Ammonia- and Nitrite-Oxidizing Bacterial Communities in a Pilot-Scale Chloraminated Drinking Water Distribution System

Nitrification in drinking water distribution systems is a common operational problem for many utilities that use chloramines for secondary disinfection. The diversity of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) in the distribution systems of a pilot-scale chloraminated drinking water treatment system was characterized using terminal restriction fragment length polymorphism (T-RFLP) analysis and 16S rRNA gene (ribosomal DNA [rDNA]) cloning and sequencing. For ammonia oxidizers, 16S rDNA-targeted T-RFLP indicated the presence of Nitrosomonas in each of the distribution systems, with a considerably smaller peak attributable to Nitrosospira-like AOB. Sequences of AOB amplification products aligned within the Nitrosomonas oligotropha cluster and were closely related to N. oligotropha and Nitrosomonas ureae. The nitrite-oxidizing communities were comprised primarily of Nitrospira, although Nitrobacter was detected in some samples. These results suggest a possible selection of AOB related to N. oligotropha and N. ureae in chloraminated systems and demonstrate the presence of NOB, indicating a biological mechanism for nitrite loss that contributes to a reduction in nitrite-associated chloramine decay.     

Tryptophanase-Positive Bacteria in the Marine Environment

The prevalence of indole-positive organisms in the gut and environment of marine animals was studied. Indole formation by a group of the isolates was found to occur only in the presence of tryptophan. The isolates examined were all assigned to the genus Vibrio.     

Influence of Inorganic Nitrogen Management Regime on the Diversity of Nitrite-Oxidizing Bacteria in Agricultural Grassland Soils

To assess links between the diversity of nitrite-oxidizing bacteria (NOB) in agricultural grassland soils and inorganic N fertilizer management, NOB communities in fertilized and unfertilized soils were characterized by analysis of clone libraries and denaturing gradient gel electrophoresis (DGGE) of 16S rRNA gene fragments. Previously uncharacterized Nitrospira-like sequences were isolated from both long-term-fertilized and unfertilized soils, but DGGE migration patterns indicated the presence of additional sequence types in the fertilized soils. Detailed phylogenetic analysis of Nitrospira-like sequences suggests the existence of one newly described evolutionary group and of subclusters within previously described sublineages, potentially representing different ecotypes; the new group may represent a lineage of noncharacterized Nitrospira species. Clone libraries of Nitrobacter-like sequences generated from soils under different long-term N management regimes were dominated by sequences with high similarity to the rhizoplane isolate Nitrobacter sp. strain PJN1. However, the diversity of Nitrobacter communities did not differ significantly between the two soil types. This is the first cultivation-independent study of nitrite-oxidizing bacteria in soil demonstrating that nitrogen management practices influence the diversity of this bacterial functional group.     

Microbial Symbiosis: Patterns of Diversity in the Marine Environment

SYNOPSIS. Symbiotic associations expand both the diversity ofpotential ecological niches and metabolic capabilities of thehost—symbiont combinations. Symbioses can also be consideredto have evolutionary potential in that the partnership can resultin a "new organism." Associations between chemoautotrophic bacteriaand marine invertebrates, discovered only 10 years ago, arenow found widely in nature, in habitats ranging from deep-seahydrothermal vents to coastal sediments. Here I review chemoautotroph—invertebrateassociations and discuss the benefits inferred for both partnerswith regard to the diversity of these symbioses in nature.     

Enumeration of Viable Bacteria in the Marine Pelagic Environment

The low percentage of living bacteria commonly obtained when comparing viable counts with total direct counts in seawater could be due more to inappropriate techniques for appreciating the growth ability of living cells than to unadapted culture conditions. The most-probable-number counts in filtered seawater cultures and the microscopic counts of 4(prm1),6-diamidino-2-phenylindole (DAPI)-stained aggregate-forming units grown on black polycarbonate filters appeared significantly correlated to the direct counts. Both these techniques show that in the superficial and intermediate water masses, the living cells may constitute an important (frequently higher than 20%) but highly variable part of the total populations. These viable counts appear more realistic than the conventional CFU counts, which provide only 0.001 to 0.2% of the total counts.     

