It turns your bacteria Jewish*. Seriously, the strong finding of this article was completely ignored. Anyway….
A recent paper describes the effect of circumsion on the bacteria that live on the penis. The authors swabbed uncircumsized and circumsized penises, and then PCR amplified the 16S rRNA gene which is found in all bacteria, and can be used as a ‘barcode’ to identify bacteria. This article has received a lot of attention because of this speculation in the discussion (italics mine):
The observed decrease in anaerobic bacteria after circumcision may be related to the elimination of anoxic microenvironments under the foreskin. Detection of these anaerobic genera in other human infectious  and inflammatory pathologies – suggests that they may mediate genital mucosal inflammation or co-infections in the uncircumcised state. Hence, the decrease in these anaerobic bacteria after circumcision may complement the loss of the foreskin inner mucosa to reduce the number of activated Langerhans cells near the genital mucosal surface and possibly the risk of HIV acquisition in circumcised men.
In other words, circumcision might reduce risk of HIV infection. But there’s a much more convincing health-related finding:
One [uncircumcised] community type appeared to be dominated by members of the Clostridiales Family XI and Prevotellaceae families.. These two families have been identified in the normal human vagina and when present in higher numbers have been associated with BV [bacterial vaginosis] a condition characterized by a shift in the composition of vaginal microbial communities that results in decreased numbers of lactic acid producing bacteria, increased numbers of strict anaerobes, and elevated vaginal pH. The coronal sulci microbiota observed in pre-circumcision samples in this study were similar to several core community types observed in the vagina….. it is unclear whether these phylotypes are acquired from the vagina or vice-versa. We previously reported that male circumcision was associated with reduced BV in female sexual partners and we hypothesize that decreased anaerobic bacteria in the order of Clostridiales and the family of Prevotellaceae may be involved in the causal pathway between male circumcision and reduction of BV in sexual partners.
This seems to be a much more compelling finding: circumcision might reduce bacterial vaginosis. While bacterial vaginosis isn’t dangerous except in very limited circumstances, it still is a nuisance. To me, that’s the compelling finding, although vaginas probably make news editors giggle, so that’s probably why vaginosis wasn’t covered.
*I’m Jewish; I’m allowed to make that joke.