## 3 Results and Discussion
### Nutrient Mineralization Activities of Bacteria in Vermicasts  
A total of 25 bacterial isolates obtained from the vermicasts of _P. losbanosensis_ and 20 isolates from _E. eugeniae_ were subjected to plate-based screening assay of nutrient mineralization. Results showed 14 bacteria (PL: 8; EE: 6) capable of fixing N on nitrogen-free malate media, as indicated by blue-colored zones with maximum activity (_p_ < 0.05) of 29 mm produced by isolate PL\({}_{16}\) than the 9 mm produced by EE\({}_{3}\) and EE\({}_{4}\) (Figures 9 and 10). Clearing zones produced by 18 isolates (PL: 10; EE: 8) confirmed P solubilization on Pikovskaya's agar with isolate PL\({}_{20}\) having a significantly higher (_p_ < 0.05) SI value of 2.57 than EE\({}_{5}\) (2.27) (Figures 9 and 11). Clearing zones were also observed on Aleksandrow agar, showing the ability of seven isolates (PL: 3; EE: 4) to solubilize K with a significantly higher (_p_ < 0.05) SI value of 3.3 produced by isolate PL\({}_{4}\) than EE\({}_{3}\) (2.67) (Figures 9 and 12). Based on these data, bacteria isolated from the vermicasts produced by the indigenous earthworms showed higher plate-based NPK mineralization activities. Figure 10: Zone of blue coloration produced by bacteria isolated from _P. losbanosensis_ (PL) and _E. eugeniae_ (EE) vermicasts capable of N fixation on nitrogen-free malate media after 5 d of incubation (n = 2). Vertical bars represent the standard error of the mean. Means separated by different letters are significantly different ([PERSON]’s mean separation test, \(p\) < 0.05). Figure 9: Blue coloration and clearing zones produced by representative bacterial isolates from _P. losbanosensis_ (PL) and _E. eugeniae_ (EE) vermicasts capable of N fixation on nitrogen-free malate media (**a**), P solubilization on Pikovskaya’s agar (**b**), and K solubilization on Aleksandrow agar (**c**) after 5 d of incubation (n = 2). Zones were first observed after 24 h of incubation, with increasing diameters as time progressed. The presence of N-fixing bacteria (NFB) in earthworms' vermicasts was previously reported in _E. fetida_, namely _Azotobacter_, _Beijernickia_, and _Dersia_[10], and in _E. eugeniae_, including _Aerononas caviae_ and _Bacillus xianenensis_[51]. The presence and activity of NFB in vermicasts have been confirmed to increase N mineralization in relation to the continuous casting activity of earthworms [52] as well as higher levels of microbial respiration, population, and enzyme activity [9]. Also, N mineralization involving NH\({}_{4}\)+ production is directly proportional to the size of vermicasts [53]. This was the case in _Amynthas khami_ Thai, 1984, wherein an increase in NH\({}_{4}\)+ was observed from vermicasts with increasing size brought by fixation, denitrification, and immobilization in the microbial biomass. In contrast, the stabilization of vermicasts linked with a high rate of nitrification resulted in the decline in NH\({}_{4}\)+ content obtained from _L. rubellus_ vermicasts [21]. Reduced ammonia content and a higher level of nitrate were also observed, wherein 96% of mineral N in fresh vermicasts is composed of ammonia converted to nitrate via nitrification [54]. Figure 11: P solubilization index (SI) of bacteria isolated from _P. losbanosensis_ (PL) and _E. eugeniae_ (EE) capable of P solubilization on [PERSON]’s agar after 5 d of incubation (n = 2). Vertical bars represent the standard error of the mean. Means separated by different letters are significantly different ([PERSON]’s mean separation test, \(p<0.05\)). Figure 12: K solubilization index (SI) of bacteria isolated from _P. losbanosensis_ (PL) and _E. eugeniae_ (EE) capable of K solubilization on [PERSON] agar after 5 d of incubation (n = 2). Vertical bars represent the standard error of the mean. Means separated by different letters are significantly different ([PERSON]’s mean separation test, \(p<0.05\)). Consistent with the results of the present study, vermicasts of _E.