Vivia Bruni

Crude oil‐induced structural shift of coastal bacterial communities of rod bay (Terra Nova Bay, Ross Sea, Antarctica) and characterization of cultured cold‐adapted hydrocarbonoclastic bacteria

For preliminary screening of human impact on Antarctic coasts, the compositions of microbial communities were analyzed in seawater at two sites located in the Terra Nova Bay of Antarctica (Ross Sea) by a combination of 16S rRNA gene sequencing and culture techniques. The bacterial community in the sample from the Rod Bay site, located at the proximity to the Italian Station, was characterized by a high abundance of 16S rRNA gene sequences belonging to the microflora typically found in soil and freshwater environments. In contrast, the seawater sample from the Adelie Cove station, a pristine reference site, contained 16S rRNA gene sequences typically found in marine areas affected by algal blooms and sea ice decay. The addition of crude oil to the Rod Bay seawater sample rapidly induced a shift in the composition of the bacterial community with appearance of novel taxonomic groups and a dramatic increase in the relative abundance of gamma-Proteobacteria sequences, whereas no significant changes were detected in the bacterial community of the Adelie Cove sample under the same conditions. Bacteria-exhibiting features with potential interest for industrial and environmental applications were isolated from the Rod Bay oil-enriched sample. In particular, hydrocarbon-degrading, cold-adapted bacteria were selectively enriched, isolated and screened for their ability to synthesize polyunsaturated fatty acids. Twenty two bacterial strains were isolated from the oil enrichment culture and identified. Eighteen isolates were found to be members of gamma-Proteobacteria, while the remainder were representatives of alpha-Proteobacteria, CFB and high G + C divisions.

Biodiversity of cultivable psychrotrophic marine bacteria isolated from Terra Nova Bay (Ross Sea, Antarctica)

A set of 146 Antarctic marine isolates from the Ross Sea was characterized by a combination of molecular techniques in order to determine the degree of inter- and intraspecific variability. Isolates were analyzed by amplified rDNA restriction analysis (ARDRA) using the tetrameric enzyme AluI, resulting in 52 different groups, corresponding to at least 52 different bacterial species, indicating a high degree of interspecific variability. The phylogenetic position of bacteria belonging to some ARDRA groups was obtained by sequencing of 16S rDNA. Random amplified polymorphic DNA (RAPD) analysis, carried out on the largest ARDRA groups, revealed a high intraspecific genetic variability, too. The analysis of plasmid content revealed the existence of horizontal gene transfer between strains belonging to the same and to different species. A comparison of the whole body of morphological, physiological and biochemical data was finally carried out.

Phylogenetic characterization of the heterotrophic bacterial communities inhabiting a marine recirculating aquaculture system.

Aims:  The aim of the present work was to characterize the heterotrophic bacterial community of a marine recirculating aquaculture system (RAS).

Faecal pollution indicators in the Terra Nova Bay (Ross Sea, Antarctica)

The occurrence of faecal bacteria indicators (total coliforms, faecal coliforms and streptococci) in pristine waters and near Italian Base stations of the Terra Nova Bay was investigated. High bacterial densities were found at the station near to the outfall of the sewage disposal plant and when the population at Base was more abundant. In all other stations further from the outfall, the bacterial indicators were absent or present in very small numbers. Faecal bacteria were not detected in samples collected at pristine sites (Penguin Bay and Evans Cove) except for only 1 enterococcus per 100 ml at Evans Cove. In the seawater samples in which faecal coliforms and faecal streptococci were found, the latter were generally more abundant and in 4 samples only streptococci were isolated, although in low number. This could suggest that faecal streptococci are more suitable bacteria for investigation of the human impact on the Antarctic marine environment.

