A novel alphaproteobacterial strain JXJ CY 41 T was isolated from a culture mass of Microcystis, collected from Lake Dianchi, south-west, China. Strain JXJ CY 41 T was gram-strain-negative, aerobic, motile, with rod-shaped cells (0.4-1.0 × 1.7-3.5 μm). It was positive for catalase and starch hydrolysis, negative for oxidase and hydrolysis of Tweens (20, 40, and 80). Growth occurred at 10-44 °C, pH 5.0-10.0, and 0-5.0% (w/v) NaCl. Major fatty acids included C 16:0 (28.1%), 11-methyl C 18:1 ω7c (36.7%) and C 18:1 ω7c (20.8%). Q10 was the sole ubiquinone. The polar lipids were diphosphatidylglycerol, phosphatidylglycerol, glycolipid, and an unidentified lipid. The DNA G + C content was 63.1%. Its 16S rRNA gene sequence showed high similarities with Devosia oryziradicis G19 T (99.5%; not validly published), D. yakushimensis Yak96B T (98.3%) and D. ginsengisoli Gsoil 520 T (98.1%), and less than 98.1% similarities with other members of the genus Devosia. The digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) values between strain JXJ CY 41 T and its 5 closest similar strains were 19.9-24.1% and 75.7-80.5%, respectively. Based on the data above, strain JXJ CY 41 T was identified as a novel species of the genus Devosia, for which the epithet Devosia lacusdianchii sp. nov. was proposed. The type strain is JXJ CY 41 T (= KCTC 72812 T = CGMCC 1.17502 T ). Strain JXJ CY 41 T exhibited different interactions with Microcystis aeruginosa FACHB-905 (Maf) under different conditions, and Maf could control the bacterial cellular density by secreting unknown specific chemical compounds according to its nutritional requirements.