Cellulolytic activities in Bacillus subtilis have been demonstrated and it is known that the eglS gene encodes an endoglucanase that could play a key role. Three Bacillus subtilis strains (RZ164, RS351, and RS273) isolated from corn stover with contrasting cellulase activity were examined in this work. The aim was to analyze the influence of eglS gene on the ability of bacteria to grow on a liquid medium supplied with carboxymethyl cellulose (CMC) or microcrystalline cellulose (MCC) as sole carbon sources. All strains displayed similar growth in CMC medium and comparable exoglucanase and endoglucanase activity. However, the expression of eglS did not correlate among strains. On the other hand, when MCC was the carbon source tested, the growth of RS351 was higher than that obtained by RZ164 and RS273 strains. This behavior could be related to the level of cellulase activities displayed by this strain. Besides, eglS expression was higher in RS351 strain, suggesting a direct participation of this enzyme when the carbon source is MCC. Taken together, eglS could be involved in different roles exerted by these strains on either exo- or endoglucanase activity and under either substrate. The enzymes described here could be considered good alternatives for biomass conversion.