Genomic information of Kocuria isolates from sake brewing process

Kuratsuki bacteria and sake making

Kuratsuki bacteria enter during the sake-making process and interact with sake yeast until their growth is attenuated by the ethanol produced by sake yeast. Due to the interaction between kuratsuki bacteria and sake yeast, the metabolism of sake yeast changes, affecting the composition of esters and organic acids and subsequently the flavor and taste of sake. We cultivated kuratsuki bacteria and sake yeast, and performed test making at sake breweries to clarify the interaction among microorganisms in the sake-making process. We aim to propose a sake-making process that controls the flavor and taste of sake by utilizing the functions of kuratsuki bacteria.

Effect of kuratsuki Kocuria on sake's taste varies depending on the sake yeast strain used in sake brewing

Although sake yeast mainly produces the taste of sake, sake brewery-inhabiting (kuratsuki) bacteria affect the taste of sake. Thus, kuratsuki bacteria may alter the metabolism of sake yeast through interactions between kuratsuki bacteria and sake yeast. This study aimed to confirm the effects of the combination of kuratsuki Kocuria TGY1127_2 and different sake yeast strains, AK25, K901, and K1801 on the taste of sake. Although the Brix and acidity during sake production using AK25 differed between sake with and without kuratsuki Kocuria, those using K901 and K1801 did not differ. Thus, sake yeast AK25 interacted with kuratsuki Kocuria and changed its characteristics of ethanol fermentation. In addition, the taste intensity changes, measured with a taste sensor TS-5000Z, showed that the effects of adding kuratsuki Kocuria varied among different sake yeasts. Thus, each sake yeast strain interacted with the kuratsuki bacterium and produced different metabolites, resulting in a change in the taste of sake. The findings of this study can lead to the brewing of sake using different types of kuratsuki bacteria which can affect the taste of sake.

A dark matter in sake brewing: Origin of microbes producing a Kimoto-style fermentation starter

Introduction

In Kimoto-style fermentation, a fermentation starter is produced before the primary brewing process to stabilize fermentation. Nitrate-reducing bacteria, mainly derived from brewing water, produce nitrite, and lactic acid bacteria such as Leuconostoc can proliferate because of their tolerance toward low temperature and their low nutritional requirements. Later, Lactobacillus becomes the dominant genus, leading to weakly acidic conditions that contribute to control yeasts and undesired bacterial contaminants. However, the sources of these microorganisms that play a pivotal role in Sake brewing have not yet been revealed. Thus, comprehensive elucidation of the microbiome is necessary.

Methods

In this study, we performed 16S rRNA amplicon sequencing analysis after sampling from floor, equipment surfaces, and raw materials for making fermentation starters, including koji, and water in Tsuchida Sake brewery, Gunma, Japan.

Results

Amplicon sequence variants (ASVs) between the external environments and the fermentation starter were compared, and it was verified that the microorganisms in the external environments, such as built environments, equipment surfaces, and raw materials in the sake brewery, were introduced into the fermentation starter. Furthermore, various adventitious microbes present in the fermentation starter of early days and from the external environments were detected in a nonnegligible proportion in the starter, which may impact the taste and flavor.

Discussion

These findings illuminate the uncharacterized microbial dark matter of sake brewing, the sources of microbes in Kimoto-style fermentation.

A Case of an Ex Vivo Onychomycosis Model Introduced with a Cultured Colony of Kocuria koreensis from a Diabetic Ingrown Toenail

A 57-year-old male patient with >10-year history of type 2 diabetes presented with a left big toenail deformity and pain. A physical examination revealed a white and yellow-to-brown patch on the nail as well as thickening and ingrowth of the nail plate. The nail plate was opened using nippers, and a fungal culture revealed Trichophyton interdigitale with yellow yeast. The yeast isolate was identified as Kocuria koreensis, a Gram-positive aerobic coccoid with keratinolytic properties that is part of the normal flora of the skin. We created an ex vivo onychomycosis model of T. interdigitale infection of the human nail by placing a sterilized normal nail on the cultured slant. K. koreensis initially spread over the normal nail, and T. interdigitale then penetrated the nail plate. After one year and six months, a spiral ingrown nail developed. A histopathological examination of the spiral revealed onychomycosis with superficial and deep abscesses of Gram-positive cocci infection. We performed PCR from paraffin-embedded material, and the sequences obtained were identical to those of T. interdigitale and K. koreensis. These results suggest that the development of onychomycosis by T. interdigitale is introduced and accelerated by K. koreensis, and the symbiosis of these microorganisms is suspected in the nail. This ex vivo model has a number of limitations. Therefore, further research on co-infected cases is needed to confirm this hypothesis.

Diversity of Bacillus Isolates from the Sake Brewing Process at a Sake Brewery

We collected 92 isolates belonging to the genus Bacillus from the sake brewing process at Shiraki Tsunesuke Sake Brewery in Gifu, Japan to determine whether there is strain specificity at individual sake breweries. After distributing the isolates into seven groups, we observed that at least two groups (68 isolates) were kuratsuki bacteria at Shiraki Tsunesuke Sake Brewery. The kuratsuki Bacillus isolates were collected from different samples at the early and late stages of sake brewing in 2021 and 2019, respectively. These results showed that kuratsuki Bacillus entered the sake brewing process at this location. These kuratsuki Bacillus isolates had a high ethanol tolerance. Our previous paper showed the existence of kuratsuki Kocuria at Narimasa Sake Brewery in Toyama, Japan, but this study demonstrated that it is not found at Shiraki Tsunesuke Sake Brewery. Therefore, each sake brewery has specific kuratsuki bacterial strains, which are isolated with high frequency and contribute a specific flavor or taste to each sake brewery.