Community Construction And Metabolic Potentials Of Nitrospira In Coastal Wetlands

Coastal wetland is a key zone for biogeochemical cycling of various material elements,in which nitrification mediated by microorganisms is an essential step of the nitrogen cycle.Thus,the studies about community constructing mechanism and physio-biochemical characteristics of nitrifying microorganisms in coastal wetland are of great significance.The second step of nitrification is catalyzed by nitrite-oxidizing bacteria(NOB),which counteract nitrogen loss by converting nitrite to nitrate and therefore supply nitrogen source to various organisms.Nitrospira represents a dominant group of nitrite-oxidizers in natural and engineered ecosystems,and is the most phylogenetically diverse NOB genus.NOB have a reputation for being stubborn to cultivation under laboratory conditions,thus hitherto,many studies have addressed their environmental distribution.However,their physiological repertoire and metabolic mechanism are lagging because of the lack of pure culture and genome sequences.Meanwhile,in large spatial scales,few studies on the community structure of NOB have been conducted.Here,16 coastal wetlands in eastern China have been selected as research areas to explore the community constructing mechanism of Nitrospira.Based on the Nitrospira enrichment culture,we combined genomic information and physiological experiments to reveal its metabolic versatility.The main findings are as follows:(1)Nitrospira was ubiquitous in coastal wetlands,and was more abundant than complete ammonia oxidizer(comammox).Meanwhile,Nitrospira of the sediment samples were phylogenetically affiliated with Nitrospira lineage?,lineage?and lineage?.The distribution of lineage?and lineage?differed significantly among the coastal wetlands.In addition,the co-occurrence network analysis showed that lineage?and lineage?were mostly symbiotic,and both of them competed with lineage?.(2)The Nitrospira community tended to separate with different p H,and the diversity was affected by temperature,ammonia and ferric ion content.The response to temperature was different between Nitrospira lineage?and lineage?,lineage?and lineage?showed opposite response characteristics to p H,particle size and sulfur content.(3)In this study,we obtained a Nitrospira lineage?enrichment culture named“Candidatus Nitrospira sp.ZN2”for the first time from natural ecosystem.The high-quality genome of Nitrospira affiliated to lineage?was reconstructed,and the genomic potential of Ca.Nitrospira sp.ZN2 in energy metabolism and oxidative defense was revealed.(4)The optimal growth temperature and salinity of Ca.Nitrospira sp.ZN2 for nitrite oxidation are 28?and 0.5‰,respectively,and Ca.Nitrospira sp.ZN2 has low tolerance to higher temperature and salinity.In addition,Ca.Nitrospira sp.ZN2 showed higher nitrite oxidation activity in elevated substrate levels,which was consistent with other Nitrospira lineage?strains.(5)Ca.Nitrospira sp.ZN2 can grow from respiration of H₂.Under anoxic conditions,nitrate was reduced to nitrite with H₂ as electron donor.In comparison with comammox Nitrospira inopinata,we postulated that the H₂ metabolism in Ca.Nitrospira sp.ZN2 was catalyzed by group 2a[Ni Fe]hydrogenase.(6)Based on the genome annotation and physiological analyses,we found that Ca.Nitrospira sp.ZN2 can grow on formate or acetate.Our results suggested that Nitrospira lineage?also have the potential for formate metabolism.Meanwhile,it is also indicated that NOB might have the ability to use another organic compound,acetate as an alternative energy source.