BACTERIAL GRAZING-RESISTANCE DEVELOPED DURING CO-EXISTENCE WITH A BACTERIVOROUS PROTIST

Two types of transformants with di ff erent drug resistance were developed from the phenol-oxidizing bacterium, Cupriavidus sp. KN1. The first transformant is Cupriavidus sp. KN1-TGF that has green fluorescence and tetracycline resistance. The second transformant is Cupriavidus sp. KN1-KRF that has red fluorescence and kanamycin resistance. These two strains can be selectively colonized with antibiotic-containing media, and they can be also distinguished by fluorescent color. First, Cupriavidus sp. KN1-TGF cells remaining after predation with the flagellate, Spumella sp. TGKK2, were mixed with Cupriavidus sp. KN1-KRF that did not contact with the flagellate TGKK2 to investigate the change in characteristics for the protistan predation. As a result, Cupriavidus sp. KN1-KRF was preferentially predated. On the other hand, Cupriavidus sp. KN1-TGF in the same tube was relatively resistant to predation. Similar phenomena were observed when the conditions of these two strains were reversed. Next, two complete mixing reactors connected in series were operated. Bacteria were cultured in the first reactor, and the protistan predation was made in the second reactor. Two runs were operated, one with Cupriavidus sp. KN1-TGF and the other with Cupriavidus sp. KN1-KRF. Then the first reactor e ffl uent that contains Cupriavidus sp. KN1-KRF was mixed with the second reactor e ffl uent that contains residual Cupriavidus sp. KN1-TGF and the flagellate TGKK2 in a tube. The cells of Cupriavidus sp. KN1-KRF not in contact with the protist were preferentially predated. This phenomenon was similarly confirmed by combinatorial inversion that Cupriavidus sp. KN1-TGF from the first reactor was mixed with Cupriavidus sp. KN1-KRF from the second reactor.