Diversity and Detection of Nitrate Assimilation Genes in Marine Bacteria

A PCR approach was used to construct a database of nasA genes (called narB genes in cyanobacteria) and to detect the genetic potential for heterotrophic bacterial nitrate utilization in marine environments. A nasA-specific PCR primer set that could be used to selectively amplify the nasA gene from heterotrophic bacteria was designed. Using seawater DNA extracts obtained from microbial communities in the South Atlantic Bight, the Barents Sea, and the North Pacific Gyre, we PCR amplified and sequenced nasA genes. Our results indicate that several groups of heterotrophic bacterial nasA genes are common and widely distributed in oceanic environments.     

Assessment of Three Methods for Detection and Quantification of Nitrite-Oxidizing Bacteria and Nitrobacter in Freshwater Sediments (MPN-PCR, MPN-Griess, Immunofluorescence)

Abstract Nitrification in freshwater, a key process in the nitrogen cycle, is now well known to take place predominantly on suspended particles and in sediment. Nitrobacter is the most commonly isolated nitrite oxidizing bacteria from water environments. Three methods for counting nitrite oxidizing communities (especially Nitrobacter) in sediment were investigated: MPN-Griess, fluorescent antibodies (immunofluorescence), and a more recent molecular method coupling specific DNA amplification by PCR and statistical MPN quantification. After preliminary adjustments of the MPN-PCR technique, the detection level and the yield of each method were determined by inoculating a sediment with a pure Nitrobacter culture. The best recovery yield was obtained with the immunofluorescence technique (21.3%) and the lowest detection level was reached with the MPN-Griess method (10³ Nitrobacter/g dry weight sediment). The MPN-PCR method resulted in the lowest recovery yields and needs further adaptation to become a reliable and precise tool for investigations of nitrifying bacteria in sediment. Received: 6 July 1998; Accepted: 17 December 1998     

Viral Contribution to Dissolved DNA in the Marine Environment as Determined by Differential Centrifugation and Kingdom Probing

Dissolved or filterable (<0.2-(mu)m-pore-size filter) DNA is a ubiquitous component of the dissolved organic matter in the surface waters of this planet. In an effort to understand the composition and possible sources, we subjected dissolved DNA concentrated by vortex flow filtration from offshore and coastal environments to differential centrifugation and probing with 16S rRNA-targeted kingdom oligonucleotide probes. Initial studies with calf thymus soluble DNA and T2 phage particles indicated that high-speed ultracentrifugation (201,000 x g for 90 min), a method to separate viral particles from soluble DNA used by other investigators, resulted in pelleting of nearly all the DNA and virus particles. Lower-speed centrifugation (11,200 to 25,800 x g for 90 min) resulted in >99% of the virus particles being collected in the pellet and (equiv)65% of the calf thymus DNA remaining in the supernatant. Employing this approach, we estimate that approximately 50% of the filterable DNA from marine environments is truly soluble or free DNA and that the other half is composed of bound forms (viral particles and, potentially, colloids). Of the bound form, 17 to 30% could be accounted for by viral particles, by calculating the amount of viral DNA on the basis of viral abundance, leaving a portion of the bound form uncharacterized. Kingdom probing with universal, eubacterial, and eucaryotic probes indicated that dissolved DNA hybridized with all of these probes, while purified standard viral DNAs did not, or hybridized only slightly with the universal probe (tailed oligonucleotide only). Collectively, these data indicate that DNA in viral particles is a small component of the dissolved DNA, the majority being of eubacterial and eucaryotic origin.     

Physiological Properties of Nitrogen-scavenging Bacteria from the Marine Environment

Nine selected strains of marine bacteria from the marine environment, although taxonomically heterogeneous in character, exhibited a capacity for prolonged growth on 'nitrogen-free' media; only one strain, a Klebsiella sp., fixed dinitrogen under any of a considerable range of test conditions. The non-nitrogen-fixing bacteria were able to scavenge low levels of nitrogenous materials, principally ammonia, from the atmosphere. Contrary to previous suggestions, this growth did not have an abnormally low cellular protein and nitrogen content. Some strains with apparently low intracellular protein contents, as determined on a cellular dry weight basis, showed accumulations of carbonaceous storage products which distorted the cytochemical analyses. Representative strains grown in chemostat culture showed a high affinity (i.e. low Ks values—0.35–0.52 μmol/1) for the NH₄+ ion, compared with Escherichia coli (1.75 μmol/1) and preliminary studies of their glutamine synthetases suggested that the affinities ( K_m values—0.25–0.29 μmol/1) of this enzyme for hydroxylamine were similar to the few values reported for other marine bacteria.     

