Bacterial preferences and growth kinetic variation inUronema marinum andUronema nigricans (Ciliophora: Scuticociliatida)

Acrylate protects a marine bacterium from grazing by a ciliate predator

Cleavage of dimethylsulfoniopropionate (DMSP) can deter herbivores in DMSP-producing eukaryotic algae; however, it is unclear whether a parallel defence mechanism operates in marine bacteria. Here we demonstrate that the marine bacterium Puniceibacterium antarcticum SM1211, which does not use DMSP as a carbon source, has a membrane-associated DMSP lyase, DddL. At high concentrations of DMSP, DddL causes an accumulation of acrylate around cells through the degradation of DMSP, which protects against predation by the marine ciliate Uronema marinum. The presence of acrylate can alter the grazing preference of U. marinum to other bacteria in the community, thereby influencing community structure.

Small doses, big troubles: modeling growth dynamics of organisms affecting microalgal production cultures in closed photobioreactors

The destruction of mass cultures of microalgae by biological contamination of culture medium is a pervasive and expensive problem, in industry and research. A mathematical model has been formulated that attempts to explain contaminant growth dynamics in closed photobioreactors (PBRs). The model simulates an initial growth phase without PBR dilution, followed by a production phase in which culture is intermittently removed. Contaminants can be introduced at any of these stages. The model shows how exponential growth from low initial inocula can lead to "explosive" growth in the population of contaminants, appearing days to weeks after inoculation. Principal influences are contaminant growth rate, PBR dilution rate, and the size of initial contaminant inoculum. Predictions corresponded closely with observed behavior of two contaminants, Uronema sp. and Neoparamoeba sp., found in operating PBRs. A simple, cheap and effective protocol was developed for short-term prediction of contamination in PBRs, using microscopy and archived samples.

Early detection of protozoan grazers in algal biofuel cultures

Future micro-algal biofuels will most likely be derived from open-pond production systems. These are by definition open to "invasion" by grazers, which could devastate micro-algal mass-cultures. There is an urgent requirement for methodologies capable of early detection and control of grazers in dense algal cultures. In this study a model system employing the marine alga Nannochloropsis oculata was challenged by grazers including ciliates, amoebae and a heterotrophic dinoflagellate. A FlowCAM flow-cytometer was used to detect all grazers investigated (size range <20->80 μm in length) in the presence of algae. Detection limits were <10 cells ml(-1) for both "large" and "small" model grazers, Euplotes vannus (80 × 45 μm) and an unidentified holotrichous ciliate (~18 × 8 μm) respectively. Furthermore, the system can distinguish the presence of ciliates in N. oculata cultures with biotechnologically relevant cell densities; i.e. >1.4 × 10(8) cells ml(-1) (>0.5 g l(-1) dry wt.).

In vitro culture and cryopreservation of Uronema marinum isolated from farmed New Zealand groper (Polyprion oxygeneios)

An in vitro culture method was developed for the ciliated protozoa Uronema marinum isolated from New Zealand aquacultured groper (Polyprion oxygeneios). Both formulated media and sterile seawater supplemented with homogenised fish tissue as a food source supported growth of U. marinum achieving cell densities of up to 1 x 10(5)cells/mL in culture. A cryopreservation method based on a cryomix formula of 20% glycerol, 10% fetal bovine serum and 70% cultured U. marinum, incorporating a slow freeze method to -80 degrees C, then liquid nitrogen storage, allowed cryogenic storage of cells and successful re-culture up to 12 months in storage.