Storage and Algal Association of Bacteria That Protect Microchloropsis salina from Grazing by Brachionus plicatilis

Abstract

Loss of algal production from the crashes of algal mass cultivation systems represents a significant barrier to the economic production of microalgal-based biofuels. Current strategies for crash prevention can be too costly to apply broadly as prophylaxis. Bacteria are ubiquitous in microalgal mass production cultures, however few studies investigate their role and possible significance in this particular environment. Previously, we demonstrated the success of selected protective bacterial communities to save Microchloropsis salina cultures from grazing by the rotifer Brachionus plicatilis. In the current study, these protective bacterial communities were further characterized by fractionation into rotifer-associated, algal-associated, and free-floating bacterial fractions. Small subunit ribosomal RNA amplicon sequencing was used to identify the bacterial genera present in each of the fractions. Here, we show that Marinobacter, Ruegeria, and Boseongicola in algae and rotifer fractions from rotifer-infected cultures likely play key roles in protecting algae from rotifers. Several other identified taxa likely play lesser roles in protective capability. The identification of bacterial community members demonstrating protective qualities will allow for the rational design of microbial communities grown in stable co-cultures with algal production strains in mass cultivation systems. Such a system would reduce the frequency of culture crashes and represent an essentially zero-cost form of algal crop protection.

Keywords: Brachionus plicatilis; Microchloropsis salina; algal biofuels; bacterial communities.

Figure 1

Daily chlorophyll fluorescence for M. salina cultures treated with bacterial communities (1p.2, 2p.1, 2p.2, 5p.1, 5p.2, 6p.1, 6p.2) in comparison to an untreated M. salina control (con) in the presence of rotifers (+R; thick lines) and absence (thin lines). Measurements were averaged for biological triplicates for each condition and error bars represent standard deviation (n = 3). Rotifers were added on day 2. Data were normalized to the culture with the highest chlorophyll fluorescence (6p.1) over the cultivation period.

Figure 2

Averaged stacked bar graph of the bacterial OTUs present in different fractions in the absence (top) and presence (+R, bottom) of B. plicatilis. Taxonomy is shown at the genus level unless otherwise stated. Bacterial OTUs <1% of the total abundance is categorized in ‘Other’ (grey).