Effects of Cellulolytic Bacteria on Nitrogen-Fixing Bacteria, 16S rRNA, nifH Gene Abundance, and Chemical Properties of Water Hyacinth Compost

Abstract

This research investigated alterations to and the interdependency of nitrogen-fixing bacteria, 16S ribosomal ribonucleic acid gene (16S rRNA) and nitrogenase reductase gene (nifH) gene abundance, and chemical properties of water hyacinth compost when using cellulolytic bacteria isolated from soil and leaf litter (CSL) inoculum. The un- and inoculated treatments in the compost were designed with three replications. Microbiological analysis involved examination of the total number of bacteria and gene abundance in the compost based on quantitative real-time polymerase chain reaction (qPCR). Some chemical properties of the compost were also analyzed. The results indicated that applying cellulolytic bacteria into compost could increase the amounts of bacteria, especially nitrogen-fixing bacteria. The pH of the compost increased slightly for the first 4 weeks. The amount of nitrogen and organic matter (OM) in the compost increased continuously during the composting period. The concentration of ammonium changed markedly in the range 1.5–2 times at the 4th and 10th weeks of the composting process, which was consistent with an increase of nitrogen-fixing bacteria. The concentration of nitrate doubled at the 12th week. The abundance of 16S rRNA and nifH genes was significantly correlated with the number of bacteria, total nitrogen, ammonium, nitrate, and OM. The inoculated cellulolytic bacteria not only accelerated the nitrogen mineralization process but also promoted bacterial numbers in the compost. These bacteria also affected the transformation of nutrients and correlated positively with gene abundance.