Bacterial succession in necrotic tissue of agria cactus (Stenocereus gummosus).

The bacterial communities associated with the development of necroses in injured agria cactus tissue were examined in the field by using both human-induced injuries and cactus tissue inoculated with cactophilic bacteria. Whole-cell bacterial fatty acids were used to determine when and where each of 23 detected species occurred. This information was then used to describe successional patterns of bacterial colonization. Although the number of bacterial species in human-induced injuries reached a maximum on day 16, the Shannon-Weaver diversity index increased to a plateau, which reflects a stable bacterial community. The potential of the bacterial community to macerate the injured cactus tissue was also examined, and the results indicate that the bacteria initially colonizing the newly injured cactus tissue were more likely to contain pectinolytic, proteolytic, and lipolytic enzymes than were the bacteria entering the injuries once tissue maceration had already begun. The cactophilic fruit fly Drosophila mojavensis has been previously shown to carry bacteria to newly injured cactus tissue. In these studies, exclusion of these insects did not significantly affect bacterial succession or community structure. This supports our contention that bacteria colonize injured tissue primarily by passive transport, e.g., on wind-blown particles.