Isolation of a hadal trench-derived Citricoccus sp. strain NyZ702 capable of 4-hydroxybenzoate degradation

Abstract:

[Background] Hadal trench sediments have been reported to harbor abundant microbial cells and have active microbial carbon turnover. Therefore, isolation of microbial resources from trench sediments is of great significance for understanding the biogeochemical cycle and energy metabolism in the hadal trench. It is well known that aromatic compounds are widely spread in the environments. Omics analysis has revealed possible presence of aromatics-degrading microbes in the trench environment. However, there were little reports on the pure culture of trench derived aromatics-degrading microbes nor the possible degradation mechanism.[Objective] To isolate and cultivate bacteria capable of aromatics degradation from the Mariana Trench sediments and characterize its degradation pathway.[Methods] 4-Hydroxybenzoate (4HBA) was used as the sole carbon source to isolate bacteria from the Mariana Trench sediment. Morphological observation and phylogenetic analysis were used to identify the isolate. Growth curves were conducted to verify its optimum growth conditions and degradation ability. The metabolic intermediates during whole cells transformation and the activity of crude cell extracts against the substrate were analyzed, based on which a putative catabolic pathway was reconstructed. [Results] An aerobic bacterium was isolated from the trench sediment and belonged to Citricoccus genus, according to the phylogenetic analysis of its 16S rRNA gene. Colonies of this bacterium, designated Citricoccus sp. strain NyZ702, on LB agar plate were lemon yellowish, opaque, swell, neat edge and round with a diameter of 1—2 mm after 4-day cultivation at 30℃. Cells observed with Scanning Electric Microscope were spherical with a diameter of 0.4—0.6 μm without flagella. The strain was halotolerant with an optimal salt concentration of 2%—8% (W/V). The strain was able to utilize 4HBA as the sole carbon source and protocatechuate was detected as its catabolic intermediate, indicating it degraded 4HBA through the protocatechuate pathway. The cell extracts of this strain showed monooxygenase activity against 4HBA using NADPH as the cofactor. [Conclusion] A 4HBA degrading bacterium, Citricoccus sp. strain NyZ702 was isolated from the trench sediment and its 4HBA degradation was via protocatechuate as the intermediate metabolite. This study would enrich the microbial resources derived from the hadal trench, providing a certain theoretical foundation for the future research of aromatics degradation in the hadal trenches.

Key words:hadal trench;microbial isolation;aromatics degradation;protocatechuate pathway