Black swimming dots in cell culture: the identity, detection method and judging criteria

Abstract

Black swimming dots (BSDs) -- the biological UFO in cell culture -- have perplexed biologists for decades. BSDs are extremely tiny dots found in dishes of cultured cells. It is still controversial on their origin and identity. BSDs are very hard to be removed and bring adverse impact to cell experiments (Supplementary Table 1). Here we wish to answer three urgent questions about BSDs. First, is the identity of BSDs nonliving matter or living organism? Second, is there any reliable method to tell whether the donor cattle for FBS production or the animals for primary cells isolation carry BSDs? Third, what are the judging criteria for BSDs when \"tiny black dots\" were observed? In 2015, we happened to observe BSDs in the perivitelline space of mouse oocytes and embryos; and the cells derived from these mice exhibited typical properties of BSDs infected cells (described in Supplementary Information). With these BSDs infected (BSD+) mice, we demonstrate that BSDs per se are ...