Distribution and biogeochemical importance of bacterial populations in a thick clay-rich aquitard system

• Published in: Microbial ecology Vol. 40; no. 4; pp. 273 - 291
• Main Authors: Lawrence, J. R, Hendry, M. J, Wassenaar, L. I, Germida, J. J, Wolfaardt, G. M, Fortin, N, Greer, C. W
• Format: Journal Article
• Language: English
• Published: New York, NY Springer-Verlag 01-11-2000; Springer-Verlag New York Inc; Springer; Springer Nature B.V
• Subjects: Animal, plant and microbial ecology; Bacteria; Biological and medical sciences; carbon; Clay; Clays; Community composition; community structure; confocal microscopy; Cretaceous; Culture techniques; denaturing gradient gel electrophoresis; DNA; Fatty acids; Fundamental and applied biological sciences. Psychology; genes; Geologic units; Geology; glucose; Groundwater; hydraulic conductivity; microbial biomass; Microbial ecology; Microbiology; Microorganisms; Mineralization; nitrate reductase; permeability; Polymerase chain reaction; Pore water; ribosomal DNA; ribulose-bisphosphate carboxylase; Sediment yield; Sediments; Stable isotopes; Sulfate reduction; sulfate-reducing bacteria; Sulfates; Various environments (extraatmospheric space, air, water); Canada; Saskatchewan; North America; America; Freshwater environment; Microbial activity; Sulfatoreduction; Bacteria; Population structure; Sediments; Microbial biomass; Microbial community; Population density; Ground water; Aquifers
• ISSN: 0095-3628; 1432-184X
• DOI: 10.1007/s002480000073

To investigate the distribution of microbial biomass, populations and activities within a clay-rich, low hydraulic conductivity (10⁻¹¹ to 10⁻¹² m s⁻¹) aquitard complex, cores were aseptically obtained from a series of overlying clayey deposits; a fractured till, unfractured till (20–30 ka BP), a disturbed interfacial zone (20–30 ka BP), and a Cretaceous clay aquitard (71–72 Ma BP). The results of confocal microscopy studies, culture methods, molecular approaches, and extractive fatty acid analyses all indicated low bacterial numbers that were non-homogeneously distributed within the sediments. Various primers for catabolic genes were used to amplify extracted DNA. Results indicated the presence of eubacterial 23S rDNA, and thenarH gene for nitrate reductase and ribulose-1,5-biphosphate carboxylase (RuBP carboxylase). Although there was no evidence of limitation by electron acceptors or donors, sulfate-reducing bacteria were not detected below the fractured till zone, using PCR, enrichment, or culture techniques. Denaturing gradient gel electrophoresis (DGGE) analyses indicated differences in community composition and abundance between the various geologic units. Results of FAME analyses of sediments yielded detectable extractable fatty acids throughout the aquitard complex. Bacterial activities were demonstrated by measuring mineralization of (¹⁴C) glucose. Porewater chemistry and stable isotope data were in keeping with an environment in which extremely slow growing, low populations of bacteria exert little impact. The observations also support the contention that in low permeability sediments bacteria may survive for geologic time periods.