Volume 19, No. 5, 2022
Tolerances Of Rhizospheric And Endophytic Bacteria Isolated From Paspalum Notatum In Mercury-Contaminated Environments
Alexander Pérez-Cordero , Donicer E Montes-Vergara and Diego Carrillo-González
Abstract
The aim of this study was to isolate rhizospheric and endophytic bacteria from mercurycontaminated soils in southern Bolivar (Colombia) and to evaluate in vitro their tolerance capacity to different mercury concentrations. A completely random sampling was carried out, collecting, at the same time, samples of soil, rhizosphere and plant tissues (root, stem and leaves) in a mercury-contaminated environment. The samples were sent to specialized laboratories for determination of mercury concentration by instrumental cold vapor atomic absorption spectrophotometry. The populations of rhizospheric and endophytic bacteria were correlated with the mercury values present in each environment. Finally, the sensitivity and tolerance of the bacteria to different mercury concentrations was evaluated in vitro. The average mercury contents in soil were 5.9, in rhizosphere 5.3 and 4.5 kg/ kg in P. notatum. The amount of bacteria ranged as follows: in soil 2 x 105 , in rhizosphere 2.6 x 1011 CFU/ g soil and in tissue 5.45 x 107 CFU/ g tissue. A total of 40 bacterial morphotypes were isolated, five rhizosphere bacteria and 35 as endophytic bacteria from the three identified plant species. The mercury sensitivity test, related to the PNM4RizHgLIM isolate from rhizosphere of Paspalum notatum, as well as PNM10RHgLIM from root with the highest mercury tolerance percentages with 85.4% and 79.1% respectively at 500 mg/L concentrations. This was followed by the morphotypes PNM6RHgLIM with 77.1% at 400 mg/L, PN1RHgLIM with 72.8% at 350 mg/L and finally PNM3THgLIM with 68.7% at 300 mg/L. Sequencing analysis linked the PNM6RHgLIM isolate with sequence homology to Bacillus thuringiensis strain F14; PNM4RizHgLIM to Bacillus cereus strain ML259 and Bacillus mycoides O-1; PNM10RHgLIM with Bacillus cereus strain LB1016; PNM1HgLIM of stem with species belonging to the genus Bacillus sp and PNM3HgLIM of stem with bacteria of the Pseudomonas sp. group. There is presence of bacteria in rhizosphere and as endophytes present in soils contaminated with high concentration of mercury in the south of Bolivar(Colombia) that showed capacity to tolerate high concentrations of mercury in vitro and possibly accompanied by other studies could contribute to remediate environments contaminated with this metal.
Pages: 148-167
Keywords: Bacteria, rhizosphere, endophytes, pasture.