Microbial degradation of polycyclic aromatic hydrocarbons in soil by bacterium-fungus co-cultures

Fungal-bacterial consortia: A promising strategy for the removal of petroleum hydrocarbons

Nowadays, petroleum hydrocarbon pollution is one of the most widespread types of contamination that poses a serious threat to both public health and the environment. Among various physicochemical methods, bioremediation is an eco-friendly and cost-effective way to eliminate petroleum hydrocarbon pollutants. The successful degradation of all hydrocarbon components and the achievement of optimal efficiency are necessary for the success of this process. Using potential microbial consortia with rich metabolic networks is a promising strategy for addressing these challenges. Mixed microbial communities, comprising both fungi and bacteria, exhibit diverse synergistic mechanisms to degrade complex hydrocarbon contaminants, including the dissemination of bacteria by fungal hyphae, enhancement of enzyme and secondary metabolites production, and co-metabolism of pollutants. Compared to pure cultures or consortia of either fungi or bacteria, different studies have shown increased bioremediation of particular contaminants when combined fungal-bacterial treatments are applied. However, antagonistic interactions, like microbial competition, and the production of inhibitors or toxins can observed between members. Furthermore, optimizing environmental factors (pH, temperature, moisture, and initial contaminant concentration) is essential for consortium performance. With the advancements in synthetic biology and gene editing tools, it is now feasible to design stable and robust artificial microbial consortia systems. This review presents an overview of using microbial communities for the removal of petroleum pollutants by focusing on microbial degradation pathways, and their interactions. It also highlights the new strategies for constructing optimal microbial consortia, as well as the challenges currently faced and future perspectives of applying fungal-bacterial communities for bioremediation.

Potential and prospects of Actinobacteria in the bioremediation of environmental pollutants: Cellular mechanisms and genetic regulations

Increasing industrialization and anthropogenic activities have resulted in the release of a wide variety of pollutants into the environment including pesticides, polycyclic aromatic hydrocarbons (PAHs), and heavy metals. These pollutants pose a serious threat to human health as well as to the ecosystem. Thus, the removal of these compounds from the environment is highly important. Mitigation of the environmental pollution caused by these pollutants via bioremediation has become a promising approach nowadays. Actinobacteria are a group of eubacteria mostly known for their ability to produce secondary metabolites. The morphological features such as spore formation, filamentous growth, higher surface area to volume ratio, and cellular mechanisms like EPS secretion, and siderophore production in Actinobacteria render higher resistance and biodegradation ability. In addition, these bacteria possess several oxidoreductase systems (oxyR, catR, furA, etc.) which help in bioremediation. Actinobacteria genera including Arthrobacter, Rhodococcus, Streptomyces, Nocardia, Microbacterium, etc. have shown great potential for the bioremediation of various pollutants. In this review, the bioremediation ability of these bacteria has been discussed in detail. The utilization of various genera of Actinobacteria for the biodegradation of organic pollutants, including pesticides and PAHs, and inorganic pollutants like heavy metals has been described. In addition, the cellular mechanisms in these microbes which help to withstand oxidative stress have been discussed. Finally, this review explores the Actinobacteria mediated strategies and recent technologies such as the utilization of mixed cultures, cell immobilization, plant-microbe interaction, utilization of biosurfactants and nanoparticles, etc., to enhance the bioremediation of various environmental pollutants.

