engleski

Characterization and differentiation of the oligotrophic waters by culturable particle-attached and free-living bacterial community

A tool based on cellular fatty acids of culturable heterotrophic bacterioplankton was developed in order to characterize and differentiate northern Adriatic, particularly oligotrophic high-salinity, waters. Variances in growing abilities and population dominance of particle-attached and free-living bacteria cultured in three media, Marine Broth, diluted Marine Broth (1:10) and R2 broth were used. Three groups of water layers were distinguished by Hierarchical clustering analysis: eutrophic, oligotrophic and oligotrophic nutrient-selected. Significance of the difference between resulting groups was tested by two-way ANOVA (with replication). Eutrophic layers were characterized by readily culturable particle attached and free-living fractions of the bacterial community in all three media, all dominated by fast-growing γ -Proteobacteria. In contrast, low productive, oligotrophic water layers were characterized by much weaker culturability, different population dominance of the free-living community in respect to attached counterpart or even growth arrest in response to all media. The free-living bacteria from "strictly" oligotrophic environments demonstrated minimum culturability in Marine Broth while that from selective oligotrophic environment were culturable and dominated either by Cytophaga-Flavobacter complex, α-Proteobacteria or γ-Proteobacteria. The conclusive evidence on selective and refractory nature of organic compounds in these waters bears the dominant culturability of Cytophaga-Flavobacter complex and α-Proteobacteria in free-living communities in all growth-media. Response in fatty acid dominance ratios significantly depends on trophic state and fraction (p < 0.05) although the effect of trophic state is completely different in attached and free fraction. In both fractions, tested separately, a significant influence of trophic state was present (p < 0.05), while effect of media on fatty acid response was insignificant (p > 0.05). A certain interaction between media and trophic status was present in attached fraction (p < 0.05), yet in free fraction it was not observed (p > 0.05), meaning that any systematic difference between trophic states is the same for each media tested. Accordingly, the free-living fraction of bacterioplankton is more informative attribute and can be used solely as an indicator of the water layer trophic condition.

Culturable bacteria ; Fatty acids ; northern Adriatic Sea ; Oligotrophic bacteria

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