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At least 19 recordsLinked to original sources
PubMed2006

Methylibium petroleiphilum gen. nov., sp. nov., a novel methyl tert-butyl ether-degrading methylotroph of the Betaproteobacteria.

A Gram-negative, rod-shaped, motile, non-pigmented, facultative aerobe that grew optimally at pH 6.5 and 30 degrees C (strain PM1T) was isolated for its ability to completely degrade the gasoline additive methyl tert-butyl ether. Analysis of the 16S rRNA gene sequence indicated that this bacterium was a member of the class Betaproteobacteria in the Sphaerotilus-Leptothrix group. The 16S rRNA gene sequence identity to other genera in this group, Leptothrix, Aquabacterium, Roseateles, Sphaerotilus, Ideonella and Rubrivivax, ranged from 93 to 96 %. The chemotaxonomic data including Q-8 as the major quinone, C16 : 1omega7c and C16 : 0 as the major fatty acids and a DNA G+C content of 69 mol%, support the inclusion of strain PM1T in the class Betaproteobacteria. It differed from other members of the Sphaerotilus-Leptothrix group by being a facultative methylotroph that used methanol as a sole carbon source, and by also being able to grow heterotrophically in defined media containing ethanol, toluene, benzene, ethylbenzene and dihydroxybenzoates as sole carbon sources. On the basis of the morphological, physiological, biochemical and genetic information, a new genus and species, Methylibium petroleiphilum gen. nov., sp. nov., is proposed, with PM1T (=ATCC BAA-1232T=LMG 22953T) as the type strain.

Base Composition↗
PubMed2005

Mitsuaria chitosanitabida gen. nov., sp. nov., an aerobic, chitosanase-producing member of the 'Betaproteobacteria'.

Four strains (3001(T), 2, 12 and 13), which were isolated as chitosanase-producing bacteria from soil from Matsue city (Japan), were studied phenotypically, genotypically and phylogenetically. Based on sequence analysis of 16S rRNA genes, DNA G+C content (67.4-69.2 mol%), quinone type (UQ-8), major fatty acid composition (3-OH 10:0, 3-OH 14:0) and other phylogenetic studies, strains 3001(T), 12 and 13 were found to occupy a separate position in the 'Betaproteobacteria'. Roseateles depolymerans, Rubrivivax gelatinosus and Ideonella dechloratans were their closest neighbours (93-95% 16S rRNA gene sequence similarity). The 16S rRNA gene sequence and other characteristics suggested that strain 2 belonged to the genus Flavobacterium. DNA-DNA hybridization experiments supported the conclusion that strains 3001(T), 12 and 13 were of the same species (72-78% DNA hybridization) and only distantly related to I. dechloratans and R. gelatinosus. It is proposed that strains 3001(T), 12 and 13 represent a novel genus and species for which the name Mitsuaria chitosanitabida gen. nov., sp. nov. is proposed. The type strain of Mitsuaria chitosanitabida is 3001(T) (=IAM 14711(T)=ATCC BAA-476(T)).

Bacteria, Aerobic↗
PubMed2006

Methyloversatilis universalis gen. nov., sp. nov., a novel taxon within the Betaproteobacteria represented by three methylotrophic isolates.

The taxonomic positions and phylogenetic relationships of two new methylotrophic isolates from Lake Washington (USA) sediment, FAM5T and 500, and the previously described methylotrophic strain EHg5 isolated from contaminated soil in Estarreja (Portugal) were investigated. All three strains were facultative methylotrophs capable of growth on a variety of C1 and multicarbon compounds. Optimal growth occurred at pH 7.5-8 and 30-37 degrees C. The major fatty acids were C16:1omega7c and C16:0. The major quinone was ubiquinone Q8. Neither methanol dehydrogenase nor methanol oxidase activities were detectable in cells grown on methanol, suggesting an alternative, as-yet unknown, mechanism for methanol oxidation. The isolates assimilated C1 units at the level of formaldehyde, via the serine cycle. The DNA G+C content of the strains ranged between 64 and 65 mol%. 16S rRNA gene sequence similarity between the three new isolates was 99.85-100%, but was below 94% with other members of the Betaproteobacteria, indicating that the isolates represent a novel taxon. Based on physiological, phenotypic and genomic characteristics of the three isolates, a new genus, Methyloversatilis gen. nov., is proposed within the family Rhodocyclaceae. The type strain of Methyloversatilis universalis gen. nov., sp. nov. is FAM5T (=CCUG 52030T=JCM 13912T).

