| Abstrakt: |
Serpentine soils exhibit unique chemical properties, characterized by high concentrations of heavy metals (usually Ni, Fe, Cr, and Co) and limited availability of micronutrients, rendering them unfavorable for numerous microbial species. In response, serpentine bacteria have evolved various adaptive strategies that enable their undisturbed proliferation. Furthermore, serpentine habitats have diverse bacterial communities with potential use in industrial biotechnology and agriculture. Thus, the primary objective of this study was to examine the heavy metal tolerance and quantify biofilm production of bacterial serpentine isolates. In total, 24 sequenced rhizospheric and endophytic serpentine isolates associated with Robinia pseudoacacia L. were retrieved from the bacterial repository of the University of Sarajevo - Institute for Genetic Engineering and Biotechnology. Heavymetal tolerance was evaluated on tryptone yeast agar plates supplemented with Ni, Cu and Co salts with final metal concentrations 100 mg/L and 200 mg/L. After 15 day incubation period at room temperature, positive results were confirmed by observable growth. Biofilm production was assessed utilizing the Microtiter plate assay (MPA) with modifications to accommodate rhizospheric and endophytic bacteria. Absorbance was measured at 570 nm using a Thermo Scientific MultiskanTM reader. The biofilm production was graded based on OD according to the standard scale: nonproducers, weak, moderate and strong producers. All the rhizospheric isolates tolerated 100 mg/L concentration of the tested metals while only one isolate failed to grow in the presence of 200 mg/L Ni. No isolates were able to tolerate 200 mg/L Cu. In contrast, tolerance to the tested heavy metals was not a common trait in endophytic isolates. Similar trend was observed regarding biofilm production. While rhizospheric bacteria consistently produced biofilms (2 moderate and 12 low-producers), only three endophytic isolates yielded low biofilm production. Rhizospheric Pseudomonas isolates exhibited strong heavy metal tolerance and prominent biofilm producing abilities as opposed to limited tolerance and weak biofilm production by endophytic Bacillus, Brevibacillus and Lysinibacillus. Bacteria produce biofilms as a survival strategy in a response to environmental stressors. Biofilm production requires energy expenditure and endophytes, having procured nutrients and protection by plants, forego this ability. It is an important input when selecting isolates for biotechnological applications. [ABSTRACT FROM AUTHOR] |
