Combining electrokinetic transport and bioremediation for enhanced removal of crude oil from contaminated marine sediments: Results of a long-term, mesocosm-scale experiment.

Marine sediments represent an important sink of harmful petroleum hydrocarbons after an accidental oil spill. Electrobioremediation techniques, which combine electrokinetic transport and biodegradation processes, represent an emerging technological platform for a sustainable remediation of contaminated sediments. Here, we describe the results of a long-term mesocosm-scale electrobioremediation experiment for the treatment of marine sediments contaminated by crude oil. A dimensionally stable anode and a stainless-steel mesh cathode were employed to drive seawater electrolysis at a fixed current density of 11 A/m2. This approach allowed establishing conditions conducive to contaminants biodegradation, as confirmed by the enrichment of Alcanivorax borkumensis cells harboring the alkB-gene and other aerobic hydrocarbonoclastic bacteria. Oil chemistry analyses indicated that aromatic hydrocarbons were primarily removed from the sediment via electroosmosis and low molecular weight alkanes (nC6 to nC10) via biodegradation.

Comprehensive two-dimensional gas chromatography-mass spectrometry of complex mixtures of anaerobic bacterial metabolites of petroleum hydrocarbons.

Anaerobic biotransformation of petroleum hydrocarbons is an important alteration mechanism, both subsurface in geological reservoirs, in aquifers and in anoxic deep sea environments. Here we report the resolution and identification, by comprehensive two-dimensional gas chromatography-mass spectrometry (GC×GC-MS), of complex mixtures of aromatic acid and diacid metabolites of the anaerobic biodegradation of many crude oil hydrocarbons. An extended range of metabolites, including alkylbenzyl, alkylindanyl, alkyltetralinyl, alkylnaphthyl succinic acids and alkyltetralin, alkylnaphthoic and phenanthrene carboxylic acids, is reported in samples from experiments conducted under sulfate-reducing conditions in a microcosm over two years. The range of metabolites identified shows that the fumarate addition mechanism applies to the alteration of hydrocarbons with up to C8 alkylation in monoaromatics and that functionalisation of up to three ring aromatic hydrocarbons with at least C1 alkylation occurs. The GC×GC-MS method might now be applied to the identification of complex mixtures of metabolites in samples from real environmental oil spills.

Nitrification in hybrid bioreactors treating simulated domestic wastewater.

AIM: To provide deeper insights into nitrification process within aerobic bioreactors containing supplemental physical support media (hybrid bioreactors). METHODS AND RESULTS: Three bench-scale hybrid bioreactors with different media size and one control bioreactor were operated to assess how biofilm integrity influences microbial community conditions and bioreactor performance. The systems were operated initially at a 5-day hydraulic retention time (HRT), and all reactors displayed efficient nitrification and chemical oxygen demand (COD) removal (>95%). However, when HRT was reduced to 2.5 days, COD removal rates remained high, but nitrification efficiencies declined in all reactors after 19 days. To explain reduced performance, nitrifying bacterial communities (ammonia-oxidizing bacteria, AOB; nitrite-oxidizing bacteria, NOB) were examined in the liquid phase and also on the beads using qPCR, FISH and DGGE. Overall, the presence of the beads in a reactor promoted bacterial abundances and diversity, but as bead size was increased, biofilms with active coupled AOB-NOB activity were less apparent, resulting in incomplete nitrification. CONCLUSIONS: Hybrid bioreactors have potential to sustain effective nitrification at low HRTs, but support media size and configuration type must be optimized to ensure coupled AOB and NOB activity in nitrification. SIGNIFICANCE AND IMPACT OF THE STUDY: This study shows that AOB and NOB coupling must be accomplished to minimize nitrification failure.

The quantitative significance of Syntrophaceae and syntrophic partnerships in methanogenic degradation of crude oil alkanes.