Alcohol Oxidoreductases↗
PubMed2005

Silvimonas terrae gen. nov., sp. nov., a novel chitin-degrading facultative anaerobe belonging to the 'Betaproteobacteria'.

A taxonomic study was carried out on a bacterial strain, designated KM-45T, isolated from forest soil collected near Daejeon, South Korea. Comparative 16S rRNA gene sequence analysis indicated a clear affiliation of this bacterium to the 'Betaproteobacteria' and that it was related most closely to Chitinibacter tainanensis BCRC 17254T, Formivibrio citricus DSM 6150T and Iodobacter fluviatilis ATCC 33051T (92.4, 91.2 and 88.9 % 16S rRNA gene sequence similarity, respectively). Cells were Gram-negative, facultatively anaerobic, motile and rod-shaped. The strain grew well on R2A medium and utilized a broad spectrum of carbon sources. The G+C content of the genomic DNA was 58 mol% and the predominant ubiquinone was Q-8. Major fatty acids were C(16 : 0), C(16 : 1)omega7c/iso-C(15 : 0) 2-OH, C(18 : 1)omega7c/omega9t/omega12t and C(17 : 0) cyclo. On the basis of the evidence presented, it is proposed that strain KM-45T should be placed in a novel genus and species, for which the name Silvimonas terrae gen. nov., sp. nov. is proposed. The type strain is KM-45T (=KCTC 12358T=NBRC 100961T).

Bacteria, Anaerobic↗
PubMed2007

Endosymbiosis in statu nascendi: close phylogenetic relationship between obligately endosymbiotic and obligately free-living Polynucleobacter strains (Betaproteobacteria).

Bacterial strains affiliated to the phylogenetically shallow subcluster C (PnecC) of the Polynucleobacter cluster, which is characterized by a minimal 16S rRNA gene sequence similarity of approximately 98.5%, have been reported to occur as obligate endosymbionts of ciliates (Euplotes spp.), as well as to occur as free-living cells in the pelagic zone of freshwater habitats. We investigated if these two groups of closely related bacteria represent strains fundamentally differing in lifestyle, or if they simply represent different stages of a facultative endosymbiotic lifestyle. The phylogenetic analysis of 16S rRNA gene and 16S-23S ITS sequences of five endosymbiont strains from two different Euplotes species and 40 pure culture strains demonstrated host-species-specific clustering of the endosymbiont sequences within the PnecC subcluster. The sequences of the endosymbionts showed characteristics indicating an obligate endosymbiotic lifestyle. Cultivation experiments revealed fundamental differences in physiological adaptations, and determination of the genome sizes indicated a slight size reduction in endosymbiotic strains. We conclude that the two groups of PnecC bacteria represent obligately free-living and obligately endosymbiotic strains, respectively, and do not represent different stages of the same complex life cycle. These closely related strains occupy completely separated ecological niches. To our best knowledge, this is the closest phylogenetic relationship between obligate endosymbionts and obligately free-living bacteria ever revealed.

Animals↗
PubMed2004

Emended description of the species Lampropedia hyalina.

Three Lampropedia hyalina strains from different habitats were compared by phenotypic, chemotaxonomic and molecular characteristics. All strains form coccoid cells and have been reported to grow as square tablets of eight to 64 cells. However, two of these strains (ATCC 11041T and ATCC 43383) have apparently lost this ability, and the third strain may temporarily lose this capacity under certain cultivation conditions. The three strains showed only minor differences in metabolic characteristics: the main significant physiological difference was the ability to accumulate polyphosphate under alternating anaerobic-aerobic conditions found for DSM 15336. The three strains showed high similarity in fatty acid composition and only slight differences in the G + C content (63-67 mol%) and DNA-DNA reassociation (90-95 % relatedness). Comparative 16S rRNA gene sequence analyses on these three strains and three Lampropedia hyalina 16S rRNA gene sequences deposited at NCBI showed that they are all very similar (> 98.8 %) and that they form a distinct group among the 'Betaproteobacteria', showing between 94.6 and 93 % 16S rRNA gene similarity to members of various genera such as Acidovorax, Aquaspirillum, Brachymonas, Comamonas, Delftia and Xenophilus. Fluorescent in situ hybridization with oligonucleotide probes targeting betaproteobacteria on the 16S rRNA and 23S rRNA gene level further supported the conclusion that all investigated strains are members of the 'Betaproteobacteria'. Two oligonucleotide probes were designed and successfully applied for culture-independent identification of Lampropedia hyalina by means of fluorescent in situ hybridization.

