Abstract
We used metagenomic sequencing combined with morphological and chemical analyses to investigate microbial taxa and functions related to copper-resistance and microbiologically influenced corrosion in mature copper-associated biofilms in coastal seawater for 44 months. Facultative anaerobic microbes such as Woeseia sp. were found to be the dominant groups on the copper surface. Genes related to stress response and possible heavy metal transport systems, especially RNA polymerase sigma factors (rpoE) and putative ATP-binding cassette (ABC) transport system permease protein (ABC.CD.P) were observed to be highly enriched in copper-associated biofilms, while genes encoding DNA-methyltransferase and RNA polymerase subunit were highly enriched in aluminum-associated biofilms and seawater planktonic cells, respectively. Moreover, copper-associated biofilms harbored abundant copper-resistance genes including cus, cop and pco, as well as abundant genes related to extracellular polymeric substances, indicating the presence of diverse copper-resistance patterns. The proportion of dsr in copper-associated biofilms, key genes related to sulfide production, was as low as that in aluminum biofilm and seawater, which ruled out the possibility of microbial sulfide-induced copper-corrosion under field conditions. These results may fill knowledge gaps about the in situ microbial functions of marine biofilms and their effects on toxic-metal corrosion.
Highlights
As a prominent mode of microbial life under various natural environments, biofilm consists of cells surrounded by a self-produced matrix of hydrated extracellular polymeric substances (EPS); these components form the 3D architecture of biofilms and contribute to within-biofilm cohesion and surface adhesion (Flemming and Wingender, 2010)
Scanning electron microscopy and energy dispersive X-ray spectroscopy (EDS) analyses indicated that copper alloy was corroded and the morphology of the marine biofilm formed on copper alloy differed from that of the biofilm formed on aluminum alloy (Figure 1)
The current study provides the first evidence of the genetic potential of copper-resistance and microbiologically influenced corrosion (MIC) mechanisms in mature biofilms formed on copper surface in natural marine environments
Summary
As a prominent mode of microbial life under various natural environments, biofilm consists of cells surrounded by a self-produced matrix of hydrated extracellular polymeric substances (EPS); these components form the 3D architecture of biofilms and contribute to within-biofilm cohesion and surface adhesion (Flemming and Wingender, 2010). A previous study has shown that biofilm formation was slower in copper pipes than in plastic pipes, but no difference in microbial numbers was observed between these two materials after 200 days (Lehtola et al, 2004) This finding occurred possibly because the mature biofilms on copper alloys have successfully developed adaptation strategies to survive in toxic conditions after long-term exposure. Major gaps still exist in our knowledge on these adaptation mechanisms, especially regarding the microbial structural and functional features of mature copper-resistance biofilms after a long-term exposure in seawater
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