INSIGHTS OF ALKANE DEGRADATION IN MICROAEROBIOSIS BY Pseudomonas extremaustralis USING TRANSCRIPTOMIC AND PHYSIOLOGICAL APPROACH

PAULA M. TRIBELLI; LETICIA ROSSI; MARTINIANO M. RICARDI; LOPEZ, NANCY I.; LAURA J. RAIGER IUSTMAN

San Miguel de Tucuman

Congreso; XII Congreso Argentino de Microbiologia General SAMIGE 2017; 2017

SAMIGE

Hydrocarbon contamination has become a tough problem worldwide. One of the most widely distributed of these compounds is diesel, a complex mixture of n-alkanes, branched alkanes, and small amounts of aromatic moieties.Pseudomonas species are capable to use n-alkanes as carbon source by activating the hydrocarbon as a key first step using the enzyme 1-alkane monooxygenase encoded by alkB. Diesel degradation has been studied mostly under aerobic conditions in this genus, however in the environment uneven distribution of water flow, nutrients, and microbial populations creates a dynamic spectrum of aerobic,microaerobic, and anaerobic conditions.Pseudomonas extremaustralis is a bacterium isolated from Antarctica that shows high stress resistance and a wide microaerobic metabolism. P. extremaustralis is also capable to grow using diesel as sole carbon source only when cultured in biofilm condition. In this work we analyzed RNA-deep sequence experiments comparing the expression profile in aerobic and microaerobic planktonic cultures. Surprising, genes involved in n-alkane degradation presented differential expression in microaerobic conditions in comparison with aerobic cultures. The alkB gene, encoding the key enzyme for alkane degradation, alkane 1-monoxygenase, praA and praB encoding hydrocarbon facilitating proteins, and other genes related with this pathway such as those coding an alcohol and aldehyde dehydrogenase that were found up-regulated under low oxygen conditions.Additionally, genes encoding for some steps of fatty acid b-oxidation were also up-regulated while rubredoxin coding genes necessaries for the oxidation reaction of alkanes presented a non-differential expression between aerobic and microaerobic conditions. In-silico analysis of the promoter zone of alkB gene showed a putative Anr-box upstream the ATG, suggesting a regulation driven by oxygen availability. Cultures in minimal medium showed that P.extremaustralis was able to grow under microaerobic condition using diesel as sole carbon source in presence or absence of KNO3 as secondary electron acceptor. Degradation of n-alkanes (C13 to C19 fraction) after 7 days reached 20.5 % and 22.87% when KNO3 was present or absent, respectively, indicating that the remnant oxygen present in this culture condition was the responsible of alkane oxidation step. Under aerobic conditions P. extremaustralis was able to grow only in a biofilm structure tightly attached to the bottle glass at the culture-air interface but no alkane degradation was observed, in line with alkB expression experiments. This study showed a novel effect of micro aerobiosis on alkane degradation pathway in Pseudomonas species.