Aerobiosis↗
PubMed2006

Community structures and activities of nitrifying and denitrifying bacteria in industrial wastewater-treating biofilms.

The bacterial community structure, in situ spatial distributions and activities of nitrifying and denitrifying bacteria in biofilms treating industrial wastewater were investigated by combination of the 16S rRNA gene clone analysis, fluorescence in situ hybridization (FISH) and microelectrodes. These results were compared with the nitrogen removal capacity of the industrial wastewater treatment plant (IWTP). Both nitrification and denitrification occurred in the primary denitrification (PD) tank and denitrification occurred in the secondary denitrification (SD) tank. In contrast, nitrification and denitrification rates were very low in the nitrification (N) tank. 16S rRNA gene clone sequence analysis revealed that the bacteria affiliated with Alphaproteobacteria, followed by Betaproteobacteria, were numerically important microbial groups in three tanks. The many clones affiliated with Alphaproteobacteria were closely related to the denitrifying bacteria (e.g., Hyphomicrobium spp., Rhodopseudomonas palustris, and Rhodobacter spp.). In addition, Methylophilus leisingeri affiliated with Betaproteobacteria, which favorably utilized methanol, was detected only in the SD-tank to which methanol was added. Nitrosomonas europaea and Nitrosomonas marina were detected as the ammonia-oxidizing bacteria affiliated with Betaproteobacteria throughout this plant, although the dominant species of them was different among three tanks. Nitrifying bacteria were mainly detected in the upper parts of the PD-biofilm whereas their populations were low in the upper parts of the N-biofilm. The presence of denitrifying bacteria affiliated with Hyphomicrobium spp. in SD- and N-biofilms was verified by FISH analysis. Microelectrode measurements showed that the nitrifying bacteria present in the N- and PD-biofilms were active and the bacteria present in the SD-biofilm could denitrify.

Bacteria↗
PubMed2006

Comparison of the RpoH-dependent regulon and general stress response in Neisseria gonorrhoeae.

In the gammaproteobacteria the RpoH regulon is often equated with the stress response, as the regulon contains many of the genes that encode what have been termed heat shock proteins that deal with the presence of damaged proteins. However, the betaproteobacteria primarily utilize the HrcA repressor protein to control genes involved in the stress response. We used genome-wide transcriptional profiling to compare the RpoH regulon and stress response of Neisseria gonorrhoeae, a member of the betaproteobacteria. To identify the members of the RpoH regulon, a plasmid-borne copy of the rpoH gene was overexpressed during exponential-phase growth at 37 degrees C. This resulted in increased expression of 12 genes, many of which encode proteins that are involved in the stress response in other species. The putative promoter regions of many of these up-regulated genes contain a consensus RpoH binding site similar to that of Escherichia coli. Thus, it appears that unlike other members of the betaproteobacteria, N. gonorrhoeae utilizes RpoH, and not an HrcA homolog, to regulate the stress response. In N. gonorrhoeae exposed to 42 degrees C for 10 min, we observed a much broader transcriptional response involving 37 differentially expressed genes. Genes that are apparently not part of the RpoH regulon showed increased transcription during heat shock. A total of 13 genes were also down-regulated. From these results we concluded that although RpoH acts as the major regulator of protein homeostasis, N. gonorrhoeae has additional means of responding to temperature stress.

Gene Expression Regulation, Bacterial↗
PubMed2006

Microbial community analysis with a high PHA storage capacity.

Activated sludge was submitted to aerobic dynamic substrate feeding for the production of biodegradable plastics. Two sequencing batch reactors were operated with acetate or propionate as sole carbon substrates. With acetate a homopolymer of polyhydroxybutyrate (PHB) was obtained and with propionate a copolymer of hydroxybutyrate and hydroxyvalerate P(HB/HV) was produced. Three main morphotypes were identified in both sludges: two belong to the Alphaproteobacteria class and the third to the Betaproteobacteria class. Bacilli belonging to Betaproteobacteria were shown by FISH analysis, applied in combination with Nile Blue post-staining, to be the main responsible for PHAs storage. The latter were affiliated to Azoarcus genus within Betaproteobacteria.

