Facilitation of robust growth of Prochlorococcus colonies and dilute liquid cultures by "helper" heterotrophic bacteria - PubMed (original) (raw)

Facilitation of robust growth of Prochlorococcus colonies and dilute liquid cultures by "helper" heterotrophic bacteria

J Jeffrey Morris et al. Appl Environ Microbiol. 2008 Jul.

Abstract

Axenic (pure) cultures of marine unicellular cyanobacteria of the Prochlorococcus genus grow efficiently only if the inoculation concentration is large; colonies form on semisolid medium at low efficiencies. In this work, we describe a novel method for growing Prochlorococcus colonies on semisolid agar that improves the level of recovery to approximately 100%. Prochlorococcus grows robustly at low cell concentrations, in liquid or on solid medium, when cocultured with marine heterotrophic bacteria. Once the Prochlorococcus cell concentration surpasses a critical threshold, the "helper" heterotrophs can be eliminated with antibiotics to produce axenic cultures. Our preliminary evidence suggests that one mechanism by which the heterotrophs help Prochlorococcus is the reduction of oxidative stress.

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Figures

FIG. 1.

FIG. 1.

(A) Dilution series of Prochlorococcus strain MIT 9215 on a dilute lawn of approximately 1,000,000 cells of EZ55 on Pro99 agar medium lacking organic carbon. Numbers above the dilution spots indicate the dilution (_n_-fold) of the source culture of 3.5 × 108 cells of MIT 9215 ml−1; a 10-μl volume was spotted for each dilution. (B) Approximately 106 Prochlorococcus strain MIT 9215 cells were spread evenly onto agar. Cells of heterotrophic roseobacters Phaeobacter sp. strain Y4I and Sagittula stellata E-37 were then applied over the MIT 9215 cells as horizontal streaks (indicated by arrows). MIT 9215 cells (green) grew only where the heterotrophs were streaked.

FIG. 2.

FIG. 2.

Growth of MIT 9215 in liquid Pro99 medium with or without helper heterotrophs. Dilutions of MIT 9215 were grown in the absence (A) or presence (B) of ∼5 × 105 CFU of EZ55 ml−1. Initial concentrations of MIT 9215 cells were 3.5 × 100 (⧫), 3.5 × 101 (□), 3.5 × 102 (▪), 3.5 × 103 (▵), 3.5 × 104 (▴), 3.5 × 105 (○), and 3.5 × 106 (•) cells ml−1. Error bars indicate one standard deviation of the mean for three replicate cultures. The dotted horizontal lines represent the limit of detection for chlorophyll-based fluorescence (10 arbitrary units [AU]); values below this limit were reported as 10 AU.

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