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The spatial scaling of biodiversity, such as the taxa-area relationship (TAR) and distance-decay relationship (DDR), is a typical ecological pattern that is followed by both microbes and macrobes in natural ecosystems. Previous studies focusing on microbes mainly aimed to address whether and how different types of microbial taxa differ in spatial scaling patterns, leaving the underlying mechanisms largely untouched. In this study, the spatial scaling of different microbial domains and their associated ecological processes in an intertidal zone were comparatively investigated. The significant spatial scaling of biodiversity could be observed across all microbial domains, including archaea, bacteria, fungi, and protists. Among them, archaea and fungi were found with much stronger DDR slopes than those observed in bacteria and protists. For both TAR and DDR, rare subcommunities were mainly responsible for the observed spatial scaling patterns, except for the DDR of protists and bacteria. This was also evidenced by extending the TAR and DDR diversity metrics to Hill numbers. Further statistical analyses demonstrated that different microbial domains were influenced by different environmental factors and harbored distinct local community assembly processes. Of these, drift was mainly responsible for the compositional variations of bacteria and protists. Archaea were shaped by strong homogeneous selection, whereas fungi were more affected by dispersal limitation. Such differing ecological processes resulted in the domain-level differentiation of microbial spatial scaling. This study links ecological processes with microbial spatial scaling and provides novel mechanistic insights into the diversity patterns of microbes that belong to different trophic levels. IMPORTANCE As the most diverse and numerous life form on Earth, microorganisms play indispensable roles in natural ecological processes. Revealing their diversity patterns across space and through time is of essential importance to better understand the underlying ecological mechanisms controlling the distribution and assembly of microbial communities. However, the diversity patterns and their underlying ecological mechanisms for different microbial domains and/or trophic levels require further exploration. In this study, the spatial scaling of different microbial domains and their associated ecological processes in a mudflat intertidal zone were investigated. The results showed different spatial scaling patterns for different microbial domains. Different ecological processes underlie the domain-level differentiation of microbial spatial scaling. This study links ecological processes with microbial spatial scaling to provide novel mechanistic insights into the diversity patterns of microorganisms that belong to different trophic levels.

Two strains designated as c1 T and c7 T , were isolated from the landfill leachate of a domestic waste treatment plant in Huizhou City, Guangdong Province, PR China. The cells of both strains were aerobic, rod-shaped, non-motile and formed yellow colonies on Reasoner's 2A agar plates. Strain c1 T grew at 10-42 °C (optimum, 30 °C), pH 4.5-10.5 (optimum, pH 7.0) and 0-2.0 % (w/v) NaCl (optimum, 0-0.5 %). Strain c7 T grew at 10-42 °C (optimum, 30 °C), pH 4.5-10.5 (optimum, pH 6.0) and 0-2.0 % (w/v) NaCl (optimum, 0-0.5 %). Phylogenetic analyses revealed that strains c1 T and c7 T belong to the genus Novosphingobium . The 16S rRNA gene sequence similarities of strains c1 T and c7 T to the type strains of Novosphingobium species were 94.5-98.2 % and 94.3-99.1 %, respectively. The calculated pairwise average nucleotide identity values among strains c1 T , c7 T and the reference strains were in the range of 75.2-85.9 % and the calculated pairwise average amino acid identity values among strains c1 T , c7 T and reference strains were in the range of 72.0-88.3 %. Their major respiratory quinone was Q-10, and the major cellular fatty acids were C 18 : 1  ω 7 c , C 18 : 0 , C 16 : 1  ω 7 c , C 16 : 0 and C 14 : 0 2OH. The major polar lipids of strains c1 T and c7 T were phosphatidylethanolamine, diphosphatidylglycerol, phosphatidylglycerol, sphingoglycolipid, unidentified lipids and unidentified phospholipid. Based on phenotypic, chemotaxonomic, phylogenetic and genomic results from this study, strains c1 T and c7 T should represent two independent novel species of Novosphingobium , for which the names Novosphingobium percolationis sp. nov. (type strain c1 T =GDMCC 1.2555 T =KCTC 82826 T ) and Novosphingobium huizhouense sp. nov. (type strain c7 T =GDMCC 1.2556 T =KCTC 82827 T ) are proposed. The gene function annotation results of strains c1 T and c7 T suggest that they could play an important role in the degradation of organic pollutants.