Evidence of structural and functional adaptation in epilithon exposed to zinc

Abstract

Artificial streams were used to study the effect of chronic zinc dosing (0.00,0.05 or 1.00 mg Zn 1-') on epilithic communities during summer and early fall, 1984 and 1985. Following zinc addition, epilithon was periodically measured for '4C-glucose and 14C-glutamate respiration, ash-free dry weight (AFDW), protein, carbohydrate, chlorophyll a (Chl a), pheophytin a (pheo a), and colony forming units (CFU) on zinc amended and unamended media. Transient peaks in glucose respiration rates mg-' protein and AFDW occurred within 5 to 10 days in streams dosed with 1.0 mg Zn 1-' and coincided with decreases in AFDW, protein, carbohydrate, Chl a, and pheo a. Respiration of glutamate did not show a significant response to dosing (a = 0.05). Epilithic plate counts demonstrated more total and zinc-tolerant CFU in dosed than in control epilithon after 20 days. After 30 days, greater biomass and lower protein: carbohydrate ratios were evident in epilithon dosed with 1.0 mg Zn 1-' compared to unamended treatments. Peaks in glucose respiration suggested the presence of zinc-tolerant heterotrophs transiently capable of increased respiration of glucose but not glutamate. Concurrently, minimal but measurable biomass inferred the persistence of zinc-tolerant microorganisms in zinc-dosed epilithon. By the end of the studies, results indicated that metal-tolerant populations replaced metal-sensitive organisms under conditions of elevated zinc concentration. These zinc adapted communities had lower potential value as a food source to grazers (low protein: carbohydrate ratio) and were no longer distinctive with respect to glucose respiration.

Different responses to high light stress of toxic and non-toxicMicrocystis aeruginosaacclimated under two light intensities and zinc concentrations

“…Moreover, under HL condition, the specific growth rate of this strain was decreased by high zinc concentration. Our results are in accordance with previous studies indicating that long-term high zinc concentration exposure can decrease the growth rate of diatoms and cyanobacteria (Colwell, Hornor, and Cherry 1989;Loez, Topalian, and Salibian 1995).…”

Effects of iron and copper treatments on the bacterioplankton assemblages from surface waters along the north branch of the Kalamazoo River, Michigan, USA

“…The similarity in bacterial abundance to the different metal concentrations, but with significant changes over the study period, is further indicative of tolerance by the exposed bacterial populations within the assemblages to the metal treatments. These observation corroborates earlier similar studies that have also reported high metal tolerance over time by indigenous bacterial assemblages in aquatic environments . For instance, Kim et al reported that the addition of copper slightly stimulated bacterial growth in the microlayers as compared to subsurface water in their study.…”

“…Moreover, the lack of concentration-dependent toxicity of both metal treatments on the indigenous bacterial populations as observed in this study is not uncommon and the reasons could be attributed to and/or explained by various factors including, the bacterial transformation of metals such as mercuric chloride and methyl mercury to elemental mercury [32], complexation of the metals with organic matter [33], and through bacterial incorporation and accumulation [28,34]. In particular, Colwell et al [28] suggested that the tolerance of and adaptation to Zn exposure observed was as a direct results of the incorporation of Zn within the structural milieu of the epilithic biofilm assemblages in their study. Freshwater environments are known to comprise of relatively high concentrations of various inorganic nutrients, such as chlorides and nitrates primarily due to several anthropogenic disturbances [15,16].…”

Microscale and Molecular Assessment of Impacts of Nickel, Nutrients, and Oxygen Level on Structure and Function of River Biofilm Communities

“…This has been reported in pure culture biofilm studies in which Pseudomonas aeruginosa adopted a metal-resistant phenotype when exposed to metal contamination (69). Colwell et al (12) found that the numbers of Zn-tolerant bacteria increased with time in periphyton exposed to 1 mg of Zn liter Ϫ1 . Similarly, Vaccaro et al (72) found an increase in Cu tolerance of heterotrophs during a marine mesocosm experiment.…”

“…This is in agreement with both a potential loss of redundancy and recruitment of resistant taxa. It is also important to note here that the interaction between different biological components of the community (bacteria, microalgae, and protozoa) and sorption of contaminants by the biofilm will complicate the community responses and their interpretation (12,24,55).…”