Impact of lignocellulosic waste-immobilised white-rot fungi on enhancing the development of 14C-phenanthrene catabolism in soil

In this study, an investigation was carried out to explore the the impact of white-rot fungi (WRF) on enhancing the development of phenanthrene catabolism in soil over time (1, 25, 50, 75 and 100 d). The WRF were immobilised on spent brewery grains (SBG) prior to inoculation to the soil. The results showed that SBG-immobilised WRF-amended soils reduced the lag phases and increased the extents of ¹⁴C-phenanthrene mineralisation. Greater reductions in the lag phases and increases in the rates of mineralisation were observed in immobilised Trametes versicolor-amended soil compared to the other WRF-amendments. However, the presence of Pleurotus ostreatus and Phanerochaete chrysosporium influenced biodegradation more strongly than the other fungal species. In addition, fungal enzyme activities increased in the amended soils and positively correlated with the extents of ¹⁴C-phenanthrene mineralisation in all soil amendments. Maximum ligninolytic enzyme activities were observed in P. ostreatus-amended soil. Microbial populations increased in all amended soils while PAH-degrading fungal numbers increased with increased soil-PAH contact time and strongly positively correlated with fastest rates of mineralisation. The findings presented in this study demonstrate that inoculating the soil with these immobilised WRFs generally enhanced the mineralisation of the ¹⁴C-phenanthrene in soil. This has the potential to be used to stimulate or enhance PAH catabolism in field-contaminated soils.

Biodiversity and oil degradation capacity of oil-degrading bacteria isolated from deep-sea hydrothermal sediments of the South Mid-Atlantic Ridge

Studies have reported that various hydrocarbons and hydrocarbon-degrading bacteria are found in global deep-sea hydrothermal regions. However, little is known about degradation characteristics of culturable hydrocarbon-degrading bacteria from these regions. We speculate that these bacteria can be used as resources for the bioremediation of oil pollution. In this study, six oil-degrading consortia were obtained from the hydrothermal region of the Southern Mid-Atlantic Ridge through room-temperature enrichment experiments. The dominant oil-degrading bacteria belonged to Nitratireductor, Pseudonocardia, Brevundimonas and Acinetobacter. More varieties of hydrocarbon-degrading bacteria were obtained from sediments (preserved at 4 °C) near hydrothermal vents. Most strains had the ability to degrade high molecular weight petroleum components. In addition, Pseudonocardia was shown to exhibit a high degradation ability for phytane and pristine for the first time. This study may provide new insights into the community structure and biodiversity of culturable oil-degrading bacteria in deep-sea hydrothermal regions.

Bioremediation of Polycyclic Aromatic Hydrocarbons from Industry Contaminated Soil Using Indigenous Bacillus spp

Polycyclic aromatic hydrocarbons (PAHs) are reportedly toxic, ubiquitous and organic compounds that can persist in the environment and are released largely due to the incomplete combustion of fossil fuel. There is a range of microorganisms that are capable of degrading low molecular weight PAHs, such as naphthalene; however, fewer were reported to degrade higher molecular weight PAHs. Bacillus spp. has shown to be effective in neutralizing polluted streams containing hydrocarbons. Following the growing regulatory requirement to meet the PAH specification upon disposal of contaminated soil, the following study aimed to identify potential Bacillus strains that could effectively remediate low and high molecular weight PAHs from the soil. Six potential hydrocarbon-degrading strains were formulated into two prototypes and tested for the ability to remove PAHs from industry-contaminated soil. Following the dosing of each respective soil system with prototypes 1 and 2, the samples were analyzed for PAH concentration over 11 weeks against an un-augmented control system. After 11 weeks, the control system indicated the presence of naphthalene (3.11 µg·kg−1), phenanthrene (24.47 µg·kg−1), fluoranthene (17.80 µg·kg−1) and pyrene (28.92 µg·kg−1), which illustrated the recalcitrant nature of aromatic hydrocarbons. The soil system dosed with prototype 2 was capable of completely degrading (100%) naphthalene, phenanthrene and pyrene over the experimental period. However, the accumulation of PAHs, namely phenanthrene, fluoranthene and pyrene, were observed using prototype 1. The results showed that prototype 2, consisting of a combination of Bacillus cereus and Bacillus subtilis strains, was more effective in the biodegradation of PAHs and intermediate products. Furthermore, the bio-augmented system dosed with prototype 2 showed an improvement in the overall degradation (10–50%) of PAHs, naphthalene, phenanthrene and pyrene, over the un-augmented control system. The following study demonstrates the potential of using Bacillus spp. in a bioremediation solution for sites contaminated with PAHs and informs the use of biological additives for large-scale environmental remediation.

