# Morphological Study of _Bacillus thuringiensis_ Crystals and Spores
## 4 Discussion
_israelensis_ strain AM65-52 have a smaller volume to the _israelensis_ Lebanese AR23 and Tunisian BUPM98 strains, much like the _kurstaki_ strains in which the reference strain HD1 produces less voluminous spores than the Lebanese LIPMKA. While their number is affected by the change of culture media, the size of _B. thuringiensis_ spores is not [37]. The causes of variation in spore size and morphology are still unknown. Nevertheless, a key player in this variation might be related to the spore forming units, from the inside-out, endospore, cortex, spore-coat, interspace and exosporium basal layer and nap [40]. A change in the size of one of these units, particularly the thickness of the exosporium layers and/or the interspace between the cortex and the exosporium basal layer, can cause a change in the spore size. In _B. anthracis_ spores, the genes responsible for the formation and volume change of each spore unit are well described. Indeed, there is chromosomal genetic relatedness between _B. anthracis_ and _B. thuringiensis_, and a closeness in spore morphology, allowing the use of _B. thuringiensis_ spores as _B. anthracis_ surrogates in aerosolization tests [39]. However, a detailed description of _B. thuringiensis_ spore forming units and genes is yet to be presented. In this study, we were not able to extract a direct correlation between this variation and the genomic components of the strains, e.g., plasmid size and nature. With regard to the prospects of this study, a thorough genomic, transcriptomic and proteomic study should be conducted to elucidate the variations of crystal and spore sizes within the same family. In addition, this study could pave the way to future morphological analysis of _B. thuringiensis_ crystals and spores using another optical method, such as laser speckle imaging. Conceptualization, H.L., N.F., F.P., B.L.J., R.L., M.K., G.L.B. and M.A. ; formal analysis, H.L., N.F., F.P., B.L.J., R.L., M.K., G.L.B. and M.A. ; methodology, H.L., N.F., F.P., B.L.J., R.L., M.K., G.L.B. and M.A. ; resources, M.C., D.B. and M.K. ; software, H.L., N.F., M.K. and M.A. ; validation, F.P., B.L.J., R.L., M.K., G.L.B. and M.A. ; writing--original draft, H.L., N.F., F.P., B.L.J., R.L., M.K., G.L.B. and M.A. ; writing--review and editing, H.L., N.F., F.P., B.L.J., R.L., M.K., G.L.B. and M.A. All authors have read and agreed to the published version of the manuscript. This research was funded by EranetMed (2-72-093 BIOSMAN); National Council for Scientific Research in Lebanon (CNRS-L/FS-108); Saint Joseph University (USJ-CR/FS-109). Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Acknowledgments: [PERSON] acknowledges the National Council for Scientific Research in Lebanon for granting him a doctoral fellowship. The authors thank Doctor [PERSON] from the \"Plateforme PIMM at Universite de Bretagne Occidentale, Brest, France\" for scanning electron microscope images. Conflicts of Interest: The authors declare no conflict of interest. References  
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