Chemotaxis of a Ralstonia sp. SJ98 toward co-metabolizable nitroaromatic compounds

Deciphering Bacterial Chemorepulsion: The Complex Response of Microbes to Environmental Stimuli

Bacterial motility relying on flagella is characterized by several modes, including swimming, swarming, twitching, and gliding. This motility allows bacteria to adapt remarkably well to hostile environments. More than 50% of bacteria naturally contain flagella, which are crucial for bacterial chemotaxis motility. Chemotaxis can be either positive, where bacteria move towards a chemical source, or negative, known as chemorepulsion, where bacteria move away from the source. Although much is known about the mechanisms driving chemotaxis towards attractants, the molecular mechanisms underlying chemorepulsion remain elusive. Chemotaxis plays an important role in the colonization of the rhizosphere by rhizobacteria. Recently, researchers have systematically studied the identification and recognition mechanisms of chemoattractants. However, the mechanisms underlying chemorepellents remain unclear. Systematically sorting and analyzing research on chemorepellents could significantly enhance our understanding of how these compounds help probiotics evade harmful environments or drive away pathogens.

Annotation of chemotaxis gene clusters and proteins involved in chemotaxis of Bacillus subtilis strain MB378 capable of biodecolorizing different dyes

This study explores the chemotactic potential of Bacillus subtilis MB378 against industrial dyes. Initial screening with swim plate assay showed significant movement of Bacillus subtilis MB378 towards test compounds. According to quantitative capillary assay, B. subtilis MB378 exhibited high chemotaxis potential towards Acid Orange 52 (CI: 9.52), followed by Direct Red 28 (CI: 8.39) and Basic Green 4 (CI: 5.21) in glucose-supplemented medium. Sequencing and gene annotation results evidently showed presence of chemotaxis genes and flagellar motor proteins in Bacillus subtilis draft genome. Methyl-accepting proteins (involved in chemotaxis regulation) belonged to pfam00672, pfam00072, and pfam00015 protein families. Annotated chemotaxis machinery of MB378 comprised 8 Che genes, 5 chemoreceptor genes, associated flagellar proteins, and rotary motors. Chemotaxis genes of B. subtilis MB378 were compared with genes of closely related Bacillus strains (168, WK1, and HTA426), depicting highly conserved regions showing evolutionary relation between them. Considering results of present study, it can be speculated that test compounds triggered chemotactic genes, which made these compounds bioavailable to the bacterium. Hence, the bacterium recognized and approached these compounds and facilitated biodegradation and detoxification of these compounds.

Construction of a hydrocarbon-degrading consortium and characterization of two new lipopeptides biosurfactants

Apparent solubility and bioavailability of hydrophobic compounds are the major problems in the bioremediation process, which could be overcome by the bacteria capable of biosurfactant production and concurrent hydrocarbon degradation. In this work, we constructed an artificial bacterial consortium containing Lysinibacillus, Paenibacillus, Gordonia and Cupriavidus spp. from glyceryl tributyrate enriched bacteria collected from the non-contaminated site. The consortium was capable of using common raw materials (olive oil, paraffin oil, and glycerol) and polyaromatic hydrocarbons pollutants (naphthalene and anthracene) as the sole carbon source with simultaneous biosurfactant production. Two new lipopeptide isoforms, containing heptapeptide and lipid moieties, were structurally elucidated by LC-MS/MS, FTIR, NMR and molecular networking analysis. Our findings indicate that hydrocarbons degradation and biosurfactant production is an intrinsic property of non-contaminated soil community. Interestingly, we observed the hyper chemotactic activity of Lysinibacillus strains towards glyceryl tributyrate, which has not been reported before. The study may deepen our understanding of microbial strains and consortium with the potential to be used for bioremediation of hydrocarbons contaminated environments.

A novel Sphingobacterium sp. RB, a rhizosphere isolate degrading para-nitrophenol with substrate specificity towards nitrotoluenes and nitroanilines

Sphingobacterium sp. RB, a novel bacterial strain isolated from a soil sample, was able to utilize para-nitrophenol (PNP) as sole source of carbon and energy at high concentrations (1.0–5.0 mM). The culture completely degraded 3.0 mM PNP within 36 h with proportionate increase in biomass. With 5.0 mM PNP (700 ppm), 70% degradation was observed within 72 h of incubation. Scanning electron microscope images of the isolate in the presence and absence of PNP showed no significant morphological variations. Liquid chromatography–mass spectrometry analysis indicated that the biodegradation of PNP in this bacterium proceeded via the formation of 1,2,4-benzenetriol. Cells previously exposed to PNP (induced) were 30% more effective in degrading PNP. With catechol and phenol, such induction was not observed. Uninduced cells of Sphingobacterium sp. RB were capable of degrading a variety of other nitroaromatic compounds, including 2-nitroaniline, 2,4-dinitroaniline, 2-nitrotoluene, 3-nitrotoluene and 2,4-dinitrophenol, within 72 h, thus proving its candidacy as a potent bioremediation agent. To the best of our knowledge, this is the first report on a Sphingobacterium species degrading PNP via formation of 1,2,4-benzenetriol.

