Abstract
Alginate, mainly derived from brown algae, is an important carbon source that can support the growth of marine microorganisms in the Arctic and Antarctic regions. However, there is a lack of systematic investigation and comparison of alginate utilization pathways in culturable bacteria from both polar regions. In this study, 88 strains were isolated from the Arctic and Antarctic regions, of which 60 strains could grow in the medium with alginate as the sole carbon source. These alginate-utilizing strains belong to 9 genera of the phyla Proteobacteria and Bacteroidetes. The genomes of 26 alginate-utilizing strains were sequenced and genomic analyses showed that they all contain the gene clusters related to alginate utilization. The alginate transport systems of Proteobacteria differ from those of Bacteroidetes and there may be unique transport systems among different genera of Proteobacteria. The biogeographic distribution pattern of alginate utilization genes was further investigated. The alginate utilization genes are found to cluster according to bacterial taxonomy rather than geographic location, indicating that the alginate utilization genes do not evolve independently in both polar regions. This study systematically illustrates the alginate utilization pathways in culturable bacteria from the Arctic and Antarctic regions, shedding light into the distribution and evolution of alginate utilization pathways in polar bacteria.
Highlights
Brown algae, mainly distributed in cold coastal seawater, are multicellular organisms that constitute important biomass in coastal ecosystems
Among the 88 strains, 60 could grow in the minimal medium with alginate as the sole carbon source, which belonged to 9 genera of the phyla Proteobacteria (Gammaproteobacteria) and Bacteroidetes (Flavobacteriia): Pseudoalteromonas (22), Cellulophaga (16), Psychromonas (5), Paraglaciecola (5), Cobetia (3), Polaribacter (3), Algibacter (3), Formosa (2), and Colwellia (1)
Martin et al and Dong et al screened alginate-degrading bacteria from French beach and Arctic brown algae, which belonged to the classes Gammaproteobacteria and Flavobacteriia of the phyla Proteobacteria and Bacteroidetes (Martin et al, 2015; Dong et al, 2012)
Summary
Mainly distributed in cold coastal seawater, are multicellular organisms that constitute important biomass in coastal ecosystems. Alginate is a kind of polysaccharide that exists in the cell wall of brown algae, and it can make up 10 to 45% of the algal dry weight (Mabeau and Kloareg, 1987). Microorganisms are able to secrete alginate lyase (Aly) to degrade alginate into oligosaccharides and monosaccharides, which are further transported into the periplasm for further utilization (Wargacki et al, 2012). In the 1960s, the alginate utilization pathway and related enzymes were firstly reported in Pseudomonas sp. Until 2012, the enzymes and transporters involved in the alginate utilization pathway mainly from Vibrio splendidus 12B01 were cloned into Escherichia coli, which conferred E. coli the ability to degrade alginate to produce ethanol (Wargacki et al, 2012). In 2016, pectin degradation protein (KdgF) was confirmed to catalyze the conversion of unsaturated monouronates derived from pectin and alginate to linear ketonized form (Hobbs et al, 2016), which was previously thought to occur spontaneously
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