Advisor at Japan Food Research Laboratories
Happy new year to you all!
Figure1 is a new year’s greeting using luminous bacteria. These were made by Mr. K., who did his graduation-thesis study at Food Chain Conservation Laboratory of Hokkaido University. These letters were written on salted agar medium using luminous bacteria shown at the upper left of Figure1. These luminous bacteria came from a Pointhead flounder caught in Ishikari Bay and dried overnight. This specimen had been brought to a local public health center because it emitted bluish white light at night as shown in Figure2. Due to the efforts of Mr. K. and his colleagues, luminous bacteria were isolated from the specimen and identified as Photobacterium kishitanii.
Some kinds of luminous bacteria live around us, but many of them live in the sea. There is astonishingly wide variety of organisms on this planet, isn’t there? Luminous bacteria such as P. kishitani do not produce luminescence in small numbers. They became luminous when their number grows. Their emission is also called “cold light” as it does not cast heat. Dr. Osamu Shimomura received the Novel Prize for researching the cold light of Aequorea Victoria. Now his research discovery is applied in making cancer cells fluorescent.
Sea creatures are wide-ranged and, above all, marine bacteria are exceptionally myriad. No less than tens to hundreds of thousands of bacteria are detected in 1ml of seawater, and 100 to 1000 times of that amount are detected from marine soil. It is generally believed that human beings have not cultured and detected all the bacteria on this planet so far. Therefore, even more microorganisms possibly live in the sea.
Land-dwelling microorganisms do not necessarily require salt (NaCl) to grow. With high level of salt, they become growth-arrested and sometimes destroyed. Although some microorganisms in the sea can grow with or without salt, many kinds of marine bacteria need salt to grow. P. kishitanii also cannot live without salt, and needs oxygen to become luminous.
P. kishitanii, which is a marine bacterium, can grow and become luminous at low temperature. It is heat-labile and killed at about 30°C. As I mentioned in my column #6, food-poisoning incidents caused by Listeria or Yersinia, which can proliferate at low temperature, are reported from different parts of the world. These food-poisoning microorganisms can grow even in refrigerators. Figure2 in my column #6 shows growth curves of Listeria. Figure3 in this column shows proliferation and luminescence of P. kishitanii on salted agar. Comparing these two figures, you can see that P. kishitanii has greater proliferative capacity at low temperature than Listeria or Yersinia, and starts proliferating earlier than these food-poisoning microorganisms. It also emits light. These facts prove that P. kishitanii is capable of warning against proliferation of food-poisoning microorganisms at low-temperature environment such as in refrigerators.
P. kishitanii was considered suitable for warning indicator of low-temperature food preservation even at home because it is destroyed without salt or at moderately high temperature. In fact, however, it requires some more efforts to be actually used as an indicator in practice because it turned out to be capable of producing histamine through histidine decarboxylation.
May this year be radiant and wonderful! Cheers! (Figure4)
Ministry of Health, Labour and Welfare: Food Poisoning Caused by Listeria
Bureau of Social Welfare and Public Health, Tokyo Metropolitan Government: Food Poisoning Caused by Histamine
Isshiki, K. “Development of Temperature Indicator for Warning Temperature Rise in Cold Chain”, Journal of Japan Confectionery and Innovative Food Ingredients Research Center, 14, 54-65, 2012