Toshiyuki Shimada is looking forward to reconnecting with oboe players, his brethren.

Bruce Hangen can’t wait to hear what the Kotzschmar Organ sounds like, now that it’s been rebuilt.

Paul Vermel, well, he’s just happy to be here. “It’s been 40 years,” the 92-year-old former music director of the Portland Symphony Orchestra effused. “I’m very excited to be back with the orchestra.”

The three former conductors will join current maestro Robert Moody on the Merrill Auditorium stage Saturday, as the orchestra closes its 90th season by bringing together the four men who led the orchestra more than half its creative life. They have 48 years among them in Portland, and counting.

Beginning with Vermel in 1967, each conductor led the orchestra through moments of creative growth. Until then, the orchestra was mostly a volunteer, community orchestra. Vermel (1967-75) helped the PSO become more professional, Hangen (1976-86) helped modernize it and Shimada (1986-2006) made it the toast of the town with the renovation of Merrill Auditorium. Moody, who began in 2007, has infused the orchestra with energy and contemporary programming, and solidified its stature as one of the country’s finest small-city orchestras.

Moody’s job is to keep the orchestra relevant in the 21st century, but Saturday’s concert is all about honoring the orchestra’s legacy.

“It’s truly an honor to meet these guys and share the podium with them,” Moody said. “We are a very small fraternity, just the four of us. We have stories that only the four of us can share.”

Moody has become friends with Vermel in the past year, since the former PSO maestro returned to Maine to retire. Vermel attends PSO concerts, and has offered feedback and counsel in person and in letters, Moody said. “Oh my gosh, he’s been such a ray of light for me,” Moody said. “I find that I am really benefiting from his experience and his years.”

When Moody extended the invitation to his predecessors, he asked each to choose a piece to conduct. He hoped each would pick music that suggested a personal connection or showed off a strength of the orchestra.

Vermel, who recently retired as conductor of the Northwest Symphony Orchestra near Chicago, chose Beethoven’s Egmont Overture because it’s a short, spirited work, and one of his favorite openers.

He and his wife retired to Scarborough last year. Vermel calls it “an emotional thing” to reconnect with the PSO – “even though it’s not my orchestra anymore.” The orchestra includes three musicians from the Vermel era: bassists George Rubino and Lynn Hannings and cellist Richard Noyes.

Vermel has never conducted at Merrill. When he led the PSO, it played its concerts in the old City Hall Auditorium. His early memories were of an orchestra that needed cohesion. He raised its professional standards and encouraged it to think big. “It was a good orchestra, but it needed more time playing together,” he said. “It was the beginning of a good orchestra.”

When Hangen took over in 1975, the orchestra was humming. He led a period of growth, both artistically and commercially. He hired more talented and qualified musicians and introduced, with orchestra general manager Russell Burleigh, “Magic of Christmas.” The holiday concert became a community tradition, and introduced the orchestra to families and new audiences.

Hangen, who lives in Massachusetts and teaches at the Boston Conservatory, has worked professionally in Portland many times since he left in 1986. He conducted “Magic of Christmas,” as well as the PORTopera orchestra. Saturday’s concert will mark the first time he’s been back to conduct the full orchestra in a classical concert. He’s looking forward to seeing the many musicians he hired who are still playing with the orchestra.

Hangen said he would always be indebted to Portland and the PSO. “It was my first job as a full-time music director. I was carving out my own way, while trying to discover both the traditions of music directorship and the traditions of the PSO that people like Paul Vermel helped establish,” he said.

Hangen will conduct Respighi’s “Fountains of Rome.” He chose it for two reasons. One, he wanted a piece that showcased the organ, and “Fountains of Rome” does that. During Hangen’s time in Portland, the Kotzschmar Organ operated at limited capacity. He’s eager to hear what it can do.

The other reason is personal. When Hangen auditioned for the PSO, he conducted Respighi’s “Pines of Rome,” a companion piece and second in the composer’s Roman Trilogy. “I did the ‘Pines of Rome’ in 1975, I’ll do ‘Fountains of Rome’ in 2015. I guess it will be 2055 when I come back for the third part of the trilogy.”

Among other things, Shimada has the distinction of being the longest-serving music director of the orchestra. He kept the PSO on its upward trajectory, recruiting young musicians and attracting guest performers with star-power like violinist Itzhak Perlman. Most noteworthy, Shimada and the PSO led the effort to renovate Merrill Auditorium. That meant relocating the orchestra to awkward venues during the renovation, including the Cumberland County Civic Center and a hotel ballroom. That challenged the orchestra and tested the loyalty of its audience.

But the effort was necessary and worthwhile, Shimada said. In a renovated Merrill tuned to the needs to the orchestra, the PSO blossomed.

His tender moment with the orchestra occurred 15 years ago as he was preparing for “Magic of Christmas.” The night before rehearsals began, Shimada got word that his father died. The musicians were aware of his grief, but Shimada kept the news from the audience. He didn’t want to take away from the celebration of the season. The family postponed the funeral so Shimada could complete two weeks of “Magic” concerts without interruption.

“The orchestra kept me going,” Shimada said. “They were so supportive of me.”

He’s stayed in touch with some musicians, but the nature of life is to move on. Shimada’s life, musically and otherwise, is now centered around his work at Yale University, where he teaches conducting and leads the Youth Symphony Orchestra, among other things.

He will lead the PSO through Paul Hindemith’s “Metamorphosis.” Hindemith was a German composer who taught at Yale and occupied an office not far from Shimada’s today. Shimada conducted the piece with the PSO years ago, and he liked the idea of revisiting it, given his Yale connections.

Moody will close the concert with one of the best-known pieces of classical music ever written, Strauss’s “Also Sprach Zarathustra,” a portion of which opens the movie “2001: A Space Odyssey.” It seemed fitting to end a concert that celebrates the past with a piece that is known for looking to the future, Moody said. It, too, showcases the Kotzschmar.

“The first 60 seconds are about the most colossal and well-recogonized music on the planet,” Moody said. “That Ubermensch idea, the superman idea that Strauss is taking on, just seemed so perfectly appropriate to represent the idea of strength garnered over our 90 years of history.”