Provided are: an obligatory anaerobic lactic acid bacterium expected as being usable as a safe remedy for a disease under an anaerobic environment, such as solid tumor, and a gene transport support, which is no danger of exerting side effects in a normal tissue a method for constructing the same and an expression vector which is useful in the construction method. The aforesaid obligatory anaerobic lactic acid bacterium is characterized by having been artificially mutated from a facultative anaerobe into an obligatory anaerobe, and being further transformable by an expression vector carrying a gene, which expresses an active protein useful in treating a disease under an anaerobic environment, transferred thereinto. The aforesaid expression vector is characterized by being an expression vector capable of functioning in an obligatory anaerobic lactic acid bacterium, which contains a plasmid replication protein gene(Rep)originating in a lactobacillus, a secretion signal sequence (PslpA-SSartP) consisting of an s-layer gene promoter originating in a lactobacillus and a PrtP protein secretion signal originating in a lactobacillus, and one or more kinds selection marker genes. Thus, it is possible to provide a remedy for a disease under an anaerobic environment and a microbial gene transport support which are highly safe and excellent.
