Department of Microbiology, Goa University, Taleigao Plateau, Goa, 403206, India.
Microb Ecol. 2013 May;65(4):934-54. doi: 10.1007/s00248-012-0148-1. Epub 2013 Jan 3.
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.
在 2009 年 2 月至 3 月的两次连续航行中，IRS-P4-2（OCM-II）在北阿拉伯海发现了夜光藻（ dinoflagellate Noctiluca miliaris ）的大规模藻类水华，用于微生物学研究。在水华期间，可培养细菌负荷比非水华水域高 2-3 倍，范围为 3.20×10(5)至 6.84×10(5)cfuml(-1)。对与夜光藻水华相关的优势异养生物的分析导致了来自北阿拉伯海近中北部重叠活跃和衰退水华阶段位置的 70 个细菌分离物的系统发育和详细代谢特征。活跃阶段的菌群主要由革兰氏阳性形式（70.59％）组成，其中大多数属于芽孢杆菌（Firmicutes 的 35.29％）。随着水华的衰退，革兰氏阴性形式（61.11％）变得占优势，这些形式属于一个多样化的γ-变形菌种群，包括希瓦氏菌（Shewanella）（16.67％）和相等分数的科贝特氏菌-假单胞菌-Psychrobacter-Halomonas 种群（36.11％）。基于部分 16S rDNA 序列的 Unifrac 主坐标分析表明，活跃期和衰退期菌群之间存在显著差异，与夜光藻的报道内吞菌群（红色）也存在显著差异。抗生素图的非参数多维尺度（NMDS）有助于区分密切相关的菌株。从分离物代谢各种复杂和简单的 C/N 底物（如碳水化合物、蛋白质/氨基酸、脂质、从有机物中产生的硫化物和溶解磷酸盐）的高效率来看，夜光藻合成的有机物似乎很快被利用和再矿化。这些菌株的很大一部分（50-41.67％）具有进一步好氧反硝化的能力，表明它们有可能从阿拉伯海夜光藻这种高有机微生境中去除氮，阿拉伯海也是高反硝化活性的地方。结果表明，夜光藻的可培养透光细菌伴生物可能在这些北阿拉伯海独特的季节性热带开阔水域水华的生物地球化学后果中发挥关键作用。
