http://www.medicalnewstoday.com/articles/amp/325687
They found that in the participants with prehypertension or hypertension, there was a reduction in the diversity of gut bacteria. In particular, species such as Prevotella and Klebsiella tended to be overgrown.
Next, the scientists transplanted fecal matter from the participants into germ-free mice, which are animals that lack gut bacteria. The mice that received fecal matter from people with hypertension also developed hypertension.
Conversely, the authors of a 2019 study in the journal Frontiers in Physiology transplanted feces from mice without hypertension into mice with hypertension. This resulted in a reduction in blood pressure in the mice with hypertension.