Association of Vampirovibrio chlorellavorus with decline and death of Chlorella sorokiniana in outdoor reactors

Microbial Biotechnology

Gao

Waller

et al. 2020

Self Cite

Microalgae as a biofuel source are of great interest. Bacterial phycosphere inhabitants of algal cultures are hypothesized to contribute to productivity. In this study, the bacterial composition of the Chlorella sorokiniana phycosphere was determined over several production cycles in different growing seasons by 16S rRNA gene sequencing and identification. The diversity of the phycosphere increased with time during each individual reactor run, based on Faith's phylogenetic diversity metric versus days post-inoculation (R = 0.66, P < 0.001). During summer months, Vampirovibrio chlorellavorus, an obligate predatory bacterium, was prevalent. Bacterial sequences assigned to the Rhizobiales, Betaproteobacteriales and Chitinophagales were positively associated with algal biomass productivity. Applications of the general biocide, benzalkonium chloride, to a subset of experiments intended to abate V. chlorellavorus appeared to temporarily suppress phycosphere bacterial growth, however, there was no relationship between those bacterial taxa suppressed by benzalkonium chloride and their association with algal productivity, based on multinomial model correlations. Algal health was approximated using a model-based metric, or the 'Health Index' that indicated a robust, positive relationship between C. sorokiniana fitness and presence of members belonging to the Burholderiaceae and Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium clade. Bacterial community composition was linked to the efficiency of microalgal biomass production and algal health.

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Association between algal productivity and phycosphere composition in an outdoor Chlorella sorokiniana reactor based on multiple longitudinal analyses

Microbial Biotechnology

Gao

Waller

et al. 2020

Self Cite

“…During a three year period from 2015-2018, the RAFT project conducted cultivation trials under different seasonal, environmental, and operational conditions, including a general biocide treatment to ameliorate the effects of a persistent predatory bacterial pathogen of DOE 1412. (Park et al, 2018; Steichen and Brown, 2018).…”

Section: Several Locations In the Southwest Region Of The United Statmentioning

confidence: 99%

Association between algal productivity and phycosphere composition in an outdoor Chlorella sorokiniana reactor based on multiple longitudinal analyses

Gao

Waller

et al. 2020

Preprint

BackgroundMicroalgae as a biofuel source are of great interest. The outdoor Regional Algal Feedstock Testbed (RAFT) was established to optimize algal biomass production in the U.S. sunbelt states. The phycosphere inhabitants, consisting in part of the bacterial community within algal cultures, are hypothesized to contribute to algal productivity. However, little is known about their identity or specific contributions. In this study the bacterial composition of the Chlorella sorokiniana phycosphere was determined over several production cycles in different growing seasons by 16S rRNA gene sequencing and identification using the SILVA database. ResultsThe C. sorokiniana bacterial phycosphere was sampled during 41 RAFT testbed cycles in two consecutive growing seasons. Eight reactors were sampled twice daily to establish baseline community composition, determined by high-throughput sequencing of 16S ribosomal RNA amplicons. The baseline diversity of the phycosphere increased overall with time during each individual reactor run, based on an increase in Faith’s phylogenetic diversity metric versus days post-inoculation (R = 0.66, p < 0.001). Bacterial assemblages were identified in samples during the stationary, growth, and death stages. During summer months, Vampirovibrio chlorellavorus, an obligate predatory bacterium, was prevalent. The possibility that a sequence correlated with biomass productivity, days post-inoculation, dissolved oxygen, and weather measurements was assessed using a rank-based multinomial regression model. Bacterial sequences assigned to the Rhizobiales, Betaproteobacteriales, and Chitinophagales were positively associated with algal biomass productivity, the industry gold standard for establishing ‘efficiency’. Applications of the general biocide, benzalkonium chloride, to a subset of RAFT experiments intended to abate V. chlorellavorus appeared to temporarily suppress phycosphere bacterial growth, however, there was no relationship between those bacterial taxa suppressed by benzalkonium chloride and their association with algal productivity, based on multinomial model correlations. Algal health was approximated using a model-based metric, or the ‘Health Index’ that indicated a robust, positive relationship between C. sorokiniana fitness and presence of members belonging to the Burholderiaceae and Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium clade.ConclusionBacterial community composition was linked to the efficiency of microalgal biomass production and algal health. Thus, bacteria associated positively with algal growth represent potential indicators of culture health and/or as augmentative candidates for enhancing productivity.

“…In a recent study (Park et al . ), a sample of the bacterium recovered from an experimental outdoor reactor in Arizona and maintained in a co‐culture with its Chlorella host was observed to attach to the outer cell surface of C. sorokiniana by scanning electron microscopy (SEM) (Fig. ).…”

Section: Introductionmentioning

confidence: 99%

Vampirovibrio chlorellavorus draft genome sequence, annotation, and preliminary characterization of pathogenicity determinants

Hovde

Starkenburg

et al. 2019

Phycological Research

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Vampirovibrio chlorellavorus is recognized as a pathogen of commercially-relevant Chlorella species. Algal infection and total loss of productivity (biomass) often occurs when susceptible algal hosts are cultivated in outdoor open pond systems. The pathogenic life cycle of this bacterium has been inferred from laboratory and field observations, and corroborated in part by the genomic analyses for two Arizona isolates recovered from an open algal reactor. V. chlorellavorus predation has been reported to occur in geographically-and environmentally-diverse conditions. Genomic analyses of these and additional field isolates is expected to reveal new information about the extent of ecological diversity and genes involved in host-pathogen interactions. The draft genome sequences for two isolates of the predatory V. chlorellavorus (Cyanobacteria; Ca. Melainabacteria) from an outdoor cultivation system located in the Arizona Sonoran Desert were assembled and annotated. The genomes were sequenced and analyzed to identify genes (proteins) with predicted involvement in predation, infection, and cell death of Chlorella host species prioritized for biofuel production at sites identified as highly suitable for algal production in the southwestern USA. Genomic analyses identified several predicted genes encoding secreted proteins that are potentially involved in pathogenicity, and at least three apparently complete sets of virulence (Vir) genes, characteristic of the VirB-VirD type system encoding the canonical VirB1-11 and VirD4 proteins, respectively. Additional protein functions were predicted suggesting their involvement in quorum sensing and motility. The genomes of two previously uncharacterized V. chlorellavorus isolates reveal nucleotide and protein level divergence between each other, and a previously sequenced V. chlorellavorus genome. This new knowledge will enhance the fundamental understanding of trans-kingdom interactions between a unique cosmopolitan cyanobacterial pathogen and its green microalgal host, of broad interest as a source of harvestable biomass for biofuels or bioproducts.