A small heat shock gene of Lactobacillus plantarum strain WCFS1 was deleted using a Cre-lox based system. Compared to the wild type, the ∆hsp 18.55 mutant strain displayed a similar growth rate when cultivated either under optimal temperature or under different stress conditions such as heat, low pH and salt stress. However, a longer lag phase was observed when the ∆hsp 18.55 mutant strain was cultivated under short intense heat stress (50 °C). This suggests that the hsp 18.55 gene of L. plantarum may be involved in recovery of L. plantarum stressed cells in the early stage of high temperature stress. In addition, morphology of the mutant cells, investigated by scanning electron microscopy, revealed that cells clumped together and had rough surfaces, and that some of the cells had a shrunken empty appearance, which clearly contrasted with the characteristic rod-shaped, smooth-surface morphology of control L. plantarum cells. Furthermore, inactivation of the hsp 18.55 gene affected membrane fluidity and physicochemical surface properties of L. plantarum WCFS1.