Interaction of Klebsiella oxytoca and Burkholderia cepacia in dual-species batch cultures and biofilms as a function of growth rate and substrate concentration

A versatile micromodel technology to explore biofilm development in porous media flows

Bacterial biofilms that grow in porous media are critical to ecosystem processes and applications ranging from soil bioremediation to bioreactors for treating wastewater or producing value-added products. However, understanding and engineering the complex phenomena that drive the development of biofilms in such systems remains a challenge. Here we present a novel micromodel technology to explore bacterial biofilm development in porous media flows. The technology consists of a set of modules that can be combined as required for any given experiment and conveniently tuned for specific requirements. The core module is a 3D-printed micromodel where biofilm is grown into a perfusable porous substrate. High-precision additive manufacturing, in particular stereolithography, is used to fabricate porous scaffolds with precisely controlled architectures integrating flow channels with diameters down to several hundreds of micrometers. The system is instrumented with: ultraviolet-C light-emitting diodes; on-line measurements of oxygen consumption and pressure drop across the porous medium; camera and spectrophotometric cells for the detection of biofilm detachment events at the outlet. We demonstrate how this technology can be used to study the development of Pseudomonas aeruginosa biofilm for several days within a network of flow channels. We find complex dynamics whereby oxygen consumption reaches a steady-state but not the pressure drop, which instead features a permanent regime with large fluctuations. We further use X-ray computed microtomography to image the spatial distribution of biofilms and computational fluid dynamics to link biofilm development with local flow properties. By combining the advantages of additive manufacturing for the creation of reproducible 3D porous microarchitectures with the flow control and instrumentation accuracy of microfluidics, our system provides a platform to study the dynamics of biofilm development in 3D porous media and to rapidly test new concepts in process engineering.

The establishment of the CBE launched biofilms as a field of specialized research

The Center for Biofilm Engineering was the first center of excellence focused on biofilms and was originally funded through the Engineering Research Center Program from the U.S. National Science Foundation. After almost 30 years, biofilm continues to be a stand-alone scientific topic of inquiry that has broad implications for fundamental and applied science and engineering of bio-systems. However, much remains to be done, not only for research discovery but also education and outreach, to increase and grow the biofilm paradigm as well as our understanding of the microbial world.

Ecological insights into the underlying evolutionary patterns of biofilm formation from biological wastewater treatment systems: Red or Black Queen Hypothesis?

Interspecies interactions and phylogenetic distances were studied to reveal the underlying evolutionary adaptations of biofilms sourced from wastewater treatment processes. Based on 380 pairwise cocultures of 40 strains from two microbial aggregates (surface-attached and mobile aggregates [flocs]) at two substrate concentrations (LB broth and 0.1× LB broth), interspecies interactions were explored using biofilm classification schemes. There was a strong source-dependence of biofilm development formed by the monocultures, that is, a higher biofilm formation potential for strains from attached aggregates than for those from sludge flocs at both substrate concentrations. Interestingly, the results showed that total biofilm reduction was dominant in the dual-species biofilm sourced from flocs in both LB broth (67.37%) and 0.1× LB broth (64.21%), indicating high interspecific competition in mobile aggregates and the independence of substrate concentrations. However, biofilm reduction was higher (33.68%) than induction (19.37%) for the biofilms formed by surface-attached aggregates in LB broth, while the opposite trend was apparent in 0.1× LB broth, suggesting the occurrence of indeterministic processes for biofilm formation and important roles of substrate concentrations. In addition, the more closely related phylogenetic relationships of cocultures from mobile aggregates were consistent with higher competition compared with those from surface-attached aggregates. Overall, the underlying evolutionary patterns of biofilms formed from mobile aggregates consistently followed the essence of the "Red Queen Hypothesis," while biofilms developed from surface-attached aggregates were not deterministic. This study advanced our understanding of biofilm-related treatment processes using the principles of microbial ecology.

