## 3 Results and Discussion
### Optimizing the Growth and Enzymatic Activity of the Isolated Sporosarcina sp. Strain  
#### 3.2.1 Effect of Temperature  
In order to ascertain the maximum benefits from the MICP process, it is important to determine the temperature at which microbial growth and urease activity is optimum. As per the findings of this  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Sample ID**} & **Closest Match to Phylogenetic** & **Genbank Accession** & \multirow{2}{*}{**Similarity**} \\  & **Grouping** & **Number** & \\ \hline M1-1-1 & _Halomonas_ sp. & AJ306891 & 99.8\% \\ \hline M2-2-1 & _Halomonas_ sp. & AJ306888 & 99.6\% \\ \hline M11-1-5 & _Sulfitobacter_ sp. & AY180103 & 98.0\% \\ \hline M11-1-7 & _Oceanobacillus_ sp. & HQ595230 & 99.9\% \\ \hline L2-2-2 & _Sporosarcina_ sp. & HQ676600 & 99.7\% \\ \hline L1-1-5 & _Bacillus_ sp. & NR\_146034 & 98.7\% \\ \hline \hline \end{tabular}
\end{table}
Table 3: Phylogenetic grouping of the isolated bacterial strains.  
Figure 3: Microbial induced carbonate precipitation capacity of isolated strains.  
study, the microbial growth of the isolate was more stable and comparatively higher at a temperature range of 20-25 \({}^{\circ}\)C whereas the growth became almost zero when the temperature was raised up to 50 \({}^{\circ}\)C (Figure 4). [PERSON] et al. [12] states that the microbial growth is generally less sensitive to temperature changes over the range of 20-30 \({}^{\circ}\)C, which was also true in this case. In addition, the strain exhibits the typical growth curve of a bacteria population over time where cell growth increases exponentially up to a maximum followed by a stationary phase and then a gradual fall (death phase) due to independent or combined effect of nutrient exhaustion, waste accumulation and/or oxygen depletion, and subsequent cell lysis [44].  
Catalysis of urea hydrolysis is a temperature dependent enzymatic reaction [43] and is closely associated with the bacterial cell population [12]. The effect of temperature on urease activity of the isolate is presented in Figure 5 indicating that enzymatic performance is maximum and stable at 25 \({}^{\circ}\)C. The activity is degraded almost to zero at 40 \({}^{\circ}\)C and 50 \({}^{\circ}\)C. This is in accordance with the findings of [PERSON] et al. [45] where microbial enzyme activity of _Bacillus megaterium_ decreased by a fraction of 47% when temperature was raised from 35 to 55 \({}^{\circ}\)C. In contrast to that, [PERSON] [46] in a very early study revealed that optimum urease activity lies at temperatures close to 60 \({}^{\circ}\)C. This was later attested to by [PERSON] et al. [47] and few others for strains _Streptococcus salivarius_[48] and _Paralodobacter_ sp. [49]. In terms of temporal stability, although the selected bacterium maintains a relatively satisfactory enzyme stability over a period of 7 days, the activity seems to drop over time as cell lysis and denaturation of the loose enzyme take place [50]. However, considering the above results as well as the tropical climate in Sri Lanka, the remaining investigations were carried out at a temperature of 25 \({}^{\circ}\)C.  
Figure 4: Variation of bacterial cell concentration of _Sporosarcina_ sp. at different temperatures.