Microbial communities cycling organic sulfur compounds in Arctic sea ice

Overview
The Arctic is undergoing significant changes due to climate warming. Arctic ice cover has significant feedbacks and regulatory function for regional and global climate, but recently the extent of ice cover in the Arctic Ocean has fallen to record low levels (Notz and Stroeve 2016). Changes in the Arctic may also affect biological processes that lead to emission of biogenic volatile compounds into the atmosphere, which are precursors for secondary organic aerosols (SOA) that play important roles as particles for cloud formation and provide climate feedbacks (Carpenter et al 2012).
Dimethylsulfide (DMS) is an organosulfur gas with a role in SOA formation. The marine environment is the largest source for atmospheric DMS (Lana et al 2011). The amount of DMS that can be emitted to the atmosphere is linked to microbial activities driving its production and degradation. These complex pathways of organosulfur compound cycling are driven by a wide range of different enzymes and microbial groups (Figure 1). Most DMS is produced by enzymatic degradation of dimethylsulfoniopropionate (DMSP) by DMSP-lyases (Curson et al 2011). DMSP is an osmolyte produced in petagram quantities (Ksionzek et al 2016) per year by a range of phytoplankton, ice algae and, as shown by us, diverse marine bacteria (Curson et al 2017). The bacterial contribution to overall DMSP production is not well understood. DMS can be used as a carbon source by methylotrophic bacteria (Neufeld et al 2007, Schäfer 2007, Schäfer et al 2010) or as recently shown at Warwick, can be co-oxidised by heterotrophic bacteria to dimethylsulfoxide (DMSO) (Lidbury et al 2016). Both DMSP and DMS degradation can also involve the production of methanethiol (MT), which is degraded in bacteria by methanethiol oxidase (Eyice et al 2018), or which can be re-methylated to produce DMS (Carrión et al 2015). In 2019, we will participate in the multidisciplinary MOSAiC campaign (https://www.mosaic-expedition.org/), which will deploy an ice breaker in Artic sea ice for an entire year to study the Arctic in unprecedented detail. MOSAiC is an opportunity to obtain samples from the Arctic and investigate sulfur cycling microorganisms in this ecosystem threatened by climate change.

Methodology
You will use a wide range of experimental and analytical approaches, including microbiological, molecular biological and bioinformatic methods to isolate and characterise microorganisms and microbial communities from Arctic samples and experimental sea ice microcosms. Work may include physiological characterisation, genome sequencing and potentially genetic analysis of isolated microorganisms. You will analyse microbial community composition and function based on high throughput sequencing approaches (amplicon sequencing) as well as metagenomics of samples raised in the project. An exciting opportunity is the availability of an ice chamber at UEA, which will facilitate experimental work aimed at optimising approaches to study sea ice microorganisms. Traditionally, these involve slow melting of sea ice, which alters the chemical environment and potentially the physiological state of ice-dwelling microbes. Hence, methods that minimise such changes need to be developed, which could then be applied to study the response of ice microbes during freeze/thaw cycles, for instance.