Spatial and Temporal Variation of Enterobacter Genotypes in Sediments and the Underlying Hyporheic Zone of an Agricultural Stream

Heavy metals contaminate numerous freshwater streams and rivers worldwide. Previous work by this group demonstrated a relationship between the structure of hyporheic microbial communities and the fluvial deposition of heavy metals along a contamination gradient during the fall season. Seasonal variation has been documented in microbial communities in numerous terrestrial and aquatic environments, including the hyporheic zone. The current study was designed to assess whether relationships between hyporheic microbial community structure and heavy-metal contamination vary seasonally by monitoring community structure along a heavy-metal contamination gradient for more than a year. No relationship between total bacterial abundance and heavy metals was observed (R 2 ‫؍‬ 0.02, P ‫؍‬ 0.83). However, denaturing gradient gel electrophoresis pattern analysis indicated a strong and consistent linear relationship between the difference in microbial community composition (populations present) and the difference in the heavy metal content of hyporheic sediments throughout the year (R 2 ‫؍‬ 0.58, P < 0.001). Correlations between heavy-metal contamination and the abundance of four specific phylogenetic groups (most closely related to the ␣, ␤, and ␥-proteobacteria and cyanobacteria) were apparent only during the fall and early winter, when the majority of organic matter is deposited into regional streams. These seasonal data suggest that the abundance of susceptible populations responds to heavy metals primarily during seasons when the potential for growth is highest.Large-scale mining and other activities have resulted in contamination of many aquatic environments around the world (50). Changes in the geochemical characteristics of heavy-metal-contaminated environments are well documented (for a review, see Moore and Luoma [50]). Heavy-metal contamination can reduce water quality and has been shown to harm numerous organisms (12,45,50,69). Several studies have examined the effects of this type of anthropogenic contamination on aquatic macrobiota (1, 12-15, 33, 47). While heavy-metal effects on the activity and composition of microbial communities in terrestrial ecosystems have been well documented (2,6,7,20,21,34,43,49,54,64,72), relatively little is known about the effects on aquatic microbial communities. In a prior study by our group, heavy-metal contamination was implicated as a structuring factor for hyporheic microbial communities in streambeds (23).The hyporheic zone is the region of heterogeneous sediments beneath and adjacent to the stream channel that is saturated with a mixture of surface and ground water (46), providing connectivity between terrestrial, groundwater, and lotic habitats. As such, this zone is an important component of lotic ecosystems (11,26,35,58,60,68,70,71). The microbial communities in the hyporheic zone play important functional roles in lotic environments (18,31,32,51,52,57,59). For example, transformation of dissolved and particulate nutrients by hyporheic microorganisms can influence the distr...

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confidence: 71%

Seasonal Dynamics of Shallow-Hyporheic-Zone Microbial Community Structure along a Heavy-Metal Contamination Gradient

Feris

Ramsey

Frazar

et al. 2004

“…However, environmental gradients can include factors that covary with the contaminant, thereby complicating analysis of results (52). Factors that influence aquatic microbial community structure include dissolved nutrient levels (8,23,35,49), carbon quality and quantity (53), flow rates and sediment porosity (33,77), pH (23), viral lysis (65,71), and grazing (36,40,65,70). These and other potential covariates were controlled for in the present experiment through the experimental design, in which microbial community inoculum, water chemistry, total carbon, temperature, and other environmental parameters were held constant while the degree of contamination with the metal mixture was adjusted.…”

Section: Discussionmentioning

confidence: 99%

Determining Rates of Change and Evaluating Group-Level Resiliency Differences in Hyporheic Microbial Communities in Response to Fluvial Heavy-Metal Deposition

