This report describes the metabolism of 6,10,14-trimethylpentadecan-2-one by a denitrifying bacterium (Marinobacter sp. strain CAB) isolated from marine sediments. Under aerobic and denitrifying conditions, this strain efficiently degraded this ubiquitous isoprenoid ketone. Several bacterial metabolites, 4,8,12-trimethyltridecan-1-ol, 4,8,12-trimethyltridecanal, 4,8,12-trimethyltridecanoic acid, Z-3,7-dimethylocten-2-oic acid, Z-3,7,11-trimethyldodecen-2-oic acid, and 6,10,14-trimethylpentadecan-2-ol, were formally identified, and different pathways were proposed to explain the formation of such isoprenoid compounds.
Using cell suspension ability as an indicator, we studied the inhibitory effect of garlic (Allium sativum) and diallyl trisulfide on six species of red tide causing algae. This included: the inhibition by 0.08% garlic solution of five algal species -Alexandrium tamarense, Scrippsiella trochoidea, Alexandrium catenella, Alexandrium minutum and Alexandrium satoanum; the effects of garlic concentration on the inhibition of A. tamarense, S. trochoidea and Chaetoceros sp.; the effects of inhibitory time on the rejuvenation of algal cells; and the effects of heating and preservation time on algal inhibition by garlic solution. In addition, whether or not the ingredients of garlic solution had a possible algicidal effect was studied by comparing inhibition of A. tamarense by garlic solution and man-made diallyl trisulfide. The results showed that 1) inhibition by garlic solution was significant on A. tamarense, A. satoanum, A. catenella and S. trochoidea, and the least effective was a concentration of 0.04% on A. tamarense and S. trochoidea. Moreover, the higher the concentration, the stronger was the inhibition, and a high inhibitory rate (IR) could be maintained for at least three days when the garlic concentration was above 0.04%. For A. tamarense, it was also found that the longer the inhibitory time and the higher the concentration, the lower was the rate of resumed cell activity. On the contrary, garlic solution could not inhibit A. minutum or Chaetoceros sp.; 2) The IR to A. tamarense was reduced slightly as the heating time of the garlic solution was lengthened, but the average IR was still above 80%. There was no significant difference between the IR of the supernatant and sediment of the garlic solution. Furthermore, no change of algal inhibition was found when the garlic solution was preserved at 20°C for several days; 3) As with garlic solution, diallyl trisulfide inhibited A. tamarense strongly; the IR was above 93% and was maintained for at least three days, as long as the concentration was 3.2-10.0 mg L −1 . Thus, diallyl trisulfide may have been the major ingredient in garlic solution which inhibited the algae but, in addition, more than one ingredient may have been inhibiting the algae. In conclusion, garlic was a good algal inhibitor with many advantages, such as being common, cheap, non toxic and with high efficiency, and diallyl trisulfide, one of the components of garlic, was similarly effective in algal inhibition. It would be useful, therefore, to further study garlic as an environmentally friendly algal inhibitor.
The influence of specific phages on the population size of their host bacteria was studied using a model system of a selected phage and its host bacterium, identified as Aeromonas sp. isolated from a lagoon in the southern Baltic Sea. For all initial phage/host ratios (PBR [phage/bacterium ratio] of 0.1 to 100), phage and host abundances reached a ratio of about 5 to 50 within the first 8 h. Interestingly, this range of phage/bacterium ratios of a single phage-host system corresponds to the ratio of virus to bacterial abundance found in natural habitats. The proportion of sensitive cells containing mature phage particles increased in the first 4 h to 40%, and then decreased (at rates dependent on the initial ratio) within 12 h (initial PBR of 100), 48 h (initial PBR of 10 and 1) and 72 h (initial PBR of 0.1) to less than 1%. There was evidence for rapid development of immunity (probably pseudolysogeny), especially at high initial phage concentrations. After 96 h incubation, carbon, nitrogen and phosphorus were added to improve the nutritional state of the bacteria. Although nutrients were added to all treatments when phage/host ratios were nearly equal, quite different reactions were observed for the bacteria populations with different initial PBRs. Those with low initial PBRs showed the most pronounced increase.KEY WORDS: Phage-host system · Immunity · Lysogeny · Pseudolysogeny · Phage/bacterium ratio · Coexistence Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 35: [131][132][133][134][135][136][137][138][139] 2004 show that no simple relationship can be expected between phages and their hosts, especially not in natural mixed communities, which are subject to further regime factors (e.g. predation, starvation). The mechanisms of the relationship between phages and hosts can be elucidated by studying isolated phagehost systems under conditions closely resembling those in situ.In this paper we present experimental data on the coexistence of phages and their bacterial host population at various initial phage/host ratios (PBRs). To simulate a bloom situation, phages and bacteria of a model system were added at concentrations comparable to those common in eutrophic habitats. If phages comprise important loss factors at normal in situ abundances, a much higher phage concentration should eliminate or deplete its host population remarkably, although a predator-prey-type oscillation in a phagehost culture might occur. However, the development of resistance or immunity by the bacterial cells should modify the phage/host ratio. MATERIALS AND METHODSPhage-host system. The bacterial host and its phages were isolated from the Zingster Strom, part of a lagoon system in the southern Baltic Sea, where the concentration of bacteria during summer often exceeds 1 × 10 7 ml -1 . The host organism is a gram-negative rod of about 1.6 × 0.4 µm (Fig. 1). Based on results from the API 20NE test system (BioMérieux) and on partial 16S rDNA sequence data (1450 bp), it was identi...
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