Marta A. Polti

Bioremediation of chromium(VI) contaminated soil by Streptomyces sp. MC1

This work provides quantitative information on Cr(VI) reduction in soil samples by an indigenous actinomycete. Streptomyces sp. MC1, previously isolated from sugarcane, has shown ability to reduce Cr(VI) in liquid minimal medium. A reduction of 100 and 75% was obtained at initial Cr(VI) concentrations of 5 and 50 mg l–1, respectively, after 48 h of incubation. Bioremediation ability of Streptomyces sp. MC1 was assayed in soil extracts and soil samples. Relative growth of Streptomyces sp. MC1 was 77 and 38% when grown in soil extract with 10 and 50 mg l–1 of Cr(VI), respectively. MC1 was able to reduce 30% of Cr(VI) after 96 h of incubation with 10 mg l–1 of Cr(VI), and reduction coincided with the exponential growth phase at pH 7 and 30 °C.

Actinobacteria: Current research and perspectives for bioremediation of pesticides and heavy metals

Actinobacteria exhibit cosmopolitan distribution since their members are widely distributed in aquatic and terrestrial ecosystems. In the environment they play relevant ecological roles including recycling of substances, degradation of complex polymers, and production of bioactive molecules. Biotechnological potential of actinobacteria in the environment was demonstrated by their ability to remove organic and inorganic pollutants. This ability is the reason why actinobacteria have received special attention as candidates for bioremediation, which has gained importance because of the widespread release of contaminants into the environment. Among organic contaminants, pesticides are widely used for pest control, although the negative impact of these chemicals in the environmental balance is increasingly becoming apparent. Similarly, the extensive application of heavy metals in industrial processes lead to highly contaminated areas worldwide. Several studies focused in the use of actinobacteria for cleaning up the environment were performed in the last 15 years. Strategies such as bioaugmentation, biostimulation, cell immobilization, production of biosurfactants, design of defined mixed cultures and the use of plant-microbe systems were developed to enhance the capabilities of actinobacteria in bioremediation. In this review, we compiled and discussed works focused in the study of different bioremediation strategies using actinobacteria and how they contributed to the improvement of the already existing strategies. In addition, we discuss the importance of omic studies to elucidate mechanisms and regulations that bacteria use to cope with pollutant toxicity, since they are still little known in actinobacteria. A brief account of sources and harmful effects of pesticides and heavy metals is also given.

Versatility of Streptomyces sp. M7 to bioremediate soils co-contaminated with Cr(VI) and lindane.

The aim of this work was to study the impact of environmental factors on the bioremediation of Cr(VI) and lindane contaminated soil, by an actinobacterium, Streptomyces sp. M7, in order to optimize the process. Soil samples were contaminated with 25 µg kg(-1) of lindane and 50 mg kg(-1) of Cr(VI) and inoculated with Streptomyces sp. M7. The lowest inoculum concentration which simultaneously produced highest removal of Cr(VI) and lindane was 1 g kg(-1). The influence of physical and chemical parameters was assessed using a full factorial design. The factors and levels tested were: Temperature: 25, 30, 35°C; Humidity: 10%, 20%, 30%; Initial Cr(VI) concentration: 20, 50, 80 mg kg(-1); Initial lindane concentration: 10, 25, 40 µg kg(-1). Streptomyces sp. M7 exhibited strong versatility, showing the ability to bioremediate co-contaminated soil samples at several physicochemical conditions. Streptomyces sp. M7 inoculum size was optimized. Also, it was fitted a model to study this process, and it was possible to predict the system performance, knowing the initial conditions. Moreover, optimum temperature and humidity conditions for the bioremediation of soil with different concentrations of Cr(VI) and lindane were determined. Lettuce seedlings were a suitable biomarker to evaluate the contaminants mixture toxicity. Streptomyces sp. M7 carried out a successful bioremediation, which was demonstrated through ecotoxicity test with Lactuca sativa.

Role of Actinobacteria in Bioremediation

The class Actinobacteria represents an important component of the microbial population in soils. Their metabolic diversity and specific growth characteristics make them well suited as agents for bioremediation. Actinobacteria have an active role in the removal of xenobiotic heavy metals. Their ability has been demonstrated in culture media and in soil samples, either using pure cultures or consortia of Actinobacteria. They have a great adaptability that can be used to benefit the environment. Both whole cells and their products have potential applications in bioremediation processes.