Soil indigenous microorganisms weaken the synergy of Massilia sp. WF1 and Phanerochaete chrysosporium in phenanthrene biodegradation

Biodegradation is a promising way to reduce phenanthrene (PHE) in environment. PHE biodegradation by bioaugmentation of axenic and mixed cultures of Massilia sp. WF1 (a highly efficient PHE-degrading bacteria) and Phanerochaete chrysosporium (P. chrysosporium, an extensively researched model fungus in organic pollutant bioremediation) was investigated in aqueous and autoclaved/un-autoclaved soil cultures. In the liquid cultures, the strain WF1 could use PHE (ca. 10 mg L^-1) as the sole carbon source, and the presence of d-fructose (500 mg L^-1) had no obvious effect on its PHE degradation; while the opposite was observed for P. chrysosporium. The bioaugmentation of strain WF1 and P. chrysosporium co-culture showed the highest PHE-degradation efficiency, especially in the aqueous and the autoclaved soil (PHE, ca. 50 mg kg^-1) cultures, indicating a synergistic interaction of the co-culture during PHE dissipation. It was further observed that the indigenous microorganisms (mainly the Gram-positive bacteria) played a dominant role during PHE biodegradation and showed an antagonistic action against the strain WF1-P. chrysosporium co-culture, which weakened the synergistic action of the co-culture in the un-autoclaved soil. Besides, the abundances of PAH-RHDα GP and nidA genes were negatively correlated with residual PHE in the soil. Our findings provide the scientific support for bioremediation of PAHs in environment.

Potential use of fungal-bacterial co-cultures for the removal of organic pollutants

Fungi and bacteria coexist in a wide variety of natural and artificial environments which can lead to their association and interaction - ranging from antagonism to cooperation - that can affect the survival, colonization, spatial distribution and stress resistance of the interacting partners. The use of polymicrobial cultivation approaches has facilitated a more thorough understanding of microbial dynamics in mixed microbial communities, such as those composed of fungi and bacteria, and their influence on ecosystem functions. Mixed (multi-domain) microbial communities exhibit unique associations and interactions that could result in more efficient systems for the degradation and removal of organic pollutants. Several previous studies have reported enhanced biodegradation of certain pollutants when using combined fungal-bacterial treatments compared to pure cultures or communities of either fungi or bacteria (single domain systems). This article reviews: (i) the mechanisms of pollutant degradation that can occur in fungal-bacterial systems (e.g.: co-degradation, production of secondary metabolites, enhancement of degradative enzyme production, and transport of bacteria by fungal mycelia); (ii) case studies using fungal-bacterial co-cultures for the removal of various organic pollutants (synthetic dyes, polycyclic aromatic hydrocarbons, pesticides, and other trace or volatile organic compounds) in different environmental matrices (e.g. water, gas/vapors, soil); (iii) the key aspects of engineering artificial fungal-bacterial co-cultures, and (iv) the current challenges and future perspectives of using fungal-bacterial co-cultures for environmental remediation.

Reconstruction and evaluation of oil-degrading consortia isolated from sediments of hydrothermal vents in the South Mid-Atlantic Ridge