Diversity and Metabolism of Marine Bacteria Cultivated on Dissolved DNA

Dissolved DNA (dDNA) is a potentially important source of energy and nutrients in aquatic ecosystems. However, little is known about the identity, metabolism, and interactions of the microorganisms capable of consuming dDNA. Bacteria from Eel Pond (Woods Hole, MA) were cultivated on low-molecular-weight (LMW) or high-molecular-weight (HMW) dDNA, which served as the primary source of carbon, nitrogen, and phosphorus. Cloning and sequencing of 16S rRNA genes revealed that distinct bacterial assemblages with comparable levels of taxon richness developed on LMW and HMW dDNA. Since the LMW and HMW dDNA used in this study were stoichiometrically identical, the results confirm that the size alone of dissolved organic matter can influence bacterial community composition. Variation in the growth and metabolism of isolates provided insight into mechanisms that may have generated differences in bacterial community composition. For example, bacteria from LMW dDNA enrichments generally grew better on LMW dDNA than on HMW dDNA. In contrast, bacteria isolated from HMW dDNA enrichments were more effective at degrading HMW dDNA than bacteria isolated from LMW dDNA enrichments. Thus, marine bacteria may experience a trade-off between their ability to compete for LMW dDNA and their ability to access HMW dDNA via extracellular nuclease production. Together, the results of this study suggest that dDNA turnover in marine ecosystems may involve a succession of microbial assemblages with specialized ecological strategies.     

Diversity of Thiosulfate-Oxidizing Bacteria from Marine Sediments and Hydrothermal Vents

Species diversity, phylogenetic affiliations, and environmental occurrence patterns of thiosulfate-oxidizing marine bacteria were investigated by using new isolates from serially diluted continental slope and deep-sea abyssal plain sediments collected off the coast of New England and strains cultured previously from Galapagos hydrothermal vent samples. The most frequently obtained new isolates, mostly from 10³- and 10⁴-fold dilutions of the continental slope sediment, oxidized thiosulfate to sulfate and fell into a distinct phylogenetic cluster of marine alpha-Proteobacteria. Phylogenetically and physiologically, these sediment strains resembled the sulfate-producing thiosulfate oxidizers from the Galapagos hydrothermal vents while showing habitat-related differences in growth temperature, rate and extent of thiosulfate utilization, and carbon substrate patterns. The abyssal deep-sea sediments yielded predominantly base-producing thiosulfate-oxidizing isolates related to Antarctic marine Psychroflexus species and other cold-water marine strains of the Cytophaga-Flavobacterium-Bacteroides phylum, in addition to gamma-proteobacterial isolates of the genera Pseudoalteromonas and Halomonas-Deleya. Bacterial thiosulfate oxidation is found in a wide phylogenetic spectrum of Flavobacteria and Proteobacteria.     

Diversity Dynamics of Marine Bacteria Studied by Immunofluorescent Staining on Membrane Filters

Of 34 strains of marine bacteria isolated on a general seawater medium, 5 were selected for detailed studies of their population dynamics in the plankton. The isolates were characterized as Aeromonas sp., Chromobacterium cf. lividum, Vibrio sp., and two Pseudomonas spp. Specific antibodies were produced by immunization of rabbits, and bacterial cells were stained on black Uni-Pore membrane filters by an indirect immunofluorescent staining procedure. The method proved to be very specific and practical for use in a large-scale field sampling program. Growth of all five isolates was stimulated by high values for net primary production, chlorophyll a, and dissolved organic carbon. Calculation of a diversity index based on specific and total counts is proposed as a way of characterizing the dynamics of organotrophic bacterial populations in the sea.     

