Metabolic and stress responses of Acinetobacter oleivorans DR1 during long‐chain alkane degradation

Abstract

Summary Acinetobacter oleivorans DR1 can utilize C12–C30 alkanes as a sole carbon source but not short‐chain alkanes (C6, C10). Two copies of each alkB‐, almA‐ and ladA‐type alkane hydroxylase (AH) are present in the genome of DR1 cells. Expression and mutational analyses of AHs showed that alkB1 and alkB2 are the major AH‐encoding genes under C12–C30, and the roles of other almA‐ and ladA genes are negligible. Our data suggested that AlkB1 is responsible for long‐chain alkane utilization (C24–C26), and AlkB2 is important for medium‐chain alkane (C12–C16) metabolism. Phylogenetic analyses revealed large incongruities between phylogenies of 16S rRNA and each AH gene, which implies that A. oleivorans DR1 has acquired multiple alkane hydroxylases through horizontal gene transfer. Transcriptomic and qRT‐PCR analyses suggested that genes participating in the synthesis of siderophore, trehalose and poly 3‐hydroxybutyrate (PHB) were expressed at much higher levels when cells used C30 than when used succinate as a carbon source. The following biochemical assays supported our gene expression analyses: (i) quantification of siderophore, (ii) measurement of trehalose and (iii) observation of PHB storage. Interestingly, highly induced both ackA gene encoding an acetate kinase A and pta gene encoding a phosphotransacetylase suggested unusual ATP synthesis during C30 alkane degradation, which was demonstrated by ATP measurement using the ΔackA mutant. Impaired growth of the ΔaceA mutant indicated that the glyoxylate shunt pathway is important when C30 alkane is utilized. Our data provide insight into long‐chain alkane degradation in soil microorganisms.

Trehalose, a temperature‐ and salt‐induced solute with implications in pathobiology of Acinetobacter baumannii

“…Trehalose does not only function in osmo‐ and thermostress response, but is also produced in Acinetobacter oleivorans DR1 during growth on alkanes (Park et al ., ). Alkane‐induced trehalose formation was abolished in that species by disruption of the otsA gene.…”

Survival and Energy Producing Strategies of Alkane Degraders Under Extreme Conditions and Their Biotechnological Potential

“…The glyoxylate shunt in the mesophilic alkane-degrading bacteria, Acinetobacter oleivorans DR1, is activated to generate energy during triacontane metabolism ( Park et al, 2017 ). The glyoxylate shunt requires isocitrate lyase (encoded by aceA ) and malate synthase (encoded by aceB or glcB ), which are activated under oxidative stress or in the presence of C 2 carbon sources ( Ahn et al, 2016 ).…”

“…The interface between alkane degraders and hydrocarbon compounds may form microoxic or anoxic niches because of hydrophobicity ( Suter et al, 2017 ). In addition, alkane oxidation generates excessive acetyl-CoA ( Sabirova et al, 2006 ; Schönfeld and Wojtczak, 2016 ; Park et al, 2017 ), creating appropriate conditions for aerobic fermentation, which is also called the Crabtree effect ( Zhou et al, 2017 ). Acetate assimilation via the Pta-AckA pathway occurs in the presence of long-chain alkanes (triacontane), producing ATP ( Park et al, 2017 ).…”

“…In addition, alkane oxidation generates excessive acetyl-CoA ( Sabirova et al, 2006 ; Schönfeld and Wojtczak, 2016 ; Park et al, 2017 ), creating appropriate conditions for aerobic fermentation, which is also called the Crabtree effect ( Zhou et al, 2017 ). Acetate assimilation via the Pta-AckA pathway occurs in the presence of long-chain alkanes (triacontane), producing ATP ( Park et al, 2017 ). Although studies on the Pta-Ack pathway during alkane metabolism are limited, evidence shows that extremophiles can synthesize ATP via the Pta-AckA pathway.…”

“…However, a recent study showed that a novel Rieske-type alkane monooxygenase degrades pentane (C 5 ) to tetracosane (C 24 ) using NADH as a cofactor ( Li et al, 2013 ). In addition, many bacteria possess multiple alkane hydroxylases (AH), and therefore, it is possible that a wide range of alkanes can be degraded by one microorganism ( Whyte et al, 1998 ; Rozhkova-Novosad et al, 2007 ; Amouric et al, 2010 ; Liu et al, 2011 ; Park et al, 2017 ).…”