Isolation of Mimosine-Degrading Endophytic Bacteria from the Invasive Plant: Leucaena leucocephala

Abstract

Leucaena leucocephala is an invasive plant in the state of Hawaii and other Pacific regions. It was listed as one of the 100 worst invasive alien species in the world (Lowe et al. 2000). One of the reasons for its invasiveness is its ability to produce a toxic chemical called mimosine. β-N-(3-hydroxy-4-pyridone)-α-aminopropionic acid, a non-protein forming amino acid that acts as a strong iron chelator which inhibits growth of some rhizobacteria (Fox and Borthakur, 2001). Mimosine is also an allelochemical, where it negatively affects the growth of surrounding plants (Xuan et al. 2006). However, there are currently three bacterial strains (TAL 1145, Pseudomonas sp. STM 905 and Synergistes jonesii) that are capable of degrading mimosine to its intermediate form 3-hydroxy-4-pyridone (HP) (Soedarjo et al. 1994, Awaya et al. 2005). Mimosine degrading capabilities has shown to be an advantageous trait as microorganism capable of doing so are able to use mimosine as a carbon/nitrogen source (Soedarjo et al. 1994). Bacterial endophytes have been recently recognized as major contributors to plant growth promotion, health, stress tolerance and preventing plant pathogens. Perhaps there are bacterial endophytes that are benefiting Leucaena and aiding it in its invasiveness. The main objectives of this study were to: 1) Isolate endophytic bacteria from the shoot tips of Leucaena leucocephala and identify them using 16S rRNA sequencing; and,- 2) determine if isolates were capable of degrading mimosine. After surface sterilization of shoot samples, eight total endophytic bacterial isolates (SH01-SH08) were cultured in 869 agar. Three of the eight isolates (SH05, SH07 and SH08) were able to degrade mimosine after monitoring their growth in AB minimal broth with 3 mM mimosine and 1 mM FeCl3. Those three isolates are all members of the genus Pseudomonas. Considering that the young shoots of Leucaena contain the highest concentration of mimosine, between 4-10% (Jones, 1979), this means isolates were able to tolerate that specialized niche and translocate from the soil up to the aerial parts of the plant.