Heme b in marine cyanobacteria and the (sub-) tropical North Atlantic

• Main Author: Honey, David James
• Format: Thesis
• Language: English
• Published: 2012
• Subjects: North Atlantic
• Online Access: https://eprints.soton.ac.uk/359063/; https://eprints.soton.ac.uk/359063/1/Honey%252C%2520David_PhD_2013.pdf

Heme b is the iron containing prosthetic group to an important pool of iron proteins known as the hemoproteins. Hemoproteins are functionally diverse, playing key roles in photosynthetic and respiratory electron transfer (e.g. cytochrome b6f, photosystem II, cytochrome bc1) among other fundamental biological processes. Heme b is the most naturally abundant heme structure, but data regarding hemes in the marine environment are limited. An investigation has been conducted to improve our understanding of heme b abundance in marine organisms through laboratory monoculture studies of three marine cyanobacteria grown under varying total iron concentration. The unicellular cyanobacteria Synechococcus sp. WH7803 was examined under three total iron concentrations: 12 nmol L-1 (low), 120 nmol L-1 (medium) and 1200 nmol L-1 (high). The marine diazotrophs (i.e. nitrogen fixers) Crocosphaera watsonii (WH8501) and Trichodesmium erythraeum (IMS101) were studied under six total iron concentrations between 0 and 120 nmol L-1. Cultures were analysed for heme b, chlorophyll a, particulate organic carbon (POC) and particulate organic nitrogen (PON) concentration. Nitrogen fixation rates and biophysical measurements (Fv/Fm and ?PSII) were also obtained for diazotroph cultures. Field data regarding the concentration of heme b, chlorophyll a, POC and PON as well as nitrogen fixation rates were collected during two research cruises in the subtropical North Atlantic (STNA, D346) and tropical North Atlantic (TNA, D361); an oceanographic region known to demonstrate high nitrogen fixation rates and receive significant dust (iron) deposition from the Saharan and Sahel deserts of Western Africa. Cultures of Synechococcus sp. WH7803 showed evidence of iron stress at low iron treatments via reduced maximum growth rates (?max), total biovolume and chlorophyll a concentration. This was also reflected by a significant reduction in cellular heme b content per unit carbon (heme:C) at the lowest iron concentration. An estimated heme b requirement ...