Screening of Indigenous Microorganisms as Potential Biofertilisers for Periurban Horticulture Areas

In Buenos Aires periurban area, horticultural practices are one of the most important activities. Pesticides and fertilisers are used without any control to cover the farmers’ needs, obtaining high crop yields at short terms and modifying soil ecosystem in the long term. The aim of this work was to isolate indigenous strains from periurban horticultural units with pesticide degrading capacity and to evaluate their plant growth-promoting properties in order to design biofertilisers to be applied in the restoration of these exploited soils. After the screening, eight strains were isolated and identified. They showed not only the capacity to produce indole-3- acetic acid, to fix nitrogen, to secrete siderophores and to solubilise calcium phosphate but also tolerated the mixture of pesticides usually used for horticultural practices. By their behaviour in mixed cultures and plant growth-promoting properties, these autochthonous isolates represent a promising alternative as biofertilisers according to soil type and activity

Study of the phosphorylation of photosynthetic membrane associated peptides in Rhodovulum sulfidophilum

Durante más de 10 años, nuestro grupo ha estudiado la relación que existe entre la fosforilación de péptidos asociados a las membranas fotosintéticas de bacterias fototróficas pertenecientes a distintos géneros y la síntesis del aparato fotosíntético. Estudios similares han sido llevados a cabo por diferentes grupos de investigación tanto en organismos fotosintéticos como en cloroplastos de plantas superiores. En Rhodobacter capsulatus se demostró la existencia de péptidos del complejo antena, sobre todo de los péptidos α2 y β1 de, que sufrían una modificación postraduccional por fosforilación y que dicha modificación estaba regulada por las condiciones ambientales en que el cultivo bacteriano se desarrollaba. Esta modificación estaba también relacionada con la regulación genética de la síntesis de los componentes del aparato fotosíntético y el mecanismo de inserción del mismo en las membranas. En el transcurso de este trabajo de tesis se ha observado que en Rhodovulum sulfidophilum existe un péptido de un peso molecular aparente de 6 kDa, al que se lo denominó péptido P, que se fosforila in vivo exclusivamente en tirosina. A pesar de que este péptido resultó no corresponder a ninguna de las proteínas que unen bacterioclorofila descriptas hasta el momento, su fosforilación parece depender de condiciones que regulan, en genreal, la sintesis del aparato fotosíntético, o sea que responde a los cambios en las condiciones de crecimiento: luz-oscuridad, aerobiosis-anaerobiosis. Es probable que este péptido fosforilable esté relacionado con los sitios de iniciación del crecimiento de las membranas intracitoplasmáticas. Durante este trabajo de tesis se también se construyó y caracterizó una mutante LH1- , no polar, denominada rsLRI. Dicha mutante se obtuvo por deleción de los genes pufBA, que codifican para las apoproteínas LH1β y LHIα.During the last ten years, our group has studied the relationship existing between phosphorylation of peptides of photosynthetic membranes in phototrophic bacteria belonging to different genera, and the synthesis of the photosynthetic apparatus. Similar studies have been performed in chloroplast of higher plants. In Rhodobacter capsulatus the LH2α and LH1β polypeptides were phosphorylated in vivo and the process was regulated by ambient growth conditions. This postranslational modification was related to the gene expression of the antenna polypeptides and their insertion in the membrane The present thesis work has revealed that in Rhodovulum sulfidophilum a small polypeptide of apparent MW of 6 kDa (P peptide) was phosphorylated exclusively in tyrosine This peptide could not be identified as a belonging to the photosynthetic apparatus although its phosphorylation depends on those conditions that regulates the synthesis of the photosynthetic apparatus. Thus it was govemed by changes in light-dark or aerobiosisanaerobiosis conditions. It is possible that peptide P was related with the initiation sites present in the intracitoplasmic membranes. In this work we have obtained and characterised a mutant resulting in a non-polar LH1- mutant was obtained by deleting pufBA genes codifying for LHl and βLH1α polypeptidesFil:Raiger-Iustman, Laura J.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Functional enrichment of differentially expressed genes using Blast2GO software.

<p>A. Down-regulated genes. B. Up-regulated genes. P<0.05 using Fisher’s Test.</p

Estimation of alcohol dehydrogenase activity using p-rosaniline plate assay in wild type (WT), <i>ppqB</i> and <i>pqqB</i>/pBBR1MCS5 <i>pqqBCDE</i> strains.

<p>Activity was considered as positive in magenta colonies, while white colonies were considered as negative. A. Plates incubated at 30°C during 24 h. B. Plates were incubated at 8°C during 7 days. C. Determination of p-rosaniline index at 30°C. D. Determination of p-rosaniline index at 8°C. The asterisk (*) denotes significant differences (<i>P</i><0.05) between strains (indicating by connector lines) using the Student's <i>t</i> test.</p

Organization of genes coding for ethanol oxidation in <i>P</i>. <i>extremaustralis</i> and other <i>Pseudomonas</i> species.

<p>Arrows indicate the direction of gene transcription and the relative size of each open reading frame (ORF).</p

Growth of the wild type (WT), <i>ppqB</i> and <i>exaA</i> strains.

<p>A. Growth at 30°C. B. Growth at 8°C. Values represent the mean ± standard deviations (SD) from three independent cultures.</p