Effect of some granular insecticides currently used for the treatment of maize crops (Zea mays) on the survival of inoculated Azospirillum lipoferum.

Four insecticides, carbofuran, chlormephos, terbufos and benfuracarb, currently used on maize (Zea mays) at sowing, were tested for their compatibility with Azospirillum lipoferum strain CRT1 used as an inoculant to improve maize growth and yield. The growth or survival of A lipoferum was studied in the presence of the insecticides: (1) in liquid and solid cultures of the bacteria, (2) when a commercial inoculant (Azogreen-m, Liphatech, Meyzieu, France) was inoculated directly on insecticide granules, (3) when inoculated Azogreen-m granules were mixed with insecticide granules and (4) when inoculated Azogreen-m granules were delivered separately to the seed bed. Of the four insecticides tested, only terbufos had a slight effect on growth of A lipoferum in solid cultures. All the insecticides decreased the survival of A lipoferum when the bacteria were inoculated directly on to the granules, or when inoculated Azogreen-m granules were mixed with an insecticide. We hypothesize that the discrepancies between bacterial culture tests and survival studies might be explained by the conditions of desiccation encountered during inoculation of the granules. Desiccation stress could increase the toxic effect of the insecticides. We therefore suggest including desiccation stress in the biotest used to assess inoculant-pesticide compatibility.

Changes in the physiological and agricultural characteristics of peat-based Bradyrhizobium japonicum inoculants after long-term storage.

Commercial soybean inoculants processed with sterilised peat and stored at 20 degrees C for 1-8 years were used as experimental materials to assess the changes in the physiological activity of Bradyrhizobium japonicum after storage. Viable counts decreased and physiological characteristics of the bacterium changed during storage, with an increase in the time taken for colony appearance on a medium without yeast extract, an increase in the lag time for nodule appearance on soybean grown in glass tubes and a decrease in survival on seeds. All the inoculants produced a significant increase in grain yield in a field experiment. The percentage of efficient cells in the field (relative to the plate counts) decreased as the length of storage increased. These results suggest that the physiological activity of B. japonicum cells changes after storage. Practical implications for inoculant quality control are discussed.

Oligonucleotide probes based on 16S rRNA sequences for the identification of four Azospirillum species.

Partial sequences of the 16S rRNA molecules of nine strains belonging to four Azospirillum species were used to design species-specific oligonucleotide probes. Azospirillum strains sequences were analyzed and three homologous fragments containing 16 nucleotides were determined. These three probes were found to be characteristic of A. lipoferum (Al), A. irakense (Ai), and A. brasilense/amazonense species (Aba) and of few nontarget organisms. The specificity of these three probes was tested both against sequences in the GenBank data base and in numerous colony hybridization experiments. As a few non-target organisms hyridized with the different Azospirillum probes, the use of these probes in bulk soil hybridization is not permitted. However, their use together with specific isolation techniques is validated.

Glutamine synthetase and glutamyltransferase in the kidney of man, dog, and rat.

Glutamine synthetase (GS) is known to exist in the kidney of the rat, guinea pig, rabbit, and sheep but not in that of the dog, pig, cat, or pigeon. No data is available in man. Assay of histologically normal renal tissue obtained in human subjects during surgery for abdominal vascular disease failed to demonstrate significant GS activity. In addition, L-glutamine gamma-glutamyltransferase (GT) activity was also very low. The same results were observed in the dog, in which both GS and GT activities did not exceed 15% of those found in the kidney of the normal rat. In the latter animal both GS and GT activities are higher in the outer medulla (312 and 1,165 mumol/h per g wet wt, respectively) than in the cortex (230 and 844, respectively). During metabolic acidosis, GT activity did not change but GS activity decreased in the outer medulla by 40%. When renal cortex slices from normal rats were incubated in the presence of ammonia, glutamate, and octanoate (as a source of ATP), net synthesis of glutamine was readily demonstrated in contrast to slices from normal DOGS. The present studies demonstrate that the kidney of man, like that of the dog, is devoid of significant glutamine synthetase and glutamine gamma-glutamyltransferase activities. In the rat, we have confirmed the functional significance of GS activity in the kidney. We have also shown that renal GT activity is ammoniagenic in vitro in this animal, but the contribution of this system to total ammonia production in vivo remains to be demonstrated.

Ammoniagenesis: d-glutamyltransferase as a source of ammonia in the rat kidney.

The contribution of D-glutamyltransferase (D-GT) (EC 2.3.2.1) to total renal ammonia production was determined by employing DL-methionine-DL-sulfoximine (MSO) as an inhibitor of D-GT. Rat kidney homogenates were assayed for NH3-liberating activity under optimal D-GT or gamma-glutamyltranspeptidase (gamma-GTP) (EC 2.3.2.2) conditions. MSO inhibits only D-GT activity. The contribution of D-GT to total renal ammonia production was then evaluated in the isolated perfused rat kidney employing identical substrate (5 mM L-glutamine) and inhibitor (15 mM MSO) concentrations as employed in the homogenate study. Under these conditions, MSO inhibits 70 percent of the total ammonia production by the normal kidney; in addition, the ratio of ammonia produced per glutamine taken up rose from 1.0 to 1.8. In kidneys from chronically acidotic rats, MSO reduced total ammonia production only 35 percent while the NH3/glutamine ratio rose from 1.0 to 1.8. D-GT appears to be the predominant source of NH3 production in the normal rat kidney; gamma-GTP does not contribute significantly. The rise in the NH3/glutamine ratio after D-GT inhibition is consistent with glutamine utilization via the activated mitochondrial glutaminase (EC 3.5.1.2)-glutamate dehydrogenase (EC 1.4.1.2) pathway.