Libraries of 16S rRNA genes cloned from methanogenic oil degrading microcosms amended with North Sea crude oil and inoculated with estuarine sediment indicated that bacteria from the genera Smithella (Deltaproteobacteria, Syntrophaceace) and Marinobacter sp. (Gammaproteobacteria) were enriched during degradation. Growth yields and doubling times (36 days for both Smithella and Marinobacter) were determined using qPCR and quantitative data on alkanes, which were the predominant hydrocarbons degraded. The growth yield of the Smithella sp. [0.020 g(cell-C)/g(alkane-C)], assuming it utilized all alkanes removed was consistent with yields of bacteria that degrade hydrocarbons and other organic compounds in methanogenic consortia. Over 450 days of incubation predominance and exponential growth of Smithella was coincident with alkane removal and exponential accumulation of methane. This growth is consistent with Smithella's occurrence in near surface anoxic hydrocarbon degrading systems and their complete oxidation of crude oil alkanes to acetate and/or hydrogen in syntrophic partnership with methanogens in such systems. The calculated growth yield of the Marinobacter sp., assuming it grew on alkanes, was [0.0005 g(cell-C)/g(alkane-C)] suggesting that it played a minor role in alkane degradation. The dominant methanogens were hydrogenotrophs (Methanocalculus spp. from the Methanomicrobiales). Enrichment of hydrogen-oxidizing methanogens relative to acetoclastic methanogens was consistent with syntrophic acetate oxidation measured in methanogenic crude oil degrading enrichment cultures. qPCR of the Methanomicrobiales indicated growth characteristics consistent with measured rates of methane production and growth in partnership with Smithella.

Factors affecting current production in microbial fuel cells using different industrial wastewaters.

This study evaluated how different types of industrial wastewaters (bakery, brewery, paper and dairy) affect the performance of identical microbial fuel cells (MFCs); and the microbial composition and electrochemistry of MFC anodes. MFCs fed with paper wastewater produced the highest current density (125 ± 2 mA/m(2)) at least five times higher than dairy (25 ± 1 mA/m(2)), brewery and bakery wastewaters (10 ± 1 mA/m(2)). Such high current production was independent of substrate degradability. A comprehensive study was conducted to determine the factor driving current production when using the paper effluent. The microbial composition of anodic biofilms differed according to the type of wastewater used, and only MFC anodes fed with paper wastewater showed redox activity at -134 ± 5 mV vs NHE. Electrochemical analysis of this redox activity indicated that anodic bacteria produced a putative electron shuttling compound that increased the electron transfer rate through diffusion, and as a result the overall MFC performance.

Methanogenic degradation of petroleum hydrocarbons in subsurface environments remediation, heavy oil formation, and energy recovery.

Hydrocarbons are common constituents of surface, shallow, and deep-subsurface environments. Under anaerobic conditions, hydrocarbons can be degraded to methane by methanogenic microbial consortia. This degradation process is widespread in the geosphere. In comparison with other anaerobic processes, methanogenic hydrocarbon degradation is more sustainable over geological time scales because replenishment of an exogenous electron acceptor is not required. As a consequence, this process has been responsible for the formation of the world's vast deposits of heavy oil, which far exceed conventional oil assets such as those found in the Middle East. Methanogenic degradation is also a potentially important component of attenuation in hydrocarbon contamination plumes. Studies of the organisms, syntrophic partnerships, mechanisms, and geochemical signatures associated with methanogenic hydrocarbon degradation have identified common themes and diagnostic markers for this process in the subsurface. These studies have also identified the potential to engineer methanogenic processes to enhance the recovery of energy assets as biogenic methane from residual oils stranded in petroleum systems.

Mathematical model for microbial fuel cells with anodic biofilms and anaerobic digestion.

This study describes the integration of IWA's anaerobic digestion model (ADM1) within a computational model of microbial fuel cells (MFCs). Several populations of methanogenic and electroactive microorganisms coexist suspended in the anolyte and in the biofilm attached to the anode. A number of biological, chemical and electrochemical reactions occur in the bulk liquid, in the biofilm and at the electrode surface, involving glucose, organic acids, H2 and redox mediators. Model output includes the evolution in time of important measurable MFC parameters (current production, consumption of substrates, suspended and attached biomass growth). Two- and three-dimensional model simulations reveal the importance of current and biomass heterogeneous distribution over the planar anode surface. Voltage- and power-current characteristics can be calculated at different moments in time to evaluate the limiting regime in which the MFC operates. Finally, model simulations are compared with experimental results showing that, in a batch MFC, smaller electrical resistance of the circuit leads to selection of electroactive bacteria. Higher coulombic yields are so obtained because electrons from substrate are transferred to anode rather than following the methanogenesis pathway. In addition to higher currents, faster COD consumption rates are so achieved. The potential of this general modelling framework is in the understanding and design of more complex cases of wastewater-fed microbial fuel cells.

