Culturable Bacterial Flora Associated with the Dinoflagellate Green Noctiluca miliaris During Active and Declining Bloom Phases in the Northern Arabian Sea

Abstract

A massive algal bloom of the dinoflagellate Noctiluca miliaris (green) was located in the Northern Arabian Sea by IRS-P4-2 (OCM-II) for microbiological studies, during two consecutive cruises of February-March 2009. Culturable bacterial load during bloom were ≈ 2-3-fold higher in comparison to non-bloom waters and ranged from 3.20 × 10(5) to 6.84 × 10(5) cfu ml(-1). An analysis of the dominant heterotrophs associated with Noctiluca bloom resulted in phylogenetic and a detailed metabolic characterization of 70 bacterial isolates from an overlapping active and declining bloom phase location near north-central Arabian Sea. The active phase flora was dominated by Gram-positive forms (70.59 %), a majority of which belonged to Bacillus (35.29 %) of Firmicutes. As the bloom declined, Gram-negative forms (61.11 %) emerged dominant, and these belonged to a diverse γ-proteobacterial population consisting of Shewanella (16.67 %) and equal fractions of a Cobetia-Pseudomonas-Psychrobacter-Halomonas population (36.11 %). A Unifrac-based principal coordinate analysis of partial 16S rDNA sequences showed significant differences among the active and declining phase flora and also with reported endocytic flora of Noctiluca (red). A nonparametric multidimensional scaling (NMDS) of antibiogram helped differentiation among closely related strains. The organic matter synthesized by N. miliaris appears to be quickly utilized and remineralized as seen from the high efficiency of isolates to metabolize various complex and simple C/N substrates such as carbohydrates, proteins/amino acids, lipids, sulfide production from organic matter, and solubilize phosphates. The ability of a large fraction of these strains (50-41.67 %) to further aerobically denitrify indicates their potential for nitrogen removal from these high-organic microniches of the Noctiluca bloom in the Arabian Sea, also known for high denitrification activity. The results indicate that culturable euphotic bacterial associates of Noctiluca are likely to play a critical role in the biogeochemical ramifications of these unique seasonally emerging tropical open-water blooms of the Northern Arabian Sea.

Microbial dynamics during harmful dinoflagellate Ostreopsis cf. ovata growth: Bacterial succession and viral abundance pattern

“…cf. ovata late stationary growth phase (OTU #16), consistently with the pattern generally observed for recalcitrant substrate degrading Actinobacteria in both algal cultures and natural outbreaks bacterial succession (Bagatini et al., ; Basu, Deobagkar, Matondkar, & Furtado, ; Vanucci, Guidi, et al., ). During the O .…”

“…Inhibitory/algicidal activity has been also strongly suggested for (Bagatini et al, 2014;Basu, Deobagkar, Matondkar, & Furtado, 2013;Vanucci, Guidi, et al, 2016). During the O. cf.…”

Revisiting the <i>Noctiluca scintillans</i> Paradox in Northern Arabian Sea

“…Therefore, our data do not show the presence of hypoxic waters within the euphotic zone. High surface DO, 3.06 ml l -1 (~134 M) and 2.71 ml l -1 (~121 M) during active and declining bloom phases respectively, has also been reported during a Noctiluca bloom in 2009 in the Northern Arabian Sea 21 . The reported DO concentrations also show well-oxygenated surface layer during the bloom period.…”

Associated Bacteria and Their Effects on Growth and Toxigenicity of the Dinoflagellate Prorocentrum lima Species Complex From Epibenthic Substrates Along Mexican Coasts

“…Marine bacteria are frequently found in association with epibenthic P. lima cell aggregations and the growth substrate (Basu et al, 2013;Park et al, 2018). Interactions between bacteria and benthic dinoflagellates occur within the phycosphere-a zone surrounding the dinoflagellate cell wherein leaked or excreted metabolites tend to be retained in higher concentrations and this can potentially enhance cell-to-cell chemical communication between adjacent bacteria and the dinoflagellate.…”