Fig. 5

a Pareto charts ranking the standardized effects of the tested factors. The vertical line in chart represent a reference line, any factor that extends past this line is of significant effect at α = 0.05 (significance level). E-value (the standardized effect of each factor) was calculated using Minitab software (version 17). The magnitude of the E-value of the tested factor indicated its significance in affecting the response, while the positive or negative sign of the E-value was an indication of its positive or negative influence on the responses, respectively. b Normal probability plot of residuals for isolate B1. The straight line in the graph represents the mathematical regression equation (which determines the expected data), while the dots in the plots represent the actual observed data. As shown in figure the dots generally formed a line consistent with regression line, therefore the residuals (the difference between observed data and expected data) are considered normally distributed