Gram-positive bacteria are among some of the most industrially and clinically important bacteria, from lactic acid bacteria that are essential for the production of fermented dairy products to multi-drug resistant strains of Enterococcus faecium and Staphylococcus aureus. The success of these bacteria is in part due to their large repertoire of non-classical secretory pathways that range in function from cell-to-cell communication, nutrient acquisition, motility, and even pathogenesis.

While all bacteria encode the classical translocation machineries (Sec and Tat systems), Gram-positive bacteria have evolved at least 7 non-classical secretion pathways: ABC transporters, flagella export apparatus (FEA), holins, membrane vesicles, SecA2, type IV pili assembly apparatus, and the type VII secretion system. In addition to the 7 non-classical secretion pathways, we have annotated those secreted by a non-classical mechanism that has yet to be discovered as “Unknown”. In these cases, there is a clear distinction between bacteria exporting proteins due to cell lysis and secreting proteins using “unknown” mechanisms, where the bacterial cell is not lysed.