The influence of protozoa with a filtered and non-filtered seawater culture of Tetraselmis sp., and effects to the bacterial and algal communities over 10 days

Isolation and identification of herbivorous ciliates from contaminated microalgal cultures

Ciliates are a common but understudied group of grazers that can invade microalgal cultures. To estimate the potential impact of ciliates on microalgal culture productivity, the identification of species that can invade these cultures is essential. Furthermore, isolation of these herbivorous ciliates allows to use them in experiments that investigate the impact of ciliate grazing on the productivity of microalgal cultures. The main aims of this study were to isolate and identify ciliates that invade cultures of the freshwater microalgae Chlorella and Chlamydomonas, and to establish a live collection of these ciliates for usage in future experiments. To this end, we optimized a method for isolating ciliates from contaminated microalgal cultures and we developed a new PCR primer set for amplifying the partial 18S rDNA of ciliates belonging to the classes Spirotrichea, Oligohymenophorea and Colpodea. As a result, we isolated 11 ciliates from microalgal enrichment cultures inoculated with non-sterile dust and various freshwater sources. Of these 11 species, 7 were found to be feeding on Chlamydomonas. Ciliate species that fed on Chlorella could not be isolated in this study. Ciliate species feeding on Chlamydomonas were identified based on a combination of morphological observations and molecular analyses of partial 18S rDNA sequences.

Metabolic engineering of phosphite metabolism in Synechococcus elongatus PCC 7942 as an effective measure to control biological contaminants in outdoor raceway ponds

BACKGROUND

The use of cyanobacteria and microalgae as cell factories to produce biofuels and added-value bioproducts has received great attention during the last two decades. Important investments have been made by public and private sectors to develop this field. However, it has been a challenge to develop a viable and cost-effective platform for cultivation of cyanobacteria and microalgae under outdoor conditions. Dealing with contamination caused by bacteria, weedy algae/cyanobacteria and other organisms is a major constraint to establish effective cultivation processes.

RESULTS

Here, we describe the implementation in the cyanobacterium Synechococcus elongatus PCC 7942 of a phosphorus selective nutrition system to control biological contamination during cultivation. The system is based on metabolic engineering of S. elongatus to metabolize phosphite, a phosphorus source not normally metabolized by most organisms, by expressing a bacterial phosphite oxidoreductase (PtxD). Engineered S. elongatus strains expressing PtxD grow at a similar rate on media supplemented with phosphite as the non-transformed control supplemented with phosphate. We show that when grown in media containing phosphite as the sole phosphorus source in glass flasks, the engineered strain was able to grow and outcompete biological contaminants even when the system was intentionally inoculated with natural competitors isolated from an irrigation canal. The PtxD/phosphite system was successfully used for outdoor cultivation of engineered S. elongatus in 100-L cylindrical reactors and 1000-L raceway ponds, under non-axenic conditions and without the need of sterilizing containers and media. Finally, we also show that the PtxD/phosphite system can be used as selectable marker for S. elongatus PCC 7942 transgenic strains selection, eliminating the need of antibiotic resistance genes.

CONCLUSIONS

Our results suggest that the PtxD/phosphite system is a stable and sufficiently robust strategy to control biological contaminants without the need of sterilization or other complex aseptic procedures. Our data show that the PtxD/phosphite system can be used as selectable marker and allows production of the cyanobacterium S. elongatus PCC 7942 in non-axenic outdoor reactors at lower cost, which in principle should be applicable to other cyanobacteria and microalgae engineered to metabolize phosphite.

Strategies to control biological contaminants during microalgal cultivation in open ponds

Microalgal biomass is in great demand for many applications, including aquaculture feed. The most suitable system for microalgal culture is open pond cultivation, but it is also highly vulnerable to biological contamination. Contamination greatly reduces the biomass yield and depending on the contaminant, the quality of the biomass as a feed additive is compromised. Five groups of organisms that are the most common contaminants, including grazers, fungi, photosynthetic organisms, bacteria and viruses, are presented and the best possible ways to control these contaminants are indicated. Selection of a fast growing species along with selective technologies previously used for wastewater treatment can keep grazer population in control, while exploiting host-specific characteristic of fungal infection can protect from fungal attacks. Control of photosynthetic organisms and bacteria by good cultivation practices and the use of probiotics are critically important, as these organisms compete with the microalgal culture for sunlight and organic substrate.

Pollution tolerant protozoa in polluted wetland

This study for the first time confirmed that eight dominating protozoan species, Cryptomonas erosa, Euglena axyuris, Euglena caudate, Euglena gasterosteus, Euglena acus, Vorticella campanula, Vorticella convallaria and Epistylis lacustris, were the pollution tolerant species at chemical oxygen demand 54-104mg/L. These species cannot be used as indicator for clean water quality as commonly believed. The protozoa can be actively participating in the energy transfer chain between nano-planktonic and higher plants in polluted wetlands.