Chemical and Microbial Characterization of Feed and Faeces of Two Giant Pill-Millipedes from Forests in the Western Ghats of India

Soil macroinvertebrates are highly diverse and their major ecological service include breakdown of organic matter and in turn improve soil fertility and pill-millipedes are well-known for their significant role in ingestion, disintegration and decomposition of organic matter in soil. This study characterized the feed, the decomposing leaf litter of coconut (Cocos nucifera), and faeces of two endemic giant pill-millipedes Arthrosphaera disticta and A. fumosa collected from forests of the Western Ghats of India based on chemical features and microbial profile. In both millipedes, electric conductivity and total phosphorus were significantly increased in faeces, while the crude protein, organic carbon, total nitrogen and total phenolics were significantly decreased, as compared to those in feed. Heterotrophic bacteria, actinomycetes, rhizobia and phosphate-solubilizing bacteria were significantly higher in faeces than in feed, while filamentous fungi and yeast substantially decreased in faces compared to feed in both the millipedes. Spectrum of fatty acid methyl esters was considerably different between feed and faeces of both the millipedes. The total saturated fatty acids were higher than the total unsaturated fatty acids in feed as well as faeces, while the ratio of unsaturated/saturated fatty acids decreased from feed to faeces. Dodecanoic and tetradecanoic acids in A. disticta and octadecanoic acid in A. fumosa significantly increased, while (9Z)-octadec-9-enoic and (9E,12E)-octadeca-9,12-dienoic acids in A. disticta and hexadecanoic, tetracosanoic and (9E,12E)-octadeca-9,12-dienoic acids in A. fumosa significantly decreased in faeces compared to feed, indicating millipede-dependent changes in fatty acids. Icosanoic acid was present in faeces of both the millipedes, and hexadec-9-enoic acid was confined to faeces of A disticta, while pentadecanoic, heneicosanoic, (9Z,12Z,15Z)-9,12,15-octadecatrienoic and eicosenoic acids were confined to faeces of A. fumosa. Pill-millipedes enrich the soil quality by leaf litter conditioning in their gut through specific microbial communities. Fingerprinting of fatty acid methyl esters in faeces of these millipedes reflected the activity of specific microbial population in their guts.