Effect of propanil, linuron, and dicamba on the degradation kinetics of 2,4-dichlorophenoxyacetic acid by Burkholderia sp. A study by differential analysis of 2,4-dichlorophenoxyacetic acid degradation data

The successive application of distinct pesticides, or mixtures of them, is a frequent practice that could adversely affect the microbial species inhabiting soil and aquatic ecosystems. The ability of soil or aquatic microbiota to degrade a pesticide could be affected by the presence of another. If the degradation rate of the first compound is inhibited, its dissipation half-life in the environment could be hazardously enlarged. Few studies have been made to quantify the impact on the biodegradation rate of pesticides in soils or water by the presence of other pesticides. In this work, a method for assessing the effect of a pesticide on the biodegradation rate of another, measuring its effect on the biodegradation kinetics of a single bacterial strain is presented. The mathematical analysis is a powerful tool to study the stoichiometry and kinetics of microbial processes, which was used to evaluate independently, in detail, the effect of three pesticides (propanil, linuron, and dicamba) on the biodegradation kinetics of 2,4-dichlorophenoxyacetic acid by a strain of Burkholderia sp. It was evidenced that linuron and dicamba caused a decay of more than 40% in the top instantaneous degradation rate of 2,4-dichlorophenoxyacetic acid, while propanil showed a minimal effect.

Facilitation as Attenuating of Environmental Stress among Structured Microbial Populations

There is currently an intense debate in microbial societies on whether evolution in complex communities is driven by competition or cooperation. Since Darwin, competition for scarce food resources has been considered the main ecological interaction shaping population dynamics and community structure both in vivo and in vitro. However, facilitation may be widespread across several animal and plant species. This could also be true in microbial strains growing under environmental stress. Pure and mixed strains of Serratia marcescens and Candida rugosa were grown in mineral culture media containing phenol. Growth rates were estimated as the angular coefficients computed from linearized growth curves. Fitness index was estimated as the quotient between growth rates computed for lineages grown in isolation and in mixed cultures. The growth rates were significantly higher in associated cultures than in pure cultures and fitness index was greater than 1 for both microbial species showing that the interaction between Serratia marcescens and Candida rugosa yielded more efficient phenol utilization by both lineages. This result corroborates the hypothesis that facilitation between microbial strains can increase their fitness and performance in environmental bioremediation.

Inhibition of Flavobacterium psychrophilum biofilm formation using a biofilm of the antagonist Pseudomonas fluorescens FF48

The most important bacterial pathology currently occurring in Chilean freshwater salmon farming is the cold-water disease produced by the psychrotrophic bacteria Flavobacterium psychrophilum. The main aim of this study was to characterize the inhibitory activity of an antagonist strain on the formation of biofilms of a F. psychrophilum strain. The antagonistic strain Pseudomonas fluorescens FF48 was isolated from the sediment beneath the salmon cages of a freshwater Chilean salmon farm and was identified by using the 16S rRNA gene sequence analysis. The production of siderophores, mainly during the stationary phase of growth of the antagonist strain was demonstrated using the Chrome Azurol S method and through F. psychrophilum inhibition under iron saturation conditions. Subsequently, the effect of the antagonist supernatant on the formation of F. psychrophilum biofilm was tested using the crystal violet staining method observing an inhibition of the growth of F. psychrophilum, but no effect was observed when iron saturation concentrations were used. Furthermore, when the antagonist strain was previously deposited on the support, it completely inhibited the formation of F. psychrophilum biofilms, but when both bacteria were inoculated simultaneously no inhibitory effect was detected. In conclusion, it was demonstrated that FF48 strain is able to inhibit the formation of F. psychrophilum biofilms in vitro probably mediated by the siderophore production, suggesting its potential use as a biocontrol biofilm in freshwater fish rearing systems to prevent the persistence of biofilms of the fish pathogenic species F. psychrophilum.

