The winnowing: establishing the squid-vibrio symbiosis

Magnesium promotes flagellation of Vibrio fischeri

The bacterium Vibrio fischeri requires bacterial motility to initiate colonization of the Hawaiian squid Euprymna scolopes. Once colonized, however, the bacterial population becomes largely unflagellated. To understand environmental influences on V. fischeri motility, we investigated migration of this organism in tryptone-based soft agar media supplemented with different salts. We found that optimal migration required divalent cations and, in particular, Mg2+. At concentrations naturally present in seawater, Mg2+ improved migration without altering the growth rate of the cells. Transmission electron microscopy and Western blot experiments suggested that Mg2+ addition enhanced flagellation, at least in part through an effect on the steady-state levels of flagellin protein.

Complete genome sequence of Vibrio fischeri: a symbiotic bacterium with pathogenic congeners

Vibrio fischeri belongs to the Vibrionaceae, a large family of marine gamma-proteobacteria that includes several dozen species known to engage in a diversity of beneficial or pathogenic interactions with animal tissue. Among the small number of pathogenic Vibrio species that cause human diseases are Vibrio cholerae, Vibrio parahaemolyticus, and Vibrio vulnificus, the only members of the Vibrionaceae that have had their genome sequences reported. Nonpathogenic members of the genus Vibrio, including a number of beneficial symbionts, make up the majority of the Vibrionaceae, but none of these species has been similarly examined. Here we report the genome sequence of V. fischeri ES114, which enters into a mutualistic symbiosis in the light organ of the bobtail squid, Euprymna scolopes. Analysis of this sequence has revealed surprising parallels with V. cholerae and other pathogens.

Microbial factor-mediated development in a host-bacterial mutualism

Tracheal cytotoxin (TCT), a fragment of the bacterial surface molecule peptidoglycan (PGN), is the factor responsible for the extensive tissue damage characteristic of whooping cough and gonorrhea infections. Here, we report that Vibrio fischeri also releases TCT, which acts in synergy with lipopolysaccharide (LPS) to trigger tissue development in its mutualistic symbiosis with the squid Euprymna scolopes. As components of PGN and LPS have commonly been linked with pathogenesis in animals, these findings demonstrate that host interpretation of these bacterial signal molecules is context dependent. Therefore, such differences in interpretation can lead to either inflammation and disease or to the establishment of a mutually beneficial animal-microbe association.

Application of Real Time PCR for the Detection and Enumeration of Vibrio parahaemolyticus from Seafood in Sarawak (Malaysia)

Vibrio parahaemolyticus has been associated as the major cause of food poisoning and gastroenteritis in manycountries including Southeast Asia. Their human infection is regularly associated with the consumption of rawor undercooked seafood and contaminated water supplies. A rapid method of detection is important to monitorthe occurrence of V. parahaemolyticus in both food and environment samples especially in Malaysia. Thus, theaim of this study was to detect and enumerate V. parahaemolyticus from seafood by using the real-time PCRbased on the SYBR green assay. targeting the thermolabile (tl) gene. The assay was applied on 24 seafoodsamples comprised of 6 cockles, 6 prawns, 6 squids and 6 fishes. In this study, all of the six cockles and prawnswere positive for the presence of V. parahaemolyticus while fish samples have only 2 positive isolates.However, this study recorded no presence of V. parahaemolyticus in squids. Overall, the real-time PCR assaywas proven to be highly specific, and is sensitive in detecting and enumerating V. parahaemolyticus in theseafood samples. In addition, this study has proven that seafood (especially cockles and prawns) are potentialsources for V. parahaemolyticus.