Thorns serve as mechanical defenses of plants against herbivory. However, plant thorns harbor microorganisms that are potentially pathogenic. These pathogens may be transferred to herbivores and other animals and provide an additional defense for the plants. Thorns from 5 plant species native to the Rio Grande Valley of South Texas were collected and used to isolate bacteria colonizing the thorn surface. Thorns, leaves and stems of plants were visualized using Scanning Electron Microscopy (SEM) to observe any bacteria on the plant surface. Isolated bacteria were tested for their ability to grow in aerobic versus anaerobic environments, to produce hemolysis, carbon source utilization, and were gram-stained. Bacteria were identified by sequencing of the 16S rRNA gene. A total of 69 pure cultures were obtained of which 61 were positively identified. The majority of the bacteria were gram-positive and facultative (i.e., able to grow both aerobically and anaerobically). Many (23%) were hemolytic suggesting that they were opportunistic blood-borne pathogens. All isolated organisms metabolized a collection of 31 tested organic substrates and metabolic activity was observed to be more efficient among anaerobically-isolated microorganisms compared to microorganisms isolated aerobically. SEM revealed that bacteria were found on the thorn surface but also on the stems and leaves of the plants. Identification using the 16S rRNA gene revealed the presence of 10 species representing 7 genera. The most commonly identified organisms were Bacillus cereus, Serratia marcescens, and Pseudomonas aeruginosa, all of which are opportunistic pathogens.
Charles, Felicia A.; Cepeda, Sergio; McDonald, Andrew; and Lowe, Kristine L., "Opportunistic Pathogenic Bacteria Colonize Thorns of Native Rio Grande Valley Plants" (2013). Biology Faculty Publications and Presentations. 59.
Subtropical Plant Science