Marco Bosco

Frequency and biodiversity of 2,4-diacetylphloroglucinol-producing rhizobacteria are differentially affected by the genotype of two maize inbred lines and their hybrid

Rhizobacteria (2808) were isolated on Pseudomonas-selective S1 medium from two maize inbred lines and from their hybrid at three plant growth stages. Positive phl D hybridization was found for 364 of them. The PhlD+ isolates were significantly more numerous in the rhizosphere of the hyrid than in those of parental lines. Furthermore, the frequency of PhlD+ was significantly higher for the hybrid at the flowering stage. An amplified rDNA restriction analysis showed that the hybrid genotype also increases the genetic diversity of PhlD+ populations when compared with its inbred parent lines, and this could be an effect of heterosis. Influence of the hybrid on the frequency and diversity of the bacterial PhlD+ population varied along the plant growth stage.

Genetic diversity of phl D gene from 2,4-diacetylphloroglucinol-producing Pseudomonas spp. strains from the maize rhizosphere

In biocontrol Pseudomonads, phlD is an essential gene involved in the biosynthesis of 2,4-diacetylphloroglucinol (DAPG). HaeIII restriction of amplified phlD gene, previously proposed as the most discriminant analysis, showed no polymorphism among 144 Pseudomonas strains isolated from maize roots. However, these strains fell into three statistically significant DAPG production level groups. phlD sequences of 13 strains belonging to the three DAPG groups revealed a KspI restriction site only in good DAPG-producing strains. This result was confirmed on the 144 strains, 82 of which were identified as good-DAPG producers by both biochemical and amplified phlD KspI restriction analysis. They are candidates as potential biocontrol agents.

Soil antimony pollution and plant growth stage affect the biodiversity of auxin-producing bacteria isolated from the rhizosphere of Achillea ageratum L

Abstract A total of 4512 rhizobacteria were isolated at three stages of plant growth from Achillea ageratum colonizing a polluted site with an antimony concentration gradient. For 222 of these isolates auxin production (aux(+)) was verified in vitro. The percentage of aux(+) isolates increased with soil antimony concentration, as well as with plant growth stage. An amplified rDNA restriction analysis clustered the aux(+) isolates into 51 clusters, one of which was numerically predominant and present throughout plant development and at all antimony concentrations. The aux(+) population was genetically very diverse, and this diversity was related to both antimony concentration and plant growth stage.

Ion interaction with carboxymethylagar : a polarographic study

Synthetic polycarboxylates are currently used to complex and eventually precipitate metal ions for different purposes, e.g. in waste-water treatments [l]. High affinity complexes and the occurrence of specificity may allow the selective removal of ions. The search for more specific complexing agents and the need for biodegradable systems have driven the attention of researchers to natural polycarboxylates. Among them, carboxylate polysaccharides are known to form strong complexes with specific ions. Alginates, extracted from brown algae 121, and pectins, extracted from higher plants [3], are known to interact strongly with a number of divalent cations. In particular, calcium ions are able to induce the formation of strong gels in alginate or pectate aqueous systems [4]. The mechanism of ion-induced gel formation in these polysaccharide systems implies polymer chain rearrangements; in fact, parallel to polymer chain association, a disorder-to-order conformational transition occurs [5,6]. In addition to Ca2+, other divalent ions (e.g. Cu2+ and Ni2+) can form gels with the above-mentioned polysaccharides. These gels exhibit different gel strengths with respect to that measured with calcium ions, indicating different energetics of complexation. One of the advantages of natural polymers is the presence of peculiar stereochemical motives on the back-bone chain. These features can favour the occur-