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

ROSSI LETICIA; RAIGER IUSMAN LAURA; TRIBELLI PAULA M.; LOPEZ NANCY I; RICARDI MARTINIANO

San Mighel de Tucuman

Congreso; XII Congreso Argentino de Microbiologia; 2017

SAMIGE

Hydrocarbon contamination has become a tough problem worldwide. One of the most widelydistributed of these compounds is diesel, a complex mixture of n-alkanes, branched alkanes, andsmall amounts of aromatic moieties. Pseudomonas species are capable to use n-alkanes as carbonsource by activating the hydrocarbon as a key first step using the enzyme 1-alkane monooxygenaseencoded 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 populationscreates a dynamic spectrum of aerobic, microaerobic, and anaerobic conditions. Pseudomonasextremaustralis is a bacterium isolated from Antarctica that shows high stress resistance and a widemicroaerobic metabolism. P. extremaustralisis also capable to grow using diesel as sole carbonsource only when cultured in biofilm condition. In this work we analyzed RNA-deep sequenceexperiments comparing the expression profile in aerobic and microaerobic planktonic cultures.Surprising, genes involved in n-alkane degradation presented differential expression in microaerobicconditions in comparison with aerobic cultures. The alkB gene, encoding the key enzyme for alkanedegradation, alkane 1-monoxygenase, praA and praB encoding hydrocarbon facilitating proteins, andother genes related with this pathway such as those coding an alcohol and aldehyde dehydrogenasethat were found up-regulated under low oxygen conditions. Additionally, genes encoding for somesteps of fatty acid b-oxidation were also up-regulated while rubredoxin coding genes necessaries forthe oxidation reaction of alkanes presented a non-differential expression between aerobic andmicroaerobic conditions. In-silico analysis of the promotor zone of alkB gene showed a putativeAnr-box upstream the ATG, suggesting a regulation driven by oxygen availability. Cultures in minimalmedium showed that P.extremaustralis was able to grow under microaerobic condition using diesel assole carbon source in presence or absence of KNO3 as secondary electron acceptor. Degradation ofn-alkanes (C13 to C19fraction) after 7 days reached 20.5 % and 22.87% when KNO3 was present orabsent, respectively, indicating that the remnant oxygen present in this culture condition was theresponsible of alkane oxidation step. Under aerobic conditions P. extremaustralis was able to growonly in a biofilm structure tightly attached to the bottle glass at the culture-air interface but no alkanedegradation was observed, in line with alkB expression experiments. This study showed a novel effectof microaerobiosis on alkane degradation pathway in a Pseudomonas species.Congr