1. On the link between a lack of exposure to bacteria and the development of allergies and asthma. This is commonly referred to as the “hygiene hypothesis,” and is an ongoing area of study and debate in the scientific community. Here’s a good overview from the BBC.
2. On the role of helicobacter pylori’s affect on health. The link between this bacteria and stomach ulcers is well established, and mainstream scientific consensus continues to favor eradication. However, as Sandor stated there is some evidence that it may have beneficial effects on obesity (as well as allergies), but research into this question is nascent. Here’s a recent editorial from the peer-reviewed journal Therapeutic Advances in Gastroenterology discussing the possible benefits of helicobacter pylori.
3. On the claim that “There are a trillion bacteria inside each of us.” Sandor was being overly conservative with this estimate. According to some, the number is closer to 39 trillion. Source.
4. On the link between gut bacteria and mental health, the BBC has a good overview of the research on this topic. The big picture takeaway is that yes, the gut microbiome has a profound effect on mental health, although the nuances of exactly how are still an area of ongoing research.
5. On the claim that plants have exudates which attract bacteria, here’s one study from the peer-reviewed journal Frontiers in Microbiology which examines the topic

 

(in order of appearance)
Artist – Song – Album
Sign Libra – Sea of Vapours – Sea to Sea
Sign Libra – Sea of Tranquility – Sea to Sea
Mary Lattimore – The Warm Shoulder – Collected Pieces
M. Sage – River Turns Woodley (for Frogman) – Paradise Crick
Moss Covered Technology – Intro – Brick and Air
OE – Suchness – Suchness
The OO-Ray – Generate – Middle
Jimmy Behan – The Echo Garden – Through The Trees
Pierre Rousseau – Tendresse – M​é​moire De Forme
Quixosis – Antitesis – Descomposiciones
Glitch Bird – Intemperie – Intemperie
Alex Hentze – Soplo de Vida – Soplo de Vida