Heavy metal tolerance and removal potential in mixed-species biofilm

Abstract

The aim of the study was to examine heavy metal tolerance (Cd, Zn, Ni and Cu) of single- and mixed-species biofilms (Rhodotorula mucilaginosa and Escherichia coli) and to determine metal removal efficiency (Cd, Zn, Ni, Cu, Pb and Hg). Metal tolerance was quantified by crystal violet assay and results were confirmed by fluorescence microscopy. Metal removal efficiency was determined by batch biosorption assay. The tolerance of the mixed-species biofilm was higher than the single-species biofilms. Single- and mixed-species biofilms showed the highest sensitivity in the presence of Cu (E. coli-MIC 4 mg/ml, R. mucilaginosa-MIC 8 mg/ml, R. mucilaginosa/E. coli-MIC 64 mg/ml), while the highest tolerance was observed in the presence of Zn (E. coli-MIC 80 mg/ml, R. mucilaginosa-MIC 161 mg/ml, R. mucilaginosa-E. coli-MIC 322 mg/ml). The mixed-species biofilm exhibited better efficiency in removal of all tested metals than single-species biofilms. The highest efficiency in Cd removal was shown by the E. coli biofilm (94.85%) and R. mucilaginosa biofilm (97.85%), individually. The highest efficiency in Cu (99.88%), Zn (99.26%) and Pb (99.52%) removal was shown by the mixed-species biofilm. Metal removal efficiency was in the range of 81.56%-97.85% for the single- and 94.99%-99.88% for the mixed-species biofilm.

Heavy metal tolerance and removal efficiency of the Rhodotorula mucilaginosa and Saccharomyces boulardii planktonic cells and biofilm

“…In our previous investigations, we concluded that R. mucilaginosa biofilm was few times more tolerant and had a higher potential for removing Hg 2+ , Cu 2+ and Pb 2+ ions than planktonic cells (GRUJIĆ et al 2017a). Furthermore, the R. mucilaginosa/Escherichia coli mixed biofilm was more efficient in removing heavy metals than their mono-species biofilms (BUZEJIĆ et al, 2016, GRUJIĆ et al, 2017b. These findings led to the further development of studies on the Cd 2+ , Zn 2+ and Ni 2+ ion tolerance and removal efficiency of planktonic cells and biofilm of R. mucilaginosa and Saccharomyces boulardii, including comparative analysis with the previously obtained results.…”

Finding the best combination of autochthonous microorganisms with the most effective biosorption ability for heavy metals removal from wastewater

“… Golby et al (2014) found that Rhodococcus erythropolis isolated from the community was less tolerant in the presence of metals compared to mixed biofilm, so it was unable to perform biomineralization of metals. By comparing the individual and mixed biofilms of Rhodotorula mucilaginosa and Escherichia coli, Grujić et al (2017b) found a higher resistance of mixed biofilms to the presence of HMs. Scientists confirmed that different regulatory processes (biochemical and genetic) take place within the biofilm that allow microorganisms to develop a better mechanism of tolerance and improve their resistance in the presence of HMs ( Harrison et al, 2007 ).…”

“…The direct colony approach was used to create a microorganism suspension. The turbidity of the suspension was adjusted using a densitometer (DEN-1, Biosan, Latvia), McFarland 1.0, to equate to 10 8 CFU/ml for bacteria and 10 6 CFU/ml for yeasts ( Grujić et al, 2017b ).…”

“…Individual biofilms have been widely studied in the process of HMs removal in recent years ( Harrison et al, 2006 ; Singh et al, 2006 ; Grujić et al, 2017a , 2018 ). However, research on HMs removal by mixed biofilms is limited ( Buzejić et al, 2016 ; Grujić et al, 2017b ).…”

The Role of the Cyanobacterial Type IV Pilus Machinery in Finding and Maintaining a Favourable Environment

“…Heterotrophic bacteria such as P. aeruginosa [ 74 ] and Klebsiella pneumoniae [ 75 ] show significantly increased resilience to many antibiotics in intact biofilms compared to planktonic cultures. Although the non-infectious cyanobacteria are less likely to encounter antibiotic treatment, the same principle of EPS shielding cells from harmful extraneous effects has been extended to salt and metal ion toxicity [ 76 , 77 , 78 ], phage infection [ 79 ], and predation by some (though not all) grazers [ 80 ]. Work on the Pseudomonas genus has shown that functional, retractile T4P are also required for infection by a number of bacteriophages [ 81 , 82 , 83 ].…”