# Morphological Study of _Bacillus thuringiensis_ Crystals and Spores
## 3 Results
### B. thuringiensis Spore Morphology and Size Distribution  
After analyzing the morphological results for the crystals of the different strains, we analyzed the morphological data of their spores, in order to see if we could find any differences in size and shape among the different strains of _B. thuringiensis_. Histograms of the size distribution of the spore length for the seven strains are presented according to the normal distribution. The x-axis corresponds to the spore size ranges, the left-hand y-axis represents the percentage of the number of spores belonging to the ranges and the right-hand y-axis represents the cumulative percentage (Figure 9). Figure 8: (**a**) SEM image taken of the H3 purified crystals. (**b**) Graph representing the radius size distribution in terms of frequency and cumulative percentage for the spherical crystals. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multicolumn{6}{c}{**Spherical Crystals**} \\ \hline
**Strain** & \(N\) & \multicolumn{3}{c}{**Radius (\(\upmu\)m)**} & \multicolumn{3}{c}{**Volume * (\(\upmu\)m\({}^{3}\))**} \\ \hline  & & **Average** & **Unc.** & **Range** & **Average** & **Unc.** \\ \hline AM65-52 & 229 & 0.394 & 0.009 & 0.206–0.683 & 0.283 & 0.021 \\ AR23 & 941 & 0.381 & 0.003 & 0.228–0.530 & 0.242 & 0.006 \\ BUPM98 & 1500 & 0.37 & 0.003 & 0.143–0.524 & 0.225 & 0.005 \\ H3 & 1350 & 0.411 & 0.003 & 0.217–0.615 & 0.307 & 0.007 \\ \hline \hline \end{tabular} \({}^{\star}\) Volumes were calculated using _equation_ ((4/3) \(\pi r^{3}\)).  
\end{table} 
Table 3: Morphological data of crystals of the three _B. thuringiensis_ var. _israelensis_ and _B. thuringiensis_ H3 spherical crystals for \(N\) measurements. While comparing spore size distribution histograms, a variation in the mean size values of the different strains was noticed. For instance, when comparing _kurstaki_ strains, the highest frequency of measured spores for HD1 has a size of [1.02-1.22] \(\upmu\)m, compared to a larger size of [1.53-1.68] \(\upmu\)m for LIPMKA and a smaller one for BLB1, [0.65-0.72] \(\upmu\)m.  
Figure 9: Histograms representing the size distribution in terms of frequency and cumulative percentage of the length L of the spores synthesized by the seven strains of _B. thuringiensis_: (**a**) \(\mathrm{HD1}\), (**b**) \(\mathrm{ LIPMKA}\), (**c**) BLB1, (**d**) AM65-52 (**e**) AR23, (**f**) BUPM98 and (**g**) \(\mathrm{H3}\). Similar variation was also observed for _israelensis_ strains, for which spore length showed highest frequency in the intervals [0.96-1.08], [1.37-1.44] and [1.51-1.58] \(\upmu\)m for AM65-52, AR23 and BUPM98, respectively. This difference was also obtained in the variation of the average spore width observed for each of the seven _B. thuringiensis_ strains, as shown by the morphological data reported in Table 4.  
Since the length mean values between the seven strains were significantly different (\(p=0\)), the null hypothesis was rejected. The HSD test shows that spores of LIPMKA were statistically different from the other _kurstalk_ strains. This significant difference was also observed between the length mean values of H3 spores and those of the _israelensis_ strains, and between AM65-52 on one hand and AR23 and BUPM98 on the other. No statistical difference was detected between AR23 and BUPM98 strains. In order to better analyze the morphological results of the spores, we represent in Figure 10 the variation of the aspect ratio and the spores' volume for the seven considered strains. The aspect-ratio of the spores produced by anti-dipteran strains presents a statistically significant difference (\(p=0\)). HSD post-hoc test revealed significant difference between AM65-52 and BUPM98, whereas no difference between BUPM98 and AR23 was detected. Among the _israelensis_ strains, AM65-52 spores are the most spherical. H3 strain synthesizes spores that are more spherical in shape than the _israelensis_ strains, since they presented the highest aspect ratio of 0.754 \(\pm\) 0.072. This was also revealed by the post-hoc HSD test.