Plant-available inorganic nutrient levels are increased in rice-derived distillery effluents inoculated with microbes.

AIMS: The purpose of this study was to assess the effects of microbes on plant-available inorganic nutrients and a phytohormone in rice-derived distillery effluents. METHODS AND RESULTS: The effects of 37 microbial strains on the components of distillery effluents were investigated. Inoculation of several Aspergillus and Bacillus strains resulted in accumulation of a large quantity of ammonium nitrogen (NH4-N; 774 ± 490 and 1059 ± 463 mg l(-1), respectively) in the effluent. However, a decrease in the liquid phase during Aspergillus incubation suggested the requirement for additional treatment of the solid residue, whereas the growth of Bacillus subtilis was inhibited by the acidic conditions in the raw distillery effluent. Interestingly, Aspergillus caelatus, Aspergillus oryzae and Aspergillus tamarii yielded greater increases in nitrate concentrations (30-39 mg l(-1)). Colorimetric and gas chromatography-mass spectrometry analyses revealed that Wickerhamomyces strains generated 7-26 mg l(-1) of indole-3-acetic acid (IAA) when the effluent pH was adjusted to 7·0. CONCLUSIONS: Inoculation of several Aspergillus and Bacillus strains into distillery effluents resulted in the production of a large quantity of NH4-N. SIGNIFICANCE AND IMPACT OF THE STUDY: This study provides information that will facilitate the bioconversion of distillery effluent into fast-acting liquid fertilizers.

A rapid and simple PCR method for identifying isolates of the genus Azospirillum within populations of rhizosphere bacteria.

AIMS: To develop a rapid and simple genus-specific polymerase chain reaction (PCR) method for detecting and identifying isolates of the genus Azospirillum which is well-recognized as plant growth-promoting rhizobacterium. METHODS AND RESULTS: Nine pairs of PCR primers were designed based on the Azospirillum 16S rRNA, ipdC, nifA and nifH genes to assess their genus specificity by testing against 12 Azospirillum (from seven species) and 15 non-Azospirillum reference strains, as compared with the fAZO/rAZO pair reported by Baudoin et al. (J Appl Microbiol, 108, 2010, 25). Among the primer pairs assessed, the Az16S-A pair designed on the 16S rRNA gene sequence showed the highest genus specificity: it successfully yielded a single amplicon of the expected size in all the 12 Azospirillum strains and for a close relative, Rhodocista centenaria. The PCR with the Az16S-A primers generated a detectable amount of the amplicon from ≥10³ CFU ml⁻¹ of Azospirillum cell suspensions even in the presence of contaminants and accurately discriminated Azospirillum and non-Azospirillum species in both 35 Azospirillum-like and 70 unknown isolates from plant roots and rhizosphere soils. CONCLUSIONS: We developed a rapid and simple PCR method for detecting and identifying Azospirillum isolates within populations of rhizosphere bacteria. SIGNIFICANCE AND IMPACT OF THE STUDY: The method developed would serve as a useful tool for isolating a variety of indigenous Azospirillum bacteria from agricultural samples.