Improved diagnosis of central venous catheter-related bloodstream infections using the HB&L UROQUATTRO™ system

The diagnosis of catheter-related bloodstream infections (CRBSIs) in febrile patients with indwelling central venous catheters (CVCs) needs improvement. To diagnose CRBSIs more efficiently, we have developed a novel culture approach using the catheter tips removed from febrile patients. CVCs and blood cultures from 1,070 patients with only CVC-related infections were obtained over a period of 3 years (January 2009 to December 2011). The CVCs were evaluated by a semi-quantitative catheter culture method according to Maki's method and by our novel method, which is based on the use of the HB&L UROQUATTRO™ system (Alifax, Padova, Italy). Using our new method, 571 (571/1,070) of the infections were confirmed as CRBSIs. The remaining 487 patients had infections that were associated with hematologic malignancies, neutropenia, prior exposure to antibiotics, and a decreased CVC removal rate. Twelve samples were identified as false-positives. The percentage of patients with CRBSIs confirmed using the HB&L UROQUATTRO™ system was 53.36 % versus 34.95 % (p-value 0.004) using Maki's method (374/1,070 CVC Maki-positive samples). Our results indicate that our new culture method allows for an improved CRBSI diagnosis rate. A significant number of tip cultures (18.41 %) tested positive for CRBSIs using our system but were negative when tested using Maki's method. Moreover, the use of the HB&L UROQUATTRO™ system allowed us to significantly reduce diagnosis time; a negative CRBSI diagnosis could be made within 6 h and a positive diagnosis could be made within 22-28 h.

The effects of metabolite molecules produced by drinking water-isolated bacteria on their single and multispecies biofilms

The elucidation of the mechanisms by which diverse species survive and interact in drinking water (DW) biofilm communities may allow the identification of new biofilm control strategies. The purpose of the present study was to investigate the effects of metabolite molecules produced by bacteria isolated from DW on biofilm formation. Six opportunistic bacteria, viz. Acinetobacter calcoaceticus, Burkholderia cepacia, Methylobacterium sp., Mycobacterium mucogenicum, Sphingomonas capsulata and Staphylococcus sp. isolated from a drinking water distribution systems (DWDS) were used to form single and multispecies biofilms in the presence and absence of crude cell-free supernatants produced by the partner bacteria. Biofilms were characterized in terms of mass and metabolic activity. Additionally, several physiological aspects regulating interspecies interactions (sessile growth rates, antimicrobial activity of cell-free supernatants, and production of iron chelators) were studied to identify bacterial species with biocontrol potential in DWDS. Biofilms of Methylobacterium sp. had the highest growth rate and M. mucogenicum biofilms the lowest. Only B. cepacia was able to produce extracellular iron-chelating molecules. A. calcoaceticus, B. cepacia, Methylobacterium sp. and M. mucogenicum biofilms were strongly inhibited by crude cell-free supernatants from the other bacteria. The crude cell-free supernatants of M. mucogenicum and S. capsulata demonstrated a high potential for inhibiting the growth of counterpart biofilms. Multispecies biofilm formation was strongly inhibited in the absence of A. calcoaceticus. Only crude cell-free supernatants produced by B. cepacia and A. calcoaceticus had no inhibitory effects on multispecies biofilm formation, while metabolite molecules of M. mucogenicum showed the most significant biocontrol potential.

Modelling the bacterial communities associated with cystic fibrosis lung infections