Crude-oil biodegradation via methanogenesis in subsurface petroleum reservoirs.

Biodegradation of crude oil in subsurface petroleum reservoirs has adversely affected the majority of the world's oil, making recovery and refining of that oil more costly. The prevalent occurrence of biodegradation in shallow subsurface petroleum reservoirs has been attributed to aerobic bacterial hydrocarbon degradation stimulated by surface recharge of oxygen-bearing meteoric waters. This hypothesis is empirically supported by the likelihood of encountering biodegraded oils at higher levels of degradation in reservoirs near the surface. More recent findings, however, suggest that anaerobic degradation processes dominate subsurface sedimentary environments, despite slow reaction kinetics and uncertainty as to the actual degradation pathways occurring in oil reservoirs. Here we use laboratory experiments in microcosms monitoring the hydrocarbon composition of degraded oils and generated gases, together with the carbon isotopic compositions of gas and oil samples taken at wellheads and a Rayleigh isotope fractionation box model, to elucidate the probable mechanisms of hydrocarbon degradation in reservoirs. We find that crude-oil hydrocarbon degradation under methanogenic conditions in the laboratory mimics the characteristic sequential removal of compound classes seen in reservoir-degraded petroleum. The initial preferential removal of n-alkanes generates close to stoichiometric amounts of methane, principally by hydrogenotrophic methanogenesis. Our data imply a common methanogenic biodegradation mechanism in subsurface degraded oil reservoirs, resulting in consistent patterns of hydrocarbon alteration, and the common association of dry gas with severely degraded oils observed worldwide. Energy recovery from oilfields in the form of methane, based on accelerating natural methanogenic biodegradation, may offer a route to economic production of difficult-to-recover energy from oilfields.

The expanded bed biofilter: combined nitrification, solids destruction, and removal of bacteria.

Developed for tertiary nitrification, this biofilter also removed carbonaceous BOD (cBOD) and (SS). Because the biofilter is expanded, it cannot clog, and therefore does not require backflushing; yet, it removed a significant proportion of the influent SS. This unanticipated capability was due to the activities of heterotrophic bacteria, protozoa, and metazoa (nematode and oligochaete worms). The expanded bed is an intensified process, which is based on natural immobilization of microbes to small support particles. Using glassy coke as the support material, an attached layer of microbes develops, forming particulate biofilms having a superficial surface area of 1 800 m2 m(-3)(expandedbed). Autotrophic nitritifiers (Nitrosomonas spp.) were detected in the biofilm using rRNA-based molecular methods and were likely responsible, at least in part, for reducing the ammonia concentration by up to 99% (to 0.1 mg L(-1)), while the other organisms reduced cBOD and SS by up to 56% and 62%, respectively. Furthermore, the influent concentrations of Escherichia coli, coliform and heterotrophic bacteria were reduced by over 80%. It thereby provides a single process solution for combined tertiary nitrification and solids removal. Operating the process to consistently achieve < 0.5mg NH3N L(-1) and at the same time removing a significant fraction of cBOD and SS, it can replace processes such as SAFs or NTFs followed by a sandfilter.

Acidophilic microbial communities associated with a natural, biodegraded hydrocarbon seepage.

Characterization of microbial communities present in a surface petroleum seep in which hydrocarbons have been biodegraded for thousands of years in order to improve the understanding on natural petroleum biodegradation. DNA was extracted from a natural, surface petroleum seep and subjected to culture independent analysis (rRNA gene-based denaturing gradient gel electrophoresis and phylogenetic analysis of clone libraries). Molecular analysis suggested dominance by acidophilic bacteria, especially Alphaproteobacteria (mainly bacteria related to Acidiphilium and Acidocella). Archaea were not detected, but fungi were present. pH of the samples was around 3.5. Acidophilic microbial communities are associated with an acidic petroleum seep. Microbial community structure analysis gives information on the environmental conditions under which petroleum biodegradation occurs. This knowledge could be applied to define conditions for specific cultivation or activity measurements. The activity of acidophilic micro-organisms deserves more attention with respect to their involvement in natural petroleum degradation. This knowledge will contribute to the design of oil bioremediation strategies for polluted acidic settings.

A stable isotope titration method to determine the contribution of acetate disproportionation and carbon dioxide reduction to methanogenesis.

