Soil Bioremediation of Cr(VI) Using Wild Type Actinomycete Strains

POLTI, MARTA ALEJANDRA; AMOROSO, MARÍA JULIA; ABATE; CARLOS MAURICIO

Soil Remediation

Nova Science Publishers

Lugar: Nueva York; Año: 2009; p. 1 - 23

Chromium (VI) compounds are toxic and carcinogenic and they are widely distributed as anthropogenic pollutant but the reduced form, Cr(III), is less toxic. This chapter provides information on Cr(VI) reduction by indigenous actinomycetes in soil samples. Forty-one isolated actinomycetes were used to study qualitative and semi-quantitative Cr(VI) resistance. Chromate-removing activity was estimated using the Cr(VI) specific colorimetric reagent 1,5-diphenylcarbazide. In solid medium, 20% of the isolates from El Cadillal (EC) and 14% from a copper filter plant (CFP) were able to grow at 13 mM Cr(VI). All isolates from sugar cane (SCP) could grow up to 17 mM Cr(VI). In liquid medium with 1 mM of Cr(VI), EC, CFP and SCP strains were able to remove 24%, 30% and more than 40% of Cr(VI), respectively. The highest and lowest Cr(VI) specific removal values were 75.5 mg g-1 cell by M3 (CFP), and 1.5 mg g-1 cell by C35 (EC) strains. Eleven Cr(VI) resistant strains were characterized and identified as species of the genera Streptomyces (10) and Amycolatopsis (1). Differences on actinomycete community composition between contaminated and non-contaminated soil were found. Streptomyces sp. MC1 showed ability to reduce Cr(VI) in liquid minimal medium. The reduction reached 100 and 84% at a Cr(VI) initial concentration of 5 and 50 mg l-1, respectively. Bioremediation ability of Streptomyces sp. MC1 was investigated 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), the reduction coincided with the exponential growth phase at pH 7 and 30 ºC. In soil samples, Streptomyces sp. MC1 was able to reduce up to 90% of the Cr(VI) (50 mg kg-1) after 7 days. All results were compared with uninoculated soil samples with Cr(VI). Bioremediation by Streptomyces sp. MC1 was not inhibited by natural soil microbial flora. Besides, Streptomyces sp. MC1 growth was not inhibited by 50 mg kg-1 of Cr(VI). In contrast to results from other authors, Polti et al. (2008) have observed complete Cr(VI) removal without addition of any substrate and with a normal soil humidity level without any previous treatment. These results confirm the Cr(VI) bioremediation potential of Streptomyces sp. MC1. Studies at field scale are required for future applications.