Ubiquitous Dissolved Inorganic Carbon Assimilation by Marine Bacteria in the Pacific Northwest Coastal Ocean as Determined by Stable Isotope Probing

In order to identify bacteria that assimilate dissolved inorganic carbon (DIC) in the northeast Pacific Ocean, stable isotope probing (SIP) experiments were conducted on water collected from 3 different sites off the Oregon and Washington coasts in May 2010, and one site off the Oregon Coast in September 2008 and March 2009. Samples were incubated in the dark with 2 mM ¹³C-NaHCO₃, doubling the average concentration of DIC typically found in the ocean. Our results revealed a surprising diversity of marine bacteria actively assimilating DIC in the dark within the Pacific Northwest coastal waters, indicating that DIC fixation is relevant for the metabolism of different marine bacterial lineages, including putatively heterotrophic taxa. Furthermore, dark DIC-assimilating assemblages were widespread among diverse bacterial classes. Alphaproteobacteria, Gammaproteobacteria, and Bacteroidetes dominated the active DIC-assimilating communities across the samples. Actinobacteria, Betaproteobacteria, Deltaproteobacteria, Planctomycetes, and Verrucomicrobia were also implicated in DIC assimilation. Alteromonadales and Oceanospirillales contributed significantly to the DIC-assimilating Gammaproteobacteria within May 2010 clone libraries. 16S rRNA gene sequences related to the sulfur-oxidizing symbionts Arctic96BD-19 were observed in all active DIC assimilating clone libraries. Among the Alphaproteobacteria, clones related to the ubiquitous SAR11 clade were found actively assimilating DIC in all samples. Although not a dominant contributor to our active clone libraries, Betaproteobacteria, when identified, were predominantly comprised of Burkholderia. DIC-assimilating bacteria among Deltaproteobacteria included members of the SAR324 cluster. Our research suggests that DIC assimilation is ubiquitous among many bacterial groups in the coastal waters of the Pacific Northwest marine environment and may represent a significant metabolic process.     

Identification and Enumeration of Marine Chroococcoid Cyanobacteria by Immunofluorescence

We used an indirect immunofluorescence technique to permit the identification and enumeration of individual or closely related strains of chroococcoid cyanobacteria of the general Synechococcus and Synechocystis in natural seawater samples. Antisera directed against each of five strains (two phycoerythrin-containing Synechococcus strains, two phycocyanin-containing Synechococcus strains, and one Synechocystis strain) were produced and tested for cross-reactions with cultures of a variety of cyanobacteria and representatives of other algae and bacteria. Each antiserum was relatively specific. The observed cross-reactions occurred between strains that were isolated from similar oceanic environments. We were able, therefore, to apply this technique to field samples. Preliminary results for April to December 1982 in Great South Bay, New York, show that Synechocystis populations are present only during spring and summer, phycocyanin-containing Synechococcus strains are only a minor component in the spring and summer, and phycoerythrin-containing Synechococcus populations become significant in summer and remain so until late fall or winter.     

Isolation and Characterization of Methanesulfonic Acid-Degrading Bacteria from the Marine Environment

Two methylotrophic bacterial strains, TR3 and PSCH4, capable of growth on methanesulfonic acid as the sole carbon source were isolated from the marine environment. Methanesulfonic acid metabolism in these strains was initiated by an inducible NADH-dependent monooxygenase, which cleaved methanesulfonic acid into formaldehyde and sulfite. The presence of hydroxypyruvate reductase and the absence of ribulose monophosphate-dependent hexulose monophosphate synthase indicated the presence of the serine pathway for formaldehyde assimilation. Cell suspensions of bacteria grown on methanesulfonic acid completely oxidized methanesulfonic acid to carbon dioxide and sulfite with a methanesulfonic acid/oxygen stoichiometry of 1.0:2.0. Oxygen electrode-substrate studies indicated the dissimilation of formaldehyde to formate and carbon dioxide for energy generation. Carbon dioxide was not fixed by ribulose bisphosphate carboxylase. It was shown that methanol is not an intermediate in methanesulfonic acid metabolism, although these strains grew on methanol and other one-carbon compounds, as well as a variety of heterotrophic carbon sources. These two novel marine facultative methylotrophs have the ability to mineralize methanesulfonic acid and may play a role in the cycling of global organic sulfur.     