A novel stable isotope titration approach was developed to determine the contributions to total methane production made by CO(2) reduction and the disproportionation of acetate in anoxic environments. (13)CH(4), (12)CH(4), (13)CO(2) and (12)CO(2) production rates were measured in the head space of replicate anaerobic microcosms titrated with increasing amounts of (13)C-labelled substrates. The contribution of CO(2) reduction was calculated from the linear relationship between ratios of labelled and total CH(4) production and ratios of labelled and total CO(2) after the addition of (13)C-bicarbonate. In the case of acetoclastic methanogenesis rates of (13)CH(4) and (12)CH(4) production were fitted to a model based on an assumption that the relationship between the concentration of (13)C-labelled acetate and the rates of labelled and unlabelled methane production followed Michaelis-Menten kinetics. A comparison of the raw data with the model supported the assumption and provided both an estimate of the contribution of acetate to methane production and an estimate of the size of the indigenous acetate pool without the need to measure acetate directly. The method was applied to a freshwater sediment in the English Lake District where it was found that 66.3% (se 4.9) of methane production was due to acetate disproportionation and 28.9% (se 1.9) of methane production resulted from CO(2) reduction. This is in agreement with theoretical predictions and other empirical measurements of methanogenesis.

The impact of sludge amendment on gas dynamics in an upland soil: monitored by membrane inlet mass spectrometry.

Studies of the land disposal of biosolids and municipal sewage have focused largely on the potential pollution of the soil with pathogens, toxic compounds or heavy metals. Little is known about the impact of sludge amendment on carbon source and sink concentrations in soils. In this study gas concentrations in Scottish soil cores (from limed and unlimed plots) were monitored continuously at 3 cm depth before, during and after sludge application using membrane inlet mass spectrometry (MIMS). Following sludge application to soil cores, significant and sustained increases in CH4 (for 8 days) and CO2 (for between 16 and 120 days) concentration were observed. This suggested short-term stimulation of indigenous methanogens, provision of a new methanogenic inoculum, or inhibition of methane oxidizers (for example by heavy metals or NH4 in sludge). Soil microbial fermentative activity was enhanced over periods of a few months as shown by elevated CO2 concentrations.

A comparitive study of ammonia-oxidizing bacteria in lab-scale industrial wastewater treatment reactors.

The diversity and community structure of the beta-proteobacterial ammonia oxidising bacteria (AOB) in a range of different lab-scale industrial wastewater treatment reactors were compared. Three of the reactors treat waste from mixed domestic and industrial sources whereas the other reactor treats waste solely of industrial origin. PCR with AOB selective primers was combined with denaturing gradient ge electrophoresis to allow comparative analysis of the dominant AOB populations and the phylogenetic affiliation of the dominant AOB was determined by cloning and sequencing or direct sequencing of bands excised from DGGE gels. Different AOB were found within and between different reactors. All AOB sequences identified were grouped within the genus Nitrosomonas. Within the lab-scale reactors there appeared to be selection for a low diversity of AOB and predominance of a single AOB population. Furthermore, the industrial input in both effluents apparently selected for salt tolerant AOB, most closely related to Nitrosococcus mobilis and Nitrosomonas halophila.

A comparison of autotrophic ammonia-oxidizing bacteria in full- and laboratory-scale wastewater treatment reactors.

Lab-scale reactors are commonly used to simulate full-scale plants as they permit the effects of defined experimental perturbations to be evaluated. Ideally, lab- and full-scale reactors should possess similar microbial populations. To determine this we compared the diversity of the beta-proteobacterial autotrophic ammonia-oxidising bacteria (AOB) in a full-scale and lab-scale biological aerated filter (BAF) using PCR with AOB selective primers combined with denaturing gradient gel electrophoresis (DGGE). PCR amplified 16S rRNA gene fragments from the nitrification unit of the lab-and full-scale BAF were subjected to cloning and sequencing to determine the phylogenetic affiliation of the AOB. A high degree of comparability between the lab-and full-scale BAF was observed with respect to AOB populations. However minor differences were apparent. The importance of these minor constituents in the overall performance of the reactor is unknown. Nonetheless the lab-scale reactor in this study did appear to reflect the dominant AOB community within the full-scale equivalent.

The effect of C/N ratio on ammonia oxidising bacteria community structure in a laboratory nitrification-denitrification reactor.

