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Isolation and characterization marine bacteria capable of degrading lignin-derived compounds.

ABSTRACT: Lignin, a characteristic component of terrestrial plants. Rivers transport large amounts of vascular plant organic matter into the oceans where lignin can degrade over time; however, microorganisms involved in this degradation have not been identified. In this study, several bacterial strains were isolated from marine samples using the lignin-derived compound vanillic acid (4-hydroxy-3-methoxybenzoic acid) as the sole carbon and energy source. The optimum growth temperature for all isolates ranged from 30 to 35°C. All isolates grew well in a wide NaCl concentration range of 0 to over 50 g/L, with an optimum concentration of 22.8 g/L, which is the same as natural seawater. Phylogenetic analysis indicates that these strains are the members of Halomonas, Arthrobacter, Pseudoalteromonas, Marinomonas, and Thalassospira. These isolates are also able to use other lignin-derived compounds, such as 4-hydroxybenzoic acid, ferulic acid, syringic acid, and benzoic acid. Vanillic acid was detected in all culture media when isolates were grown on ferulic acid as the sole carbon source; however, no 4-hydroxy-3-methoxystyrene was detected, indicating that ferulic acid metabolism by these strains occurs via the elimination of two side chain carbons. Furthermore, the isolates exhibit 3,4-dioxygenase or 4,5-dioxygenase activity for protocatechuic acid ring-cleavage, which is consistent with the genetic sequences of related genera. This study was conducted to isolate and characterize marine bacteria of degrading lignin-derived compounds, thereby revealing the degradation of aromatic compounds in the marine environment and opening up new avenues for the development and utilization of marine biological resources.

SUBMITTER: Lu P

PROVIDER: S-EPMC7540876 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Terrestrial organic carbon such as lignin is an important component of the global marine carbon. However, the structural complexity and recalcitrant nature of lignin are deemed challenging for biodegradation. It has been speculated that bacteria play important roles in lignin degradation in the marine system. However, the extent of the involvement of marine microorganisms in lignin degradation and their contribution to the oceanic carbon cycle remains elusive. In this study, two bacterial consortia capable of degrading alkali lignin (a model compound of lignin), designated LIG-B and LIG-S, were enriched from the nearshore sediments of the East and South China Seas. Consortia LIG-B and LIG-S mainly comprised of the Proteobacteria phylum with Nitratireductor sp. (71.6%) and Halomonas sp. (91.6%), respectively. Lignin degradation was found more favorable in consortium LIG-B (max 57%) than in LIG-S (max 18%). Ligninolytic enzymes laccase (Lac), manganese peroxidase (MnP), and lignin peroxidase (LiP) capable of decomposing lignin into smaller fragments were all active in both consortia. The newly emerged low-molecular-weight aromatics, organic acids, and other lignin-derived compounds in biotreated alkali lignin also evidently showed the depolymerization of lignin by both consortia. The lignin degradation pathways reconstructed from consortium LIG-S were found to be more comprehensive compared to consortium LIG-B. It was further revealed that catabolic genes, involved in the degradation of lignin and its derivatives through multiple pathways via protocatechuate and catechol, are present not only in lignin-degrading consortia LIG-B and LIG-S but also in 783 publicly available metagenomic-assembled genomes from nine nearshore regions. IMPORTANCE Numerous terrigenous lignin-containing plant materials are constantly discharged from rivers and estuaries into the marine system. However, only low levels of terrigenous organic carbon, especially lignin, are detected in the global marine system due to the abundance of active heterotrophic microorganisms driving the carbon cycle. Simultaneously, the lack of knowledge on lignin biodegradation has hindered our understanding of the oceanic carbon cycle. Moreover, bacteria have been speculated to play important roles in the marine lignin biodegradation. Here, we enriched two bacterial consortia from nearshore sediments capable of utilizing alkali lignin for cell growth while degrading it into smaller molecules and reconstructed the lignin degradation network. In particular, this study highlights that marine microorganisms in nearshore regions mostly undergo similar pathways using protocatechuate and catechol as ring-cleavage substrates to drive lignin degradation as part of the oceanic carbon cycle, regardless of whether they are in sediments or water column.

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Isolation and characterization marine bacteria capable of degrading lignin-derived compounds.

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