Transposases are mobile genetic elements (MGEs) that move within and between genomes, enabling genomic plasticity within microbes. Transposases often carry functional genes, termed cassette sequences, when they migrate within and between genomes. In marine microbial communities, transposase abundance increases with depth, but the reasons for this trend are unclear. Through analysis of metagenomes from the Tara Oceans and Malaspina Expeditions, we identify the particle-associated lifestyle as a main covariate for the high occurrence of transposases in the deep ocean. The abundance of biofilm-associated genes correlates with transposases in a strong and depth-independent manner, suggesting that MGEs readily propagate among microbial communities in crowded biofilms. Genome size positively correlates with particle-associated populations and transposase abundance. This relationship may result from selection for larger genomes, in which essential genes are more sparse and less likely to be disrupted by the recombination activities of MGEs. Genes related to defense mechanisms are enriched in cassette sequences and upregulated in the deep sea. Further, defense mechanism genes in cassette sequences experience stronger selection than other cassette genes. Thus, while transposons can spread at the expense of their microbial hosts, they introduce novel genes and potentially benefit the hosts in accessing heavily contested resources. Together, our results reveal an emerging picture of deep ocean particles as gene sharing highways that result in expanded and defensively oriented microbial genomes.
Grasslands are the basis for sustainable development in the northern farming-pastoral transition zone of China, with functions of human production, living, and ecology. Large-scale human activities inevitably lead to significant changes in grasslands, resulting in significant impacts on ecosystem services. To this end, we quantitatively estimated the ecosystem services value in each positive succession process (the improvement in the coverage or area of grasslands) and negative succession process (the degradation in the coverage or area of grasslands). The results indicated that (1) grasslands showed an improving trend from 2000 to 2015. The grassland improvement from low to high coverage dominated the positive succession process. Grassland degradation from high to low coverage dominated the negative succession process. (2) The total ecosystem services value increased by 25,294.87 × 104 yuan from 2000 to 2015. The grassland improvement from low to high coverage was the most important process that led to the increase in ecosystem service value. The degradation between grasslands and non-grasslands was the key process that led to the decrement in ecosystem services value. (3) The impact of grassland dynamics on the regional ecosystem service value showed significant spatial heterogeneity at the town scale. The results will provide some implications for the sustainable development of grassland ecosystem services to improve human well-being.
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