From a selective enrichment culture prepared with different soil samples on starch-containing polyethylene we isolated four microaerophilic microbial communities able to grow on this kind of plastic with no additional carbon source. One consortium, designated community 3S, was tested with pure isotactic polypropylene to determine whether the consortium was able to degrade this polymer. Polypropylene strips were incubated for 5 months in a mineral medium containing sodium lactate and glucose in screw-cap bottles. Dichloromethane crude extracts of the cultures revealed that the weight of extracted materials increased with incubation time, while the polypropylene sample weight decreased. The extracted materials were characterized by performing chromatographic and spectral analyses (thin-layer chromatography, liquid chromatography, gas chromatography-mass spectrometry, infrared spectrometry, nuclear magnetic resonance). Three main fractions were detected and analyzed; a mixture of hydrocarbons at different degrees of functionalization was found together with a mixture of aromatic esters, as the plasticizers usually added to polyolefinic structures.

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Growth, acetylene reduction, and respiration rate were studied in batch and continuous cultures of Arthrobacter fluorescents at different oxygen partial pressures. The optimum pO2 values for growth and acetylene reduction were 0.05 and 0.025 atm, respectively, but microorganisms can tolerate higher pO2 values. The growth of cultures provided with combined nitrogen was dependent on oxygen availability, and strict anaerobic conditions did not support growth. Acetylene reduction of a population grown in continuous culture and adapted to low pO2 (0.02 atm) was much more sensitive to oxygenation than that of a population adapted to high pO2 (0.4 atm). Their maximum nitrogenase activity, at their optimal pO2 values, were quite different. The respiratory activity of nitrogen-fixing cultures increased with increasing oxygen tensions until a pO2 of 0.2 atm. At higher pO2 values, the respiration rate began to decrease.

Slightly lower values of viability were obtained in mixed culture, but the ratio between the microorganisms was constant. The survival ofArth, giacomelloi in single culture decreased with increasing growth rate while survNal of Azo. brasilense was directly related to dilution rate.Acetylene reduction activity was generally very low in both single and mixed cultures. Respiration rate was also determined and the mixed culture showed an oxygen uptake rate higher than that of single cultures.

Respiratory activity, molar growth yields, and ATP content in. an Arthrobacter sp. ammonium-limited chemostat culture. Can. J. Microbiol. 29: 11 36-1140.ArthrobacterfIuorescens was grown in chemostat culture under ammonium-limited conditions and respiratory activity; molar growth yields and ATP content were determined over a wide range of dilution rates. Within a range of dilution rates between 0.10 h-' and 0.20 h-', morphological transition occurred, the ratio of cocci to rods appearing inversely related to growth rate. Molar growth yields for both glucose and ammonium decreased with increasing dilution rates because of the higher intracellular polysaccharide content at the lower growth rates. Different metabolic activities were shown in cocci, in rods, and during morphogenesis. A sharp decrease in in situ and potential oxygen quotient (Q(02)) and in ATP content was observed in the range of dilution rates in which morphological changes occurred.CACCIARI, I., D. LIPPI, S. IPPOLITI et W. PIETROSANTI. 1983. Respiratory activity, molar growth yields, and ATP content in an Arthrobacter sp. ammonium-limited chemostat culture. Can. J. Microbiol. 29: 1136-1 140. ArthrobacterfIuorescens a Ctt mis en cultures continues (chemostat) sous des conditions limittes d'ammonium et d'activitC respiratoire en vue de dCterminer dans une g a m e de taux de dilution les rendements molaires de croissance et la teneur en ATP. A I'intCrieur de cette gamme, entre 0,10 h-' et 0,20 h-', des transitions morphologiques sont survenues et le rapport des formes sphkriques aux formes en bkonnet s'est avCrC inversement relit5 au taux de croissance. Les rendements molaires de croissance, tant pour le glucose que pour l'ammonium, ont dtcru face a une augmentation des taux de dilution en raison de la teneur ClevCe des poly saccharides intracellulaires aux taux infkrieurs de croissance. DiffCrentes activitCs mCtaboliques se sont manifestCes chez les formes sphCriques, chez les bltonnets, et au cours de la morphogenkse. Un dtclin rapide a Ct C observt in situ du quotient oxygkne (Q(02)) potentiel et de la teneur en ATP dans les divers taw de ddution o~ des changements morphologiques sont survenus.[Traduit par le journal]

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