## 3 Results and Discussion
### Determination of Process Parameters for Optimal Exoperoxidase Production
[25] reported 35 \({}^{\circ}\)C as the temperature for optimal exoperoxidase activity by _Raoultella ornithinolytica_ OKOH-1. The reason for the inconsistencies in the optimal temperature for peroxidase production by the different bacteria species is unclear. However, all the temperatures that supported maximum peroxidase production by the various organisms are in the mesophilic range [25]. The decline in the enzyme production by _Ensifer adherens_ NWODO-2 observed at temperatures lower and higher than 30 \({}^{\circ}\)C (Figure 1b) may probably be due to decrease in metabolic activities, which consequently, may inhibit the organism growth and enzyme biosynthesis [40]. Figure 1: Determination of process parameters for optimal exoperoxidase production by _Ensifer adherens_ NWODO-2. (**a**). Initial medium pH. ANOVA: F = 123.7, \(p\) value = \(p<\) 0.0001, \(p\) value summary = *** (highly significant), R squared = 0.9900. (**b**) Incubation temperature. ANOVA: F = 63.44, \(p\) value = \(p<\) 0.0001, \(p\) value summary = *** (highly significant), R squared = 0.9814. (**c**) Agitation speed. Analysis of variance (ANOVA): F = 7.760, \(p\) value = 0.0226, \(p\) value summary = * (significant), R squared = 0.8613. Nutrient accessibility by microorganisms is influenced by agitation, which improves aeration and enhances appropriate mixing of nutrients during fermentation [41]. The influence of agitation rate on exoperoxidase production by _Ensifer adherens_ NWODO-2 as presented in Figure 1c revealed that peroxidase production under static condition and across all the studied agitation speeds (50-200 rpm) differ significantly (F = 7.760, \(p\) value = 0.0226 for ANOVA), with the optimal production recorded at 100 rpm (5.31 \(\pm\) 1.23 U mL\({}^{-1}\)). Nevertheless, the difference between peroxidase production at 150 rpm (3.50 \(\pm\) 0.12 U mL\({}^{-1}\)) and 200 rpm (2.69 \(\pm\) 0.12 U mL\({}^{-1}\)) was not significant ([PERSON]'s test). This finding shows that peroxidase production by _Ensifer adheserens_ NWODO-2 was affected by agitation as there was a significant increase in peroxidase production at 100 rpm (5.31 \(\pm\) 1.23 U mL\({}^{-1}\)) when compared with static condition (1.4 \(\pm\) 0.00 U mL\({}^{-1}\)). This result is in agreement with previous similar studies, where agitation affected the level of enzyme production [22; 42; 43]. In this study, 100 rpm was the most favourable agitation speed for peroxidase secretion by the test organism but [PERSON] [43] reported 180 rpm as the agitation rate that supported optimal lignin peroxidase production by _Bacillus megaterium_. The decrease in peroxidase production observed at 150 and 200 rpm in this study may be as a result of foaming or shearing stress on the mycelium. Although the report on the induction of peroxididases by lignin monomers in bacteria is limited, there are quite a number of studies on the inductive effect of lignin monomers on peroxidase production by ligninolytic organisms, predominantly, fungi [44; 45; 46]. In this study, the effect of supplementing the production medium with 1 mM of different lignin monomers (Guaiacol-GA, Vearatryl alcohol-VALC, vanillin-VAN, vanillic acid-VA and ferullic acid-FA) on exoperoxidase production was assessed and the results are shown in Figure 2a. The results revealed there was a significant difference in peroxidase production by _Ensifer adheserens_ NWODO-2 grown in fermentation media supplemented with the different lignin monomers (F = 1023, \(p\) value = \(p\) < 0.0001 for ANOVA). Also, [PERSON]'s test showed that supplementation of the fermentation medium with guaiacol increased peroxidase production (AL + GA = 5.25 \(\pm\) 0.00 U mL\({}^{-1}\)) by the bacteria when compared with the non-supplemented fermentation medium (AL), which served as the control (AL = 2.10 \(\pm\) 0.00 U mL\({}^{-1}\)).