Distribution and stability of sulfate-reducing prokaryotic and hydrogenotrophic methanogenic assemblages in nutrient-impacted regions of the Florida Everglades

Abstract

Although the influence of phosphorus loading on the Everglades ecosystem has received a great deal of attention, most research has targeted macro indicators, such as those based on vegetation or fauna, or chemical and physical parameters involved in biogeochemical cycles. Fewer studies have addressed the role of microorganisms, and these have mainly targeted gross informative parameters such as microbial biomass, enzymatic activities, and microbial enumerations. The objectives of this study were to characterize the dynamics of sulfate-reducing and methanogenic assemblages using terminal restriction fragment length polymorphism (T-RFLP) targeting the dissimilatory sulfite reductase (dsrA) and methyl coenzyme M reductase (mcrA) genes, respectively, and assess the impact of nutrient enrichment on microbial assemblages in the northern Everglades. T-RFLP combined with principal component analysis was a powerful technique to discriminate between soils from sites with eutrophic, transitional, and oligotrophic nutrient concentrations. dsrA T-RFLP provided a higher level of discrimination between the three sites. mcrA was a relatively weaker system to distinguish between sites, since it could not categorically discriminate between eutrophic and transition soil samples, but may be useful as an early indicator of phosphorus loading which is altering hydrogenotrophic methanogenic community in the transition zones, making them more similar to eutrophic zones. Clearly, targeting a combination of different microbial communities provides greater insight into the functioning of this ecosystem and provides useful information for understanding the relationship between eutrophication effects and microbial assemblages.

FIG. 1.

Water levels of eutrophic (F1) and oligotrophic (U3) sites of the Everglades WCA-2A.

FIG. 2.

Total phosphorus (TP), total inorganic phosphorus (Tpi), and microbial biomass phosphorus (MBP) levels (in mg/kg) in (A) eutrophic (F1), (B) transition (F4), and (C) oligotrophic (U3) sites of the Everglades WCA-2A.

FIG. 3.

Community dynamics for dsrA in (A) eutrophic, (B) transition, and (C) oligotrophic soils determined by T-RFLP analysis. Samples are labeled according to the season, month, year that were taken. SP, spring; SU, summer; FA, fall; WI, winter.

FIG. 4.

PCA ordering generated from T-RFLP profiles for dsrA of eutrophic (F1), transition (F4), and oligotrophic (U3) soils.

FIG. 5.

Community dynamics for the mcrA in (A) eutrophic (F1), (B) transition (F4), and (C) oligotrophic (U3) soils determined by T-RFLP analysis. Samples are labeled according to the season, month, and year that they were taken. SP, spring; SU, summer; FA, fall; WI, winter.

FIG. 6.

PCA ordering generated from T-RFLP profiles for mcrA of eutrophic (F1), transition (F4), and oligotrophic (U3) soils.