Insights of alkane degradation in microaerobiosis by Pseudomonas extremaustralis using transcriptomic and physiological approaches.

PM TRIBELLI; L ROSSI; MM RICARDI; NI LOPEZ AND ; LJ RAIGER IUSTMAN

San Mighel de Tucuman

Congreso; xii congreso de microbiología general - samige; 2017

Asociación Civil de Microbiología General

Hydrocarbon contamination has become a tough problem worldwide. One of the most widely distributedof these compounds is diesel, a complex mixture of n-alkanes, branched alkanes, and smallamounts of aromatic moieties. Pseudomonas species are capable to use n-alkanes as carbon source byactivating the hydrocarbon as a key first step using the enzyme 1-alkane monooxygenase encoded byalkB. Diesel degradation has been studied mostly under aerobic conditions in this genus, however in theenvironment uneven distribution of water flow, nutrients, and microbial populations creates a dynamicspectrum of aerobic, microaerobic, and anaerobic conditions. Pseudomonas extremaustralis is a bacteriumisolated 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 biofilmcondition. In this work we analyzed RNA-deep sequence experiments comparing the expression profilein aerobic and microaerobic planktonic cultures. Surprising, genes involved in n-alkane degradationpresented differential expression in microaerobic conditions in comparison with aerobic cultures. ThealkB gene, encoding the key enzyme for alkane degradation, alkane 1-monoxygenase, praA and praBencoding hydrocarbon facilitating proteins, and other genes related with this pathway such as thosecoding 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 whilerubredoxin coding genes necessaries for the oxidation reaction of alkanes presented a non-differentialexpression between aerobic and microaerobic conditions. In-silico analysis of the promotor zone of alkBgene 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 microaerobiccondition 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% whenKNO3 was present or absent, respectively, indicating that the remnant oxygen present in this culturecondition was the responsible of alkane oxidation step. Under aerobic conditions P. extremaustralis wasable to grow only in a biofilm structure tightly attached to the bottle glass at the culture-air interfacebut no alkane degradation was observed, in line with alkB expression experiments. This study showed anovel effect of microaerobiosis on alkane degradation pathway in a Pseudomonas species.