Microbial intact polar and core lipids in hydrothermal chimneys of the Iheya North Hydrothermal Field in the Mid-Okinawa Trough

The Iheya North Hydrothermal Field (~1,100 m in water depth) is located at the Mid-Okinawa Trough, which is a felsic rock-hosted and terrigenous sediment-associated hydrothermal system with the maximum fluid temperature of ~311 °C. In 2010, the IODP drilling was conducted in this field, and the artificial chimneys grew after the drilling [1]. In this study, we have analyzed the distribution of intact polar membrane lipids (IPLs) and fossilized core lipids (CLs) of natural and artificial hydrothermal chimneys using HPLC/HESI-HRMS [2] to characterize the active and inactive microbial biomass associated with the hydrothermal activities in this field. The chimney samples were collected from the central hydrothermal field, North Big Chimney (NBC), C0016B artificial chimney (the foot of the NBC), High Radioactivity Vent (HRV, 180 m Southwest from the NBC), and HDSK mound (2.8 km South from the NBC) during the the R/V Kairei KR18-14 cruise with ROV Kaiko (JAMSTEC) in 2018.

Archaeal CLs and IPLs were detected in all samples. The archaeal IPLs consist almost glycolipid, which is consistent with the higher glycolipid proportion with increasing growth temperature in cultured thermophilic archaea [3]. Bacterial IPLs were also found except the NBC. The absence of bacterial IPLs in NBC was not consistent with the predominance of Epsilonproteobacteria reported by the previous gene-based survey before the drilling [4]. Also, the lipid content of the NBC was significantly less than that of other chimneys. Those results clearly reflect the impact of drilling on the fluid chemistry and bacterial biomass. Interestingly, diacylglycerol homoserine (DGTS) was relatively abundant in C0016B. Though DGTS is widely distributed in lower plants and green algae, it is also present in anaerobic bacteria where phosphorus is limited [5]. The distribution suggests that distinctive anaerobic bacteria thrive in the present artificial chimney, even though the detectable microbial communities were not developed in 11 months after the drilling [1].

[1] Kawagucci et al. (2013) Geochem. Geophys. Geosyst. 14, 4774-4790. [2] Horai et al. (2019) Rapid Commun. Mass Spectrom. 33, 1571-1577. [3] Nakagawa et al. (2005) FEMS Microbiol. Ecol. 54, 141-155. [4] Shimada et al. (2008) J. Bacteriol. 190, 5404-541. [5] Yao et al. (2015) Environ. Microbiol. 18, 656-667.