Phylogenetic Diversity of Bacteria Associated with the Marine Sponge Rhopaloeides odorabile

Molecular techniques were employed to document the microbial diversity associated with the marine sponge Rhopaloeides odorabile. The phylogenetic affiliation of sponge-associated bacteria was assessed by 16S rRNA sequencing of cloned DNA fragments. Fluorescence in situ hybridization (FISH) was used to confirm the presence of the predominant groups indicated by 16S rDNA analysis. The community structure was extremely diverse with representatives of the Actinobacteria, low-G+C gram-positive bacteria, the β- and γ-subdivisions of the Proteobacteria, Cytophaga/Flavobacterium, green sulfur bacteria, green nonsulfur bacteria, planctomycetes, and other sequence types with no known close relatives. FISH probes revealed the spatial location of these bacteria within the sponge tissue, in some cases suggesting possible symbiotic functions. The high proportion of 16S rRNA sequences derived from novel actinomycetes is good evidence for the presence of an indigenous marine actinomycete assemblage in R. odorabile. High microbial diversity was inferred from low duplication of clones in a library with 70 representatives. Determining the phylogenetic affiliation of sponge-associated microorganisms by 16S rRNA analysis facilitated the rational selection of culture media and isolation conditions to target specific groups of well-represented bacteria for laboratory culture. Novel media incorporating sponge extracts were used to isolate bacteria not previously recovered from this sponge.     

Diversity of Bacteria in the Marine Sponge Aplysina fulva in Brazilian Coastal Waters

