A local or a stranger? Comparison of autochthonous vs. allochthonous microalgae potential for bioremediation of coal mine drainage water.

Coal mining endangers the environment by contaminating of soil, surface, and ground water with coal mine drainage water (CMW) polluted by heavy metals. Microalgal cultures, hyper-accumulators of heavy metals, represent a promising solution for CMW biotreatment. A bottleneck of this approach is the availability of microalgal strains that combine a large capacity for heavy metal biocapture with a high resilience to their toxic effects. Biotopes contaminated with heavy metals are frequently inhabited by microalgae evolved to be resilient to heavy metal toxicity. Therefore, the autochthonous (locally isolated) microalgal strains are a priori considered to be superior for biotreatment of heavy metal-polluted waste streams. Still, strains from biocollections combine a high pollutant resilience with other biotechnologically important traits such as high productivity, high CO sequestration rate etc. Moreover, the strains available "off-the-shelf" would enable rapid development of bioprocesses. Here, we compared the efficiency of CMW biotreatment with autochthonous (isolated from the coal mine drainage sump) and allochthonous microalgae (from a geographically distant phosphate-polluted site). Both autochthonous strains and allochthonous strains turned to be interchangeable under our experimental conditions. Still, the autochthonous strains showed a higher capacity for sequestration of iron, zinc, and manganese, the specific pollutants of the studied CMW. It can be important when the duration of unattended exploitation of the CMW treatment facility is a priority or spikes of the heavy metal concentration in CMW are expected. Therefore, the "off-the-shelf" strains can be a plausible solution for rapid development of CMW treatment technologies from scratch (although screening for acute toxicity of CMW is imperative). On the other hand, locally isolated strains can offer distinct advantages and should be always considered if sufficient time and other resources are available for the development of microalgae-based process for CMW treatment.