Skip to main content

Bacterial interaction in the oceans: Synergy among heterotrophic bacteria involved in the cycling of one-carbon compounds and its impact on the marine carbon cycle

Periodic Report Summary 1 - BIOSHARE (Bacterial interaction in the oceans: Synergy among heterotrophic bacteria involved in the cycling of one-carbon compounds and its impact on the marine carbon cycle)

The metabolisms of marine bacteria represent an important source and sink for compounds of environmental significance such as climatically active one-carbon compounds (C1). Yet, despite its importance for the global carbon cycle and air-sea fluxes the role of bacteria in the cycling of C1 is still poorly understood. Therefore, studying the spatio-temporal variations and the mechanisms of bacterial turnover of C1, as well as the phylogenetic and functional succession of bacterial community involved in this cycling is necessary to better predict the impacts of marine bacteria on climate regulations. The BIOSHARE project seeks to bring new understanding of these processes through three main objectives.
Objective 1 – Determination of the spatial variability of marine bacteria utilizing one carbon compounds:
Sample were obtained during the CCE- California Current Ecosystem cruise in August 2015 to study the spatial and vertical distribution of bacteria involved in C1 cycling in a gradient of productive coastal to offshore stations in the North Eastern Pacific Ocean. Furthermore, the vertical distribution and adaptability of methylotrophs to different pools of C1 compounds was assessed during a 14 d transplant experiment. The deep bacterial community was transplanted into surface water and surface community into deep water and we followed bacterial abundance, production, methanol assimilation and dissolved organic carbon. Results showed interesting capacity of deep bacteria to drawdown the surface carbon pool. The deep community in surface water had the highest rates of methanol assimilation while the same community in its native deep water showed very low assimilation rates. This suggests that deep community have the capacity to utilize C1 as carbon source but are limited by some elements necessary for C1 metabolism. Additional experiments are needed to study what elements are limiting and will be performed during year 3.
Objective 2 – temporal variations:
Here, we investigated the seasonal dynamics of coastal surface bacterioplankton involved in C1 cycling and their potential links to environmental parameters during a one year time series. Water was sampled weekly offScripps Pier in La Jolla, CA, USA, for bacterial production, abundance and methanol utilization. Results showed strong seasonal variations of methanol pool assimilation turnover rate and correlation to chl.a and temperature. Turnover rates as fast as 0.25 d-1 were observed in spring. The ability of the local bacterioplankton community to exploit one-carbon and methylated compounds as sole carbon source during different seasons was further assessed through amendment experiments. In spring and summer, we amended surface bacterioplankton with methanol and trimethylamine-N-oxide and followed bacterial abundance, production and methanol utilization rates. Bacterial community structure and functional diversity was examined at the start and end of the experiment through amplicon sequencing of 16S rRNA and methanol dehydrogenase marker genes. Elevated bacterial production, growth and methanol utilization were observed in the amended treatments with an average of 40% growth efficiency on methanol. Capacity to utilize the substrates was higher in summer. Specific taxa such as Methylophaga spp. and Alteromonas spp. were enriched in the amended treatments. Moreover, as a strong correlation between methanol utilization and chl.a was observed during the time series, we studied the response and interactions of bacteria utilizing C1 with phytoplankton. An experimental phytoplankton bloom was induced and extensively sampled during 2 weeks in order to perform a high resolution study of bacterioplankton response to C1 over the different phases of the bloom. The diel response of methylotrophs was also studied. Increase of methanol assimilation was observed during the early exponential phase of the bloom but decreased when the bloom crashed. Preliminary results suggest that methylotrophs respond to the early phase of the bloom but are quickly outcompeted by generalist bacteria during the stationary phase and crash of the bloom.

Objective 3 – model systems:
In order to better understand the mechanisms behind to bacterial C1 utilization and production, model organisms were isolated from coastal seawater, surface microlayer and kelp. Interestingly, many of these bacteria were generalist taxa growing on different carbon substrates including C1. They showed different affinity for methanol suggesting that a wide range of marine bacteria with different life strategies are involved in C1 cycling. These systems will be further studied during the last year of the BIOSHARE project.
In summary, preliminary results from the BIOSHARE project show that marine bacteria capabilities to use one-carbon and methylated compounds may have predictable seasonal and spatial impacts on the marine carbon cycle and air-sea fluxes. We anticipate these results to bring new information on bacterial source and sink of atmospheric compounds important for climate change prediction.