Role of Geitlerinema sp. DE2011 and Scenedesmus sp. DE2009 as Bioindicators and Immobilizers of Chromium in a Contaminated Natural Environment

Abstract

The aim of this work was to study the potential of the two phototrophic microorganisms, both isolated from Ebro Delta microbial mats, to be used as bioindicators and immobilizers of chromium. The results obtained indicated that (i) the Minimum Metal Concentration (MMC) significantly affecting Chlorophyll a intensity in Geitlerinema sp. DE2011 and Scenedesmus sp. DE2009 was 0.25 µM and 0.75 µM, respectively, these values being lower than those established by current legislation, and (ii) Scenedesmus sp. DE2009 was able to immobilize chromium externally in extracellular polymeric substances (EPS) and intracellularly in polyphosphate (PP) inclusions. Additionally, this microorganism maintained high viability, including at 500 µM. Based on these results, we postulate that Geitlerinema sp. DE2011 and Scenedesmus sp. DE2009 are good chromium-indicators of cytotoxicity and, further, that Scenedesmus sp. DE2009 plays an important role in immobilizing this metal in a contaminated natural environment.

Figure 1

xyz CLSM optical sections (a) and (b) and their corresponding binary images of live (b) and dead (d) Scenedesmus sp. DE2009 cells analysed using the modified FLU-CLSM-IA method.

Figure 2

λscan plots of Geitlerinema sp. DE2011 (a) and Scenedesmus sp. DE2009 (b) contaminated with a wide range of chromium concentrations.

Figure 3

CLSM images of control (a) and chromium contaminated (b) cultures of Geitlerinema sp. DE2011 (scale bars represent 10 µm) and λscan plot (c). SEM images of control (d) and 200 µM chromium contaminated (e) cultures. Scale bars represent 2 µm. Contaminated EDX spectrum (f). TEM images of control (g) and 200 µM chromium contaminated (h) cultures. Scale bars represent 1 µm. Contaminated EDX spectrum (i).

Figure 4

CLSM images of control (a) and chromium contaminated (b) cultures of Scenedesmus sp. DE2009 (scale bars represent 10 µm) and λscan plot (c). SEM images of control (d) and 200 µM chromium contaminated (e) cultures. Scale bars represent 2 µm. Contaminated EDX spectrum (f). Arrow indicates the main Cr peak at 5.4 keV. TEM images of control (g) and 200 µM chromium contaminated (h) cultures. Scale bars represent 1 µm. Contaminated EDX spectrum (i). Cr peaks are indicated by arrows.

Figure 5

Percentages of live and dead Scenedesmus sp. DE2009 cells at different Cr(III) concentrations. The bars indicate the Standard Error of the Means (S.E.M.).