Bacterial bioluminescence: its control and ecological significance.

It has been previously demonstrated that luciferase synthesis in the luminous marine bacteria, Beneckea harveyi and Photobacterium fischeri is induced only when sufficient concentrations of metabolic products (autoinducers) of these bacteria accumulate in growth media Thus, when cells are cultured in liquid medium there is a lag in luciferase synthesis A quantitative bioassay for B harveyi autoinducer was developed and it was shown that many marine bacteria produce a substance that mimics its action, but in different amounts, (20–130% of the activity produced by B harveyi) depending on the species and strain This is referred to as alloinduction None of the bacteria tested produced detectable quantities of inducer for P fischeri luciferase synthesis These findings may have significance with respect to the ecology of B harveyi and P fischeri

Induction of luciferase synthesis in Beneckea harveyi by other marine bacteria

Bioluminescent marine bacteria of the species Vibrio fischeri are the specific light organ symbionts of the sepiolid squid Euprymna scolopes. Although they share morphological and physiological characteristics with other strains of V. fischeri, when cultured away from the light organ association the E. scolopes symbionts depress their maximal luminescence over 1,000-fold. The primary cause of this reduced luminescence is the underproduction by these bacteria of luciferase autoinducer, a molecule involved in the positive transcriptional regulation of the V. fischeri lux operon. Such an absence of visible light production outside of the symbiotic association has not been previously reported among light organ symbionts of this or any other species of luminous bacteria. Levels of luminescence approaching those of the E. scolopes bacteria in the intact association can be restored by the addition of exogenous autoinducer to bacteria in laboratory culture and are affected by the presence of cyclic AMP. We conclude that some condition(s) specific to the internal environment of the light organ is necessary for maximal autoinduction of luminescence in the symbionts of this squid-bacterial association.

Depressed light emission by symbiotic Vibrio fischeri of the sepiolid squid Euprymna scolopes.

Depressed Light Emission bySymbiotic Vibrio fischeri ofthe Sepiolid Squid Euprymna scolopes

Although the study of microbe-host interactions has been traditionally dominated by an interest in pathogenic associations, there is an increasing awareness of the importance of cooperative symbiotic interactions in the biology of many bacteria and their animal and plant hosts. This review examines a model system for the study of such symbioses, the light organ association between the bobtail squid Euprymna scolopes and the marine luminous bacterium Vibrio fischeri. Specifically, the initiation, establishment, and persistence of the benign bacterial infection of the juvenile host light organ are described, as are efforts to understand the mechanisms underlying this specific colonization program. Using molecular genetic techniques, mutant strains of V. fischeri have been constructed that are defective at specific stages of the development of the association. Some of the lessons that these mutants have begun to teach us about the complex and long-term nature of this cooperative venture are summarized.

LESSONS FROM A COOPERATIVE, BACTERIAL-ANIMAL ASSOCIATION: The Vibrio fischeri–Euprymna scolopes Light Organ Symbiosis

Luminous bacteria isolated from the light organs of the Australian Pinecone fish Cleidopus gloriamaris have been studied. The isolates were from fish from four different geographical estuarine systems on the east coast of Australia. All isolates were found to be strains of Vibrio fischeri, a species not hitherto demonstrated conclusively as forming a symbiotic association. Some ecological considerations are discussed.

J. M. Fitzgerald

Papers

Classification of luminous bacteria from the light organ of the Australian Pinecone fish, Cleidopus gloriamaris