Marine Bacterioplankton Diversity and Community Composition in an Antarctic Coastal Environment

The bacterial community inhabiting the water column at Terra Nova Bay (Ross Sea, Antarctica) was examined by the fluorescent in situ hybridization (FISH) technique and the genotypic and phenotypic characterization of 606 bacterial isolates. Overall, the FISH analysis revealed a bacterioplankton composition that was typical of Antarctic marine environments with the Cytophaga/Flavobacter (CF) group of Bacteroidetes that was equally dominant with the Actinobacteria and Gammaproteobacteria. As sampling was performed during the decay of sea-ice, it is plausible to assume the origin of Bacteroidetes from the sea-ice compartment where they probably thrive in high concentration of DOM which is efficiently remineralized to inorganic nutrients. This finding was supported by the isolation of Gelidibacter, Polaribacter, and Psychroflexus members (generally well represented in Antarctic sea-ice) which showed the ability to hydrolyze macromolecules, probably through the production of extracellular enzymes. A consistently pronounced abundance of the Gammaproteobacteria (67.8%) was also detected within the cultivable fraction. Altogether, the genera Psychromonas and Pseudoalteromonas accounted for 65.4% of total isolates and were ubiquitous, thus suggesting that they may play a key role within the analyzed bacterioplankton community. In particular, Pseudoalteromonas isolates possessed nitrate reductase and were able to hydrolyze substrates for protease, esterase, and β-galactosidase, thus indicating their involvement in the carbon and nitrogen cycling. Finally, the obtained results highlight the ability of the Actinobacteria to survive and proliferate in the Terra Nova Bay seawater as they generally showed a wide range of salt tolerance and appeared to be particularly competitive with strictly marine bacteria by better utilizing supplied carbon sources.

Vertical and temporal microbial community patterns in a meromictic coastal lake influenced by the Straits of Messina upwelling system

The vertical and temporal dynamics of total picoplankton, heterotrophic nanoflagellates and ciliates were monitored monthly from May 2002 to April 2003, along with environmental parameters, in Lake Faro, a meromictic coastal basin characterized by a permanently anoxic monimolimnion and sulfide-rich bottom waters. A two-layer discrimination was delineated in the water column of the lake, based on the correlations between environmental and biological descriptors and on the ciliated protozoa community composition. The latter showed a clear zonation pattern along the water column with two main recognizable facies: a superficial and a deep one. Choreotrichida and Strombidiida dominated the upper facies nearly throughout the study period, while Tintinnida were only found in summer months. The mixotrophic cyclotrichid Myrionecta rubra was also frequently observed in the upper facies. Typical of the deep facies was the occurrence of Pleuronematida (Cyclidium sp.) and of flagellates of the order Cryptomonadida (Chilomonas sp.), which were the main potential picoplankton grazers during a summer bloom of photosynthetic sulfur bacteria. Sporadic inputs of Levantine Intermediate Waters (LIW) from the upwelling system of the Straits of Messina, although limited to the mixolimnion, clearly affected the physical and chemical environment, as well as the microbial biomass and the ciliated protozoa assemblage composition, all along the water column of the lake, suggesting that meromictic basins, although strongly stratified, may experience perturbation effects from the surface down to the bottom, with important consequences on their biogeochemical cycles and on their ecology.

Lipolytic activity of Antarctic cold-adapted marine bacteria (Terra Nova Bay, Ross Sea)

Aims:  The aim of this study was to investigate the lipolytic activity of cold‐adapted Antarctic marine bacteria and, furthermore, the combined effect of some environmental factors on this enzymatic process.

Predation impact of ciliated and flagellated protozoa during a summer bloom of brown sulfur bacteria in a meromictic coastal lake.

