Benzoate mediates the simultaneous repression of anaerobic 4-methylbenzoate and succinate utilization in Magnetospirillum sp. strain pMbN1

Sven Lahme,Ralf Rabus,Annemieke Strijkstra,Marvin Dörries,Kathleen Trautwein,Lars Wöhlbrand

doi:10.1186/preaccept-6383322813809955

Abstract

At high concentrations of organic substrates, microbial utilization of preferred substrates (i.e., supporting fast growth) often results in diauxic growth with hierarchical substrate depletion. Unlike the carbon catabolite repression-mediated discriminative utilization of carbohydrates, the substrate preferences of non-carbohydrate-utilizing bacteria for environmentally relevant compound classes (e.g., aliphatic or aromatic acids) are rarely investigated. The denitrifying alphaproteobacterium Magnetospirillum sp. strain pMbN1 anaerobically degrades a wide variety of aliphatic and aromatic compounds and is unique for anaerobic degradation of 4-methylbenzoate. The latter proceeds via a distinct reaction sequence analogous to the central anaerobic benzoyl-CoA pathway to intermediates of central metabolism. Considering the presence of these two different anaerobic “aromatic ring degrading” pathways, substrate preferences of Magnetospirillum sp. strain pMbN1 were investigated. Anaerobic growth and substrate consumption were monitored in binary and ternary mixtures of 4-methylbenzoate, benzoate and succinate, in conjuction with time-resolved abundance profiling of selected transcripts and/or proteins related to substrate uptake and catabolism. Diauxic growth with benzoate preference was observed for binary and ternary substrate mixtures containing 4-methylbenzoate and succinate (despite adaptation of Magnetospirillum sp. strain pMbN1 to one of the latter two substrates). On the contrary, 4-methylbenzoate and succinate were utilized simultaneously from a binary mixture, as well as after benzoate depletion from the ternary mixture. Apparently, simultaneous repression of 4-methylbenzoate and succinate utilization from the ternary substrate mixture resulted from (i) inhibition of 4-methylbenzoate uptake, and (ii) combined inhibition of succinate uptake (via the two transporters DctPQM and DctA) and succinate conversion to acetyl-CoA (via pyruvate dehydrogenase). The benzoate-mediated repression of C4-dicarboxylate utilization in Magnetospirillum sp. strain pMbN1 differs from that recently described for “Aromatoleum aromaticum” EbN1 (involving only DctPQM). The preferential or simultaneous utilization of benzoate and other aromatic acids from mixtures with aliphatic acids may represent a more common nutritional behavior among (anaerobic) degradation specialist than previously thought. Preference of Magnetospirillum sp. strain pMbN1 for benzoate from mixtures with 4-methylbenzoate, and thus temporal separation of the benzoyl-CoA (first) and 4-methylbenzoyl-CoA (second) pathway, may reflect a catabolic tuning towards metabolic efficiency and the markedly broader range of aromatic substrates feeding into the central anaerobic benzoyl-CoA pathway.

Highlights

IntroductionAt high concentrations of organic substrates, microbial utilization of preferred substrates (i.e., supporting fast growth) often results in diauxic growth with hierarchical substrate depletion
At high concentrations of organic substrates, microbial utilization of preferred substrates often results in diauxic growth with hierarchical substrate depletion
Succinate-adapted cells of Magnetospirillum sp. strain pMbN1 growing with a mixture of succinate and benzoate displayed diauxic growth (Figure 1a)

Summary

Introduction

At high concentrations of organic substrates, microbial utilization of preferred substrates (i.e., supporting fast growth) often results in diauxic growth with hierarchical substrate depletion. Strain pMbN1 anaerobically degrades a wide variety of aliphatic and aromatic compounds and is unique for anaerobic degradation of 4-methylbenzoate. The latter proceeds via a distinct reaction sequence analogous to the central anaerobic benzoyl-CoA pathway to intermediates of central metabolism. Despite the high diversity of potential carbon sources, their total concentration generally does not exceed the μM range These low concentrations cause microorganisms to simultaneously utilize multiple different substrates [2,3]. The mechanisms underlying substrate utilization preferences were termed carbon catabolite repression (CCR) and have been studied intensively for carbohydrates in a limited number of bacteria, and involve different phosphotransferase systems (PTS) for sugar uptake [5,6]. In contrast to Azoarcus sp. strain CIB, related “Aromatoleum aromaticum” EbN1 preferred benzoate over succinate by repressing succinate uptake via the C4-dicarboxylate TRAP transporter DctPQM [10]

Methods

Results

Discussion

Conclusion