## 3 Results
### Biodiversity Observations
#### 3.3.3 Microbial Population Count and Urease Activity Test  
The time course of cell growth and urease activity over 15 d are shown in Figure S8. The cell concentration increased for 2 d and then reached the stationary phase. The urease activity of the cell culture increased with cell growth. Based on this result, the production of urease would be a growth-associated system. Considering microbial-based sand solidification, which should be sustained for relatively long duration for adequate solidification, the long-term stability of the enzyme would be advantageous in the MICP process [36]. As shown in Figure S8 (Supplementary Material), the urease activity of _P. tetradonis_ is higher than that of _O. profundus_ and _V. maritimus_. The bacteria expressed the highest urease activity after 48 h incubation, with only appreciable levels at 24 and 72 h. Even though the bacterial strains are considered biosafety level one (safe for the human body and environment), but some strains of _V. maritimus_ are pathogenic [40, 41] therefore for further research, only _O. profundus_ and _P. tetradonis_ were used to continue the deep research to develop the MICP method. The _tetradonis_ were used to continue the deep research to develop the MICP method. The test tube precipitation test results are a good relative indication test tube precipitation test results are a good relative indication of the potential of each strain for sand solidification by MICP [42, 43, 44]. This is because the improvement  
Figure 4: Phylogenetic trees result of 16S rDNA nucleotide sequence of local bacteria taxonomy (red-frame).  
in strength is proportional to the amount of bio-precipitate formed. Same calcium chloride solution mixed with urease [0.5 M] then dissolved into 7 mL distilled water with urease, calcium chloride and bacteria composition in the ratio of 1:1:1 whereas 10 mL in total, hence the control tube is without bacteria [45; 46]. The results indicate that the strain of _P. tetradonis_ shows the highest performance for microbial induced carbonate precipitation and the weight of precipitate is approximately two times more than the others (Figure 5).  
In the MICP biocementation technique, urease enzyme activity is the key bioindicator of whether the artificial beachrock process is successful or not. The effect of different temperature conditions is shown in Figure 6a for both species. High activity was obtained in the range 10-80 \({}^{\circ}\)C, but the maximum urease activity was obtained at \(\sim\)40 \({}^{\circ}\)C in this study. Most of urease molecules are known to be composed of protein subunits and the subunits of this urease bind strongly to each other. This leads to high stability of the urease during long-term cultivation [39; 42; 44]. Urease activity under different pH conditions is shown in Figure 6b. The results show maximum activity at pH 2.0-12.0. Considering these ranges of temperature and pH, the results were different from those of [PERSON] et al. [39]. In that work, it is mentioned that the results for maximum temperature show an exponential increase toward the environment temperature of the buffer solution, and the method for measurement of urease activity involved the use of an ammonia meter with Tris/HCl buffer solution. Meanwhile, in this research, to measure urease activity, we used ethylene diamine tetra acetic acid (EDTA)buffer solution for the indophenol blue method then detected changes of optical density (630 nm) with a colorimeter. The results of [PERSON] et al. [39] and this research are quite different except for the patterns of bacterial growth and urease activity. All bacteria strain activities were carried out three times to minimize the measurement error factor.  
Figure 5: Microbial induced carbonate precipitation capacity of isolated strains.  
Figure 6: (**a**) Effect of reaction temperature on urease activity of the whole cell at pH 7 (1 mM EDTA-disodium salt solution); (**b**) Effect of reaction pH on urease activity of the whole cell at 37 \({}^{\circ}\)C 1 mM EDTA-disodium salt solution.