In this study, sediments were collected from two different sites in the deep-sea hydrothermal region of the South Atlantic Ocean. Two microbial enrichment cultures (H7S and H11S), which were enriched from the sediments collected at two sample sites, could effectively degrade petroleum hydrocarbons. The bacterial diversity was analyzed by high-throughput sequencing method. The petroleum degradation ability were evaluated by gas chromatography–mass spectrometry and gravimetric analysis. We found that the dominant oil-degrading bacteria of enrichment cultures from the deep-sea hydrothermal area belonged to the genera Pseudomonas, Nitratireductor, Acinetobacter, and Brevundimonas. After a 14-day degradation experiment, the enrichment culture H11S, which was obtained near a hydrothermal vent, exhibited a higher degradation efficiency for alkanes (95%) and polycyclic aromatic hydrocarbons (88%) than the enrichment culture H7S. Interestingly, pristane and phytane as biomarkers were degraded up to 90% and 91% respectively by the enrichment culture H11S, and six culturable oil-degrading bacterial strains were isolated. Acinetobacter junii strain H11S-25, Nitratireductor sp. strain H11S-31 and Pseudomonas sp. strain H11S-28 were used at a density ratio of 95:4:1 to construct high-efficiency oil-degrading consortium H. After a three-day biodegradation experiment, consortium H showed high degradation efficiencies of 74.2% and 65.7% for total alkanes and PAHs, respectively. The degradation efficiency of biomarkers such as pristane and high-molecular-weight polycyclic aromatic hydrocarbons (such as CHR) reached 84.5% and 80.48%, respectively. The findings of this study indicate that the microorganisms in the deep-sea hydrothermal area are potential resources for degrading petroleum hydrocarbons. Consortium H, which was artificially constructed, showed a highly efficient oil-degrading capacity and has significant application prospects in oil pollution bioremediation.

Analysis of the biodegradative and adaptive potential of the novel polychlorinated biphenyl degrader Rhodococcus sp. WAY2 revealed by its complete genome sequence

The complete genome sequence of Rhodococcus sp. WAY2 (WAY2) consists of a circular chromosome, three linear replicons and a small circular plasmid. The linear replicons contain typical actinobacterial invertron-type telomeres with the central CGTXCGC motif. Comparative phylogenetic analysis of the 16S rRNA gene along with phylogenomic analysis based on the genome-to-genome blast distance phylogeny (GBDP) algorithm and digital DNA–DNA hybridization (dDDH) with other Rhodococcus type strains resulted in a clear differentiation of WAY2, which is likely a new species. The genome of WAY2 contains five distinct clusters of bph, etb and nah genes, putatively involved in the degradation of several aromatic compounds. These clusters are distributed throughout the linear plasmids. The high sequence homology of the ring-hydroxylating subunits of these systems with other known enzymes has allowed us to model the range of aromatic substrates they could degrade. Further functional characterization revealed that WAY2 was able to grow with biphenyl, naphthalene and xylene as sole carbon and energy sources, and could oxidize multiple aromatic compounds, including ethylbenzene, phenanthrene, dibenzofuran and toluene. In addition, WAY2 was able to co-metabolize 23 polychlorinated biphenyl congeners, consistent with the five different ring-hydroxylating systems encoded by its genome. WAY2 could also use n-alkanes of various chain-lengths as a sole carbon source, probably due to the presence of alkB and ladA gene copies, which are only found in its chromosome. These results show that WAY2 has a potential to be used for the biodegradation of multiple organic compounds.

