What happens when the heavy metal-resistant microorganism Fusarium tricinctum M6 encounters Cu(II)?

PAEZ, MD; CALLEGARI, EA; VILLEGAS LB; BONILLA, JO; GIL, RA

Congreso; SAIB | SAMIGE Reunión Conjunta; 2020

Fusarium tricinctum M6 was previously isolated from sediments of the abandoned gold mine located in San Luis, Argentina. This environment is affected by acid mine drainages, one of the most documented environmental issues associated with mining activities. The microorganism has shown the capability to resist and remove Cu(II) from liquid culture media, reaching a removal capacity of 30-35% after 36 h of incubation when faced with 40 µg mL-1 Cu(II) at 200 rpm and 30°C. In the present work, we aimed to study the copper effects on the morphology, the microelemental composition and the protein expression in F. tricinctum M6 cells exposed to the metal. For this purpose, Scanning Electron Microscopy coupled to X-Ray Dispersive Energy Spectrometry (SEM-EDS) was applied to analyze the microelemental composition and the surface mapping of the microbial biomass, in the presence and absence of Cu(II). Likewise, shotgun proteomic techniques were applied at the intra and extracellular levels to understand the removal and resistance mechanisms. SEM images showed the toxic effects of the Cu(II) presence on the microbial biomass morphology. In the biomass obtained in the absence of copper, the peaks of the metal were not detected. However, in the presence of the metal, SEM-EDS results showed a uniform distribution of copper in the biomass at 5.23% (w/w). The copper presence influenced on other biomass´ constituent elements. The proportion of P was higher, while the peaks of K and Ca appeared in lower intensity when compared to the control. The Na and Mg peaks disappeared, while N was detected at 6.02% w/w in the cells grown in the copper presence. On the other hand, when exposed to Cu(II), F. tricinctum M6 showed differential expression of intra and extracellular proteins involved in different metabolic processes. The proteins overexpressed at the intracellular level in the presence of Cu(II) are mainly involved in protein biosynthesis, oxidation-reduction processes, degradation metabolism, nucleic acid binding proteins, oxidative stress indicator proteins, Kinases/Phosphatases, energy metabolism, carbohydrate metabolism and proteins responsible for post-translational modifications. When analyzing the extracellular proteins of the cells exposed to the metal, proteins of carbohydrate metabolism and oxidation-reduction processes were identified. Remarkable, a large number of proteins with metal ion binding sites were detected both at the intra and extracellular levels, which can be involved in the sequestration and transport of the copper ions. The results obtained in the present work indicated bioadsorption of the metal on the cell surface, where electronegative elements such as P and N may be involved in the uptake of metal ions, while an ion exchange with other metals can also occur on the microbial surface. Likewise, an important readjustment of the protein expression helps the microorganism to counteract the stress produced by Cu(II).