In many human diseases that cystic fibrosis (CF) patients suffer from, for example, lung infections, bacteria have been considered to grow as biofilms. The ability of key CF pathogens such as Pseudomonas aeruginosa to resist antibiotic therapies may be due to the poor drug penetration of these biofilms. The overall aim of this study was to develop biofilm models in vitro that resembled the bacterial species composition of CF sputa. Here, this was a step towards a longer term goal of forming multiple bacterial biofilm models in vitro that would serve, in turn, as better assays of antibiotic susceptibilities than conventionally grown cells. Biofilm models were constructed from 31 CF sputum samples, using a modified microtitre plate assay. Three forms of assessment of these biofilms were made, namely, the mass, microscopic analysis and species composition. Species composition in sputa and biofilms, characterised by terminal restriction fragment length polymorphism (T-RFLP) analysis of ribosomal gene polymerase chain reaction (PCR) products amplified from directly extracted nucleic acids, indicated that the bacterial community in sputa was well reproduced in the biofilm models. Typically, fresh sputa contained 4.6 +/- 2.3 bacterial species, with the species number decreasing to 4.0 +/- 1.6 over 5 days-this was not statistically significant (p = 0.29). This study outlines a novel methodology by which to generate and study bacterial biofilms communities. It is also hoped that the versatility of this in vitro approach, combined with its simplicity and high reproducibility, will make it an effective system to study CF sputum biofilm development and, in the longer term, serve as a means of assessing antibiotic susceptibilities.

Distribution of cepacian biosynthesis genes among environmental and clinical Burkholderia strains and role of cepacian exopolysaccharide in resistance to stress conditions

The genus Burkholderia includes strains pathogenic to animals and plants, bioremediators, or plant growth promoters. Genome sequence analyses of representative Burkholderia cepacia complex (Bcc) and non-Bcc strains for the presence of the bce-I gene cluster, directing the biosynthesis of the exopolysaccharide (EPS) cepacian, further extended this previously described cluster by another 9 genes. The genes in the bce-II cluster were named bceM to bceU and encode products putatively involved in nucleotide sugar precursor biosynthesis and repeat unit assembly, modification, and translocation across the cytoplasmic membrane. Disruption of the B. cepacia IST408 bceQ and bceR genes, encoding a putative repeat unit flippase and a glycosyltransferase, respectively, resulted in the abolishment of cepacian biosynthesis. A mutation in the bceS gene, encoding a putative acyltransferase, did not affect EPS production yield significantly but decreased its acetylation content by approximately 20%. Quantitative real-time reverse transcription-PCR experiments confirmed the induction of genes in the bce-I and bce-II clusters in a Burkholderia multivorans EPS producer clinical isolate in comparison to the level for its isogenic EPS-defective strain. Fourier Transform infrared spectroscopy analysis confirmed that the exopolysaccharide produced by 10 Burkholderia isolates tested was cepacian. The ability of Burkholderia strains to withstand desiccation and metal ion stress was higher when bacteria were incubated in the presence of 2.5 g/liter of cepacian, suggesting that this EPS plays a role in the survival of these bacteria by contributing to their ability to thrive in different environments.

Biofilm growth of individual and dual strains of Klebsiella oxytoca from the dairy industry on ultrafiltration membranes

Formation of biofilms in dairy membrane plants causes membrane pore blocking, product contamination and subsequent economic loss. To investigate the biofilm growth, two Klebsiella oxytoca strains, K. B006 and TR002, previously isolated from New Zealand dairy membrane plants, were grown both individually and combined on three types of ultrafiltration (UF) membranes in different concentrations of whey medium in biofilm reactors (CBR 90, BioSurface Technologies, Bozeman, USA). Biofilms of both the individual and combined strains grew on the membrane surfaces to levels of 4.9-7.99 log colony-forming units (CFU) cm(-2) measured by standard plate counting after removing the cells by sonication. More biofilm grew on used polyethersulfone (PES) membranes than on new PES and polyvinylidene fluoride (PVDF) membranes. Both strains formed good biofilms, although K. B006 formed a denser biofilm than TR002. This corresponded to our previous study on the attachment of these organisms, where K. B006 attached in greater numbers than K. TR002. The dual strains produced a higher biofilm density than single strains on the new membranes. Biofilm density tended to increase with increased whey concentration. The saturated biofilm was approximately 10(8) CFU cm(-2). PES membranes appeared to support biofilm growth less readily than did PVDF membranes and therefore may be the preferred material for UF membranes to reduce problems with microbial colonisation. Used membranes were more readily colonised with biofilm than were new membranes. Therefore, selecting a membrane type and monitoring membrane age will help manage biofilm development during UF.

