Isolation of Indole Utilizing Bacteria Arthrobacter sp. and Alcaligenes sp. From Livestock Waste

Abstract

Indole is an interspecies and interkingdom signaling molecule widespread in different environmental compartment. Although multifaceted roles of indole in different biological systems have been established, little information is available on the microbial utilization of indole in the context of combating odor emissions from different types of waste. The present study was aimed at identifying novel bacteria capable of utilizing indole as the sole carbon and energy source. From the selective enrichment of swine waste and cattle feces, we identified Gram-positive and Gram-negative bacteria belonging to the genera Arthrobacter and Alcaligenes. Bacteria belonging to the genus Alcaligenes showed higher rates of indole utilization than Arthrobacter. Indole at 1.0 mM for growth was completely utilized by Alcaligenes sp. in 16 h. Both strains produced two intermediates, anthranilic acid and isatin, during aerobic indole metabolism. These isolates were also able to grow on several indole derivatives. Interestingly, an adaptive response in terms of a decrease in cell size was observed in both strains in the presence of indole. The present study will help to explain the degradation of indole by different bacteria and also the pathways through which it is catabolized. Furthermore, these novel bacterial isolates could be potentially useful for the in situ attenuation of odorant indole and its derivatives emitted from different types of livestock waste.

Keywords: Alcaligenes sp.; Arthrobacter sp.; Biodegradation; Environmental biotechnology; Indole.

Fig. 1

Phylogenetic neighbor-joining tree of Arthrobacter sp. strain B1 (a) and Alcaligenes sp. strain B5 (b) based on 16S rRNA gene sequences. The phylogenetic tree shows the relationships between individual isolates and species within the respective genus. Bootstrap values (expressed as percentages of 1000 replications) greater than 50 % are given at nodes. Bar 0.005 % sequence variation. GenBank accession numbers are given in parentheses

Fig. 2

Growth characteristics and degradation kinetics of Arthrobacter sp. strain B1 and Alcaligenes sp. strain B5 in carbon-free MSM supplemented with different concentrations of indole. Circle, 0.2 mM; shaded triangle, 0.5 mM; shaded circle, 1.0 mM; square, 2.0 mM; shaded square, 5.0 mM. Growth of strain B1 (a), indole depletion by strain B1 (b), growth of strain B5 (c), and indole depletion by strain B5 (d)

Fig. 3

Scanning electron microscopic photographs of Arthrobacter sp. strain B1 and Alcaligenes sp. strain B5. SEM was used to examine the cell morphologies of cells grown on nylon filters in MSM medium containing indole (0.1 and 0.5 mM) or glucose (2 %) for 24 h at 37 °C. As a control, 1/4-LB medium was used without indole. The scale bar represents 3 μm. The experiment was performed in triplicate with two independent cultures and at least 20 random spots were observed

Fig. 4

HPLC chromatographs of culture filtrates during aerobic indole degradation by Arthrobacter sp. strain B1 and Alcaligenes sp. strain B5. Standard chemicals of catechol, isatin, 2-oxindole, and indole (a), Arthrobacter sp. strain B1 (b), and Alcaligenes sp. strain B5 (c). At the panel A, two wavelengths (243 nm and 271 nm) in the PDA detector were used to show chromatographs of four standard chemicals

Fig. 5

LC chromatographs and ESIMS mass spectra of culture filtrates during aerobic indole degradation. Standard chemicals of anthranilic acid and indole (a), Arthrobacter sp. strain B1 (b), and Alcaligenes sp. strain B5 (c). Mass spectra of anthranilic acid are shown as insets

Fig. 6

Common metabolic pathways of aerobic degradation of indole by Arthrobacter sp. strain B1 and Alcaligenes sp. strain B5. Metabolic intermediates (isatin and anthranilic acid) of indole degradation were detected in this study