# Malaysian Virgin Soil Extracts as Natural Growth Enhancer for Targeted Green Microalgae Species
## 3 Results and Discussion
### Effects of Soil Extracts on the Growth of Microalgae  
Figure 2 illustrates the typical growth pattern of _Nammochloropsis acamica_ when cultivated with a medium amended with soil extracts obtained using five different extraction methods. The supplementation of the soil extracts supported enhanced growth of _Nammochloropsis oceanica_ in comparison to the control system containing the medium alone significantly (\(p<0.05\)). The growth pattern of _Nammochloropsis oceanica_ resembled the sigmoid growth \begin{table}
\begin{tabular}{l c c c c} \hline \hline
**Treatment Methods** & **DOC (mg/L)** & **TDN (mg/L)** & **TDP (mg/L)** & **C:N:P Ratio** \\ \hline Natural extraction (24 h) & 58.67 & 5.07 & 0.08 & 73.3:6.3.0.1 \\ Autoclave 105 \({}^{\circ}\)C once & 135.30 & 10.30 & 0.12 & 123.0:10:8.0.1 \\ Autoclave 105 \({}^{\circ}\)C twice & 161.80 & 10.60 & 0.12 & 161.8:10:6.0.1 \\ Autoclave 121 \({}^{\circ}\)C once & 229.60 & 13.40 & 0.14 & 164.0:9.6.0 \\ Autoclave 121 \({}^{\circ}\)C twice & 336.56 & 13.40 & 0.14 & 240.4:9.5.0.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Effect of different extraction methods on nutrient recovery. curve for all treatment methods and the lag phase was observed for 2 d after inoculation, whereby the cell density increased gradually from an average optical density of 0.024 at day 0 to 0.063 after 2 d of the incubation period (the average value was determined as the mean of optical density between five different treatment methods). _Nannochloropsis oceanica_ grew more prominently into the exponential phase which began on day 2 and lasted until day 4 with an average optical density of 0.224 between the five different treatment methods, exhibiting 293% higher cell density compared to the control system containing the medium alone. The mid-log phase was achieved on day 3 with an average optical density of 0.147, indicating the rapid growth of the microalgae. The growth of _Nannochloropsis oceanica_ was continuously monitored for 9 d and the highest optical density was observed with the autoclave treatment method at 121 \({}^{\circ}\)C once, yielding an optical density of 0.341 \(\pm\) 0.029. When compared with natural extraction and autoclave 105 \({}^{\circ}\)C once treatment methods, the utilization of the autoclave treatment method at 121 \({}^{\circ}\)C once resulted in 64% higher cell density, depicting a significant growth rate of the microalgae when soil extracts obtained from this treatment method were used as growth enhancer (\(p<0.05\)). In addition, the growth of _Nannochloropsis oceanica_ was substantially influenced by the autoclave treatment methods (\(p<0.05\)), except for natural extraction (24 h) and autoclave 105 \({}^{\circ}\)C once treatment methods which generated an insignificant difference (\(p>0.05\)) in terms of growth with an optical density of 0.206 \(\pm\) 0.030 and 0.210 \(\pm\) 0.026, respectively, after 9 d of the incubation period. The growth of _Nannochloropsis oculata_ was monitored for a period of 9 d and the results are depicted in Figure 3.  
The addition of soil extracts indeed supported improved growth of the microalgae with significantly increased cell density (\(p<0.05\)) compared to that of the control system containing the medium alone. Interestingly, the control system demonstrated a lag period of 2 d, whereas the experimental groups (artificial medium containing soil extracts from five different extraction methods) showed a lag period of only 1 d. The growth pattern of the experimental groups revealed a similar trend, whereby the exponential phase began after 1 d of cultivation and the growth progressed into the early stationary phase on day 2, recording an increase in the average optical density from 0.024 on day 0 to 0.267 at day 2, presenting an increase of 1013% in the cell density. On the other hand, the optical density of  
Figure 2: Optical density at 680 nm of _Nannochloropsis ocanica_. Error bars represent the standard deviation between three replicates (\(n=3\)).