The qualifications out of the way, a new study in Gastroenterology says that the gut microbiota of red wine consumers observed in three different cohorts (U.K., U.S., Netherlands) contained a greater number of different bacterial species than non-consumers. The authors took into account factors such as age, weight, the regular diet and socioeconomic status of the participants and continued to see the association. This was not observed with white wine, beer or spirits consumption.
The authors speculate that the main reason for the association is due to the polyphenols in red wine. Polyphenols are chemicals present in many fruits and vegetables which are linked to benefits but certainly act as a fuel for the microbes present in our system.
Lead author Professor Tim Spector from King's College London said, "This is one of the largest ever studies to explore the effects of red wine in the guts of nearly three thousand people in three different countries and provides insights that the high levels of polyphenols in the grape skin could be responsible for much of the controversial health benefits when used in moderation."
They also say that red wine consumption was associated with lower levels of obesity and 'bad' cholesterol which due to gut microbiota.
For any of this to be relevant, you have to convince yourself that statistics are the same as science and that anything you do with your diet is impacting your microbiome, and that you are doing so in a positive way. Since this association was being found even if someone only drank a glass of wine every two weeks makes it biologically implausible.