acids. dokdonia sp. strain med134 has a na+ ion pump on its membrane that can generate na+ gradient to produce atp for other cellular activities. dokdonia sp. strain med134 has complete embden-meyerhof-farnas pathway (glycolysis), gluconeogenesis pathway, and tricarboxylic acid (tca) cycle. the anaplerotic reaction which connects glycolysis with tca cycle utilizes several enzymes including pep carboxykinase and pep carboxylase. the prs in dokdonia sp. strain med134 are predicted to be heptahelical integral membrane proteins that pump h+ across membranes to build a proton gradient which generates atp. depends on the organism's depth in water column, the pr's maximum absorbance wavelength changes. in near surface waters, the maximum absorption wavelength of pr is around 530 nm (green light). in deeper water, the maximum absorption wavelength is 490 nm (blue light). dokdonia sp. pro95 dokdonia sp. pro95 carries two types of rhodopsins: pr as well as a rhodopsin that is related to xanthorhodopsins (xrs). xrs are light-harvesting proton pumps that are more efficient compared to prs. the prs of this strain are light-driven sodium-motive pumps (na+-rhodopsins or nars) which pump na+ from the cytoplasm to external medium. they can also pump h+ when na+ is absent. unlike dokdonia sp. strain med134, no light-induced growth is observed in dokdonia sp. pro95 despite the have high genome similarity. ecological significance of proteorhodopsin-containing dokdonia the presence of prs allows dokdonia to grow better in light compared dark conditions, especially when there is low or intermediate levels of nutrients available. cells with prs are less dependent on the amount and quality of organic carbon sources. being able to harvest energy from light gives them an advantage during nutrient deficient periods, making the retention of prs favoured by selection. alpha- and gammaproteobacteria that contain prs have enhanced cell growth due to cellular functions such as survival in environments with deficient nutrients that are promoted by light . the correlation between pr phototrophy and increased cell growth was first observed in dokdonia sp. strain med134. expression of proteorhodopsin encoding gene in dokdonia, light induces the expression of pr genes. there is a significant increase in the expression levels of pr genes in light compared to dark conditions as light can increase the strength of the pr gene promoter. the light-dark cycle can induce the upregulation of pr genes in flavobacteriia that lead to population growth. behavior biofilm in the tyrrhenian sea off the coast of naples, species of dokdonia are the most abundant in biofilms on plastic debris. 4.76 ± 7.1% of genera forming biofilms belong to dokdonia. given that dokdonia was found on plastics but not in the sediment or water column, it is possible that the habitat in biofilms on plastics is preferable to planktonic growth for species of dokdonia in the mediterranean sea. as microbial mortality is reduced in the more stable microenvironment of a biofilm, population maintenance is less dependent on environmental factors such as nutrient concentration and grazers. response to varying nutrient availability due to variable expression of pr, dokdonia sp. strain med134 growth rate is more positively influenced by light exposure when metabolizing an energy-poor carbon source such as alanine compared to that which was observed in the presence of glucose. growth rates of dokdonia sp. dokd-p16 are significantly affected by variations in dissolved copper concentration. the strain exhibited an 80% reduction in growth rates in 0.6 nm copper compared to those observed in 50 nm copper. this suggests that the presence of copper is crucial to dokdonia metabolism. iron is a common limiting nutrient in the ocean. dokdonia sp. strain med134 has various mechanisms make use of different forms of iron. it contains atp-binding cassette-type transport system that can transport iron into the cell. also, it can store iron and recycle iron from heme.