Abstract
Little is known about the molecular basis of biofilm formation in Listeria monocytogenes. The superoxide dismutase (SOD) of the deletion mutant of lm.G_1771 gene, which encodes for a putative ABC transporter permease, is highly expressed in biofilm. In this study, the sod gene deletion mutant Δsod, and double deletion mutant of the sod and lm. G_1771 genes Δ1771Δsod were used to investigate the role of SOD and its relationship to the expression of the putative ABC transporter permease in biofilm formation. Our results showed that the ability to form a biofilm was significantly reduced in the Δsod mutant and the Δ1771Δsod double mutant. Both Δsod and Δ1771Δsod mutants exhibited slow growth phenotypes and produced more reactive oxygen species (ROS). The growth was inhibited in the mutants by methyl viologen (MV, internal oxygen radical generator) treatment. In addition, the expression of one oxidation resistance gene (kat), two stress regulators encoding genes (perR and sigB), and one DNA repair gene (recA) were analyzed in both the wild-type L. monocytogenes 4b G and the deletion mutants by RT-qPCR. The expression levels of the four genes were increased in the deletion mutants when biofilms were formed. Taken together, our data indicated that SOD played an important role in biofilm formation through coping with the oxidant burden in deficient antioxidant defenses.
Highlights
Listeria monocytogenes is a Gram-positive foodborne pathogen capable of causing listeriosis both in human and animals
Our previous work identified that the sod gene and protein were up-regulated in the D1771 mutant [20]
We found that the superoxide dismutase (SOD) activity was induced in the biofilm of D1771 mutant
Summary
Listeria monocytogenes is a Gram-positive foodborne pathogen capable of causing listeriosis both in human and animals. It is estimated that 99% of the listeriosis cases are caused by contaminated food products [1]. L. monocytogenes is widely distributed in the environment and food processing equipment. It can form biofilms, survive on food processing equipment for several years, and subsequently disperse to contaminate food products [2,3]. Bacteria in biofilms are more resistant to various environmental stresses such as desiccation, UV light, antimicrobials, and sanitizers [5,6]. Biofilms that are difficult to eliminate completely impose major challenges to the food industry
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