Isolation of bacterial endophytes from nephrolepis sp. (Boston fern) and assessment of growth tolerance against heavy metals
Abstract/Summary
Bacterial endophytes have a certain threshold or tolerance towards heavy metals which can either be below or above the normal levels present in their environment. In this research study, a total of 32 bacterial endophytes (BE) were isolated from five Nephrolepis sp. samples collected in an abandoned mining site in Brgy. Kapayang, Marinduque, Philippines. The 32 BEs were initially reviewed based on their colonial morphology which was visually observed and recorded in reference to a colonial morphology atlas .Among the 32, 12 BE representatives were selected based on their cell morphology which was determined through gram staining. The growth tolerance test against four different heavy metals (Cu, Cd, Pb, and Zn) showed that gram-positive rod shaped bacteria (BEs 1, 2, 3, 4, 6, 7, 8, 9, and 10), gram-negative rod shaped bacteria (BEs 5 and 12) and gram-negative cocci (BE 11) were able to tolerate the different heavy metals tested in various concentrations. In addition, BE 3 and BE 5 along with isolated endophytic bacteria that were not identified (BEs 9 and 11) can tolerate all the given heavy metals in all the tested concentrations suggesting that aside from Bacillus sp. and the bacteria coming from the Enterobactriaceae family, there are other bacterial genera that can tolerate high heavy metal contamination. The results have indicated that the fern Nephrolepis sp. contains certain endophytic bacteria that may contribute to its survival in metalliferous environments. The isolated BEs 1- 12 could potentially aid plant growth or absorb heavy metals in heavy metal polluted environments since they can withstand varied heavy metal concentrations.