Bioremediation Potential of Heavy Metal–Resistant Actinobacteria and Maize Plants in Polluted Soil

The screening and characterization of metal resistant microorganisms and plants are important for developing novel bioremediation processes. Considering these, we assessed the potential of copper- and chromium-resistant actinomycetes for bioremediation activity in polluted soils. Also, we assessed the effects of copper concentrations on roots, shoots, and leaf growth of maize and the copper uptake and accumulation by the maize plants. Four chromium resistant Streptomyces strains reduced hexavalent chromium up to 85–95% after 21 days. The novel copper-resistant actinobacterium Amycolatopsis tucumanensis efficiently immobilized copper when inoculated into copper-polluted soil microcosms: bioavailable Cu was 31% lower in soil compared to non-bioaugmented soil. Maize plant was found interesting both as biomarker and bioremediation tool. The bioremediation activity of A. tucumanensis inoculated maize plants grown in polluted soil microcosms correlated well with the values obtained with chemical and physical methods: 20% and 17% lower tissue contents of copper were measured in roots and leaves, respectively. The roots, shoots, and leaves of maize plants also showed a great ability to accumulate copper, which however increased with metal concentration. The metal concentrations were 382 times more in roots, 157 in shoots, and only 16 in leaves, compared to the control (without CuSO4).

Actinobacteria consortium as an efficient biotechnological tool for mixed polluted soil reclamation: Experimental factorial design for bioremediation process optimization

The objective of the present work was to establish optimal biological and physicochemical parameters in order to remove simultaneously lindane and Cr(VI) at high and/or low pollutants concentrations from the soil by an actinobacteria consortium formed by Streptomyces sp. M7, MC1, A5, and Amycolatopsis tucumanensis AB0. Also, the final aim was to treat real soils contaminated with Cr(VI) and/or lindane from the Northwest of Argentina employing the optimal biological and physicochemical conditions. In this sense, after determining the optimal inoculum concentration (2gkg-1), an experimental design model with four factors (temperature, moisture, initial concentration of Cr(VI) and lindane) was employed for predicting the system behavior during bioremediation process. According to response optimizer, the optimal moisture level was 30% for all bioremediation processes. However, the optimal temperature was different for each situation: for low initial concentrations of both pollutants, the optimal temperature was 25°C; for low initial concentrations of Cr(VI) and high initial concentrations of lindane, the optimal temperature was 30°C; and for high initial concentrations of Cr(VI), the optimal temperature was 35°C. In order to confirm the model adequacy and the validity of the optimization procedure, experiments were performed in six real contaminated soils samples. The defined actinobacteria consortium reduced the contaminants concentrations in five of the six samples, by working at laboratory scale and employing the optimal conditions obtained through the factorial design.

Petroleum degradation by endophytic Streptomyces spp. isolated from plants grown in contaminated soil of southern Algeria

Petroleum hydrocarbons are well known by their high toxicity and recalcitrant properties. Their increasing utilization around worldwide led to environmental contamination. Phytoremediation using plant-associated microbe is an interesting approach for petroleum degradation and actinobacteria have a great potential for that. For this purpose, our study aimed to isolate, characterize, and assess the ability of endophytic actinobacteria to degrade crude petroleum, as well as to produce plant growth promoting traits. Seventeen endophytic actinobacteria were isolated from roots of plants grown naturally in sandy contaminated soil. Among them, six isolates were selected on the basis of their tolerance to petroleum on solid minimal medium and characterized by 16S rDNA gene sequencing. All petroleum-tolerant isolates belonged to the Streptomyces genus. Determination by crude oil degradation by gas chromatorgraph-flame ionization detector revealed that five strains could use petroleum as sole carbon and energy source and the petroleum removal achieved up to 98% after 7 days of incubation. These isolates displayed an important role in the degradation of the n-alkanes (C6-C30), aromatic and polycyclic aromatic hydrocarbons. All strains showed a wide range of plant growth promoting features such as siderophores, phosphate solubilization, 1-aminocyclopropane-1-carboxylate deaminase, nitrogen fixation and indole-3-acetic acid production as well as biosurfactant production. This is the first study highlighting the petroleum degradation ability and plant growth promoting attributes of endophytic Streptomyces. The finding suggests that the endophytic actinobacteria isolated are promising candidates for improving phytoremediation efficiency of petroleum contaminated soil.