Alkanes↗
PubMed2004

A third lineage with two-piece tmRNA.

tmRNA combines tRNA and mRNA properties and helps bacteria to cope with stalled ribosomes. Its termini normally pair in the tRNA domain, closing the mRNA portion into a looping domain. A striking variation is a two-piece form that effectively breaks open the mRNA domain loop, resulting from independent gene permutation events in alphaproteobacteria and cyanobacteria. Convergent evolution to a similar form in separate bacterial lineages suggests that loop-opening benefits tmRNA function. This argument is strengthened by the discovery of a third bacterial lineage with a loop-opened two-piece tmRNA. Whereas most betaproteobacteria have one-piece tmRNA, a permuted tmRNA gene was found for Dechloromonas aromatica and close relatives. Correspondingly, two tmRNA pieces were identified, at approximately equal abundance and at a level one-fifteenth that of ribosomes, a 189 nt mRNA piece and a 65 nt aminoacylatable piece. Together these pieces were active with purified Escherichia coli translational components, but not alone. The proposed secondary structure combines common tmRNA features differently from the structures of other two-piece forms. The origin of the gene is unclear; horizontal transfer may be indicated by the similarity of the tRNA domain to that from a cyanobacterial two-piece tmRNA, but such transfer would not appear simple since the mRNA domain is most similar to that of other betaproteobacteria.

Base Sequence↗
PubMed2006

Polaromonas aquatica sp. nov., isolated from tap water.

Two Gram-negative, rod-shaped, non-spore-forming bacteria (CCUG 39402T and CCUG 39797), isolated from different water sources, were investigated in a polyphasic study. The two isolates shared 100% 16S rRNA gene sequence similarity and it was shown that they belonged to the Betaproteobacteria, most closely related to Polaromonas vacuolata (97.8%) and Polaromonas naphthalenivorans (97.8%). A polyamine pattern with 2-hydroxyputrescine and putrescine, as well as ubiquinone Q-8, were in agreement with characteristics of Betaproteobacteria. The presence of diphosphatidylglycerol, phosphatidylglycerol and phosphatidylethanolamine, and major fatty acids C(16:1)omega7c, C(16:0) and C(17:0) cyclo supported the affiliation of the two strains to the genus Polaromonas. The results of DNA-DNA hybridization and physiological and biochemical tests allowed genotypic and phenotypic differentiation of the two isolates from the two Polaromonas species with validly published names. They therefore represent a novel species, for which the name Polaromonas aquatica sp. nov. is proposed, with the type strain CCUG 39402T (= CIP 108776T).

Betaproteobacteria↗
PubMed2006

Rubrivivax benzoatilyticus sp. nov., an aromatic, hydrocarbon-degrading purple betaproteobacterium.

A brown-coloured bacterium was isolated from photoheterotrophic (benzoate) enrichments of flooded paddy soil from Andhra Pradesh, India. On the basis of 16S rRNA gene sequence analysis, strain JA2(T) was shown to belong to the class Betaproteobacteria, related to Rubrivivax gelatinosus (99 % sequence similarity). Cells of strain JA2(T) are Gram-negative, motile rods with monopolar single flagella. The strain contained bacteriochlorophyll a and most probably the carotenoids spirilloxanthin and sphaeroidene, but did not have internal membrane structures. Intact cells had absorption maxima at 378, 488, 520, 590, 802 and 884 nm. No growth factors were required. Strain JA2(T) grew on benzoate, 2-aminobenzoate (anthranilate), 4-aminobenzoate, 4-hydroxybenzoate, phthalate, phenylalanine, trans-cinnamate, benzamide, salicylate, cyclohexanone, cyclohexanol and cyclohexane-2-carboxylate as carbon sources and/or electron donors. The DNA G+C content was 74.9 mol%. Based on DNA-DNA hybridization studies, 16S rRNA gene sequence analysis and morphological and physiological characteristics, strain JA2(T) is different from representatives of other photosynthetic species of the Betaproteobacteria and was recognised as representing a novel species, for which the name Rubrivivax benzoatilyticus sp. nov. is proposed. The type strain is JA2(T) (=ATCC BAA-35(T)=JCM 13220(T)=MTCC 7087(T)).

Base Composition↗
PubMed2006

A molecular microbial ecology approach to studying hemodialysis water and fluid.