The Interaction between Plants and Bacteria in the Remediation of Petroleum Hydrocarbons: An Environmental Perspective

Widespread pollution of terrestrial ecosystems with petroleum hydrocarbons (PHCs) has generated a need for remediation and, given that many PHCs are biodegradable, bio- and phyto-remediation are often viable approaches for active and passive remediation. This review focuses on phytoremediation with particular interest on the interactions between and use of plant-associated bacteria to restore PHC polluted sites. Plant-associated bacteria include endophytic, phyllospheric, and rhizospheric bacteria, and cooperation between these bacteria and their host plants allows for greater plant survivability and treatment outcomes in contaminated sites. Bacterially driven PHC bioremediation is attributed to the presence of diverse suites of metabolic genes for aliphatic and aromatic hydrocarbons, along with a broader suite of physiological properties including biosurfactant production, biofilm formation, chemotaxis to hydrocarbons, and flexibility in cell-surface hydrophobicity. In soils impacted by PHC contamination, microbial bioremediation generally relies on the addition of high-energy electron acceptors (e.g., oxygen) and fertilization to supply limiting nutrients (e.g., nitrogen, phosphorous, potassium) in the face of excess PHC carbon. As an alternative, the addition of plants can greatly improve bioremediation rates and outcomes as plants provide microbial habitats, improve soil porosity (thereby increasing mass transfer of substrates and electron acceptors), and exchange limiting nutrients with their microbial counterparts. In return, plant-associated microorganisms improve plant growth by reducing soil toxicity through contaminant removal, producing plant growth promoting metabolites, liberating sequestered plant nutrients from soil, fixing nitrogen, and more generally establishing the foundations of soil nutrient cycling. In a practical and applied sense, the collective action of plants and their associated microorganisms is advantageous for remediation of PHC contaminated soil in terms of overall cost and success rates for in situ implementation in a diversity of environments. Mechanistically, there remain biological unknowns that present challenges for applying bio- and phyto-remediation technologies without having a deep prior understanding of individual target sites. In this review, evidence from traditional and modern omics technologies is discussed to provide a framework for plant-microbe interactions during PHC remediation. The potential for integrating multiple molecular and computational techniques to evaluate linkages between microbial communities, plant communities and ecosystem processes is explored with an eye on improving phytoremediation of PHC contaminated sites.

Chemotaxis and degradation of organophosphate compound by a novel moderately thermo-halo tolerant Pseudomonas sp. strain BUR11: evidence for possible existence of two pathways for degradation

An organophosphate (OP) degrading chemotactic bacterial strain BUR11 isolated from an agricultural field was identified as a member of Pseudomonas genus on the basis of its 16S rRNA gene sequence. The strain could utilize parathion, chlorpyrifos and their major hydrolytic intermediates as sole source of carbon for its growth and exhibited positive chemotactic response towards most of them. Optimum concentration of parathion for its growth was recorded to be 200 ppm and 62% of which was degraded within 96 h at 37 °C. Growth studies indicated the strain to be moderately thermo-halo tolerant in nature. Investigation based on identification of intermediates of parathion degradation by thin layer chromatography (TLC), high performance liquid chromatography (HPLC), gas chromatography (GC) and liquid chromatography mass spectrometry (LC-MS/MS) provided evidence for possible existence of two pathways. The first pathway proceeds via 4-nitrophenol (4-NP) while the second proceeds through formation of 4-aminoparathion (4-APar), 4-aminophenol (4-AP) and parabenzoquinone (PBQ). This is the first report of chemotaxis towards organophosphate compound by a thermo-halo tolerant bacterium.

