Potatoes left alone in humid weather and moist conditions start growing an unappetizing pink slime. This is an infection (and resulting decomposition) caused by Clostridium puniceum bacteria. According to a new Science study, these pathogens secrete antibiotics to keep other microbes off their potato, and these same molecules also help the bacteria survive in otherwise hostile, oxygen-rich environments – like your kitchen counter.
C. puniceum is an obligate anaerobe; it can only live in the absence of oxygen. So researchers have long puzzled over how its slimy rot can grow on a tuber in an aerobic, or oxygenated, environment. To investigate, a team led by Christian Hertweck from the Leibniz Institute for Natural Product Research and Infection Biology in Germany injected potatoes (Solanum tuberosum) with the bacteria. Over the next four days, they watched as decomposition accompanied the accumulation of pink pigment and slime. When they analyzed the various components using a technique called liquid chromatography, the researchers isolated two products of interest: clostrubins A and B.
These metabolites demonstrated antimicrobial properties against several common, aerobic potato pathogens (with great names) – soft rot, ring rot, and common scab – suggesting that clostrubins help C. puniceum survive in oxygenated environments. Furthermore, clostrubin A showed strong antibacterial activities against the human “superbug” pathogens MRSA and vancomycin-resistant enterococci. This indicates that clostrubins might be produced by the plant pathogen to battle microbial competitors.
Next, the team tried to create a strain of C. puniceum that lacked these clostrubins by sequencing the bacterium’s genome and then knocking down the gene for clostrubin A. Under oxygen-deprived conditions, the clostrubin-negative mutant of C. puniceum led to similar bacteria growth and potato decay as normal, unaltered bacteria. However, in the presence of normal atmospheric oxygen concentrations, the growth of the mutants was dramatically reduced. They couldn’t infect potatoes in air.
Clostrubins, as it turns out, serve dual functions: they permit the survival of this anaerobic pathogen in an oxygen-rich atmosphere and ward off competing microbes. If we can harness these antibacterial properties, we might be able to reduce this wasteful statistic. About a quarter of vegetable food is lost worldwide because of infectious plant diseases.