Escherichia coli O157:H7 requires colonizing partner to adhere and persist in a capillary flow cell

The ability of a strain of waterborne Escherichia coli O157:H7 to colonize a glass flow cell and develop microcolonies when grown alone and with Pseudomonas aeruginosa PAO1 was examined. When introduced alone, planktonic E. coil were unable to attach to the glass surface. When introduced simultaneously with P. aeruginosa (co-inoculation), the two species coadhered to the surface. When E. coliwere introduced into a flow cell precolonized with a P. aeruginosa biofilm (precolonized), 10-fold more cells were retained than in the co-inoculated case. Both species were monitored nondestructively by time-lapse confocal microscopy, direct microscopy of the filtered effluent, and effluent plate counts. While more E. coli initially adhered in the precolonized system, E. coli microcolony formation occurred only in the co-inoculated system, where E. coil comprised 1% of the total surface-associated biovolume but greater than 50% of the biovolume near the edges of the flow cell. The hydrodynamics in the flow cell were evaluated using the finite volume analysis program CFX, revealing that shear stress was likely important in both initial attachment and steady-state colonization patterns. This research elucidates key factors which promote retention and subsequent biofilm development of E. coli 0157:H7.

INTRODUCTION

Bacteria exist in nature primarily in communities known as biofilms. These biofilms are usually characterized by differentiated structures, exhibit a different phenotype than their planktonic counterparts, and in nature most often consist of multispecies consortia (1, 2). An important process in shaping the formation and structure of some multispecies biofilms is the ability of certain species to coaggregate. In this process, planktonic cells adhere to genetically distinct cells in a biofilm or to other planktonic cells (3), thereby increasing biofilm formation. This process is growth-phase-dependent and is turned on and off by cells, suggestive that it may also play a role in dispersal and dissemination (4). Due to these and other complexities of the biofilm mode of growth, multiple species can coexist despite one organism having a much higher growth rate than another (5-7). In many cases, bacteria have been shown to gain a fitness advantage when residing in a mixed-species versus single-

Enhanced biofilm formation and 3-chlorobenzoate degrading activity by the bacterial consortium of Burkholderia sp. NK8 and Pseudomonas aeruginosa PAO1

AIMS

To characterize biofilm formation of a chlorobenzoates (CBs) degrading bacterium, Burkholderia sp. NK8, with another bacterial species, and the biodegradation activity against CBs in the mixed-species biofilm.

METHODS AND RESULTS

Burkholderia sp. NK8 was solely or co-cultured with each of five other representative bacteria in microtitre dishes. Biofilm formation involving the strain NK8 was synergistically promoted by co-culturing with only Pseudomonas aeruginosa PAO1. Epifluorescent microscopy revealed that cells of the bacterial strain NK8 were viable and distributed randomly in the mixed-species biofilms. Enumeration of the attached cells on the surface of wells revealed that cells of the strain NK8 increased approx. 10-fold by the co-culture with the strain PAO1 compared to those by monoculture of the strain NK8, and the degradation activity of 3-chlorobenzoate by the dual-species biofilms was more promoted than that by the strain NK8-monocultured biofilms.

CONCLUSIONS

Enhanced biofilm formation of Burkholderia sp. NK8 by the bacterial consortium occurred, but is determined by the partner bacterial species. The mixed-species biofilms have the advantage to degrade CBs on a solid surface.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study provides a significance of bacterial consortia on the biofilm formation and the degradation activity of Burkholderia sp. NK8, which contribute for complete degradation of chlorinated aromatics.

