ABSTRACT
Variations in the exogenous nitrogen level are known to significantly affect the physiological status and metabolism of microalgae. However, responses of red, green and yellow-green algae to nitrogen (N) availability have not been compared yet. Porphyridium cruentum, Scenedesmus incrassatulus and Trachydiscus minutus were cultured in the absence of N in the medium and subsequent resupply of N to the starved cells. Culture growth and in-gel changes in isoenzyme pattern and activity of glutamate synthase, glutamate dehydrogenase, malate dehydrogenase, aspartate aminotransferase, superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase were studied. The results demonstrated that the algae responded to the fully N-depleted and N-replete culture conditions by speciesspecific metabolic enzyme changes, suggesting differential regulation of both enzyme activity and cellular metabolism. Substantial differences in the activities of the antioxidant enzymes between N-depleted and N-replete cells of each species as well as between the species were also found. In the present work, besides the more general responses, such as adjustment of growth and pigmentation, we report on the involvement of specific metabolic and antioxidant enzymes and their isoforms in the mechanisms operating during N starvation and recovery in P. cruentum, T. minutus and S. incrassatulus.
ABSTRACT
One of the main factors limiting the bioremediation of subsoil environments based on bioaugmentation is the transport of selected microorganisms to the contaminated zones. The characterization of the physiological responses of the inoculated microorganisms to starvation, especially the evaluation of characteristics that affect the adhesion of the cells to soil particles, is fundamental to anticipate the success or failure of bioaugmentation. The objective of this study was to investigate the effect of nitrogen starvation on cell surface hydrophobicity and cell adhesion to soil particles by bacterial strains previously characterized as able to use benzene, toluene or xilenes as carbon and energy sources. The strains LBBMA 18-T (non-identified), Arthrobacter aurescens LBBMA 98, Arthrobacter oxydans LBBMA 201, and Klebsiella sp. LBBMA 204-1 were used in the experiments. Cultivation of the cells in nitrogen-deficient medium caused a significant reduction of the adhesion to soil particles by all the four strains. Nitrogen starvation also reduced significantly the strength of cell adhesion to the soil particles, except for Klebsiella sp. LBBMA 204-1. Two of the four strains showed significant reduction in cell surface hydrophobicity. It is inferred that the efficiency of bacterial transport through soils might be potentially increased by nitrogen starvation.
Um dos principais fatores limitantes da biorremediação in situ de solos subterrâneos, baseada na bioaumentação, é o transporte dos microrganismos selecionados até o local contaminado. A caracterização das respostas fisiológicas dos microrganismos introduzidos no subsolo a condições de escassez nutricional, notadamente a avaliação de características que afetam a adesão celular ao solo, é fundamental para se prever o sucesso da bioaumentação. O objetivo deste trabalho foi determinar o efeito da desnutrição em meio com escassez de nitrogênio sobre a hidrofobicidade celular e a adesão ao solo de quatro isolados bacterianos previamente caracterizados como capazes de utilizar benzeno, tolueno ou xileno como fonte de carbono e energia. As linhagens LBBMA 18-T (não identificada), Arthrobacter aurescens LBBMA 98, Arthrobacter oxydans LBBMA 201, and Klebsiella sp. LBBMA 204-1 foram utilizadas nos experimentos. O cultivo das células em meio deficiente em nitrogênio causou uma redução significante na força de adesão das células às partículas do solo, exceto para a Klebsiella sp. LBBMA 204-1. Dois dos quatro isolados estudados sofreram alteração significativa na hidrofobicidade celular. Os resultados sugerem que a eficiência do transporte bacteriano através do solo pode ser aumentada pela desnutrição celular.