Microorganisms can account for up to 60% of the fresh weight of marine sponges. Marine sponges have been hypothesized to serve as accumulation spots of particular microbial communities, but it is unknown to what extent these communities are directed by the organism or the site or occur randomly. To address this question, we assessed the composition of specific bacterial communities associated with Aplysina fulva, one of the prevalent sponge species inhabiting Brazilian waters. Specimens of A. fulva and surrounding seawater were collected in triplicate in shallow water at two sites, Caboclo Island and Tartaruga beach, Búzios, Brazil. Total community DNA was extracted from the samples using “direct” and “indirect” approaches. 16S rRNA-based PCR-denaturing gradient gel electrophoresis (PCR-DGGE) analyses of the total bacterial community and of specific bacterial groups—Pseudomonas and Actinobacteria—revealed that the structure of these assemblages in A. fulva differed drastically from that observed in seawater. The DNA extraction methodology and sampling site were determinative for the composition of actinobacterial communities in A. fulva. However, no such effects could be gleaned from total bacterial and Pseudomonas PCR-DGGE profiles. Bacterial 16S rRNA gene clone libraries constructed from directly and indirectly extracted DNA did not differ significantly with respect to diversity and composition. Altogether, the libraries encompassed 15 bacterial phyla and the candidate division TM7. Clone sequences affiliated with the Cyanobacteria, Chloroflexi, Gamma- and Alphaproteobacteria, Actinobacteria, Bacteroidetes, and Acidobacteria were, in this order, most abundant. The bacterial communities associated with the A. fulva specimens were distinct and differed from those described in studies of sponge-associated microbiota performed with other sponge species.The phylum Porifera (sponges) consists of benthic (sessile) organisms that occur primarily in marine environments at different depths (26). Sponges are classified into three groups, namely, the Calcarea (calcareous sponges), Hexactinellida (glass sponges), and Demospongiae (5, 26). The group Demospongiae, also called demosponges, encompasses 95% of the ca. 5,500 living sponge species described thus far (5). As typical filter feeders, demosponges are the prime bacterial filters of the sea. They are capable of pumping thousands of liters of water per day (23), using prokaryotic microorganisms as the main source of food (1, 43, 47). In addition to demosponges feeding on microorganisms, the presence of bacteria in high density in internal sponge layers (mesohyl) indicates that a selective process favoring particular prokaryotes, involving microbe-sponge interactions, is likely to occur (64). Furthermore, the dawn of the interactions between Prokarya and higher organisms may actually lie in the demosponges, whose origin is estimated to date back to 550 million years ago (5, 33).Putative interactions between demosponges and microorganisms, presumably mostly consisting of Bacteria and Archaea, were first demonstrated by transmission electron microscopy (TEM), where high amounts of microorganisms were observed in the mesohyl (1, 14, 16, 64). Hence, these bacterium-rich sponges have been termed “bacteriosponges” (46). While investigating 11 taxonomically different demosponges using TEM, Vacelet and Donadey (64) identified two different sponge types in respect of their association with bacteria. Sponges with thick mesohyl contained abundant, dense, and morphologically diverse microbial communities (i.e., bacteriosponge), while those with a well-developed aquiferous system and low-density mesohyl contained few bacterial cells and typically only single bacterial morphotypes. The two types have recently been called “high-microbial-abundance” (HMA) and “low-microbial-abundance” (LMA) sponges, respectively (23). In HMA sponges, bacterial densities may reach 10⁸ to 10¹⁰ bacterial cells per g (wet weight) of sponge, exceeding seawater concentrations by 2 to 4 orders of magnitude (15, 23). Based on the analysis of 16S rRNA genes, over 15 bacterial phyla have thus far been reported to occur in association with marine sponges (11, 23, 56). Among these are typical sponge-associated bacteria such as members of the Cyanobacteria, Chloroflexi, Proteobacteria, Acidobacteria, Verrucomicrobia, and the candidate phyla “Poribacteria” and TM6 (14, 30, 51, 56, 60, 68).Increasing research interest in the sponge-associated microbiota has emerged in the past few years, mainly due to the in spongium production of an enormous diversity of biologically active secondary metabolites (56). Recent studies suggest that certain bioactive compounds retrieved from marine sponges—such as complex polypeptides and nonribosomal peptides—are likely to be synthesized by the symbiont bacteria (27, 41, 42). Such bioactive secondary metabolites offer great promise for use in biotechnology and medicine (3, 22, 27, 41, 42, 51, 59). In particular, cytotoxic compounds, i.e., antitumoral substances and polyketides, may find application in anticancer therapies (13, 42, 51). Recent investigations revealed the presence of dibromotyrosine-derived metabolites in Aplysina fulva (Pallas, 1766) specimens collected along the Brazilian shore (39). However, a putative role of microbial symbionts in the production of such metabolites, commonly found to display biological activity, remains to be evaluated.Despite the global-scale occurrence of sponges in Earth''s marine ecosystems, the investigation of their associated bacterial communities has thus far been restricted only to certain areas (1, 11, 13, 14, 27, 54, 58, 68). To our knowledge, no studies have been conducted, to date, on sponge-associated microbes in subtropical, South Atlantic open shore waters. In the present study, we assess the diversity and composition of the bacterial community associated with the demosponge A. fulva collected at two different sites at the Brazilian shore. A suite of tools, ranging from plate count estimations and TEM to sponge DNA-based analyses of bacterial 16S rRNA genes, was used. We hypothesized that a distinct bacterial community occurs in A. fulva, which is different from that in the surrounding bulk water, as well as from those in other sponge species.     

Isolation of Marine Bacteria by In Situ Culture on Media-Supplemented Polyurethane Foam

Polyurethane foam (PUF) supplemented with various agar media was used in situ to trap marine bacteria and it consequently provided a substrate on which they could be cultivated while exposed to natural seawater in the coral reef area. The bacterial population on the PUF blocks was analyzed by denaturing gradient gel electrophoresis (DGGE) of polymerase chain reaction (PCR)-amplified 16S rDNA fragments. Changing the composition of the cultivation medium in the PUF blocks and selecting different sampling sites resulted in different bacteria being detected on the PUF blocks. For example, iron-utilizing (IU) bacteria, siderophore-producing (SP) bacteria, and petroleum-degrading (PD) bacteria were isolated from PUF blocks and it was discovered that IU and SP contained iron and PD contained hydrocarbon. This method opens up the possibility for isolating novel and useful marine bacteria.     

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.