Antagonism between Bacillus cereus and Pseudomonas fluorescens in planktonic systems and in biofilms

In the environment, many microorganisms coexist in communities competing for resources, and they are often associated as biofilms. The investigation of bacterial ecology and interactions may help to improve understanding of the ability of biofilms to persist. In this study, the behaviour of Bacillus cereus and Pseudomonas fluorescens in the planktonic and sessile states was compared. Planktonic tests were performed with single and dual species cultures in growth medium with and without supplemental FeCl3. B. cereus and P. fluorescens single cultures had equivalent growth behaviours. Also, when in co-culture under Fe-supplemented conditions, the bacteria coexisted and showed similar growth profiles. Under Fe limitation, 8 h after co-culture and over time, the number of viable B. cereus cells decreased compared with P. fluorescens. Spores were detected during the course of the experiment, but were not correlated with the decrease in the number of viable cells. This growth inhibitory effect was correlated with the release of metabolite molecules by P. fluorescens through Fe-dependent mechanisms. Biofilm studies were carried out with single and dual species using a continuous flow bioreactor rotating system with stainless steel (SS) substrata. Steady-state biofilms were exposed to a series of increasing shear stress forces. Analysis of the removal of dual species biofilms revealed that the outer layer was colonised mainly by B. cereus. This bacterium was able to grow in the outermost layers of the biofilm due to the inhibitory effect of P. fluorescens being decreased by the exposure of the cells to fresh culture medium. B. cereus also constituted the surface primary coloniser due to its favourable adhesion to SS. P. fluorescens was the main coloniser of the middle layers of the biofilm. Single and dual species biofilm removal data also revealed that B. cereus biofilms had the highest physical stability, followed by P. fluorescens biofilms. This study highlights the inadequacy of planktonic systems to mimic the behaviour of bacteria in biofilms and shows how the culturing system affects the action of antagonist metabolite molecules because dilution and consequent loss of activity occurred in continuously operating systems. Furthermore, the data demonstrate the biocontrol potential of P. fluorescens on the planktonic growth of B. cereus and the ability of the two species to coexist in a stratified biofilm structure.

Biofilm interactions between distinct bacterial genera isolated from drinking water

In the environment, multiple microorganisms coexist as communities, competing for resources and often associated as biofilms. In this study, single- and dual-species biofilm formation by, and specific activities of, six heterotrophic intergeneric bacteria were determined using 96-well polystyrene plates over a 72-h period. These bacteria were isolated from drinking water and identified by partial 16S rRNA gene sequencing. A series of planktonic studies was also performed, assessing the bacterial growth rate, motility, and production of quorum-sensing inhibitors (QSI). This constituted an attempt to identify key attributes allowing bacteria to effectively interact and coexist in a drinking-water environment. We observed that in both pure and dual cultures, all of the isolates formed stable biofilms within 72 h, with specific metabolic activity decreasing, in most cases, with an increase in biofilm mass. The largest single- and dual-biofilm amounts were found for Methylobacterium sp. and the combination of Methylobacterium sp. and Mycobacterium mucogenicum, respectively. Evidences of microbial interactions in dual-biofilm formation, associated with appreciable biomass variation in comparison with single biofilms, were found for the following cases: synergy/cooperation between Sphingomonas capsulata and Burkholderia cepacia, S. capsulata and Staphylococcus sp., and B. cepacia and Acinetobacter calcoaceticus and antagonism between S. capsulata and M. mucogenicum, S. capsulata and A. calcoaceticus, and M. mucogenicum and Staphylococcus sp. A neutral interaction was found for Methylobacterium sp.-M. mucogenicum, S. capsulata-Staphylococcus sp., M. mucogenicum-A. calcoaceticus, and Methylobacterium sp.-A. calcoaceticus biofilms, since the resultant dual biofilms had a mass and specific metabolic activity similar to the average for each single biofilm. B. cepacia had the highest growth rate and motility and produced QSI. Other bacteria producing QSI were Methylobacterium sp., S. capsulata, and Staphylococcus sp. However, only for S. capsulata-M. mucogenicum, S. capsulata-A. calcoaceticus, and M. mucogenicum-Staphylococcus sp., dual-biofilm formation seems to be regulated by the QSI produced by S. capsulata and Staphylococcus sp. and by the increased growth rate of S. capsulata. The parameters assessed by planktonic studies did not allow prediction and generalization of the exact mechanism regulating dual-species biofilm formation between the drinking-water bacteria.