Synthetic Microbial Ecology: Engineering Habitats for Modular Consortia

The metabolic diversity present in microbial communities enables cooperation toward accomplishing more complex tasks than possible by a single organism. Members of a consortium communicate by exchanging metabolites or signals that allow them to coordinate their activity through division of labor. In contrast with monocultures, evidence suggests that microbial consortia self-organize to form spatial patterns, such as observed in biofilms or in soil aggregates, that enable them to respond to gradient, to improve resource interception and to exchange metabolites more effectively. Current biotechnological applications of microorganisms remain rudimentary, often relying on genetically engineered monocultures (e.g., pharmaceuticals) or mixed-cultures of partially known composition (e.g., wastewater treatment), yet the vast potential of “microbial ecological power” observed in most natural environments, remains largely underused. In line with the Unified Microbiome Initiative (UMI) which aims to “discover and advance tools to understand and harness the capabilities of Earth's microbial ecosystems,” we propose in this concept paper to capitalize on ecological insights into the spatial and modular design of interlinked microbial consortia that would overcome limitations of natural systems and attempt to optimize the functionality of the members and the performance of the engineered consortium. The topology of the spatial connections linking the various members and the regulated fluxes of media between those modules, while representing a major engineering challenge, would allow the microbial species to interact. The modularity of such spatially linked microbial consortia (SLMC) could facilitate the design of scalable bioprocesses that can be incorporated as parts of a larger biochemical network. By reducing the need for a compatible growth environment for all species simultaneously, SLMC will dramatically expand the range of possible combinations of microorganisms and their potential applications. We briefly review existing tools to engineer such assemblies and optimize potential benefits resulting from the collective activity of their members. Prospective microbial consortia and proposed spatial configurations will be illustrated and preliminary calculations highlighting the advantages of SLMC over co-cultures will be presented, followed by a discussion of challenges and opportunities for moving forward with some designs.

Construction of PAH-degrading mixed microbial consortia by induced selection in soil

Bioremediation of polycyclic aromatic hydrocarbons (PAHs)-contaminated soils through the biostimulation and bioaugmentation processes can be a strategy for the clean-up of oil spills and environmental accidents. In this work, an induced microbial selection method using PAH-polluted soils was successfully used to construct two microbial consortia exhibiting high degradation levels of low and high molecular weight PAHs. Six fungal and seven bacterial native strains were used to construct mixed consortia with the ability to tolerate high amounts of phenanthrene (Phe), pyrene (Pyr) and benzo(a)pyrene (BaP) and utilize these compounds as a sole carbon source. In addition, we used two engineered PAH-degrading fungal strains producing heterologous ligninolytic enzymes. After a previous selection using microbial antagonism tests, the selection was performed in microcosm systems and monitored using PCR-DGGE, CO₂ evolution and PAH quantitation. The resulting consortia (i.e., C1 and C2) were able to degrade up to 92% of Phe, 64% of Pyr and 65% of BaP out of 1000 mg kg^-1 of a mixture of Phe, Pyr and BaP (1:1:1) after a two-week incubation. The results indicate that constructed microbial consortia have high potential for soil bioremediation by bioaugmentation and biostimulation and may be effective for the treatment of sites polluted with PAHs due to their elevated tolerance to aromatic compounds, their capacity to utilize them as energy source.

Comparative metagenomic analysis of PAH degradation in soil by a mixed microbial consortium

In this study, we used a taxonomic and functional metagenomic approach to analyze some of the effects (e.g. displacement, permanence, disappearance) produced between native microbiota and a previously constructed Polycyclic Aromatic Hydrocarbon (PAH)-degrading microbial consortium during the bioremediation process of a soil polluted with PAHs. Bioaugmentation with a fungal-bacterial consortium and biostimulation of native microbiota using corn stover as texturizer produced appreciable changes in the microbial diversity of polluted soils, shifting native microbial communities in favor of degrading specific populations. Functional metagenomics showed changes in gene abundance suggesting a bias towards aromatic hydrocarbon and intermediary degradation pathways, which greatly favored PAH mineralization. In contrast, pathways favoring the formation of toxic intermediates such as cytochrome P450-mediated reactions were found to be significantly reduced in bioaugmented soils. PAH biodegradation in soil using the microbial consortium was faster and reached higher degradation values (84% after 30 d) as a result of an increased co-metabolic degradation when compared with other mixed microbial consortia. The main differences between inoculated and non-inoculated soils were observed in aromatic ring-hydroxylating dioxygenases, laccase, protocatechuate, salicylate and benzoate-degrading enzyme genes. Based on our results, we propose that several concurrent metabolic pathways are taking place in soils during PAH degradation.