Feris

Ramsey

Rillig

et al. 2004

Prior field studies by our group have demonstrated a relationship between fluvial deposition of heavy metals and hyporheic-zone microbial community structure. Here, we determined the rates of change in hyporheic microbial communities in response to heavy-metal contamination and assessed group-level differences in resiliency in response to heavy metals. A controlled laboratory study was performed using 20 flowthrough river mesocosms and a repeated-measurement factorial design. A single hyporheic microbial community was exposed to five different levels of an environmentally relevant metal treatment (0, 4, 8, 16, and 30% sterilized contaminated sediments). Community-level responses were monitored at 1, 2, 4, 8, and 12 weeks via denaturing gradient gel electrophoresis and quantitative PCR using group-specific primer sets for indigenous populations most closely related to the ␣-, ␤-, and ␥-proteobacteria. There was a consistent, strong curvilinear relationship between community composition and heavy-metal contamination (R 2 ‫؍‬ 0.83; P < 0.001), which was evident after only 7 days of metal exposure (i.e., short-term response). The abundance of each phylogenetic group was negatively affected by the heavy-metal treatments; however, each group recovered from the metal treatments to a different extent and at a unique rate during the course of the experiment. The structure of hyporheic microbial communities responded rapidly and at contamination levels an order of magnitude lower than those shown to elicit a response in aquatic macroinvertebrate assemblages. These studies indicate that hyporheic microbial communities are a sensitive and useful indicator of heavy-metal contamination in streams.The hyporheic zone, the region of saturated sediments beneath a river, which is inundated with a mixture of surface and ground water, is an important component of lotic ecosystems (27,57,59). This zone supports a microbial community that performs essential functional roles for the lotic ecosystem (21,29,48,50,58). For example, hyporheic microbial communities are involved in the cycling of nutrients (58) and nutrient retention (48), constitute the majority of the biomass and activity in lotic ecosystems (21,29,56), and can account for 76 to 96% of ecosystem respiration (50). Thus, changes in microbial community structure within the hyporheic zone may alter the functioning of lotic ecosystems.Contamination of aquatic environments as a result of largescale mining activities is widespread (47). Acid mine drainage and the introduction of mining wastes into streams have been shown to alter the geochemistry of streambeds (47) and the hyporheic zone (6, 10, 74). Metals released from mining wastes reduce water quality and harm many eukaryotic organisms (7,11,12,43,47,69). In similarity to prior work in terrestrial ecosystems demonstrating that heavy-metal contamination alters the activity and composition of microbial communities (3,23,63,73), previous observational studies performed by our laboratory provided evidence that the structure of hy...

“…Besides its clinical significance, E. cloacae plays an important role as a pathogen in plants (2,34) and insects (15) and is ubiquitous in the terrestrial and aquatic environments (22). This diversity of habitats is mirrored by the genetic variety of the nomenspecies E. cloacae, which has been demonstrated in several studies by biotyping and serotyping (16,47), ribotyping and phage typing (46), pulsed-field gel electrophoresis and enterobacterial repetitive intergenic consensus PCR (ERIC-PCR) (18), and internal transcribed spacer-PCR and random amplification of polymorphic DNA (RAPD)-PCR (6).…”

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confidence: 99%

Population Genetics of the Nomenspecies Enterobacter cloacae

Hoffmann

Roggenkamp

2003

245

270

The genetic heterogeneity of the nomenspecies Enterobacter cloacae is well known. Enterobacter asburiae, Enterobacter cancerogenus, Enterobacter dissolvens, Enterobacter hormaechei, Enterobacter kobei, and Enterobacter nimipressuralis are closely related to it and are subsumed in the so-called E. cloacae complex. DNA-DNA hybridization studies performed previously identified at least five DNA-relatedness groups of this complex. In order to analyze the genetic structure and the phylogenetic relationships between the clusters of the nomenspecies E. cloacae, 206 strains collected from 22 hospitals, a veterinarian, and an agricultural center in 11 countries plus all 13 type strains of the genus and reference strain CDC 1347-71 R were examined with a combination of sequence and PCR-restriction fragment length polymorphism (PCR-RFLP) analyses of the three housekeeping genes hsp60, rpoB, and hemB as well as ampC, the gene of a class C ␤-lactamase. Based on the neighbor-joining tree of the hsp60 sequences, 12 genetic clusters (I to XII) and an unstable sequence crowd (xiii) were identified. The robustness of the genetic clusters was confirmed by analyses of rpoB and hemB sequences and ampC PCR-RFLPs. Sequence crowd xiii split into two groups after rpoB analysis. Only three strains formed a cluster with the type strain of E. cloacae, indicating that the minority of isolates identified as E. cloacae truly belong to the species; 13% of strains grouped with other type strains of the genus, suggesting that the phenotypes of these species seem to be more heterogeneous than so far believed. Three clusters represented 70% of strains, but none of them included a type or reference strain. The genetic clustering presented in this study might serve as a framework for future studies dealing with taxonomic, evolutionary, epidemiological, or pathogenetic characteristics of bacteria belonging to the E. cloacae complex.Enterobacter cloacae has become increasingly important as a nosocomial pathogen, accounting for up to 5% of hospitalacquired septicemias, 5% of nosocomial pneumonias, 4% of nosocomial urinary tract infections, and 10% of postsurgical peritonitis cases (18,35,39). Besides its clinical significance, E. cloacae plays an important role as a pathogen in plants (2, 34) and insects (15) and is ubiquitous in the terrestrial and aquatic environments (22). This diversity of habitats is mirrored by the genetic variety of the nomenspecies E. cloacae, which has been demonstrated in several studies by biotyping and serotyping (16, 47), ribotyping and phage typing (46), pulsed-field gel electrophoresis and enterobacterial repetitive intergenic consensus PCR (ERIC-PCR) (18), and internal transcribed spacer-PCR and random amplification of polymorphic DNA (RAPD)-PCR (6). The 16S ribosomal DNA (rDNA) sequences of E. cloacae did not form a coherent cluster but built a patchy tree, in which the clusters of E. cloacae strains interfused with those of Enterobacter aerogenes, Escherichia coli, Citrobacter species, and Leclercia species. This refl...