Identifying wine relevant genetic markers in wine bacteria to isolate robust MLF strains
Abstract
Over 150 Australian isolates of malolactic fermentation bacteria, collected over decades and housed in the AWRI Culture Collection (AWRI CC), were characterised by genomic (DNA) sequencing. A subgroup of these, of known provenance, was screened for tolerance to stresses encountered when grown in wine. This enabled the identification of strains with strong performance characteristics, the most promising of which will be trialled in future research at larger scale winemaking. In addition, genetic markers for stress tolerant traits have been identified. This will facilitate rapid screening of the AWRI CC to isolate candidate strains with desirable characteristics, suited to Australian winemaking conditions.
Summary
Currently there are no malolactic fermentation (MLF) starter culture strains that have been specifically selected for Australian winemaking conditions; development of commercially available strains is largely targeted to overseas markets. Strains of O. oeni isolated from Australian wineries, mostly from spontaneous MLFs, are likely to be well-suited to Australian winemaking conditions. This makes them possible candidates for development of MLF starter cultures that will be more efficient and reliable in the production of Australian wines. This project aimed to identify Australian isolates of the MLF bacterium O. oeni housed in the AWRI CC that would be suited to Australian winemaking conditions. To this end, 169 wine bacteria were characterised by genomic (DNA) sequencing and a subgroup of these was screened at laboratory- scale for tolerance to stresses encountered when grown in red, white and sparkling-base wines. Thirteen genetically distinct, stress-tolerant, strains have been identified. These will be trialled in future research, including AGWA project AWR1303, for their efficacy at lab- and pilot-scale, and in wineries with a view to identifying candidates for the generation of commercially available Australian MLF starter cultures. In addition, alignment and comparison of the genomes that were sequenced has enabled 158 strains of O. oeni to be compared to determine the genetic similarity between them. The amount of genetic variation across strains was found to be very large compared to what is found, for example, when comparing wine yeast strains. Based on the results from the sequencing work a relatedness tree was constructed, from which it is apparent that most strains cluster into three groups. One of these is a small outlying group that differs considerably from the others. There is only one previous publication that describes one strain from this group (Campbell-Sills 2015). None of the commercial strains sequenced to date are found in this group. It thus constitutes a resource with the potential to deliver novel wine-relevant traits.