Figure 1.
Growth curves of Aulacoseira granulata, Cylindrospermopsis raciborskii and Microcystis aeruginosa.
Lines represent absorbance and symbols represent chlorophyll a concentration. Dashed lines and open symbols are axenic* cultures (−), and solid lines and symbols are non-axenic cultures (+). Error bars represent standard deviation of 3 independent replicates. * C. raciborskii was not axenic. Differences in growth curves were significant to Aulacoseira granulata (ANCOVA, p<0.001, F = 31.82) and Cylindrospermopsis raciborskii (ANCOVA, p<0.001, F = 16.34). No significant effect was observed to Microcystis aeruginosa (ANCOVA, p = 0.11, F = 2.62).
Figure 2.
Scanning electron microscopy photomicrograph of the microalgae without (left) and with (right) bacterial inoculum.
Aulacoseira granulata (a,b), Microcystis aeruginosa (c,d) and Cylindrospermopsis raciborskii (e,f) cultures without (a, c, e) and with (b,d,f) environmental bacterial inoculum. Black arrows indicate some bacterial (non-phytoplankton) cells.
Figure 3.
Heatmap of the 10 most abundant specific OTUs associated with each studied phytoplankton species.
The non-resampled data was used and only the OTUs that occurred in the 3 independent replicates of one phytoplankton species and that had less than 2 reads in the treatments of the other two were considered specific. Bac_In is the bacterial inoculum; ab indicates attached bacteria and fb, free-living bacteria; dxx indicates the day of sampling. Frequencies are given by relativizing OTUs against the total number of reads of the sample, showing their low proportion. Taxonomic affiliation of two classification databases is shown after identification number: rdp/FW.
Figure 4.
Non-metric multidimensional scaling (NMDS) plot showing differences among bacterial communities by phytoplankton species, fraction and growth phase.
Solid and open symbols represent, respectively, free-living and attached communities. The crosses represent Cylindrospermopsis raciborskii controls. 1 = lag or beginning of exponential growth phase, 2 * = exponential growth phase, 3* = stationary growth phase. * To C. raciborskii 2 and 3 were stationary and senescent phases, respectively.
Table 1.
Results of Permutational MANOVA comparing bacterial community composition between fraction (attached and free-living), growth phase (age), and phytoplankton species.
Figure 5.
Heatmap displaying the 51 most abundant OTUs after resampling.
Taxonomic affiliation of two classification databases is shown after identification number: rdp/FW. A and F indicate attached and free-living communities, respectively, and dxx indicates day of sampling. Letters in brackets indicate the phytoplankton species in which that OTU was within the most abundant: a, Aulacoseira granulata (18 OTUs); c, Cylindrospermopsis raciborskii (20 OTUS); m, Microcystis aeruginosa (20 OTUs). All these OTUs, except #616, were present in triplicates in at least one treatment of the phytoplankton species where they occurred.
Figure 6.
Proportion of bacterial Classes in the replicates of each treatment of the 3 phytoplankton species.
Naïve Bayesian classification was used. Bac_In is the bacterial inoculum. Numbers 1–3 represent the replicate, ab and fb indicate attached and free-living communities respectively, Ct is control and dxx is the sampling day.
Table 2.
Relative abundance (%) of the main bacterial Classes in the three phytoplankton cultures in different sampling days (d).