A laboratory scale reactor operated as a single sludge, denitrification-nitrification bioreactor (DNB), was fed a synthetic wastewater. The effect of the C/N ratio of the influent on the structure of beta-proteobacterial autotrophic ammonia-oxidizing bacterial (AOB) communities was determined by DGGE analysis of 16S rRNA gene fragments amplified using a range of AOB-selective primers. Fluorescence in situ hybridisation (FISH) was used to determine quantitative changes in the AOB communities. When operated at a C/N ratio of 2 the DNB was effective in nitrogen removal and nitrification was measured at approximately 1.0 mg NH4+-N/g dry wt/h. Altering the C/N ratio to 5 resulted in a 50% reduction in nitrification rates. Nitrification was restored to its original level when the C/N ratio was returned to 2. AOB were detected by DGGE analysis of samples from the DNB under all operating conditions but the changes in C/N ratio and nitrification rates were accompanied by changes in the community structure of the AOB. However, quantitative FISH analysis indicated that beta-proteobacterial AOB were only present in high numbers (ca. 10(8) cells/ml) under the original operating conditions with a C/N ratio of 2. Beta-proteobacterial AOB could not be detected by FISH when the C/N ratio was 5. When nitrification activity was restored by returning the C/N ratio to 2, beta-proteobacterial AOB were still not detected and it is likely that either beta-proteobacterial AOB were not responsible for ammonia oxidation or that beta-proteobacterial AOB that did not contain the target sites for the range of 4 AOB selective probes used, were present in the reactor.

Kinetics of perchlorate- and chlorate-respiring bacteria.

Ten chlorate-respiring bacteria were isolated from wastewater and a perchlorate-degrading bioreactor. Eight of the isolates were able to degrade perchlorate, and all isolates used oxygen and chlorate as terminal electron acceptors. The growth kinetics of two perchlorate-degrading isolates, designated "Dechlorosoma" sp. strains KJ and PDX, were examined with acetate as the electron donor in batch tests. The maximum observed aerobic growth rates of KJ and PDX (0.27 and 0.28 h(-1), respectively) were only slightly higher than the anoxic growth rates obtained by these isolates during growth with chlorate (0.26 and 0.21 h(-1), respectively). The maximum observed growth rates of the two non-perchlorate-utilizing isolates (PDA and PDB) were much higher under aerobic conditions (0.64 and 0.41 h(-1), respectively) than under anoxic (chlorate-reducing) conditions (0.18 and 0.21 h(-1), respectively). The maximum growth rates of PDX on perchlorate and chlorate were identical (0.21 h(-1)) and exceeded that of strain KJ on perchlorate (0.14 h(-1)). Growth of one isolate (PDX) was more rapid on acetate than on lactate. There were substantial differences in the half-saturation constants measured for anoxic growth of isolates on acetate with excess perchlorate (470 mg/liter for KJ and 45 mg/liter for PDX). Biomass yields (grams of cells per gram of acetate) for strain KJ were not statistically different in the presence of the electron acceptors oxygen (0.46 +/- 0.07 [n = 7]), chlorate (0.44 +/- 0.05 [n = 7]), and perchlorate (0.50 +/- 0.08 [n = 7]). These studies provide evidence that facultative microorganisms with the capability for perchlorate and chlorate respiration exist, that not all chlorate-respiring microorganisms are capable of anoxic growth on perchlorate, and that isolates have dissimilar growth kinetics using different electron donors and acceptors.

Isolation and characterization of a novel hydrocarbon-degrading, Gram-positive bacterium, isolated from intertidal beach sediment, and description of Planococcus alkanoclasticus sp. nov.

