Metagenomics analysis reveals that carbon degradation rather than carbon fixation is dominant during animal carcass decay

Abstract

Background Temperature shapes microbial functional genes associated with carbon (C) cycles. However, the effects of temperature on microbial C cycle genes associated with carcass-contaminated water remains poorly understood. To fill this gap, we explored the variation of microbial carbon cycling genes in polluted water caused by animal corpse decay at five different temperature gradients (23, 26, 29, 32, and 35℃) by metagenomic sequencing. Results Corpse decay increased the total carbon by 86.6%, but temperature rise had no significant effect. The dominant phyla of C-cycle microbes were Proteobacteria, followed by Actinobacteria and Bacteroidetes. Approximately a half of carbon-cycling genes and 37.59% of carbohydrate-active enzyme genes can be predicted by temperature, while others were not sensitive to temperature. The alpha diversity of carbon cycling genes decreased with rising temperature, and beta diversity was affected by temperature and cadaver decomposition. High temperature led to an increase of those genes encoding decomposed starch, carbohydrate esters, pectin, lignin, chitin, cellulose, oligosaccharide, debranching enzymes and hemicellulose in control group, while only carbohydrate esters decomposition increased with temperature in the corpse group. The concentration of total carbon was positively related with easily degradable carbon genes (e.g., decomposed starch), but lacked correlations with refractory carbon genes (e.g., cellulose, hemicellulose and lignin). Conclusions We found that carbon degradation rather than carbon fixation was dominated during animal carcass decay, and microbes may prioritize use the degradable carbon, such as easily decomposed amylose. Our research finds that carcass decomposition regulates carbon cycle pathway, and provides possibility for predicting carbon cycle genes under global warming.