Fig. 4: Increased acidification strains of G. oxydans B58 are able to increase rare earth extraction from retorted phosphor powder (RPP).
A, B A subset of 22 disruption strains was tested for acidification with direct pH measurement. Gray circles represent the mean pH for each strain and comparisons were made with wild type by two-tailed t-test with Bonferonni correction (N = 22). pH measurements significantly different from pWT are labeled with asterisks: *p < 0.05/22; **p < 0.01/22; ***p < 0.001/22 (n = 5 biological replicates, df = 18). Error bars represent standard deviation. Individual data points are shown as black dots. C, D Ten disruption strains with the lowest final biolixiviant pH and four with the highest were tested for RPP bioleaching capabilities. Outer gray bars represent the mean total REE extracted for each biolixiviant. Inner multicolored bars represent fractional contributions of each REE. Error bars represent standard error around the mean total REE extracted. Percentages are total REE extraction efficiency (based on previously published REE amounts in the RPP26). Individual data points for total REE extracted are shown as white dots. C Comparison with a two-tailed t-test between each mutant and pWT demonstrated that eight strains were significantly better or worse at bioleaching total REEs (+p < 0.05; n = 5 biological replicates, df = 18). With a Bonferroni correction (N = 12), only one was significantly better (**p = 5.30 × 10−4 for δpstC), but two of the higher pH biolixiviants that extracted detectable REEs were significantly attenuated in bioleaching capability (***p = 1.71 × 10−11 and 6.32 × 10−14 for δtldE and δtldD, respectively). Light purple shading represents the mean and standard deviation for total REE bioleached by pWT biolixiviant. D Disruption mutants for mgdh and pqqC are only able to extract less than 1% of the REE that wild-type G. oxydans can but still extract significantly more REE than glucose alone when measured at a lesser dilution (two-tailed t-test with Bonferroni correction, N = 2: ***p = 9.71 × 10−10 and 2.47 × 10−8 for δpqqC and δmgdh, respectively, n = 5 biological replicates). E Total REE extraction is plotted versus pH for each replicate for each strain, demonstrating how the two are linearly related. Each data point is color coded by strain, as indicated in the plot legend.
