Supplementary tables for Honey Bee symbiont buffers larvae against nutritional stress and supplements lysine

Honey bees have suffered dramatic losses in recent years, largely due to multiple stressors underpinned by poor nutrition. Nutritional stress especially harms larvae, who mature into workers unable to meet the needs of their colony. In this study, we characterize the metabolic capabilities of a honey bee larvae-associated bacterium, Bombella apis (formerly Parasaccharibacter apium), and its effects on the nutritional resilience of larvae. We found that B. apis is the only bacterium associated with larvae that can withstand the antimicrobial larval diet. Further, we found that B. apis can synthesize all essential amino acids and significantly alters the amino acid content of synthetic larval diet, largely by supplying the essential amino acid lysine. Analyses of gene gain/loss across the phylogeny suggest that four amino acid transporters were gained in recent B. apis ancestors. In addition, the transporter LysE is conserved across all sequenced strains of B. apis. Finally, we tested the impact of B. apis on developing honey bee larvae subjected to nutritional stress and found that larvae supplemented with B. apis are bolstered against mass reduction despite limited nutrition. Together, these data suggest a novel role of B. apis as a nutritional mutualist of honey bee larvae.

近年来，蜜蜂种群遭遇了大幅锐减，其主要诱因是多重胁迫因素，而营养匮乏是这些胁迫的核心推手。营养胁迫尤其会对幼虫造成损伤，受影响的幼虫羽化为工蜂后将无法满足蜂群的生存需求。本研究针对一种与蜜蜂幼虫共生的细菌——蜂房芽孢杆菌（Bombella apis，曾用名Parasaccharibacter apium）的代谢功能，及其对幼虫营养抗逆性的影响展开了系统性表征。研究发现，B. apis是目前已知唯一一种能够耐受幼虫抗菌日粮的幼虫共生细菌。此外，本研究证实B. apis可合成所有必需氨基酸，并能通过供给必需氨基酸赖氨酸，显著改变人工幼虫日粮的氨基酸组成。系统发育基因组学的基因得失分析显示，B. apis的近代祖先曾获得了4种氨基酸转运蛋白编码基因。此外，赖氨酸转运蛋白LysE在所有已测序的B. apis菌株中均呈保守状态。最后，本研究评估了B. apis对遭受营养胁迫的发育中蜜蜂幼虫的作用，结果显示，即便在营养受限的条件下，添加B. apis的幼虫仍可有效抵御体重下降。综合以上研究结果，本研究揭示了B. apis作为蜜蜂幼虫营养共生菌的全新功能角色。