A culture-independent PCR-based method for the detection of Lachancea thermotolerans in wine

Nectar-dwelling microbes of common tansy are attractive to its mosquito pollinator, Culex pipiens L

Background

There is widespread interkingdom signalling between insects and microbes. For example, microbes found in floral nectar may modify its nutritional composition and produce odorants that alter the floral odor bouquet which may attract insect pollinators. Mosquitoes consume nectar and can pollinate flowers. We identified microbes isolated from nectar of common tansy, Tanacetum vulgare, elucidated the microbial odorants, and tested their ability to attract the common house mosquito, Culex pipiens.

Results

We collected 19 microbial isolates from T. vulgare nectar, representing at least 12 different taxa which we identified with 16S or 26S rDNA sequencing as well as by biochemical and physiological tests. Three microorganisms (Lachancea thermotolerans, Micrococcus lactis, Micrococcus luteus) were grown on culture medium and tested in bioassays. Only the yeast L. thermotolerans grown on nectar, malt extract agar, or in synthetic nectar broth significantly attracted Cx. pipiens females. The odorant profile produced by L. thermotolerans varied with the nutritional composition of the culture medium. All three microbes grown separately, but presented concurrently, attracted fewer Cx. pipiens females than L. thermotolerans by itself.

Conclusions

Floral nectar of T. vulgare contains various microbes whose odorants contribute to the odor profile of inflorescences. In addition, L. thermotolerans produced odorants that attract Cx. pipiens females. As the odor profile of L. thermotolerans varied with the composition of the culture medium, we hypothesize that microbe odorants inform nectar-foraging mosquitoes about the availability of certain macro-nutrients which, in turn, affect foraging decisions by mosquitoes.

Metabolic footprint analysis of metabolites that discriminate single and mixed yeast cultures at two key time-points during mixed culture alcoholic fermentations

INTRODUCTION

There has been a growing interest towards creating defined mixed starter cultures for alcoholic fermentations. Previously, metabolite differences between single and mixed cultures have been explored at the endpoint of fermentations rather than during fermentations.

OBJECTIVES

To create metabolic footprints of metabolites that discriminate single and mixed yeast cultures at two key time-points during mixed culture alcoholic fermentations.

METHODS

¹H NMR- and GC-MS-based metabolomics was used to identify metabolites that discriminate single and mixed cultures of Lachancea thermotolerans (LT) and Saccharomyces cerevisiae (SC) during alcoholic fermentations.

RESULTS

Twenty-two metabolites were found when comparing single LT and mixed cultures, including both non-volatiles (carbohydrate, amino acid and acids) and volatiles (higher alcohols, esters, ketones and aldehydes). Fifteen of these compounds were discriminatory only at the death phase initiation (T1) and fifteen were discriminatory only at the death phase termination (T2) of LT in mixed cultures. Eight metabolites were discriminatory at both T1 and T2. These results indicate that specific metabolic changes may be descriptive of different LT growth behaviors. Fifteen discriminatory metabolites were found when comparing single SC and mixed cultures. These metabolites were all volatiles, and twelve metabolites were discriminatory only at T2, indicating that LT-induced changes in volatiles occur during the death phase of LT in mixed cultures and not during their initial growth stage.

CONCLUSIONS

This work provides a detailed insight into yeast metabolites that differ between single and mixed cultures, and these data may be used for understanding and eventually predicting yeast metabolic changes in wine fermentations.

Influence of Lachancea thermotolerans on cv. Emir wine fermentation

The present paper describes the behaviour of Lachancea thermotolerans and Saccharomyces cerevisiae in pure, co-cultured and sequential fermentations in cv. Emir grape must. Faster fermentation rates were observed in wine made with a pure culture of S. cerevisiae and wine produced with simultaneously inoculated cultures of L. thermotolerans and S. cerevisiae. Both L. thermotolerans and S. cerevisiae gave high population numbers. The use of L. thermotolerans in mixed and sequential cultures led to an increase in final total acidity content in the wines, varying in the range 5.40-6.28 g/l (as tartaric acid), compared to pure culture S. cerevisiae, which gave the lowest level of total acidity (5 g/l). The increase was in the order of 1.18-2.06 g/l total acidity. Increase in final acidity by the use of L. thermotolerans might be useful to improve wines with low acidity due to global climate change. Volatile acidity levels (as acetic acid) were in the range 0.53-0.73 g/l, while the concentration of ethyl alcohol varied in the range 10.76-11.62% v/v. Sequential fermentations of wines and pure culture fermentation of L. thermotolerans resulted in reduction in the concentrations of acetaldehyde and higher alcohols, with exception of N-propanol and esters. According to the sensory analysis, wine obtained with sequential inoculation of L. thermotolerans followed by inoculation of S. cerevisiae after 24 h, and simultaneous inoculation of these yeasts, was the most preferred. Copyright © 2016 John Wiley & Sons, Ltd.