Genome annotation of Burkholderia sp. SJ98 with special focus on chemotaxis genes

Burkholderia sp. strain SJ98 has the chemotactic activity towards nitroaromatic and chloronitroaromatic compounds. Recently our group published draft genome of strain SJ98. In this study, we further sequence and annotate the genome of stain SJ98 to exploit the potential of this bacterium. We specifically annotate its chemotaxis genes and methyl accepting chemotaxis proteins. Genome of Burkholderia sp. SJ98 was annotated using PGAAP pipeline that predicts 7,268 CDSs, 52 tRNAs and 3 rRNAs. Our analysis based on phylogenetic and comparative genomics suggest that Burkholderia sp. YI23 is closest neighbor of the strain SJ98. The genes involved in the chemotaxis of strain SJ98 were compared with genes of closely related Burkholderia strains (i.e. YI23, CCGE 1001, CCGE 1002, CCGE 1003) and with well characterized bacterium E. coli K12. It was found that strain SJ98 has 37 che genes including 19 methyl accepting chemotaxis proteins that involved in sensing of different attractants. Chemotaxis genes have been found in a cluster along with the flagellar motor proteins. We also developed a web resource that provides comprehensive information on strain SJ98 that includes all analysis data (http://crdd.osdd.net/raghava/genomesrs/burkholderia/).

Genome sequence of the nitroaromatic compound-degrading Bacterium Burkholderia sp. strain SJ98

We report the 7.85-Mb genome sequence of Burkholderia sp. strain SJ98, isolated from agricultural fields of Assam, India. The draft genome of this strain will be helpful in studying the genetic pathways involved in the degradation of aromatic compounds.

Diversity and chemotaxis of soil bacteria with antifungal activity against Fusarium wilt of banana

The chemotactic response of bacteria to root exudates plays an important role in the colonization of bacteria in the rhizosphere. In this study, 420 strains of antifungal bacteria against Fusarium oxysporum f. sp. cubense (Foc) were screened for chemotaxis based on a cheA molecular diagnostic method. A total of 124 strains with antifungal efficiencies of 27.26-67.14 % generated a characteristic band of cheA. The chemotaxis of 97 bacterial strains producing a cheA band was confirmed using the drop assay and swarm plate assay using catechol, p-hydroxybenzoic acid, salicylic acid, and asparagine as the attractants. A phylogenetic analysis based on restriction fragment length polymorphisms (RFLPs) and 16S rDNA sequences indicated that the 124 chemotactic antagonists of Foc were affiliated with 18 species of Paenibacillaceae, Bacillaceae, Streptomycineae, Enterobacteriaceae, and Pseudomonadaceae. The chemical composition of banana root exudates were analyzed by GC-MS, and 62 compounds, including alkanes, alkenes, naphthalenes, benzenes, and alcohols, were evaluated. Five representative antagonists of Foc showed 1.76- to 7.75-fold higher chemotactic responses than the control to seven compounds in banana root exudates, as determination by capillary assays.

Discrimination of motile bacteria from filamentous fungi using dynamic speckle

We present a dynamic laser speckle method to easily discriminate filamentous fungi from motile bacteria in soft surfaces, such as agar plate. The method allows the detection and discrimination between fungi and bacteria faster than with conventional techniques. The new procedure could be straightforwardly extended to different micro-organisms, as well as applied to biological and biomedical research, infected tissues analysis, and hospital water and wastewaters studies.

Chemotaxis of Burkholderia sp. strain SJ98 towards chloronitroaromatic compounds that it can metabolise

Background

Burkholderia sp. strain SJ98 is known for its chemotaxis towards nitroaromatic compounds (NACs) that are either utilized as sole sources of carbon and energy or co-metabolized in the presence of alternative carbon sources. Here we test for the chemotaxis of this strain towards six chloro-nitroaromatic compounds (CNACs), namely 2-chloro-4-nitrophenol (2C4NP), 2-chloro-3-nitrophenol (2C3NP), 4-chloro-2-nitrophenol (4C2NP), 2-chloro-4-nitrobenzoate (2C4NB), 4-chloro-2-nitrobenzoate (4C2NB) and 5-chloro-2-nitrobenzoate (5C2NB), and examine its relationship to the degradation of such compounds.

Results

Strain SJ98 could mineralize 2C4NP, 4C2NB and 5C2NB, and co-metabolically transform 2C3NP and 2C4NB in the presence of an alternative carbon source, but was unable to transform 4C2NP under these conditions. Positive chemotaxis was only observed towards the five metabolically transformed CNACs. Moreover, the chemotaxis was induced by growth in the presence of the metabolisable CNAC. It was also competitively inhibited by the presence of nitroaromatic compounds (NACs) that it could metabolise but not by succinate or aspartate.