Bacteria, or bacteria-derived products, might be responsible for deleterious effects in hemodialysis patients. Most microorganisms in hemodialysis water, including potential pathogens, are difficult to isolate and might subsist in a 'viable but not culturable' state or may need specific culture media. A molecular culture-independent approach based on the analysis of the 16S rDNA obtained from total DNA has been used to better know the diversity of bacteria inhabiting hemodialysis water and fluid, and to address the possible health effects associated with their presence. Four clone libraries from 16S rDNA (274 clones) were analyzed to characterize the species or groups of bacteria present, to assess their distribution in the water circuit, and to compare the results with those previously obtained in culture-dependent analysis. One hundred and ninety-seven clones of four gene libraries were analyzed by sequencing, and were identified phylogenetically. Clones affiliated to the Alphaproteobacteria group led the diversity. The presence in several samples of Alpha-4-proteobacteria, recognized as sphingolipids producers, was to be noted. The most abundant clones were affiliated to the Betaproteobacteria branch, closely related to the genus Herbaspirillum. As known, Alphaproteobacteria and Betaproteobacteria genomes might present a manifest excess in CpG sequences and most of them show a lipopolysaccharide-rich outer membrane, both described as inducers of innate immunity responses. Another abundant group, belonging to the Cyanobacteria class, a possible source of cyanotoxins, was not related to any previously cultured bacterium. Possible risk implications for hemodialysis patients of the bacterial community detected are discussed.

Alphaproteobacteria↗
PubMed2006

Structure and activity of bacterial community inhabiting rice roots and the rhizosphere.

Root-derived carbon provides a major source for microbial production and emission of CH4 from rice field soils. Therefore, we characterized the structure and activity of the bacterial community inhabiting rice roots and the rhizosphere. In the first experiment, DNA retrieved from rice roots was analysed for bacterial 16S rRNA genes using cloning, sequencing and in situ hybridization. In the second experiment, rice plants were pulse-labelled with 13CO2 (99% of atom 13C) for 7 days, and the bacterial RNA was isolated from rhizosphere soil and subjected to density gradient centrifugation. RNA samples from density fractions were analysed by terminal restriction fragment length polymorphism fingerprinting, cloning and sequencing. The experiments showed that the dominant bacteria inhabiting rice roots and the rhizosphere particularly belonged to the Alphaproteobacteria, Betaproteobacteria and Firmicutes. The RNA stable isotope probing revealed that the bacteria actively assimilating C derived from the pulse-labelled rice plants were Azospirillum spp. (Alphaproteobacteria) and members of Burkholderiaceae (Betaproteobacteria). Both anaerobic (e.g. Clostridia) and aerobic (e.g. Comamonas) degraders were present at high abundance, indicating that root environments and degradation processes were highly heterogeneous. The relative importance of iron and sulfate reducers suggested that cycling of iron and sulfur is active in the rhizosphere.

Bacteria, Aerobic↗
PubMed2006

Recurring seasonal dynamics of microbial communities in stream habitats.

Recurring seasonal patterns of microbial distribution and abundance in three third-order temperate streams within the southeast Pennsylvania Piedmont were observed over 4 years. Populations associated with streambed sediments and rocks (epilithon) were identified using terminal restriction length polymorphism (tRFLP) and sequencing of 16S rRNA genes selectively amplified with primers for the bacterial domain. Analyses of the relative magnitudes of tRFLP peak areas by using nonmetric multidimensional scaling resolved clear seasonal trends in epilithic and sediment populations. Oscillations between two dominant groups of epilithic genotypes, explaining 86% of the seasonal variation in the data set, were correlated with temperature and dissolved organic carbon. Sequences affiliated with epilithic phototrophs (cyanobacteria and diatom chloroplasts), a Rhodoferax sp., and a Bacillus species clustered in the summer, whereas sequences most closely related to "Betaproteobacteria" (putative Burkholderia sp.), and a putative cyanobacterium clustered in the fall/spring. The sediment genotypes also clustered into two groups, and these explained 85% of seasonal variation but correlated only with temperature. A summer tRFLP pattern was characterized by prevalence of "Betaproteobacteria," "Gammaproteobacteria," and a Bacillus sp., whereas the winter/spring pattern was characterized by phylotypes most closely related to "Firmicutes," "Gammaproteobacteria," and "Nitrospirae." A close association between these headwater streams and their watersheds was suggested by the recovery of sequences related to microbial populations provisionally attributed to not only freshwaters but also terrestrial habitats.

Bacillus↗
PubMed2004

The genome sequence of an anaerobic aromatic-degrading denitrifying bacterium, strain EbN1.

