Isolation and identification of ligninolytic microbes

Background: Lignin is an organic polymer made up of various aromatic compounds which in combination with cellulose and hemicellulose forms a chief partof the woody tissues. Wood processing industries like paper-pulp industries have been among the most significant of industrial polluters of the waterways and environment. The pulp and paper industry produces large quantities of toxic brown/black effluent (around 100 million kg) that comes primarily from lignin and its derivatives (e.g., lignosulphonic acid, resins, phenols, and hydrocarbons) that are released during various processing steps of lignocellulosic materials. Discharge of such untreated effluent results in increased BOD, slime growth, thermal problems, scum formation, discoloration, loss of aesthetic quality and toxicity to the aquatic life, in the receiving water bodies. These problems can be overcome by biological treatment using certain ligninolytic microbes processing ligninolytic enzyme systems. Objective: The goal of this research work was to isolateligninolytic microbes from various environmental niche and to screen them for potential ligninolytic activity. Methods: The lignin extract was prepared from saw dust. The ligninolytic bacteria were isolated from samples of garden soil, sewage and compost using Minimal Salt Medium containing lignin extract(MSML). The isolates were qualitatively screened for ligninolytic activity using Methylene blue dye reduction test. A comparative study of growth rates of screened isolates in MSML and Nutrient broth (NB) was performed. Various biochemical tests were conducted for identification of screened isolates. Result: Ligninolytic microbes were isolated from various environmental niche. The isolated microbes were screened based on their potential to reduce the basic dye methylene blue. The isolates showed varied growth rates in MSML and NB with few having more affinity to lignin. The isolates were found to be Gram positive bacilli and cocci along with few being actinomycetes. Few isolates were motile showing varied biochemical characteristics. Conclusion: Ligninolytic microbes were found in garden soil, sewage and compost samples.The dye reducing activity of the isolates indicates the presence of the oxidative ligninolytic enzymes. Isolates showing high growth rate in MSML had greater efficiency of lignin degradation.