Diversity of free-Living nitrogen fixing Streptomyces in soils of the badlands of South Dakota

Abstract

Biological Nitrogen Fixation is critical for ecosystem productivity. Select members of Bacteria and Archaea express a nitrogenase enzyme complex that reduces atmospheric nitrogen to ammonia. Several nitrogen fixing bacteria form symbiotic associations with plants, but free-living diazotrophs also contribute a substantial amount of nitrogen to ecosystems. The aim of this study was to isolate and characterize free-living diazotrophs in arid lands of South Dakota Badlands. Samples were obtained from sod tables and the surrounding base in spring and fall. Diazotrophs were isolated on solid nitrogen free medium (NFM) under hypoxic conditions, and their16S rRNA and nifH genes sequenced. nifH was also amplified directly from soil DNA extracts. The 16S rRNA gene data indicated a diversity of putative free-living diazotrophs across 4 phyla (Actinomycetes, Proteobacteria, Bacteroidetes, and Firmicutes), but ∼50% of these clustered with Streptomyces. These Streptomyces isolates grew in liquid NFM in an ammonia-depleted environment. Only 5 of these yielded a nifH gene product using the PolF/PolR primer set. Four of these aligned with nifH of the cyanobacteria Scytonema and Nostoc, and the other one aligned with nifH of Bradyrhizobium. Six selected Streptomyces isolates, three of which were nifH positive by PCR, all indicated N incorporation, providing strong support of nitrogen fixation. All nifH amplicons from soil DNA extract resembled Cyanobacteria. This is the first known report of diazotrophic Streptomyces, other than the thermophilic, autotrophic S. thermoautotrophicus. nifH genes of these Streptomyces were related to those from Cyanobacteria. It is possible that the cyanobacteria-like nifH amplicons obtained from soil DNA were associated with Streptomyces.

From Isolation of Phosphate Solubilizing Microbes to Their Formulation and Use as Biofertilizers: Status and Needs

“…Alam et al (2012) achieved an increase in yield (11%) of geranium herbs inoculated with Streptomyces sp. The ability of some Streptomyces to fix nitrogen as free-Living is an additional advantage in offsetting nitrogen losses from soil (Dahal et al, 2017). It has been documented that Actinobacteria promotes legume symbioses through hyphal elongation for symbiotic fungi (Schrey and Tarkka, 2008) and /or by increasing nodulation for nitrogen fixing symbiosis (Sathya et al, 2017).…”

Potential of Bioremediation and PGP Traits in Streptomyces as Strategies for Bio-Reclamation of Salt-Affected Soils for Agriculture

“…However, recently, serendipity led to the finding of five nitrogen-fixing Streptomyces. The strains yielded nifH products that aligned with those of Scytonema, Nostoc, and Bradyrhizobium [126]. However, the nitrogen-fixing activity remains to be studied further in Streptomyces.…”

“…The different systems are similar in their nitrogen fixing mechanism and sensitivity to oxygen. However, they differ in their metal content and encoding genes; nifH being the most studied and conserved nitrogenase enzyme complex-encoding gene [126]. Only Streptomyces thermoautotrophicus was once believed to fix atmospheric nitrogen; however, MacKellar et al [127] demonstrated its lacking nitrogen-fixing ability.…”

Aislamiento y caracterización de Streptomyces spp rizosféricos promotores del crecimiento vegetal

“…Siguiendo la técnica del fenol hipoclorito de Lara et al (2007) se detectó una concentración de 0,63 mg/L de amonio en el medio de cultivo de Streptomyces cirratus (ST3E). De acuerdo con Dahal et al (2017) no se conocen Streptomyces fijadores de nitrógeno, es por ello que proponemos a Streptomyces cirratus (ST3E) como candidato para profundizar mayores estudios y confirmar la presencia de los genes nif y sus posibles mecanismos para poder fijar el nitrógeno atmosférico.…”