Anaerobic respiratory growth of Vibrio harveyi, Vibrio fischeri and Photobacterium leiognathi with trimethylamine N-oxide, nitrate and fumarate: ecological implications

Two symbiotic species, Photobacterium leiognathi and Vibrio fischeri, and o ne non-symbiotic species, Vibrio harveyi, of the Vibrionaceae were tested f or their ability to grow by anaerobic respiration on various electron accep ters, including trimethylamine N-oxide (TMAO) and dimethylsulphoxide (DMSO) , compounds common in the marine environment. Each species was able to grow anaerobically with TMAO, nitrate or fumarate, but not with DMSO, as an ele ctron acceptor. Cell growth under microaerophilic growth conditions resulte d in elevated levels of TMAO reductase, nitrate reductase and fumarate redu ctase activity in each strain, whereas growth in the presence of the respec tive substrate for each enzyme further elevated enzyme activity. TMAO reduc tase specific activity was the highest of all the reductases. Interestingly , the bacteria-colonized light organs from the two squids, Euprymna scolope s and Euprymna morsel, and the light organ of the ponyfish, Leiognathus equ us, also had high levels of TMAO reductase enzyme activity, in contrast to non-symbiotic tissues, The ability of these bacterial symbionts to support cell growth by respiration with TMAO may conceivably eliminate the competit ion for oxygen needed far both bioluminescence and metabolism.