AIMS: Characterization of a bacterial isolate (strain MAE2) from intertidal beach sediment capable of degrading linear and branched alkanes. METHODS AND RESULTS: A Gram-positive, aerobic, heterotrophic bacterium (strain MAE2), that was capable of extensive degradation of alkanes in crude oil but had a limited capacity for the utilization of other organic compounds, was isolated from intertidal beach sediment. MAE2 had an obligate requirement for NaCl but could not tolerate high salt concentrations. It was capable of degrading branched and n-alkanes in crude oil from C11 to C33, but was unable to degrade aromatic hydrocarbons. Comparative 16S rRNA sequence analysis placed the isolate with members of the genus Planococcus. That finding was corroborated by chemotaxonomic and physiological data. The fatty acid composition of strain MAE2 was very similar to the type species of the genus Planococcus, P. citreus (NCIMB 1493T) and P. kocurii (NCIMB 629T), and was dominated by branched acids, mainly a15:0. However, the 16S rRNA of strain MAE2 had less than 97% sequence identity with the type strains of P. citreus (NCIMB 1439T), P. kocurii (NCIMB 629T) and two Planococcus spp. (strain MB6-16 and strain ICO24) isolated from Antarctic sea ice. This indicated that strain MAE2 represented a separate species from these planococci. Morphologically, the isolate resembled P. okeanokoites (NCIMB 561T) and P. mcmeekinii S23F2 (ATCC 700539T). The cellular fatty acid composition of P. okeanokoites and P. mcmeekinii was considerably different from strain MAE2, and the mol % G + C content of P. mcmeekinii was far lower than that of MAE2. CONCLUSION: On the basis of phenotypic and genotypic data, it is proposed that strain MAE2 is a new species of Planococcus, Planococcus alkanoclasticus sp. nov., for which the type strain is P. alkanoclasticus MAE2 (NCIMB 13489T). SIGNIFICANCE AND IMPACT OF THE STUDY: Planococcus species are abundant members of the bacterial community in a variety of marine environments, including some in sensitive Antarctic ecosystems. The occurrence of hydrocarbon-degrading Planococcus spp. is potentially of importance in controlling the impact of hydrocarbon contamination in sensitive marine environments.

Use of combined microautoradiography and fluorescence in situ hybridization to determine carbon metabolism in mixed natural communities of uncultured bacteria from the genus Achromatium.

Combined microautoradiography and fluorescence in situ hybridization (FISH) was used to investigate carbon metabolism in uncultured bacteria from the genus Achromatium. All of the Achromatium species identified in a freshwater sediment from Rydal Water, Cumbria, United Kingdom, which were distinguishable only by FISH, assimilated both [(14)C]bicarbonate and [(14)C]acetate. This extends previous findings that Achromatium spp. present at another location could only utilize organic carbon sources. Achromatium spp., therefore, probably exhibit a range of physiologies, i.e., facultative chemolithoautotrophy, mixotrophy, and chemoorganoheterotrophy, similar to other large sulfur bacteria (e.g., Beggiatoa spp.).

Phylogenetic relationships of filamentous sulfur bacteria (Thiothrix spp. and Eikelboom type 021N bacteria) isolated from wastewater-treatment plants and description of Thiothrix eikelboomii sp. nov., Thiothrix unzii sp. nov., Thiothrix fructosivorans sp. nov. and Thiothrix defluvii sp. nov.

The relationship of mixotrophic and autotrophic Thiothrix species to morphologically similar chemoorganotrophic bacteria (e.g. Leucothrix species, Eikelboom type 021N bacteria) has been a matter of debate for some years. These bacteria have alternatively been grouped together on the basis of shared morphological features or separated on the basis of their nutrition. Many of these bacteria are difficult to maintain in axenic culture and, until recently, few isolates were available to allow comprehensive phenotypic and genotypic characterization. Several isolates of Thiothrix spp. and Eikelboom type 021N strains were characterized by comparative 16S rRNA sequence analysis. This revealed that the Thiothrix spp. and Eikelboom type 021N isolates formed a monophyletic group. Furthermore, isolates of Eikelboom type 021N bacteria isolated independently from different continents were phylogenetically closely related. The 16S rRNA sequence-based phylogeny was congruent with the morphological similarities between Thiothrix and Eikelboom type 021N. However, one isolate examined in this study (Ben47) shared many morphological features with the Thiothrix spp. and Eikelboom type 021N isolates, but was not closely related to them phylogenetically. Consequently, morphology alone cannot be used to assign bacteria to the Thiothrix/type 021N group. Comparative 16S rRNA sequence analysis supports monophyly of the Thiothrix/type 021N group, and phenotypic differences between the Thiothrix spp. and Eikelboom type 021N bacteria are currently poorly defined. For example, both groups include heterotrophic organisms that deposit intracellular elemental sulfur. It is therefore proposed that the Eikelboom type 021N bacteria should be accommodated within the genus Thiothrix as a new species, Thiothrix eikelboomii sp. nov., and three further new Thiothrix species are described: Thiothrix unzii sp. nov., Thiothrix fructosivorans sp. nov. and Thiothrix defluvii sp. nov.