Biodiversity of diazotrophic bacteria within the soil, root and stem of field-grown maize

Abstract

Recent studies suggest a high diversity of diazotrophic bacteria in maize. However, none of these works have been based on a sufficient number of samples to provide reasonable quantitative estimates of diazotrophic bacterial diversity. Here we present the use of molecular tools and statistical inference to assess diazotrophic bacterial diversity within rhizosphere soils, roots and stems of field grown maize. DNA was isolated from the latter collected from six maize growing regions within the southern most state in Brazil, Rio Grande do Sul. Using conserved primers, nifH Cluster I gene fragments were amplified from each of the three zones, and the products cloned and sequenced. The majority of the sequences were classified within the Proteobacteria with the α-proteobacteria and β-proteobacteria being the most abundant in the rhizosphere soil and stem samples. The γ-proteobacteria were most abundant in rhizosphere soils, less so in roots, and least in the stem samples. According to three different diversity measures, the rhizosphere soil samples possessed greater diazotrophic bacterial diversity than the roots and stems of the maize plants. Only two genera, Azospirillum and Azotobacter, were found in virtually all samples at an abundance of over 1% of the total nifH sequences obtained. Other genera were largely restricted to soil (Methylocystis, Beijerinckia, Geobacter, Rhodovulum, Methylobacterium, Gluconacetobacter, Methylocella, and Delftia), roots (Dechloromonas), or stems (Methylosinus, Raoultella, and Rhizobium). Three genera, Herbaspirillum, Ideonella, and Klebsiella, appeared to dominate in the interior of the plant but were much rarer in soil.

Evidence for the functional significance of diazotroph community structure in soil

“…Thus, extraneous variation is minimized in this experiment relative to many studies that focus on the functional significance of soil communities. In addition, the diversity of the diazotrophic community in soil is typically far lower than that of the overall community, with estimates of nifH richness generally between 11-99 OTU 0.03 g À1 soil (Bothe et al, 2002;Izquierdo and Nusslein, 2006;Roesch et al, 2008). Regardless, the response of the diazotrophic community to the effects of tillage and biomass management that we observed was complex and differed with respect to the richness, evenness and the composition of the community.…”

Maize (Zea Mays L.) Growth and Metabolic Dynamics with Plant Growth- Promoting Rhizobacteria under Salt Stress

“…The rhizosphere harbors a multitude of microorganisms that are affected by both abiotic and biotic stresses. Among these are the dominant rhizobacteria that prefer living in close vicinity to the root or on its surface and play a crucial role in soil health and plant growth [16,17]. It has been noted by many workers that Pseudomonas, Bacillus, Arthrobacter, Azospirillum, Klebsiella, and Enterobacter, isolated from the rhizosphere of various crops, showed synergistic effects on plant growth [18].…”

Community composition and functions of endophytic bacteria of Bt maize

“…Furthermore, it has been shown that different species are commonly found on multiple plant tissues and there are some with a preference for the leaves. 15,19,44 This shows that there is a correlation between endophytes and plant parts harbouring them. In the present study, Bt and non-Bt maize cultivars harboured unrelated genera that are commonly found as maize endophytes such as Pantoea, Bacillus, Enterobacter, Serratia, Yersinia, Stenotrophomonas, Pseudomonas and Acinetobacter (Table 1).…”

“…Few studies have delved into this important aspect of endophyte biology. 3,[17][18][19] In this study, we hypothesised that genetic modification of maize plants (such as Bt maize) might influence the diversity and functional attributes of endophytic bacteria associated with the plant. This led us to investigate the potential impacts of genetic modification of maize on the community composition and functions of cultivable bacterial endophytes from different plant parts that included leaves, stems, cobs and tassels/husks at two different plant growth stages.…”