Conclusions

Burkholderia sp. strain SJ98 exhibits metabolic transformation of, and inducible chemotaxis towards CNACs. Its chemotactic responses towards these compounds are related to its previously demonstrated chemotaxis towards NACs that it can metabolise, but it is independently inducible from its chemotaxis towards succinate or aspartate.

Three types of taxis used in the response of Acidovorax sp. strain JS42 to 2-nitrotoluene

Acidovorax sp. strain JS42 is able to utilize 2-nitrotoluene (2NT) as its sole carbon, nitrogen, and energy source. We report here that strain JS42 is chemotactic to 2NT and that the response is increased when cells are grown on compounds such as 2NT that are known to induce the first step of 2NT degradation. Assays with JS42 mutants unable to oxidize 2NT showed that the first step of 2NT metabolism was required for the induced response, but not for a portion of the constitutive response, indicating that 2NT itself is an attractant. The 2NT metabolite nitrite was shown to be a strong attractant for strain JS42, and sufficient nitrite was produced during the taxis assay to account for a large part of the induced response. A mutant with an inactivated ntdY gene, which is located adjacent to the 2NT degradation genes and codes for a putative methyl-accepting chemotaxis protein, showed a defect in taxis toward 2NT that may involve a reduced response to nitrite. Responses of a mutant defective for the energy-taxis receptor, Aer, indicated that a functional aer gene is required for a substantial part of the wild-type induced response to 2NT. In summary, strain JS42 utilizes three types of taxis to sense and respond to 2NT: constitutive 2NT-specific chemotaxis to directly sense 2NT, metabolism-dependent nitrite-specific chemotaxis that may be mediated by NtdY, and energy taxis mediated by Aer.

Bacterial tactic response to silver nanoparticles

In this study, we investigated the tactic response of Pseudomonas putida G7, a representative soil bacterium, towards silver nanoparticles (AgNPs). The study integrated the characterization of surface area and size distribution of AgNPs, toxicity determinations, based on ATP production, and assessment of the repellent reaction by means of an inverted capillary assay ('chemical-in-pond' method), and changes in the motility behaviour determined by computer-assisted motion analysis. Our data demonstrate, for the first time, that nanoparticles can elicit a negative tactic response in bacteria at low but environmentally relevant, sublethal concentrations. Data obtained by the chemical-in-pond method indicated that cells exposed to 0.1 mg l(-1) of two AgNPs preparations, differing in particle size (maximum diameter ≤ 100 nm and ≤ 150 nm respectively), were repelled in the gradients created inside the capillaries. However, cells exposed to similar low concentration of AgNO3 did not demonstrate any detectable repellent response, although it reduced cell viability by 20%, a decrease comparable to that caused by AgNPs. Computer analysis of swimming behaviour of cells exposed to AgNPs (0.2 mg l(-1) ) revealed a significant increase in turning events, as compared with unexposed controls, which is characteristic of bacterial repellent response. Greater AgNPs concentrations (up to 100 mg l(-1) ) also induced changes in the swimming behaviour, although they did not induce any detectable repellent response as determined by the chemical-in-pond assays. In contrast, AgNO3 failed to induce the repellent swimming behaviour within the wide range of concentrations tested (0.001-100 mg l(-1) ), and caused a significant inhibition of cell motility at a concentration above 0.1 mg l(-1) . The evidence presented here suggests there are likely to be alternative mechanisms by which nano-scale silver induces a repellent response, which is more direct than the toxic response of macro-forms of silver, attributed to ion formation and exposure.

Reductive dehalogenation mediated initiation of aerobic degradation of 2-chloro-4-nitrophenol (2C4NP) by Burkholderia sp. strain SJ98

Burkholderia sp. strain SJ98 (DSM 23195) was previously isolated and characterized for degradation and co-metabolic transformation of a number nitroaromatic compounds. In the present study, we evaluated its metabolic activity on chlorinated nitroaromatic compounds (CNACs). Results obtained during this study revealed that strain SJ98 can degrade 2-chloro-4-nitrophenol (2C4NP) and utilize it as sole source of carbon, nitrogen, and energy under aerobic conditions. The cells of strain SJ98 removed 2C4NP from the growth medium with sequential release of nearly stoichiometric amounts of chloride and nitrite in culture supernatant. Under aerobic degradation conditions, 2C4NP was transformed into the first intermediate that was identified as p-nitrophenol by high-performance liquid chromatography, LCMS-TOF, and GC-MS analyses. This transformation clearly establishes that the degradation of 2C4NP by strain SJ98 is initiated by "reductive dehalogenation"; an initiation mechanism that has not been previously reported for microbial degradation of CNAC under aerobic conditions.

