Bacterial epiphytes of Gracilaria conferta were quantified. Saprophytic bacteria reached 350 times and agar degraders 25000 times higher numbers g-' algal wet wt on tissues infected with the 'white tips disease', as compared to healthy tissues. A bactenal inducing agent of the 'white tips disease' was detected. Addition of 102 to 103 cells of this isolate rnl-I medium led to increased rates of infection. This effect did not occur if the isolate was autoclaved before addition. The virulent bacteria could always be isolated from infected tissues. It frequently, but not always, infected G. conferta and should be regarded as a facultative parasite. Several factors influenced the disease development. Temperatures above 20°C, in combination with photon flux densities of more than 200 pE m-2 S-', increased the rate of infection. Relatively low amounts (more than 25 pg ml-') of certain organic nutrients (peptone and yeast extract) led to strong manifestations of the disease. Addition of agar did not cause any symptoms, while 5 mg I-' of the antibiotic rifampicin prevented the alga from being infected.
Since 1873, the waters at Helgoland Roads (sampling station "Kabeltonne") have been sampled daily to determine temperature and salinity. In 1962, microbiological parameters were determined for the first time to establish microbiological long-term studies on marine bacteria, starting with the colony-forming units (CFU). In the following years, several other microbiological parameters were integrated for different periods of time (e.g. activity parameters like ATP and ectoenzymatic activity, marine yeasts, oil-degrading bacteria, flagellates and molecular methods like PCR followed by denaturing gradient gel electrophoresis). To date, the total count of bacteria, flagellates and viruses have been acquired using fluorescent DNA dyes and epifluorescence microscopy. Here we present both a historical overview of the methods used and examples of results obtained over the past 40 years. Furthermore, we try to evaluate challenging new methods for marine microbial ecology, appropriate for long-term studies of marine bacteria.
Surfactants. Biosurfactants, Marine Microorganisms, Toxicity, M icrotoxEight synthetic and nine biogenetic surfactants were tested on their toxicity. Because o f their possible application as oil dispersants against oil slicks on sea. the test organisms used were marine microorganisms (mixed and pure cultures o f bacteria, microalgae, and protozoa). Bac terial growth was hardly effected or stimulated, whilst that o f algae and flagellates was re duced. All substances tested were biodegradaded in sea water. The bioluminescence o f Photobacter phosphoreum (M icrotox test) was the most sensitive test system used. A ranking shows that most biogenetic surfactants were less toxic than synthetic surfactants. N o toxicity could be detected with the glucose-lipid GL. produced by the marine bacterium Alcaligenes sp. MM 1.
Three bacterial strains of marine origin were isolated during a screening for biosurfactants among n-alkane degrading microorganisms. One strain - identified as Alcaligenes sp. MM 1 - produced a novel glucose lipid. In the case of Arthrobacter sp. EK 1 the well-known trehalose tetraester was found as major component. From another pure culture classified as Arthrobacter sp. SI 1, extracellular emulsifying agents with properties indicating high molecular weight substances were detected. Furthermore trehalose corynomycolates were found at up to 2 g/1. The isolated biosurfactants showed good interfacial and emulsifying properties.
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