Aims: Examine the regulation of a spore coat protein and the effects on spore properties. Methods and Results: A c. 23 kDa band in coat/exosporial extracts of Bacillus anthracis Sterne spores varied in amount depending upon the conditions of sporulation. It was identified by MALDI as a likely orthologue of ExsB of Bacillus cereus. Little if any was present in an exosporial preparation with a location to the inner coat/cortex region established by spore fractionation and immunogold labelling of electron micrograph sections. Because of its predominant location in the inner coat, it has been renamed Cotc. It was relatively deficient in spores produced at 37°C and when acidic fermentation products were produced a difference attributable to transcriptional regulation. The deficiency or absence of Cotc resulted in a less robust exosporium positioned more closely to the coat. These spores were less hydrophobic and germinated somewhat more rapidly. Hydrophobicity and appearance were rescued in the deletion strain by introduction of the cotc gene. Conclusions: The deficiency or lack of a protein largely found in the inner coat altered spore hydrophobicity and surface appearance. Significance and Impact of the Study: The regulated synthesis of Cotc may be a paradigm for other spore coat proteins with unknown functions that modulate spore properties in response to environmental conditions.