AUTHOR=Alves Joana I. , Salvador Andreia F. , Castro A. Rita , Zheng Ying , Nijsse Bart , Atashgahi Siavash , Sousa Diana Z. , Stams Alfons J. M. , Alves M. Madalena , Cavaleiro Ana J. 

TITLE=Long-Chain Fatty Acids Degradation by Desulfomonile Species and Proposal of “Candidatus Desulfomonile Palmitatoxidans”

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.539604

DOI=10.3389/fmicb.2020.539604

ISSN=1664-302X

ABSTRACT=<p>Microbial communities with the ability to convert long-chain fatty acids (LCFA) coupled to sulfate reduction can be important in the removal of these compounds from wastewater. In this work, an enrichment culture, able to oxidize the long-chain fatty acid palmitate (C<sub>16</sub><sub>:</sub><sub>0</sub>) coupled to sulfate reduction, was obtained from anaerobic granular sludge. Microscopic analysis of this culture, designated HP culture, revealed that it was mainly composed of one morphotype with a typical collar-like cell wall invagination, a distinct morphological feature of the <italic>Desulfomonile</italic> genus. 16S rRNA gene amplicon and metagenome-assembled genome (MAG) indeed confirmed that the abundant phylotype in HP culture belong to <italic>Desulfomonile</italic> genus [<italic>ca.</italic> 92% 16S rRNA gene sequences closely related to <italic>Desulfomonile</italic> spp.; and <italic>ca</italic>. 82% whole genome shotgun (WGS)]. Based on similar cell morphology and average nucleotide identity (ANI) (77%) between the <italic>Desulfomonile</italic> sp. in HP culture and the type strain <italic>Desulfomonile tiedjei</italic> strain DCB-1<sup>T</sup>, we propose a novel species designated as “<italic>Candidatus</italic> Desulfomonile palmitatoxidans.” This bacterium shares 94.3 and 93.6% 16S rRNA gene identity with <italic>Desulfomonile limimaris</italic> strain DCB-M<sup>T</sup> and <italic>D. tiedjei</italic> strain DCB-1<sup>T</sup>, respectively. Based on sequence abundance of <italic>Desulfomonile</italic>-morphotype in HP culture, its predominance in the microscopic observations, and presence of several genes coding for enzymes involved in LCFA degradation, the proposed species “<italic>Ca.</italic> Desulfomonile palmitatoxidans” most probably plays an important role in palmitate degradation in HP culture. Analysis of the growth of HP culture and <italic>D. tiedjei</italic> strain DCB-1<sup>T</sup> with short- (butyrate), medium- (caprylate) and long-chain fatty acids (palmitate, stearate, and oleate) showed that both cultures degraded all fatty acids coupled to sulfate reduction, except oleate that was only utilized by HP culture. In the absence of sulfate, neither HP culture, nor <italic>D. tiedjei</italic> strain DCB-1<sup>T</sup> degraded palmitate when incubated with <italic>Methanobacterium formicicum</italic> as a possible methanogenic syntrophic partner. Unlike <italic>D. tiedjei</italic> strain DCB-1<sup>T</sup>, “<italic>Ca.</italic> Desulfomonile palmitatoxidans” lacks reductive dehalogenase genes in its genome, and HP culture was not able to grow by organohalide respiration. An emended description of the genus <italic>Desulfomonile</italic> is proposed. Our study reveals an unrecognized LCFA degradation feature of the <italic>Desulfomonile</italic> genus.</p>