The complete genome of Comamonas testosteroni reveals its genetic adaptations to changing environments

Members of the gram-negative, strictly aerobic genus Comamonas occur in various environments. Here we report the complete genome of Comamonas testosteroni strain CNB-2. Strain CNB-2 has a circular chromosome that is 5,373,643 bp long and has a G+C content of 61.4%. A total of 4,803 open reading frames (ORFs) were identified; 3,514 of these ORFs are functionally assigned to energy production, cell growth, signal transduction, or transportation, while 866 ORFs encode hypothetical proteins and 423 ORFs encode purely hypothetical proteins. The CNB-2 genome has many genes for transportation (22%) and signal transduction (6%), which allows the cells to respond and adapt to changing environments. Strain CNB-2 does not assimilate carbohydrates due to the lack of genes encoding proteins involved in glycolysis and pentose phosphate pathways, and it contains many genes encoding proteins involved in degradation of aromatic compounds. We identified 66 Tct and nine TRAP-T systems and a complete tricarboxylic acid cycle, which may allow CNB-2 to take up and metabolize a range of carboxylic acids. This nutritional bias for carboxylic acids and aromatic compounds enables strain CNB-2 to occupy unique niches in environments. Four different sets of terminal oxidases for the respiratory system were identified, and they putatively functioned at different oxygen concentrations. This study conclusively revealed at the genomic level that the genetic versatility of C. testosteroni is vital for competition with other bacteria in its special niches.

Diversity in bacterial chemotactic responses and niche adaptation

The ability of microbes to rapidly sense and adapt to environmental changes plays a major role in structuring microbial communities, in affecting microbial activities, as well as in influencing various microbial interactions with the surroundings. The bacterial chemotaxis signal transduction system is the sensory perception system that allows motile cells to respond optimally to changes in environmental conditions by allowing cells to navigate in gradients of diverse physicochemical parameters that can affect their metabolism. The analysis of complete genome sequences from microorganisms that occupy diverse ecological niches reveal the presence of multiple chemotaxis pathways and a great diversity of chemoreceptors with novel sensory specificities. Owing to its role in mediating rapid responses of bacteria to changes in the surroundings, bacterial chemotaxis is a behavior of interest in applied microbiology as it offers a unique opportunity for understanding the environmental cues that contribute to the survival of bacteria. This chapter explores the diversity of bacterial chemotaxis and suggests how gaining further insights into such diversity may potentially impact future drug and pesticides development and could inform bioremediation strategies.

Metabolism-independent chemotaxis of Pseudomonas sp. strain WBC-3 toward aromatic compounds

Pseudomonas sp. strain WBC-3 utilized methyl parathion or para-nitrophenol (PNP) as the sole source of carbon, nitrogen, and energy, and methyl parathion hydrolase had been previously characterized. Its chemotactic behaviors to aromatics were investigated. The results indicated that strain WBC-3 was attracted to multiple aromatic compounds, including metabolizable or transformable substrates PNP, 4-nitrocatechol, and hydroquinone. Disruption of PNP catabolic genes had no effect on its chemotactic behaviors with the same substrates, indicating that the chemotactic response in this strain was metabolism-independent. Furthermore, it was shown that strain WBC-3 had a constitutive beta-ketoadipate chemotaxis system that responded to a broad range of aromatic compounds, which was different from the inducible beta-ketoadipate chemotaxis described in other Pseudomonas strains.

Chemotaxis of Ralstonia sp. SJ98 towards p-nitrophenol in soil

Bioremediation of contaminated sites has been accepted as an efficient and cheaper alternative to physicochemical means of remediation in several cases. Although chemotactic behaviour of many bacteria has been studied earlier and assays have been developed to study bacterial chemotaxis in semi-solid media, this phenomenon has never been demonstrated in soil. For bioremediation application it is important to know whether bacteria actually migrate through the heterogenous soil medium towards a gradient of a particular chemoattractant. In the present study we have successfully demonstrated bacterial chemotaxis of a Ralstonia sp. SJ98 in soil microcosm using qualitative and quantitative plate and tray assays. The migration of bacteria has been established using several methods such as plate counting, vital staining and flow cytometry and slot blot hybridization. A non-chemotactic p-nitrophenol utilizing strain Burkholderia cepacia RKJ200 has been used as negative control. Our work clearly substantiates the hypothesis that chemotactic bacteria may enhance in situ bioremediation of toxic pollutants from soils and sediments.

