ZM401, a flocculent mutant strain of Zymomonas mobilis ZM4 was studied using genome-wide transcriptomic analysis for evidence related to phenotypic changes associated with its cell-cell attachment behaviour. Batch fermentation studies with ZM401 and its parent strain ZM4 demonstrated that similar ethanol yields and productivities could be achieved with both strains indicating the potential of the flocculent strains for cost-effective cell biomass recycling with resultant high ethanol volumetric productivities. The results showed that twofold or greater differential expression occurred for 26 genes of ZM401 when compared to those of ZM4. Among these, significant over-expression was evident for the genes ZMO1083 and ZMO1084 which are associated with bacterial cellulose synthesis, while reduced expression was found for ZMO0614, ZMO0613, and ZMO0635 which are all associated with synthesis of flagella-related proteins. Both enhanced cellulose production and reduced flagella activity are likely to facilitate more stable flocculent behaviour in ZM401. From comparative DNA sequence analysis of these 26 genes, only one single point mutation was identified. This occurred at the amino acid position A525V of ZMO1055 which encodes for diguanyl cyclase/phosphoesterase which may be related to cell motility and cellulose synthesis in Z. mobilis.