the 21-week project. At the start of the study, the citizen scientists were provided with milk or water kefir grains to initiate the fermentations. Both types of kefir grain are semi-solid, gelatinous-like substances, composed of exopolysaccharides and proteins, containing a symbiotic community of bacteria and yeast. The experimental component of the project was complemented by a number of education and outreach events, including career talks and a site visit to our research center (Kefir Day). At the end of the study, a report was provided to each citizen scientist, in which individualized results of their fermenting activities were detailed. A number of approaches were taken to obtain feedback and other insights from the citizen scientists. Evaluations took place before and after the Kefir4All project to gauge the citizen scientist's self-reported awareness, knowledge, and interest in microbiology and fermented foods. Further insights into the level of citizen science participation were gained through assessing the number of samples returned for analysis and the level of participation of the citizen scientists throughout the project. Notably, the survey results revealed a self-reported, increased interest in, and general knowledge of, science among the Kefir4All citizen scientists after undertaking the project and a willingness to take part in further citizen science projects. Ultimately, Kefir4All represents an example of the successful integration of citizen science into existing education and research systems.

Developing a better understanding of the genomic and metabolic features of acetic acid bacteria (AABs) has the potential to facilitate an improvement of the taste or flavor of fermented foods. Here, we conducted a high-resolution analysis of AABs present in fermented foods based on the investigation of 337 high-quality metagenomic-assembled genomes (MAGs) recovered from 223 metagenomic samples. Firstly, by integrating these MAGs, we built a phylogenetic tree of high-quality MAGs using GTDB-Tk. We found that AABs MAGs from food-related samples and those from other environments are generally phylogenetically distinct, with the majority of those from fermented foods being assigned to a relatively small number of genera. Functional metagenomic analysis also revealed that the fermented food-associated AABs MAGs are associated with the production of carbohydrate-active enzymes, antibiotic resistance genes, and secondary metabolites. Through these investigations, we have gained substantial insights into the diversity, function, and roles of AABs in fermented food microbiomes.