TNT and nitroaromatic compounds are chemoattractants for Burkholderia cepacia R34 and Burkholderia sp. strain DNT

Nitroaromatic compounds are toxic and potential carcinogens. In this study, a drop assay was used to detect chemotaxis toward nitroaromatic compounds for wild-type Burkholderia cepacia R34, wild-type Burkholderia sp. strain DNT, and a 2,4-dinitrotoluene (2,4-DNT) dioxygenase mutant strain (S5). The three strains are chemotactic toward 2,4,6-trinitrotoluene (TNT), 2,3-DNT, 2,4-DNT, 2,5-DNT, 2-nitrotoluene (NT), 4NT, and 4-methyl-5-nitrocatechol (4M5NC), but not toward 2,6-DNT. Of these, only 2,4-DNT is a carbon and energy source for B. cepacia R34 and Burkholderia sp. strain DNT, and 4M5NC is an intermediate in the 2,4-DNT degradation pathway. It was determined that the 2,4-DNT dioxygenase genes are not required for the chemotaxis for these nitroaromatic compounds because the DNT DDO mutant S5 has a chemotactic response toward 2,4-DNT although 2,4-DNT is not metabolized by S5; hence, 2,4-DNT itself is the chemoattractant. This is the first report of chemotaxis toward TNT, 2,3-DNT, 2,4-DNT, 2,5-DNT, 2NT, 4NT, and 4M5NC.

Accessing microbial diversity for bioremediation and environmental restoration

Biological methods for decontamination promise an improved substitute for ineffective and costly physico-chemical remediation methods, although so far only a fraction of the total microbial diversity (i.e. the culturable fraction with metabolic potential) has been harnessed for this purpose. Exploring and exploiting the "overlooked" genetic resource might ameliorate concerns associated with the degradation of recalcitrant and xenobiotic pollutants that are not degraded or only poorly degraded by known culturable bacteria. Recent advances in the molecular genetics of biodegradation and in knowledge-based methods of rational protein modification provide insight into the development of "designer biocatalysts" for environmental restoration. The application of such genetically engineered microorganisms (GEMs) in the environment has been limited, however, owing to the risks associated with uncontrolled growth and proliferation of the introduced biocatalyst and horizontal gene transfer. Programming rapid death of the biocatalyst soon after the depletion of the pollutant could minimize the risks in developing these technologies for successful bioremediation.

Nitrobenzoates and aminobenzoates are chemoattractants for Pseudomonas strains

Three Pseudomonas strains were tested for the ability to sense and respond to nitrobenzoate and aminobenzoate isomers in chemotaxis assays. Pseudomonas putida PRS2000, a strain that grows on benzoate and 4-hydroxybenzoate by using the beta-ketoadipate pathway, has a well-characterized beta-ketoadipate-inducible chemotactic response to aromatic acids. PRS2000 was chemotactic to 3- and 4-nitrobenzoate and all three isomers of aminobenzoate when grown under conditions that induce the benzoate chemotactic response. P. putida TW3 and Pseudomonas sp. strain 4NT grow on 4-nitrotoluene and 4-nitrobenzoate by using the ortho (beta-ketoadipate) and meta pathways, respectively, to complete the degradation of protocatechuate derived from 4-nitrotoluene and 4-nitrobenzoate. However, based on results of catechol 1,2-dioxygenase and catechol 2,3-dioxygenase assays, both strains were found to use the beta-ketoadipate pathway for the degradation of benzoate. Both strains were chemotactic to benzoate, 3- and 4-nitrobenzoate, and all three aminobenzoate isomers after growth with benzoate but not succinate. Strain TW3 was chemotactic to the same set of aromatic compounds after growth with 4-nitrotoluene or 4-nitrobenzoate. In contrast, strain 4NT did not respond to any aromatic acids when grown with 4-nitrotoluene or 4-nitrobenzoate, apparently because these substrates are not metabolized to the inducer (beta-ketoadipate) of the chemotaxis system. The results suggest that strains TW3 and 4NT have a beta-ketoadipate-inducible chemotaxis system that responds to a wide range of aromatic acids and is quite similar to that present in PRS2000. The broad specificity of this chemotaxis system works as an advantage in strains TW3 and 4NT because it functions to detect diverse carbon sources, including 4-nitrobenzoate.