Marine Bacteria Alteromonas spp. Require UDP-glucose-4-epimerase for Aggregation and Production of Sticky Exopolymer

The physiology and ecology of particle-associated marine bacteria are of growing interest, but our knowledge of their aggregation behavior and mechanisms controlling their association with particles remains limited. We have found that a particle-associated isolate, Alteromonas sp. ALT199 strain 4B03, and the related type-strain A. macleodii 27126 both form large (>500 um) aggregates in rich medium. A non-clumping variant (NCV) of 4B03 spontaneously arose in the lab, and whole genome sequencing revealed a partial deletion in the gene encoding UDP-glucose-4-epimerase. While 4B03 was not genetically amenable, a knock-out of galE in 27126 resulted in a loss of aggregation, mimicking the NCV. Microscopic analysis shows that both 4B03 and 27126 rapidly form large aggregates, whereas their respective galE mutants remain primarily as single planktonic cells or clusters of a few cells. 4B03 and 27126 also form aggregates with chitin particles, but their galE mutants do not. Alcian Blue staining shows that 4B03 and 27126 produce large transparent exopolymer particles (TEP), but their galE mutants are deficient in this regard. This study introduces the capabilities of rapid condition-dependent aggregation, aggregation with chitin particles, and TEP production in Alteromonas, a widespread particle-associated genus of heterotrophic marine bacteria. A genetic requirement for galE is evident for each of the above capabilities, expanding the known breadth of requirement for this gene in biofilm-related processes.

附着于颗粒的海洋细菌的生理学与生态学特征日益受到学界关注，但目前我们对其聚集行为以及调控其与颗粒结合的机制仍了解有限。本研究发现，一株分离自颗粒的交替单胞菌（Alteromonas sp.）ALT199菌株4B03，及其近缘模式菌株麦克劳德交替单胞菌（Alteromonas macleodii）27126，均可在丰富培养基中形成直径大于500微米的大型聚集体。实验室中自发获得了4B03的非聚集突变株（non-clumping variant, NCV），全基因组测序结果显示，该突变株中编码UDP-葡萄糖-4-差向异构酶的基因存在部分缺失。尽管4B03菌株无法进行遗传操作，但在27126菌株中敲除galE基因可使其丧失聚集能力，模拟NCV的表型。显微镜观察表明，4B03与27126均可快速形成大型聚集体，而二者对应的galE敲除突变株则主要以单个浮游细胞或少量细胞组成的小簇形式存在。此外，4B03与27126均可与几丁质颗粒形成聚集体，但其galE敲除突变株则无此能力。阿尔新蓝染色实验显示，4B03与27126可产生大量透明胞外聚合物颗粒（transparent exopolymer particles, TEP），而其galE敲除突变株在此方面存在缺陷。本研究阐明了交替单胞菌属（Alteromonas）——一类广泛分布的附着型异养海洋细菌属——所具备的依赖培养条件的快速聚集、与几丁质颗粒形成聚集体以及产生TEP的能力。上述各项功能均依赖galE基因，这一发现拓展了已知的该基因在生物膜相关过程中的功能范围。