Implications of Genome Alterations in Chironomus bernensis Klȍtzli (Diptera) for Assessment of Trace Metal Pollution in Two Bulgarian Rivers

Abstract

This study assesses the effect of sediment contaminants as indicated by the measurement of trace metal levels in two large Bulgarian rivers (river Maritsa and a tributary and the river Chaya) on the genome of the abundant chironomid species Chironomus bernensis Klȍtzli. Six trace metals: Cd, Cr, Cu, Mn, Pb and Zn were analysed in the sediments plus the overlying water. The polytene chromosomes of C. bernensis were very sensitive to the pollutants on the basis of numerous somatic chromosome alterations. Two biomarkers based on the degree of somatic structural chromosome alterations—the somatic and cytogenetic indices were applied. Both indices are a sensitive and reproducible approach for assessing the genotoxic effect of contaminants in the sediments. The somatic index from the differentially contaminated sites varied from 1.93 to 2.61, indicating the sensitivity of the C. bernensis genome to anthropogenic stress. The cytogenetic index revealed a high level of pollution in the rivers with a score between 0.27 and 0.37 (<0.5 indicates ‘highly polluted’). The genome of C. bernensis responded to the trace metal pollution by the appearance of a ‘B’ chromosome in between 4.4% and 7.1% of the individuals and detected for the first time in this species. Pollution also induced a heterozygous state in one of the Nucleolar Organizers in up to 3% of the sampled populations. The sensitivity of the C. bernensis genome shows that this species is a good candidate for detecting the presence of genotoxic compounds in freshwater and assessing their genotoxic effects. Copyright © 2015 John Wiley & Sons, Ltd.

Genome instability in Chironomus annularius sensu Strenzke (Diptera, Chironomidae): A biomarker for assessment of the heavy metal contaminants in Poland

“…Similar results were recorded in the model chironomid species C. riparius: the highest H index values were observed in populations with a relatively lower level of pollution (Sella et al, 2004). Studies on the genome instability of various populations of C. piger , C. riparius (Ilkova et al, 2014) and C. bernensis (Michailova et al, 2016) were successfully performed using cytogenetic indices. The present study extends these observations and demonstrates that these indices can be used as a model approach for examining the genotoxic potential of contaminants and measuring of the level of genome instability in a number of members of the genus Chironomus, including C. annularius.…”

“…Chironomid larvae are widely distributed in freshwater basins and have short life cycle. Their excellent salivary gland chromosomes make them suitable indicators of heavy metal genotoxicity at the individual level (Michailova et al, 2012) as contaminants can have a genotoxic effect, acting either on the DNA or altering chromosome structure (Al-Shami et al, 2013;Ilkova et al, 2014;Michailova et al, 2012Michailova et al, , 2016. Our previous studies (Ilkova et al, 2014;Michailova et al, , 2016 showed that genome instability can be assessed by two cytogenetic indices: Somatic (S) and Cytogenetic (C).…”

“…Their excellent salivary gland chromosomes make them suitable indicators of heavy metal genotoxicity at the individual level (Michailova et al, 2012) as contaminants can have a genotoxic effect, acting either on the DNA or altering chromosome structure (Al-Shami et al, 2013;Ilkova et al, 2014;Michailova et al, 2012Michailova et al, , 2016. Our previous studies (Ilkova et al, 2014;Michailova et al, , 2016 showed that genome instability can be assessed by two cytogenetic indices: Somatic (S) and Cytogenetic (C). The Cytogenetic index indicates the degree of pollution with three levels of pollution can be recognized: slightly polluted (0.9-0.8), moderate polluted (0.7-0.5) and highly polluted (<0.5) (Ilkova et al, 2014).…”

The use of salivary gland chromosomes of Chironomids (Diptera, Chironomidae) for assessing the pollution of aquatic ecosystems

“…piger и Ch. plumosus из водоёмов с концентрациями тяжёлых металлов Zn, Pb, Cu, Co, Fe, Ni и др., превышающими норму, был проведён в Болгарии [Todorova et al, 2000], Италии [Michilova et al, 2000], России [Vinogradova, Petrova, 2004], Польше [Szarek-Gwiazda et al, 2013], Англии [Michailova et al, 2015[Michailova et al, , 2016 и Турции [Duran et al, 2012]. В результате этих исследований установлено, что под влиянием тяжёлых металлов у этих видов появляется значительная хромосомная изменчивость.…”

“…balatonicus, Ch. bernensis) [Michailova et al, 2015[Michailova et al, , 2016, а также виды Glyptotendipes (G. glaucus, G. barbipes, G. salinus) [Michailova et al, 2002], широко распространённые в разных водоёмах, характе-Ðèñ. 2.…”