Journal
AQUATIC MICROBIAL ECOLOGY
Volume 28, Issue 2, Pages 117-129Publisher
INTER-RESEARCH
DOI: 10.3354/ame028117
Keywords
bacteria; subsurface; biofilms; colonization; microcosm; groundwater; method
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We used specially designed microcosms filled with natural substrate to study microbial colonization in a shallow aquifer. Sterilized sediments were exposed to 3 types of groundwater varying in physical, chemical and biological characteristics: (1) pristine groundwater (site PI 92); (2) groundwater in an observation well at a pristine site (OMV 11); and (3) contaminated groundwater at a landfill site (OMV 5). The number of suspended bacteria was always highest at the landfill site (4.0 +/- 4,2 [standard deviation, SD] x 10(6) cells cm(-3)), i.e. on average 16 times higher than in the well water (2.5 +/- 3.0 x 10(5) cells cm(-3)) and 96 times higher than in the pristine groundwater (4.1 +/- 1.3 x 10(4) cells cm(-3)). Sediments in the microcosms were rapidly colonized and the total number of attached bacteria after 10 mo of exposure was highest at the landfill site (1.8 +/- 0.4 x 10(8) cells cm(-3)) followed by the sediment incubated in well water (1.5 +/- 0.5 x 10(8) cells cm(-3)) and in pristine groundwater (5.0 +/- 1.5 x 10(7) cells cm(-3)). As estimated from image analysis, attached cells from the landfill site were on average characterized by higher cell carbon contents (28 +/- 36 fgC cell(-1)) than at the well water (24 +/- 23 fgC cell(-1)) and the pristine groundwater site (21 +/- 23 fgC cell(-1)). The ratio of attached to suspended bacteria after 10 mo of exposure was highest in the microcosm incubated in pristine groundwater (1657:1) and lowest at the contaminated site (59:1). On the basis of our results we emphasize the importance of attached microbial communities in porous subsurface systems and underline the need for groundwater as well as sediment samples for a serious microbiological characterization of the subsurface. Furthermore, the ratio of attached to suspended bacteria in shallow aquifer systems is suggested to be an indicator of prevailing nutrient concentrations.
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