Effects of selected multipurpose, medicinal and aromatic plants on <i>in vitro</i> methane production and microbial diversity

Abstract

The study was carried out to evaluate the effects of selected multipurpose, medicinal and aromatic plants on the in vitro methane production and microbial diversity. The plants include multi-purpose trees; Pterocarpus santallinoides, Leucaena leucocephala, Albizia lebbek, Albizia saman, Enterolobium cyclocarpum, Gliricidia sepium, Milletia griffoniana, Ficus thonningii; Aromatic plants: Ocimum basilicum, Vernonia amygdalina, Aspillia africana and Medicinal plants: Moringa oleifera, Cymbopogon citratus and Alternanthera repens. Leaf samples were collected for determination of chemical analysis, in vitro gas production and microbial analyses. Data on chemical composition were subjected to one-way analysis of variance, while data on in vitro microbial analyses was subjected to phylogeny analysis using the parsimony software. Methanogenspecific primers Met86F and Met1340R were designed to identify methanogens. There were significant differences (P<0.05) in dry matter (DM), crude protein (CP), crude fibre (CF) ether extract (EE), ash contents, neutral detergent fibre (NDF), acid detergent fibre (ADF) and lignin contents of plants. The DM values (P<0.05) ranged from 168 g/kg in V. amygdalina to 395 g/kg in P. santalinoides and the lowest (P<0.05) CP value of 23.6 g/kg was obtained in O. basillicum. Least (P<0.05) methane production was obtained from A. repens and P. santallinoides with 4.45% and 12.62% respectively. Polymerase chain reaction analyses of DNA extracts revealed that Methanobrevibacter spp. were dominant. Other detected methanogens include Methanobacteriales archaeon spp. and Methanoplasmatales spp. Eight samples of the methanogenic archaea were at least 78 to 99% similar to Methanobrevibacter spp. Three samples were at least 83 to 97% similar to Bacteriodetes bacterium clone. Two samples were at least 85 to 98% similar to Methanobacteriales archaeon spp. Moringa oleifera sample revealed 99% similarity with 16S rDNA in Methanobrevibacter spp. It is concluded that Methanobrevibacter spp. is the predominant methanogen and A. repens supressed methanogenesis.

Keywords: Multipurpose, medicinal, aromatic plants, in vitro, methanogens, phylogeny