Siderophore production by bacteria isolated from mangrove sediments: A microcosm study

Mangroves are one of the most productive ecosystems worldwide covering up to 75% of the coastline in the tropics and subtropics. They support a highly diverse community (marine and terrestrial) and serves as reservoirs of nutrients for coastal and shelf waters. Bacterial diversity in mangroves includes heterotrophs, autotrophs (nitrogen fixation) and pathogens (phytopathogens, marine, and human). All these bacterial groups require sequestration of bioavailable iron, which is largely done by the production of siderophores. In this study, microcosm experiments were conducted to test the effect of incubation conditions (temperature, iron concentration, pH, and carbon source) on growth and siderophore production in four mangrove sediment bacterial isolates-Escherichia vulneris, Enterobacter cancerogenus, Pantoea agglomerans, and Enterobacter bugandensis. Our study showed that all isolates produce more siderophores (30 to 60%) at low iron concentrations (10 nM to 1 mu M) during lag-phase and early log-phase of growth. Low temperature suppressed bacterial growth without significantly altering the siderophore production, whereas low pH suppressed both growth and siderophore production in these isolates. Although all isolates could produce siderophores when using different carbon sources, glucose served as an ideal carbon source. The observed changes in growth and siderophore production may be attributed to species-specific physiological traits, changes in bioavailability of iron and/or combination of both. Our results suggest that in a changing global environment, warming of the surrounding waters may not reduce the siderophore production and hence, they will be essential in sustaining bacterial activity in sediments.