Ecological distribution of Spirillum lipoferum Beijerinck

Abstract

A survey in various countries revealed that the N2-fixing Spirillum lipoferum Beijerinck is a very common root and soil inhabitant in the tropics. More than half of the grass root and soil samples collected in tropical countries (four African countries and Brazil) contained abundant S. lipoferum populations, while less than 10% of the samples collected in temperate South Brazil, Kenya, and the U.S.A. contained the organism. There is a pronounced vegetation effect. Panicum maximum seems the most favorable among the forage grasses, while few positive samples were found under virgin tropical forest. Legume roots contained less S. lipoferum than adjacent soils. More than 80% of the samples from cereal roots (maize, sorghum, wheat, and rye) grown in fields fertilized with PK and Mo, in Rio de Janeiro State, were positive. Maize and sorghum grown under similar conditions in Wisconsin contained less than 10% of positive samples, but when maize fields were inoculated 90% of the root samples contained S. lipoferum. Alluvial soils were more favorable than eroded hill soils. Occurrence in soil was strongly pH-dependent with a pH around 7, being optimal (correlation coefficient r = 0.90). Sporadic occurrence was observed even in soils with pH 4.8. Surface-sterilized P. maximum roots collected from soils with pH ranging from 4.8 to 7.2 contained high S. lipoferum numbers which did not correlate with soil pH (r = 0.41). Amendment with malate of acid soils was not very effective in increasing nitrogenase (N2-ase) activity, but in two soils with pH above 6.4, high N2-ase activity was obtained after 16 to 48 h of incubation. In two soils from a temperate climate region, inoculation with S. lipoferum increased N2-ase activity produced through malate amendment.

Coberturas vegetais, doses de nitrogênio e inoculação de sementes com Azospirillum brasilense em arroz de terras altas no sistema plantio direto

“…A fixação biológica do N pelas bactérias do gênero Azospirillum em associação com gramíneas (Döbereiner et al, 1976) podem contribuir com o fornecimento de parte das necessidades das plantas por este nutriente. Esse grupo de bactérias também sintetizam hormônios, como a auxina, que estimula o crescimento da parte aérea e do sistema radicular de varias gramíneas, entre elas o arroz (Radwan et al, 2004).…”

Nitrogenase Activity Associated with Roots and Stems of Field-Grown Corn (Zea mays L.) Plants

“…4, inset) Azospirillum spp. has been proposed as one of the major N2-fixing organisms responsible for the nitrogenase activity associated with corn and other grasses grown under tropical conditions (5,8,12), but it would still be premature to propose a similar role for the azospirilla occurring in New Jersey soils.…”

“…On the other hand, Azospirillum spp. was reported to occur in rather low numbers in certain temperate climates (8) and experiments conducted at Wisconsin showed no detectable nitrogenase activities on whole corn plants, even on soils inoculated previously with Azospirillum St. Sp7 (2). Nevertheless, acetylene reduction was observed after the root system had been greatly disturbed (2).…”

“…has been proposed as the major organism responsible for the nitrogenase activity in tropical grasses (5,8,12). On the other hand, Azospirillum spp.…”

Partial characterization of nif genes from the bacterium Azospirillum amazonense

“…brasilense Sp7 (ATCC29145) and A. amazonense (ATCC35119) were grown on NFB and LGI minimal media, respectively, as previously described (6,11).…”