Anaerobic phagotrophic protozoa may play an important role in the carbon flux of chemically stratified environments, especially when phototrophic sulfur bacteria account for a high proportion of the primary production. To test this assumption, we investigated the vertical and temporal distribution of microbial heterotrophs and of autotrophic picoplankton throughout the water column of the meromictic coastal lake Faro (Sicily, Italy), in the summer of 2004, coinciding with a bloom of brown-colored green sulfur bacteria. We also assessed the grazing impact of ciliated and flagellated protozoa within the sulfur bacteria plate using a modification of the fluorescently labeled bacteria uptake approach, attempting to minimize the biases intrinsic to the technique and to preserve the in situ anoxic conditions. Significant correlations were observed between ciliate biomass and bacteriochlorophyll e concentration, and between heterotrophic nanoflagellate biomass and chlorophyll a concentration in the water column. The major predators of anaerobic picoplankton were pleuronematine ciliates and cryptomonad flagellates, with clearances of 26.6 and 9.5 nL per cell h(-1), respectively, and a cumulative impact on the picoplankton gross growth rate ranging between 36% and 72%. We concluded that protozoan grazing channels a large proportion of anaerobic picoplankton production to higher trophic levels without restraining photosynthetic bacteria productivity.

Occurrence and characterization of psychrotolerant hydrocarbon-oxidizing bacteria from surface seawater along the Victoria Land coast (Antarctica)

A total of 253 hydrocarbon-oxidizing bacterial isolates were achieved from eight Antarctic surface seawater samples enriched on diesel oil at 4°C. Isolates were screened by amplified ribosomal DNA restriction analysis prior to 16S rRNA gene sequencing. Sequences were compared to those in available databases using the Basic Local Alignment Search Tool network service to determine their approximate phylogenetic affiliations. The majority of the isolates were affiliated to the Actinobacteria (75.9%) and the Gamma-Proteobacteria (22.9%). The Alpha- and Beta-Proteobacteria represented 0.8 and 0.4% of total isolates, respectively. The Actinobacteria were predominantly allocated to the genera Arthrobacter, Cryobacterium and Rhodococcus. The Gamma-Proteobacteria were mainly found to be related to the genus Pseudomonas. Conversely, the Alpha- and Beta-Proteobacterial isolates shared the highest degree of sequence identity with unclassified bacteria. Differences in the distribution of the detected phylotypes were observed among the analyzed samples. Isolates representing each phylotype were selected for further characterization, including phenotypic assays and screening for the growth ability in the presence of individual hydrocarburic substrates as the sole supplied carbon and energy source. Isolates possessed different patterns of substrate utilization. Aliphatic hydrocarbons supported the growth of a higher number of isolates than aromatics. Results confirm the ability of our Antarctic marine bacteria to utilize hydrocarbons at low temperature and therefore suggesting that isolates with different substrate specificities can act in nature as a consortium in the utilization of complex hydrocarburic mixtures.

Prokaryotic activities and abundance in pelagic areas of the Ionian Sea

The Ionian Sea represents a suitable basin for studying the biogeochemical processes mediated by microbial activities. Because of its characteristics as a crossing region between the western and eastern Mediterranean Sea, it is one of the sites most affected by changes in water mass composition and dynamics, caused by the Eastern Mediterranean Transient (EMT). To date, relatively few data exist on microbial activities in pelagic areas of the Ionian Sea. From 1998 to 2004, during different research cruises, prokaryotic parameters (abundance, extracellular enzyme activities leucine aminopeptidase, β-glucosidase, alkaline phosphatase, bacterial production and respiration) were measured together with culturable bacteria and the main physical, chemical and trophic parameters (temperature, salinity, nutrients, particulated organic matter). The aim of the study was to describe the spatial and temporal variability in microbial activities involved in the carbon and phosphorus cycles, in different layers. Results showed that organic matter transformation mediated by the microbial community displayed a significant increase in autumn, highlighting the occurrence of significant changes at meso- and bathypelagic depths. Unlike the dark ocean, bacterial growth efficiency in the Ionian Sea, which increased with depth, seemed to vary from being a source of carbon in the epipelagic layer to a sink in the meso- and bathypelagic layers. The mechanism of phosphatase regulation showed a weak inverse correlation between specific phosphatase and inorganic P in all seasons except autumn. It is worth mentioning that the reported results constitute, to the best of our knowledge, one of the available datasets giving information about microbial activities in the Ionian Sea.