Hybrid sequential treatment of aromatic hydrocarbon-polluted effluents using non-ionic surfactants as solubilizers and extractants

A treatment train combining a biological and a physical approach was investigated for the first time in order to remediate polycyclic aromatic hydrocarbons (PAHs)-polluted effluents. Given the hydrophobic nature of these contaminants, the presence of non-ionic surfactants is compulsory to allow their bioavailability. The presence of these surfactants also entails an advantage in order to ease contaminant removal by the formation of aqueous two-phase systems (ATPS). The segregation ability of environmentally benign salts such as potassium tartrate, citrate, and oxalate was discussed for extracting phenanthrene (PHE), pyrene (PYR), and benzo[a]anthracene (BaA). The biological remediation efficiency reached circa 60% for PHE and PYR, and more than 80% for BaA. The coupling of ATPS subsequent stage by using potassium citrate allowed increasing the total PAH remediation yields higher than 97% of PAH removal. The viability of the proposed solution was investigated at industrial scale by using the software tool SuperPro Designer.

Biodegradation of a mixture of PAHs by non-ligninolytic fungal strains isolated from crude oil-contaminated soil

Nine native non-ligninolytic fungal strains were isolated from Maya crude oil-contaminated soil and selected based on their ability to grow and use crude oil and several polycyclic aromatic hydrocarbons (PAHs) as carbon source, for their application to PAH removal in soil. The fungi were identified by PCR amplification of intergenic transcribed sequences regions and microbiological techniques, and results showed them to be part of the genera Fusarium, Neurospora, Aspergillus, Scedosporium, Penicillium, Neosartorya and Talaromyces. A primary selection of fungi was made in minimal medium plates, considering the tolerance to different concentrations of PAHs for each strain. The radial extension rate exhibited significant differences (p < 0.05) from 200 to 1,000 mg of PAHs mixture l⁻¹. A secondary selection of Aspergillus terreus, Talaromyces spectabilis, and Fusarium sp. was achieved based on their tolerance to 2,000 mg of a mixture of Phenanathrene and Pyrene kg⁻¹ of soil in a solid-state microcosm system for 2 weeks. The percentage of PAH removal obtained by the three strains was approximately 21 % of the mixture.

Technoeconomic assessment of phenanthrene degradation by Pseudomonas stutzeri CECT 930 in a batch bioreactor

Polycyclic aromatic hydrocarbons (PAHs) are among the most persistent pollutants that accumulate in natural environment mainly as a result of anthropogenic activities. Therefore, the improvement of the available bank of microbial resources and information is crucial to the proper management of PAHs-polluted sites and effluents. In this work, Pseudomonas stutzeri CECT 930 was selected for aerobically degrading an aqueous effluent containing phenanthrene (PHE). Maximum PHE degradation of 90% was obtained both at flask and stirred tank bioreactor scale. All the experimental data were fitted to logistic and Luedeking and Piret models, and licensed to quantitatively ascertain a stronger dependence on the biomass of the metabolites triggering the bioremediation process. In addition, PHE degradation via protocatechuate pathway was elucidated through GC-MS data. Finally, based on the promising results of biodegradation, a preliminary economic evaluation of this process at industrial scale was approached by means of simulation data obtained with SuperPro Designer.

