New Extracellular Polymeric Substance Producing Enteric Bacterium from Earthworm, Metaphire posthuma: Modulation Through Culture Conditions

An extracellular polymeric substance (EPS) producing microorganism, identified and characterized as Bacillus licheniformis strain KX657843 based on 16S rRNA sequencing and phylogenetic analysis, was isolated from earthworms (Metaphire posthuma). The bacteria was found to be uniquely influenced by the amino acid l-asparagine monohydrate. The organism produced the maximum yield of 2.7 g L⁻¹ EPS in the presence of sucrose supplemented with l-asparagine monohydrate while no EPS was produced in absence of the amino acid. The order of growth and EPS production in presence of different carbon substrates supplemented with l-asparagine monohydrate was observed as sucrose > glucose > glycerol > mannitol > citrate > cellulose > starch. l-asparagine monohydrate could serve as the sole nitrogen source for the organism but it alone cannot satisfy the requisite carbon demand for growth and EPS production. EPS production showed a positive correlation with sucrose concentration but a negative correlation with citrate levels. Analysis of extracted EPS using Fourier transform infrared spectroscopy and measurement of its zeta potential revealed the chemical composition and anionic nature of the EPS. The bacterium produced 119.235 IU mL⁻¹ extracellular l-asparaginase. This is the first report of an l-asparagine monohydrate dependent EPS producing Bacillus licheniformis from the gut of the earthworm, Metaphire posthuma.