ORIGINAL PAPER Herbicides induce change in metabolic and genetic diversity of bacterial community from a cold oligotrophic lake P. Aguayo • C. Gonza ´lez • R. Barra • J. Becerra • M. Martı ´nez Received: 12 July 2013 / Accepted: 16 October 2013 Ó Springer Science+Business Media Dordrecht 2013 Abstract Pristine cold oligotrophic lakes show unique physical and chemical characteristics with permanent fluc- tuation in temperature and carbon source availability. Incorporation of organic toxic matters to these ecosystems could alter the bacterial community composition. Our goal was to assess the effects of simazine (Sz) and 2,4 dichlo- rophenoxyacetic acid (2,4-D) upon the metabolic and genetic diversity of the bacterial community in sediment samples from a pristine cold oligotrophic lake. Sediment samples were collected in winter and summer season, and microcosms were prepared using a ration 1:10 (sedi- ments:water). The microcosms were supplemented with 0.1 mM 2,4-D or 0.5 mM Sz and incubated for 20 days at 10 °C. Metabolic diversity was evaluated by using the Biolog Ecoplate TM system and genetic diversity by 16S rDNA amplification followed by denaturing gradient gel electrophoresis analysis. Total bacterial counts and live/ dead ratio were determined by epifluorescence microscopy. The control microcosms showed no significant differences (P [ 0.05) in both metabolic and genetic diversity between summer and winter samples. On the other hand, the addition of 2,4-D or Sz to microcosms induces statistical significant differences (P \ 0.05) in metabolic and genetic diversity showing the prevalence of Actinobacteria group which are usually not detected in the sediments of these non-con- taminated lacustrine systems. The obtained results suggest that contaminations of cold pristine lakes with organic toxic compounds of anthropic origin alter their homeostasis by inhibiting specific susceptible bacterial groups. The con- comitant increase of usually low representative bacterial groups modifies the bacterial composition commonly found in this pristine lake. Keywords Bacterial diversity Á Cold oligotrophic pristine lake Á Herbicides Introduction In aquatic environments physical and chemical fluctuations modulate bacterial diversity and metabolic activity of res- ident microorganisms living in these ecosystems (Cavi- cchioli et al. 2003; Venkatesharaju et al. 2010). In addition, human activity like agriculture or forestry close to aquatic environment may also impact the homeostasis of these water systems (Gunderson 2000; Johnsen et al. 2001; Kritzberg et al. 2005; Venkatesharaju et al. 2010). Sima- zine (Sz) and 2,4-dichlorophenoxyacetic acid herbicides (2,4-D) are examples of toxic organic compounds of anthropic origin that are incorporated as contaminant to pristine lakes, which modify bacterial diversity by inhib- iting some resident bacterial groups allowing the prolifer- ations of others (Johnsen et al. 2001). Sz may alter the nitrogen cycle in lake systems (McCarty 1999) while 2,4-D may interfere the turnover of organic matters (Prado and Airoldi 2000). The impact of herbicides upon bacterial P. Aguayo Á C. Gonza ´lez Á M. Martı ´nez (&) Laboratorio de Microbiologı ´a Ba ´sica y Bioremediacio ´n, Departamento de Microbiologı ´a, Facultad de Ciencias Biolo ´gicas, Universidad de Concepcio ´n, Casilla 160-C, Concepcio ´n, Chile e-mail: mimartin@udec.cl R. Barra Centro EULA-Chile, Unidad de Sistemas de Acua ´ticos, Casilla 160-C, Concepcio ´n, Chile J. Becerra Laboratorio de Quı ´mica de Productos Naturales, Facultad de Ciencias Naturales y Oceanogra ´ficas, Universidad de Concepcio ´n, Casilla 160-C, Concepcio ´n, Chile 123 World J Microbiol Biotechnol DOI 10.1007/s11274-013-1530-y