Degradation of pyrene by immobilized microorganisms in saline-alkaline soil

Biodegradation of polycyclic aromatic hydrocarbons (PAHs) is very difficult in saline-alkaline soil due to the inhibition of microbial growth under saline-alkaline stress. The microorganisms that can most effectively degrade PAHs were screened by introducing microorganisms immobilized on farm byproducts and assessing the validity of the immobilizing technique for PAHs degradation in pyrene-contaminated saline-alkaline soil. Among the microorganisms examined, it was found that Mycobacterium sp. B2 is the best, and can degrade 82.2% and 83.2% of pyrene for free and immobilized cells after 30 days of incubation. The immobilization technique could increase the degradation of pyrene significantly, especially for fungi. The degradation of pyrene by the immobilized microorganisms Mucor sp. F2, fungal consortium MF and co-cultures of MB+MF was increased by 161.7% (P < 0.05), 60.1% (P < 0.05) and 59.6% (P < 0.05) after 30 days, respectively, when compared with free F2, MF and MB+MF. Scanning electron micrographs of the immobilized microstructure proved the positive effects of the immobilized microbial technique on pyrene remediation in saline-alkaline soil, as the interspace of the carrier material structure was relatively large, providing enough space for cell growth. Co-cultures of different bacterial and fungal species showed different abilities to degrade PAHs. The present study suggests that Mycobacterium sp. B2 can be employed for in situ bioremediation of PAHs in saline-alkaline soil, and immobilization of fungi on farm byproducts and nutrients as carriers will enhance fungus PAH-degradation ability in saline-alkaline soil.

Microbial communities to mitigate contamination of PAHs in soil--possibilities and challenges: a review

BACKGROUND, AIM, AND SCOPE

Although highly diverse and specialized prokaryotic and eukaryotic microbial communities in soil degrade polycyclic aromatic hydrocarbons (PAHs), most of these are removed slowly. This review will discuss the biotechnological possibilities to increase the microbial dissipation of PAHs from soil as well as the main biological and biotechnological challenges.

DISCUSSION AND CONCLUSIONS

Microorganism provides effective and economically feasible solutions for soil cleanup and restoration. However, when the PAHs contamination is greater than the microbial ability to dissipate them, then applying genetically modified microorganisms might help to remove the contaminant. Nevertheless, it is necessary to have a more holistic review of the different individual reactions that are simultaneously taking place in a microbial cell and of the interactions microorganism-microorganism, microorganism-plant, microorganism-soil, and microorganisms-PAHs.

PERSPECTIVES

Elucidating the function of genes from the PAHs-polluted soil and the study in pure cultures of isolated PAHs-degrading organisms as well as the generation of microorganisms in the laboratory that will accelerate the dissipation of PAHs and their safe application in situ have not been studied extensively. There is a latent environmental risk when genetically engineered microorganisms are used to remedy PAHs-contaminated soil.

Advances in the field of high-molecular-weight polycyclic aromatic hydrocarbon biodegradation by bacteria

Interest in understanding prokaryotic biotransformation of high-molecular-weight polycyclic aromatic hydrocarbons (HMW PAHs) has continued to grow and the scientific literature shows that studies in this field are originating from research groups from many different locations throughout the world. In the last 10 years, research in regard to HMW PAH biodegradation by bacteria has been further advanced through the documentation of new isolates that represent diverse bacterial types that have been isolated from different environments and that possess different metabolic capabilities. This has occurred in addition to the continuation of in-depth comprehensive characterizations of previously isolated organisms, such as Mycobacterium vanbaalenii PYR-1. New metabolites derived from prokaryotic biodegradation of four- and five-ring PAHs have been characterized, our knowledge of the enzymes involved in these transformations has been advanced and HMW PAH biodegradation pathways have been further developed, expanded upon and refined. At the same time, investigation of prokaryotic consortia has furthered our understanding of the capabilities of microorganisms functioning as communities during HMW PAH biodegradation.

Relevance of microbial coculture fermentations in biotechnology

The purpose of this article is to review coculture fermentations in industrial biotechnology. Examples for the advantageous utilization of cocultures instead of single cultivations include the production of bulk chemicals, enzymes, food additives, antimicrobial substances and microbial fuel cells. Coculture fermentations may result in increased yield, improved control of product qualities and the possibility of utilizing cheaper substrates. Cocultivation of different micro-organisms may also help to identify and develop new biotechnological substances. The relevance of coculture fermentations and the potential of improving existing processes as well as the production of new chemical compounds in industrial biotechnology are pointed out here by means of more than 35 examples.