THE PRESENCE OF BACTERIA IN EXTREMELY ALKALINE (PH>12) GROUNDWATER

In the Lake Calumet region of southeast Chicago extremely alkaline conditions (pH>12) exist in shallow groundwater and in surface waters dominated by groundwater discharge. The high pH is caused by the consumption of protons during the weathering of silicates and metallic iron in the steel slags that were used as fill. During this process metals can be released that can then be coprecipitated with the weathering products or migrate out of the system as colloids. Very little is know about which bacteria might live in this type of environment or in what geochemical reactions they could play a major role. Simple culturing tests have shown that bacteria are living in the system. Genetic sequence of 16s rRNA from bacteria at six sites with pHs over 11 show a wide diversity of PCR products. Two species, Leptothrix mobilis and an uncultured bacterium, accounted for 45 and 48 of the 340 sequencing results, respectively, and were found at multiple sites. The next most common species occurred only 8 times. Based on 489 to 599 base pairs, the PCR products from each site were all 98% similar to the Leptothrix mobilis in the database. The percentage match would indicate the analyzed bacteria may be a new strain, possibly one that has adapted to the extremely alkaline, metal-rich conditions found throughout the Lake Calumet region. The PCR results also identified many species that are present but probably not growing, including many associated with mammalian guts or infections that could have been introduced to the shallow groundwater from the surface. Leptothrix has the potential to be very important in the groundwater system because it is associated with iron and manganese oxidation. These metals are deposited as oxides in sheaths that surround a chain of cells. After the cells die the more stable sheaths could settle out or potentially migrate in the ground water as colloids. Experiments are currently underway to isolate these sheaths for analysis.