Microbial diversity in various types of paper mill sludge: identification of enzyme activities with potential industrial applications

Abstract

This study is the first comprehensive investigation of enzyme-producing bacteria isolated from four sludge samples (primary, secondary, press and machine) collected in a Kraft paper mill. Overall, 41 strains encompassing 11 different genera were identified by 16S rRNA gene analysis and biochemical testing. Both biodiversity and enzymatic activities were correlated with sludge composition. Press sludge hosted the largest variety of bacterial strains and enzymatic activities, which included hydrolytic enzymes and ligninolytic enzymes. In contrast, strains isolated from secondary sludge were devoid of several enzymatic activities. Most strains were found to metabolize Kraft liquor at its alkaline pH and to decolorize industrial lignin-mimicking dyes. Resistance to lignin or the ability to metabolize this substrate is a prerequisite to survival in any paper mill sludge type. We demonstrate here that the bacterial strains found in a typical Kraft paper mill represent a source of potential novel enzymes for both industrial applications and bioremediation.

Keywords: Bacteria; Bioplastic; Dyes; Enzymes; Pulping liquors.

Fig. 1

Examples of isolated bacterial decolorization of dye-containing plates. Decolorization of 0.05 % dye-containing plates (1.MB, 2.RBB, 3.MG and 4.CSB) after 24 h incubation at 37 °C and pH7

Fig. 2

Mechanisms of bacterial degradation of dye-containing plates

Fig. 3

Detection of bacteria producing PHA after Sudan Black B (1a, 1b) and Nile blue A (2a, 2b) staining. 1a PHA positive bacteria revealed with Sudan Black B staining. 1b PHA negative bacteria revealed with Sudan Black B staining. 2a PHA negative with Nile blue staining. 2b PHA positive with Nile blue staining