Characterization of a Pseudomonas putida rough variant evolved in a mixed-species biofilm with Acinetobacter sp. strain C6

Genetic differentiation by natural selection is readily observed among microbial populations, but a more comprehensive understanding of evolutionary forces, genetic causes, and resulting phenotypic advantages is not often sought. Recently, a surface population of Pseudomonas putida bacteria was shown to evolve rapidly by natural selection of better-adapted variants in a mixed-species biofilm consortium (S. K. Hansen, P. B. Rainey, J. A. Haagensen, and S. Molin, Nature 445:533-536, 2007). Adaptation was caused by mutations in a wapH homolog (PP4943) involved in core lipopolysaccharide biosynthesis. Here we investigate further the biofilm physiology and the phenotypic characteristics of the selected P. putida rough colony variants. The coexistence of the P. putida population in a mixed-species biofilm with Acinetobacter sp. strain C6 is dependent on the benzoate excreted from Acinetobacter during the catabolism of benzyl alcohol, the sole carbon source. Examination of biofilm development and the dynamics of the wild-type consortium revealed that the biofilm environment became oxygen limited, possibly with low oxygen concentrations around Acinetobacter microcolonies. In contrast to P. putida wild-type cells, which readily dispersed from the mixed-species biofilm in response to oxygen starvation, the rough variant cells displayed a nondispersal phenotype. However, in monospecies biofilms proliferating on benzoate, the rough variant (like the wild-type population) dispersed in response to oxygen starvation. A key factor explaining this conditional, nondispersal phenotype is likely to be the acquired ability of the rough variant to coaggregate specifically with Acinetobacter cells. We further show that the P. putida rough variant displayed enhanced production of a cellulose-like polymer as a consequence of the mutation in wapH. The resulting phenotypic characteristics of the P. putida rough variant explain its enhanced fitness and ability to form tight structural associations with Acinetobacter microcolonies.

Effect of substrate concentration on dual-species biofilm population densities of Klebsiella oxytoca and Burkholderia cepacia in porous media

The long-term operation of bioremediation technologies relies on the success of the contaminant-degrading microorganism(s) to compete for available resources with microorganisms already present in an aquifer or those that may contaminate a bioreactor. Though research has been performed studying the interaction of multiple species in batch and chemostat reactors, little work has been done looking at multi-species interactions in environments that more closely resemble field-scale applications. The research presented herein examined the interaction of Burkholderia cepacia PR1-pTOM(31c), an aerobic trichloroethylene (TCE)-degrading bacterium, with Klebsiella oxytoca, a facultative bacterium, in a flow-through porous media (PM) reactor. Growth characteristics and population distributions in PM were compared to previously reported values from batch and chemostat reactors. The faster growing organism in batch experiments (K. oxytoca) did not always have the greater population density in dual-species PM experiments. The biofilm population distribution was influenced by substrate concentration, with B. cepacia having a greater dual-species population density than K. oxytoca at a low (30 mg/L dissolved organic carbon [DOC]) substrate concentration and K. oxytoca having a greater population density at a high (700 mg/L DOC) substrate concentration. This change in species population distribution with change in substrate concentration, which was not observed in batch reactors, was also observed in chemostat reactors. Therefore, manipulation of substrate concentration enabled the control of species dominance to the advantage of the TCE degrading population in this dual-species PM system and may provide a mechanism to enhance bioremediation scenarios involving TCE or other contaminants of concern.