Bioremediation in Latin America

According to the Merriam-Webster dictionary definition, agriculture is “the science, art, or practice of cultivating the soil, producing crops, and raising livestock, and in varying degrees the preparation and marketing of the resulting products.” As it is, even though this definition is very comprehensive, there is more than meets the eye about the universe of activities involved in agronomic practices. Agriculture is witness to many changes since its dawning, evolving from animal and seed domestication to genetic modification of organisms through molecular biology techniques to better suit worldwide demand. These changes influenced land ownership as well as technology development. Different climatic and anthropological realities generate diverse productive systems that adapt to every situation. Developing countries with less appropriate technologies for industrialization have large rural populations where peasant economies are sometimes critical for subsistence. Despite all the benefits of agriculture, it sometimes faces drawbacks for proper production. Other times agriculture brings along sociopolitical and environmental problems. Cultural practices have detrimental impacts on soil quality and water availability. Moreover the environment is the ultimate recipient of pesticides, herbicides, fertilizers, and other by-products. Nonetheless bioremediation techniques involving plants and microorganisms are in constant development to try to decrease the negative effects of farming, bringing these emerging processes new options for a better management in agriculture. N. Romano-Armada • V.B. Rajal (*) Instituto de Investigaciones para la Industria Química (INIQUI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET); Universidad Nacional de Salta (UNSa), Av. Bolivia 5150, 4400, Salta, Argentina Universidad Nacional de Salta (UNSa), Av. Bolivia 5150, 4400, Salta, Argentina e-mail: vbrajal@gmail.com M.J. Amoroso Planta Piloto de Procesos Industriales Microbiológicos (PROIMI), CONICET, Av. Belgrano y Pasaje Caseros, 4000 Tucumán, Argentina Facultad de Bioquímica, Química y Farmacia, Universidad Nacional de Tucumán, 4400 Tucumán, Argentina Universidad del Norte Santo Tomás de Aquino (UNSTA), 4000 Tucumán, 4400 Tucumán, Argentina

Lindane dissipation in a biomixture: Effect of soil properties and bioaugmentation

The biomixture is the major constituent of a biopurification system and one of the most important factors in its efficiency; hence the selection of the components is crucial to ensure the efficient pesticides removal. Besides, bioaugmentation is an interesting approach for the optimization of these systems. A mixed culture of the fungus Trametes versicolor SGNG1 and the actinobacteria Streptomyces sp. A2, A5, A11, and M7, was designed to inoculate the biomixtures, based on previously demonstrated ligninolytic and pesticide-degrading activities and the absence of antagonism among the strains. The presence of lindane and/or the inoculum in the biomixtures had no significant effect on the development of culturable microorganisms regardless the soil type. The consortium improved lindane dissipation achieving 81-87% of removal at 66 d of incubation in the different biomixtures, decreasing lindane half-life to an average of 24 d, i.e. 6-fold less than t1/2 of lindane in soils. However, after recontamination, only the bioaugmented biomixture of silty loam soil enhanced lindane dissipation and decreased the t1/2 compared to non-bioaugmented. The biomixture formulated with silty loam soil, sugarcane bagasse, and peat, inoculated with a fungal-actinobacterial consortium, could be appropriate for the treatment of agroindustrial effluents contaminated with organochlorine pesticides in biopurification systems.

Cr(VI) and lindane removal by Streptomyces M7 is improved by maize root exudates

Environmental mixed pollution by both organic and inorganic compounds are detected worldwide. Phytoremediation techniques have been proposed as ecofriendly methods for cleaning up polluted sites. Several studies have demonstrated enhanced dissipation of contaminants at the root‐soil interface through an increase in microbial activity caused by the release of plant root exudates (REs). The aim of this study was to evaluate the effectiveness for Cr(VI) and lindane removal by Streptomyces M7 cultured in a co‐contaminated system in presence of maize REs. Our results showed when REs were added to the contaminated minimal medium (MM) as the only carbon source, microbial removal of Cr(VI) and lindane increased significantly in comparison to contaminant removal obtained in MM with glucose 1 g L−1. The maximum removal of 91% of lindane and 49.5% of Cr(VI) were obtained in the co‐contaminated system. Moreover, Streptomyces M7 showed plant growth promoting traits which could improve plant performance in contaminated soils. The results presented in this study provide evidence that maize REs improved growth of Streptomyces M7 when REs were used as a carbon source in comparison to glucose. Consequently, lindane and Cr(VI) removal was considerably enhanced making evident the phytoremediation potential of the actinobacteria‐plant partnership.