Recent research on microbial degradation of aromatic and other refractory compounds in anoxic waters and soils has revealed that nitrate-reducing bacteria belonging to the Betaproteobacteria contribute substantially to this process. Here we present the first complete genome of a metabolically versatile representative, strain EbN1, which metabolizes various aromatic compounds, including hydrocarbons. A circular chromosome (4.3 Mb) and two plasmids (0.21 and 0.22 Mb) encode 4603 predicted proteins. Ten anaerobic and four aerobic aromatic degradation pathways were recognized, with the encoding genes mostly forming clusters. The presence of paralogous gene clusters (e.g., for anaerobic phenylacetate oxidation), high sequence similarities to orthologs from other strains (e.g., for anaerobic phenol metabolism) and frequent mobile genetic elements (e.g., more than 200 genes for transposases) suggest high genome plasticity and extensive lateral gene transfer during metabolic evolution of strain EbN1. Metabolic versatility is also reflected by the presence of multiple respiratory complexes. A large number of regulators, including more than 30 two-component and several FNR-type regulators, indicate a finely tuned regulatory network able to respond to the fluctuating availability of organic substrates and electron acceptors in the environment. The absence of genes required for nitrogen fixation and specific interaction with plants separates strain EbN1 ecophysiologically from the closely related nitrogen-fixing plant symbionts of the Azoarcus cluster. Supplementary material on sequence and annotation are provided at the Web page http://www.micro-genomes.mpg.de/ebn1/.

Adaptation, Physiological↗
PubMed2005

Functional genomics of an anaerobic aromatic-degrading denitrifying bacterium, strain EbN1.

Nitrate-reducing bacteria of the recently recognized Azoarcus/Thauera group within the Betaproteobacteria contribute significantly to the biodegradation of aromatic and other refractory compounds in anoxic waters and soils. Strain EbN1 belongs to a distinct cluster (new genus) and is the first member of this phylogenetic group, the genome of which has been determined (4.7 Mb; one chromosome, two plasmids) by [Rabus R, Kube M, Heider J, Beck A, Heitmann K, Widdel F, Reinhardt R (2005) The genome sequence of an anaerobic aromatic-degrading denitrifying bacterium, strain EbN1. Arch Microbiol 183:27-36]. Ten anaerobic and four aerobic aromatic-degradation pathways were recognized on the chromosome, with the coding genes mostly forming clusters. Presence of paralogous gene clusters (e.g. for anaerobic ethylbenzene degradation) suggests an even broader degradation spectrum than previously known. Metabolic versatility is also reflected by the presence of multiple respiratory complexes and is apparently controlled by an extensive regulatory network. Strain EbN1 is unique for its capacity to degrade toluene and ethylbenzene anaerobically via completely different pathways. Bioinformatical analysis of their genetic blueprints and global expression analysis (DNA-microarray and proteomics) of substrate-adapted cells [Kühner S, Wöhlbrand L, Fritz I, Wruck W, Hultschig C, Hufnagel P, Kube M, Reinhardt R, Rabus R (2005) Substrate-dependent regulation of anaerobic degradation pathways for toluene and ethylbenzene in a denitrifying bacterium, strain EbN1. J Bacteriol 187:1493-1503] indicated coordinated vs sequential modes of regulation for the toluene and ethylbenzene pathways, respectively.

Anaerobiosis↗
PubMed2004

Elevated salinity selects for a less diverse ammonia-oxidizing population in aquarium biofilters.

The activity and changes in the structure of the community of the ammonia-oxidizing bacteria belonging to the Betaproteobacteria were monitored in freshwater and artificial seawater biofilters for two months after inoculation with a commercial nitrifying consortium. Both in freshwater and artificial seawater, ammonium oxidation proceeded immediately after addition of the inoculum, although initial activity in artificial seawater was lower than in freshwater. Denaturing gradient gel electrophoresis of the ammonia-oxidizing bacterial community of the inoculum and the freshwater and the artificial seawater aquaria as a function of time showed that initially only one dominant ammonia-oxidizer, closely related to Nitrosomonas marina, was detectable in all the systems. The fingerprint of the ammonia-oxidizing bacterial community in the artificial seawater biofilters continued to be dominated by this single band. In the freshwater aquaria, in contrast, the composition of the ammonia-oxidizer community became more diverse after one month, with 4-7 new bands appearing in the denaturing gradient gel fingerprint. Since the inoculum is cultivated at an average salinity of 11 gl(-1), it is argued that the elevated salinity selects for a less diverse ammonia-oxidizer community in the inoculum and the artificial seawater aquaria.

Ammonia↗