Effect of Predation by Colpoda sp. in Nitrogen Fixation Rate of Two Free-Living Bacteria

Abstract Biological nitrogen fixation (BNF) is limited to several groups of prokaryotes, which can reduce nitrogen through complex endosymbiotic relationships or as free-living nitrogen-fixing bacteria (FLNFB). Predation of FLNFB by protozoa releases reduced nitrogen, enhancing the formation of plant and bacterial biomass as well as nitrogen (N) mineralization within soil microbial communities. We aim to evaluate the predation effect of Colpoda sp. on two FLNFB Azospirillum lipoferum and Stenotrophomonas sp. during their exponential and lag phase. The likelihood of Colpoda sp. to feed on the former species was needed to ensure there is a predation effect. The kinetics of bacterial population growth was determined in the predators’ presence or absence and the effect of predation on the biological fixation of N was evaluated through the reduction of acetylene to ethylene technique. Colpoda sp. showed a non-significant difference in preferences between the two species offered as prey. Consequently, the abundance of A. lipoferum and Stenotrophomonas sp. decreased significantly due to predator’s pressure. However, it had a higher positive effect on the formation of new bacterial biomass on Stenotrophomonas sp.as revealed by the increase of its specific growth rate. Likewise, predation promoted greater nitrogen fixation in A. lipoferum and Stenotrophomonas sp. during the lag phase (0.34 nM and 0.38 nM) than in the exponential phase (0.27 nM and 0.17 nM). We concluded that predation by Colpodasp stimulates the rate of nitrogen fixation of A. lipoferum and Stenotrophomonas sp.

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Novel aspects of nitrogen fixation

Outlook on Agriculture ◽

10.1177/003072707700900406 ◽

1977 ◽

Vol 9 (4) ◽

pp. 180-185 ◽

Cited By ~ 5

Author(s):

J M Day ◽

J F Witty

Keyword(s):

Nitrogen Fixation ◽

Green Algae ◽

Root Nodule ◽

Atmospheric Nitrogen ◽

Biological Fixation ◽

Free Living ◽

Tropical Grasses ◽

Blue Green Algae ◽

Synthetic Fertilizers ◽

Living Bacteria

Only a fraction of the total agricultural need for nitrogen comes from natural or synthetic fertilizers. The remainder is satisfied largely through the biological fixation of atmospheric nitrogen. Whilst this is most efficiently effected by the Rhizobium-legume root nodule, free-living bacteria and blue-green algae are known to be capable of fixing appreciable amounts. Recently, attention has been focused on bacteria closely associated with roots of certain tropical grasses.

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Nitrogen fixation by rhizosphere and free-living bacteria in salt marsh sediments1

Limnology and Oceanography ◽

10.4319/lo.1979.24.1.0126 ◽

1979 ◽

Vol 24 (1) ◽

pp. 126-132 ◽

Cited By ~ 53

Author(s):

John M. Teal ◽

Ivan Valiela ◽

Diane Berlo

Keyword(s):

Nitrogen Fixation ◽

Salt Marsh ◽

Free Living ◽

Living Bacteria

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Expression of the nodulation and nitrogen fixation genes in Rhizobium meliloti during development

Genome ◽

10.1139/g89-054 ◽

1989 ◽

Vol 31 (1) ◽

pp. 354-360 ◽

Cited By ~ 2

Author(s):

San Chiun Shen ◽

Shui Ping Wang ◽

Guan Qiao Yu ◽

Jia Bi Zhu

Keyword(s):

Nitrogen Fixation ◽

Rhizobium Meliloti ◽

Abnormal Development ◽

Wild Type ◽

Free Living ◽

Nod Genes ◽

Nodule Initiation ◽

Fix Genes ◽

Nitrogen Fixation Genes

Genes that specify nodulation (nod genes) are only active in the free-living rhizobia or in the nodule initiation state of rhizobia. As soon as the repression of nod genes occurs in the bacteroids of the nodule, nifA is induced, while ntrC is inactivated and thus the nifA-mediated nif/fix genes are turned on. Limitation of available oxygen brings about the induction of nifA, which reflects the actual status of nif/fix gene activities in symbiotic state of rhizobia. Oxygen thus appears to be a major symbiotic signal to the expression of bacteroid nif/fix genes. Mutation of nifA or shortage of nifA product in wild-type rhizobia caused by the inhibition of multicopy nifH/fixA promoters leads to an abnormal development of nodules and premature degradation of bacteroids in nodules.Key words: nitrogen fixation, nodulation, nif/fix regulation, nifA mutant.

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Opening a next-generation black box: ecological trends for hundreds of species-like taxa uncovered within a single bacterial >99% 16S rRNA operational taxonomic unit

10.22541/au.161368667.78191317/v1 ◽

2021 ◽

Author(s):

Martin Hahn ◽

Andrea Huemer ◽

Alexandra Pitt ◽

Matthias Hoetzinger

Keyword(s):

16S Rrna ◽

Sequence Similarity ◽

16S Rrna Genes ◽

Rrna Genes ◽

Rrna Gene ◽

Taxon Richness ◽

Large Set ◽

Free Living ◽

Environmental Distribution ◽

Living Bacteria

Current knowledge on environmental distribution and taxon richness of free-living bacteria is mainly based on cultivation-independent investigations employing 16S rRNA gene sequencing methods. Yet, 16S rRNA genes are evolutionarily rather conserved, resulting in limited taxonomic and ecological resolutions provided by this marker. We used a faster evolving protein-encoding marker to reveal ecological patterns hidden within a single OTU defined by >99% 16S rRNA sequence similarity. The studied taxon, subcluster PnecC of the genus Polynucleobacter, represents a ubiquitous group of planktonic freshwater bacteria with cosmopolitan distribution, which is very frequently detected by diversity surveys of freshwater systems. Based on genome taxonomy and a large set of genome sequences, a sequence similarity threshold for delineation of species-like taxa could be established. In total, 600 species-like taxa were detected in 99 freshwater habitats scattered across three regions representing a latitudinal range of 3400 km (42°N to 71°N) and a pH gradient of 4.2 to 8.6. Besides the unexpectedly high richness, the increased taxonomic resolution revealed structuring of Polynucleobacter communities by a couple of macroecological trends, which was previously only demonstrated for phylogenetically much broader groups of bacteria. A unexpected pattern was the almost complete compositional separation of Polynucleobacter communities of Ca-rich and Ca-poor habitats, which strongly resembled the vicariance of plant species on silicate and limestone soils. The presented new cultivation-independent approach opened a window to an incredible, previously unseen diversity, and enables investigations aiming on deeper understanding of how environmental conditions shape bacterial communities and drive evolution of free-living bacteria.

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