Extreme marine habitats are inhabited by diverse microorganisms which have developed a wide variety of adaptations to help them succeed in these challenging environments. Microorganisms isolated from harsh environments are a rich source of new and stable enzymes with unique properties that could improve industrial processes and make them more economical and environmentally friendly. In this study, we isolated and examined bacteria capable of surviving in eutrophic sea pit. We further examined the microbial capacity to synthesize hydrolytic enzymes and antimicrobial compounds of biotechnological or medical interest.
We investigated microbial diversity in an underwater sea pit piled with ~15 m high Posidonia oceanica waste biomass that has accumulated for over a century. The pit is located in the central Eastern Adriatic; the entrance to the pit is located 7 m below the sea surface and the bottom of the pit is at 32 m below the surface level. The degree of biomass decomposition increases towards the bottom of the pit (Fig. 1A). The samples of the degrading biomass were collected at 19 m and 29 m depth and incubated at 16 °C on 13 different solid media to recover culturable microbes adapted to this niche. Isolates were identified using either MALDI-TOF MS or 16S rDNA and were tested for antibacterial and antifungal activity. Different extracellular enzymatic activities of isolates were assessed with specific substrates for proteases, esterases, lipases, amylases, cellulases, and chitinases. Out of 298 cultivable isolates across 13 media, 67 isolates exhibited 99% 16S rRNA gene sequence identity to Alcanivorax borkumensis (γ-proteobacteria). Analysis of rpoB sequences from four Alcanivorax isolates displayed 90% similarity to A. borkumensis suggesting so far unreported species. This genus is known to thrive on petroleum and is therefore useful for biodegradation of oil spills. Our isolates showed strong esterase and lipase activities. This microorganism can tolerate up to 10% salt in medium supplemented with 1% of oil and form specific mold-like hydrophobic clumps at the liquid medium surface. Confocal time-lapse microscopy has shown that this bacterium can colonize oil droplets more rapidly than A. borkumensis (Fig. 1B). Different assays revealed capacity of this bacterium to degrade various hydrocarbon substrates. The currently ongoing whole genome sequencing will reveal a more complete arsenal of enzymes associated with oil bioremediation and other metabolic processes.